# Floor Joists Over Concrete Slab



## scootermcrad (Jul 23, 2012)

Hey everyone!

Been getting a lot of wonderful information around here lately! Great forum! Hopefully you guys can help me with a project I have in the works, or at least on the drawing board, if you will.

*The Room:*

We have a 22x14 (ish) room that was added to our house at some point in the 40's or 50's. It is brick construction with a concrete slab floor poured inside. For some reason, the slab is just a mess. It appears to be sloped away from the house, and seams to have been poured in two sections, one stepped higher than the other. Sort of like an addition to an addition, if I had to guess. The slope is probably 2 to 3 inches over the length of the slab. It is also flat in parts and not in others.

*Our Intentions:*

We would like to put narrow oak plank flooring in this room, to match the rest of the house, and it is also going to be a family/TV/entertainment room. We will probably do surround sound in this room as well. I'm thinking of building a floor structure over the concrete. This would give me a nice level and flat floor that I can run wires under, duct work for HVAC, as well as give us a nice feel to the floor, instead of sub-floor and wood flooring right over a fresh level slab. I only want to raise it up a minimal amount. Just a few inches.

*The questions:*

1- What is the PROPER way to accomplish this? I'm assuming I will need a vapor barrier of some kind over the slab? What about air circulation?

2- What about insulation? What are my options?

3- Any links or examples I can refer to?

Any help would be appreciated!

Thanks everyone!


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## scootermcrad (Jul 23, 2012)

Back to the top for a new day...

Is this a dumb idea?  I searched around for info on the web, but didn't see a whole lot.


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## scootermcrad (Jul 23, 2012)

This is sort of what I had in mind.










Maybe I'm using the wrong terminology. They call them sleeper joists. Makes sense.

One thing I'll say, given the age of the slab and from what I've seen of the rest of the construction, the slab was probably poured right over grade with no vapor barrier or insulation, as shown in the above drawing. I could be wrong, maybe it WAS done, but I feel like I would be a fool to assume that there is a vapor barrier and insulation below that slab.


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## oh'mike (Sep 18, 2009)

If the slab always remains dry--your plan will work-----


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## scootermcrad (Jul 23, 2012)

oh'mike said:


> If the slab always remains dry--your plan will work-----


Okay. So I can put sleepers right down on the slab without a vapor barrier of any kind? Once I've created a closed airspace below the floor will I need to provide some kind of venting for the cavity to prevent a moisture issue? should I maybe provide a slight gap between the wall and subfloor-finished floor to allow air to circulate?

Up until we bought the house, the slab actually had carpet over it for at least 5 years with no moisture issues and we found no mold upon removal of the carpet.


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## oh'mike (Sep 18, 2009)

Lay the sleepers over a layer of tar paper--level and fasten to the concrete---then add your flooring--

I've done that twice without an issue----the key is a dry slab----

It's always a risk----let's see if anyone else has a suggestion.


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## scootermcrad (Jul 23, 2012)

oh'mike said:


> Lay the sleepers over a layer of tar paper--level and fasten to the concrete---then add your flooring--
> 
> I've done that twice without an issue----the key is a dry slab----
> 
> It's always a risk----let's see if anyone else has a suggestion.


Great! Thanks! I assume it's best not to penetrate the tar paper. What is suggested for securing the joists and shims to the floor?

This is the general layout of the room. Should the sleepers run the longer length of the floor, I assume, with blocking between?


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## oh'mike (Sep 18, 2009)

How high are you raising the floor?

You will penetrate the vapor barrier with the fasteners----can't be helped----I would use .22 caliber studs---or Tapcons


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## scootermcrad (Jul 23, 2012)

oh'mike said:


> How high are you raising the floor?
> 
> You will penetrate the vapor barrier with the fasteners----can't be helped----I would use .22 caliber studs---or Tapcons


The least amount I can get away with. I need to figure out exactly how much slope there is to the floor and where the slope is at, first. I have a feeling that half of the floor is sloped on the end by the stairs (closer to the house) and the other half is not as sloped (further from the house).

My first thought is to actually start with a 2x6 sleeper joist (on end, like normal) and cut it to match the slope of the floor. It would be incredibly time consuming and every joist would have to be cut individually and placed, but I have a feeling that would give me 3"+ nailing depth for my sub-flooring at the high end.

Is that a bad idea?? Am I in the wrong frame of mind on how to set up these joists? The room has a pretty tall ceiling, but I don't want to lose anymore ceiling height than needed.


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## notmrjohn (Aug 20, 2012)

" provide some kind of venting for the cavity to prevent a moisture issue?" No. Barrier on slab keeps moisture from coming up from below. If water vapor can enter space from above thry flooring, it can also exit to above. Have you done the ol' plastic taped to the concrete moisture test? 18 to 24 inch squares of at least 6 mil plastic taped around all sides, wait 24 hours, see if moisture condensed under neath?

At least 6 mil plastic , edges overlapped 6" and taped might be better barrier than felt. Bring edges up walls and seal to them at least as high as top of sleepers.

Run sleepers across short dimension, easier to handle and level. But compare cost of number of 22' vs 14' you will need.They should run at right angles to final floor planks. And random lengths with joints offset from each other are better than full span. There are no real joints between lenghts.Lessee if I can explain that. To cross the 14' space, you lay a 4' sleeper from one wall, at other wall you lay another 4' in line with first leaving 6' gap.You span that distance with a* 7'* sleeper about 1/4" to side of first two, ovelapping both ends 6" Make sure they are level and are really fastened securly to slab, loose ones are gonna squeek. Shim them up to level, a dab of construction adhesive between shims and sleeper and fasten to slab thru shims. Use lots of fasteners, so you'll want to use a power driver.

Alternativly use pressure treated sleepers, foam between, vapor barrier over that. That way you can use adhesive between sleepers and slab. 
The type of subfloor, type and placement of vapor barriers, underlayment are gonna depend on your flooring.

Ah, I can shut up, take a look here. http://www.hardwoodinfo.com/articles/view/pro/28/241

BTW have you thought about radiant heat floor? There are some combination subfloor radiant heat products, I dunno a thing about installing or reliability as sub-floor or heat.

Another BTW, are you sure slab was poured inside brick wall? From slope it sounds more like it was a patio deck, that was later bricked in. If that is case it probably does* not* have a barrier under it.


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## scootermcrad (Jul 23, 2012)

notmrjohn said:


> " provide some kind of venting for the cavity to prevent a moisture issue?" No. Barrier on slab keeps moisture from coming up from below. If water vapor can enter space from above thry flooring, it can also exit to above. Have you done the ol' plastic taped to the concrete moisture test? 18 to 24 inch squares of at least 6 mil plastic taped around all sides, wait 24 hours, see if moisture condensed under neath?
> 
> At least 6 mil plastic , edges overlapped 6" and taped might be better barrier than felt. Bring edges up walls and seal to them at least as high as top of sleepers.
> 
> ...


Great info! Thanks! And yes, the explanation helped! And, since I want to run the flooring length-wise in the room, that makes sense.

The slab, oddly enough, does appear to be poured inside the walls. The addition to the house was used for the original builder's wife to have a little shop in. Eventually it became a family room of sorts, as times went on and the house changed hands several times. If I dig down below the level of the slab outside, the brick continues below the level of the slab. So, it does appear that it was intentionally built that way and not a patio slab with walls built on top.

I will try the moisture test with the tape! Thanks! And I will definitely check into the radiant sub-flooring products. That would be super nice for the winter time.

So, QUESTIONS, then... If I put 2x4 sleepers down and level them out over the 22 foot length (14 foot length is level. Slab only seems to slope the length of the 22 foot dimension). By the time I get to the other end of the room, I'll probably be a 4x4's worth of height, or more. What about the shims themselves?? Various thicknesses of plywood? How far am I spacing these sleepers apart?? Also, what would be the suggested sub-floor materials?

Gonna pull out some string and level to see if I can figure out the slope behavior of this slab. Now it's going to drive me crazy if I don't do this soon! HAHA! :whistling2:

The flooring I'm going to be using will be reclaimed 1-1/2" wide x 3/4" thick red oak. Using reclaimed because we want it to match the character of the existing floors in the house as much as possible, plus we have a connection to get it at a very reasonable price.

I also ran across this as well...

http://www.february-11.com/2h_floors_o.html


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## scootermcrad (Jul 23, 2012)

Should the sleepers by about 16" OC, like normal, or should they be closer?


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## oh'mike (Sep 18, 2009)

16" spacing will be fine-----plywood shims will work----stick with exterior grade plywood---

For sheeting use BC exposure one---or CDX tongue and groove


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## scootermcrad (Jul 23, 2012)

oh'mike said:


> 16" spacing will be fine-----plywood shims will work----stick with exterior grade plywood---
> 
> For sheeting use BC exposure one---or CDX tongue and groove


Fantastic! Thank you sir! :thumbsup:


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## notmrjohn (Aug 20, 2012)

You are lucky on the direction of slope, lots easier to shim entire sleeper length equally than having one end higher than other. You could even use plywood of proper thickness, ripped down and running full length of sleeper. I wonder if slope was intentional so floor could be sluiced down with hose or bucket back when it was a shop.One end is 3 1/2" lower than other? That is considerable, perhaps the room was a garage at one time. I once had to level a shorter span of almost that slope by ripping 2X4's on a taper from full to nothing. 

"Gonna pull out some string and level " This is a great excuse... er... need to buy a rotatable laser level. http://www.walmart.com/ip/Trademark-Global-Premium-Laser-Level/16890848?findingMethod=rr Strike a level chalk line an inch above high end, then all around room at that level. Stretch your strings across and along room from the lines.

You can space sleepers closer, but as mike sez, 16" is fine, that's what they'd be if they were joists. Comparing your pic and link I posted, you can see pic has gapped butt joints of sleepers, instead of off set laps. The butt jointed sleeprs should be used under butt joints of your sub-floor, or plan your offset ones to be at least 5 foot long at those joints, 6" past long edge of plywood each side. Short sleepers between long ones for side seams are not needed but would add stiffness. Note that butt seams of sub-floor are staggered. 

I'd use the T&G CDX. The mastic under plastic is up to you, would keep plastic from bunching up as you work wouldn't hurt under sleepers areas, might help seal the nial holes thru plastic, watch your step, plastic can be slippery. Figure out what thicknesses of shims you'll need, buy a "shim set" of plywood, from 1/8", 3/16"/ 1/4, 5/8, 3/4 what ever to make your different thicknesses. At low end you could double 2x's, adhesive between them, if butt joints, stagger them, not joint right over another. Fasten one to floor, over shim if needed, then fasten top one to it, I'd use deck screws. Which reminds me, screws and nails should be rated for use with pressure treated. Ram-Set has such rated fastener called Ram Guard.

Po'lly take you less time to do job than it took me to one finger peck all this blather. Let me know how that new laser level works out, I need a new one. Mines getting so dim I can't see it, or mebbee its my eyes.


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## scootermcrad (Jul 23, 2012)

Holy cow! I didn't realize the laser levels had come down so much. Yeah, I'll be getting on of those for sure! :yes::thumbup:

I've used the T&G CDX before. It is pretty nice stuff! I think I may go that direction.

It's very possible that the slope was planned for wash-down reasons, since it was intended to be a flower shop. It made for some strange and unfortunate modifications to the house (that I'm slowly, but surely, UN-doing). There is actually an end door in the construction that will be going away before we do this floor project. There's also a flat roof (er... very low sloped roof) on the addition. But THAT is a WHOOOOOOLE 'nother story! HAHA! There will be a post on that eventually as well.

Last night I was telling my wife about the education I've been getting from this thread and I mentioned the heated sub-floor... Yeah. I guess we'll be doing that as well.... :laughing: HAHA! So if any of you can refer me to a good thread on heated sub-floor products that would work for this application, it would be much appreciated.

Can of worms opened... 

Thanks everyone!


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## scootermcrad (Jul 23, 2012)

Okay! I'm finally updating this thread. We are back on this project. We are all-in on this! End wall has been removed and roof is being completely reconstructed. 

When demo'ing everything, we got a good look at the slab. There were two slabs poured at two different times. They are on-grade and there is no vapor barrier. We found two floor drains (one is plugged one will need to be plugged).

We reclaimed 1-1/2"x3/4" oak flooring that matches our flooring and now it's back to focusing on what to do about the slab when they're done with construction.

Latest thinking:

1) Level the slab with self-leveling compound (if possible), put a vapor barrier down, lay my subfloor plywood, and put down the floors

2) Sleeper system as already discussed with vapor barrier down, PT 2x4 sleepers, foam board in between, subfloor over, floors down over that

3) Any combination of the above but adding radiant floor heating of some kind 

With construction under-way, I can't check the floor until later this week to see just how out of level it is, but I suspect it will be beyond what I can level with self-leveling compound, so focusing on a sleeper system with or without radiant floor will be the continued focus, I think.

NEW QUESTIONS!

Should I use a standard 6 mil vapor barrier, or are there new vapor retarders available that provide a level of insulation as well?

I may as well put some kind of insulation under the floor. What type of foam board is recommended to provide some added comfort?

Should I really consider the radiant floors if I can do some good insulation? NC winters are pretty mild and I'm concerned about types of radiant floor for this project as well as the cost associated with them. I would really like some feedback on this.

Thanks guys! Happy to be back working on this again! It's getting pretty serious and I'm trying to make a huge dent in the project by the end of the year so we can use this space.

CHEERS!
S


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## scootermcrad (Jul 23, 2012)

Another update. I finally was able to get in to the room last night with the laser level and get an idea of what's going on with this slab.

The original part of the slab that was built in the 40's is about 1-1/2" higher than the portion that was added later. There is quite a bit of slope. Total displacement from one end of the room to the other is 3" on one side and 4" on the other. The newer portion has slope in two directions. Clearly this room was intended to shed water towards a drain that was in the lowest corner. This will be too much for leveling compound.

It appears that the original portion has slightly less slope than the later added. That might work in my favor for sleepers.

I see a couple different methods... 
1) PT lumber glued and Tapcon'd directly to the slab with vapor barrier between the sleepers and the sub floor. 
2) Vapor barrier down first, then PT lumber OVER the vapor barrier and Tapcon'd down with subfloor over that.

Which makes more sense for my situation? What about shimming the heights? Is there any clever pre-made shims out there for this application? Which side of the vapor barrier does the insulation need to be on and what type of insulation board should I consider?

So back to the top with this! Thanks guys!


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## radioman99 (Nov 21, 2016)

what i would do is use the 2X6 you mentioned and cut for slope. its really doesnt take long. all you need to do is set board on floor and lift the low end up till its level. use a large compass and scribe the board to the floor and cut. i would have a bundle to cedar shingles for shimming for the area that didnt cut right or floor dipped too much in one area and circular saw couldnt follow your scribe. I love the cedar shingles as its tapered nice and long and wide. put down the vapor barrier on the concrete and floor joist on that. no need for tapcons unless the wood is cut down to 2 inch or less on the tapered end. use lots of blocking. block the whole floor in 2 preferably 3 rows. run your wiring under the floor to area you needif you cant go around the walls then insulate it with foam boards. if you can spring the cost have it sprayed in. then you can cover up with tg subfloor and be sure to glue the heck out of it with lots of screws so it wont squeak when you walk in it. remember the blocking ? that should help with squeaks. 

If you decide to use sleepers -- remember the sleepers will flex more unless its been shimmed the heck out of it 'every foot or less and tapconed thru sleeper and shim. if your floor only slopes less say 1 1/2 or less then i would use sleepers but you say you have 3-4 inches - that is alot. you need a proper floor. 

your other option is to call in a concrete guy and have them pour a new floor on top of old. this way you can can two options after doing this - one use snaplock floors with the Pergo GOLD 100-sq ft Premium 3-mm Flooring Underlayment or lowes brand or simalar ( i used it and love it) or two - use sleepers like you said and glue and tapcon it with hopefully little shimming needed.


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## scootermcrad (Jul 23, 2012)

radioman99 said:


> what i would do is use the 2X6 you mentioned and cut for slope. its really doesnt take long. all you need to do is set board on floor and lift the low end up till its level. use a large compass and scribe the board to the floor and cut. i would have a bundle to cedar shingles for shimming for the area that didnt cut right or floor dipped too much in one area and circular saw couldnt follow your scribe. I love the cedar shingles as its tapered nice and long and wide. put down the vapor barrier on the concrete and floor joist on that. no need for tapcons unless the wood is cut down to 2 inch or less on the tapered end. use lots of blocking. block the whole floor in 2 preferably 3 rows. run your wiring under the floor to area you needif you cant go around the walls then insulate it with foam boards. if you can spring the cost have it sprayed in. then you can cover up with tg subfloor and be sure to glue the heck out of it with lots of screws so it wont squeak when you walk in it. remember the blocking ? that should help with squeaks.
> 
> If you decide to use sleepers -- remember the sleepers will flex more unless its been shimmed the heck out of it 'every foot or less and tapconed thru sleeper and shim. if your floor only slopes less say 1 1/2 or less then i would use sleepers but you say you have 3-4 inches - that is alot. you need a proper floor.
> 
> your other option is to call in a concrete guy and have them pour a new floor on top of old. this way you can can two options after doing this - one use snaplock floors with the Pergo GOLD 100-sq ft Premium 3-mm Flooring Underlayment or lowes brand or simalar ( i used it and love it) or two - use sleepers like you said and glue and tapcon it with hopefully little shimming needed.


Hey! Thanks for your response! I appreciate it! Thanks for the tips.

At the minimum, I will put a 2x4 flat at the top of the slope, and work out/down the slope from there. I love the cedar shingle idea. Certainly rot resistant.

I was going to price out spray foaming everything, so there are no air gaps. The guy will be out to do the rest of the room, so the cost will probably be minimal to have him do the floor while he's at it. I'll use the gray electrical conduit under the floor for wire runs, where needed. The room will have surround sound, so I figured this was the best option.

The other good that comes from this, although sort of strange, is that the feel of the floors over joists/sleepers just seems to have a better feel than over a solid slab. Odd detail, but I like it.

Thanks! Keep the tips coming!


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## radioman99 (Nov 21, 2016)

i really dont think you need electrical conduit . its just an added expense unless you are expecting mice to chew em. just lay in 12/2 romex for everything you need , same goes for your surround sound wiring. i only use conduit when its going to be exposed somewhere inside or outside use. just make sure you have ZERO junction boxes.


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## scootermcrad (Jul 23, 2012)

radioman99 said:


> i really dont think you need electrical conduit . its just an added expense unless you are expecting mice to chew em. just lay in 12/2 romex for everything you need , same goes for your surround sound wiring. i only use conduit when its going to be exposed somewhere inside or outside use. just make sure you have ZERO junction boxes.


The conduit is so I can fish more audio cable later in case I decide to switch things up with my surround sound arrangement. That's all. Not really for protection, so much.

Electrical will simply be run as normal. I actually probably will not be going through the floor with the electrical at all. Just the audio so I have the shortest distance between receiver and speakers.


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## radioman99 (Nov 21, 2016)

that makes perfect sense -- sounds like you getting this project rolling alright.


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## scootermcrad (Jul 23, 2012)

radioman99 said:


> that makes perfect sense -- sounds like you getting this project rolling alright.


Yeah, it just took a major roof leak to get the ball rolling and restructure everything. Once that happened, it was game on. And NOW we have a baby on the way, so I'm really pushing to get things buttoned up.

Beginning of the year will show some progress on the sleeper/joist system. I'm also considering having the floor spray foamed while the cathedral ceiling and walls are being done. Should make for a toasty room! :smile:


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## Mrbuilder (Nov 15, 2016)

oh'mike said:


> 16" spacing will be fine-----plywood shims will work----stick with exterior grade plywood---
> 
> For sheeting use BC exposure one---or CDX tongue and groove


 Or you could use Advantech. It's actually an OSB product that has been impregnated :vs_OMG:with a waterproof adhesive. It won't delaminate, is 3/4" thick, might save you a couple bucks, and it's tongue and groove.

just a thought.........:vs_cool::vs_coffee:


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## 123pugsy (Oct 6, 2012)

Mrbuilder said:


> Or you could use Advantech. It's actually an OSB product that has been impregnated :vs_OMG:with a waterproof adhesive. It won't delaminate, is 3/4" thick, might save you a couple bucks, and it's tongue and groove.
> 
> just a thought.........:vs_cool::vs_coffee:


I used this for my sub floors.
At first I thought it was just OSB but it's much more than that.
It weighs a ton and is very strong.


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## scootermcrad (Jul 23, 2012)

Mrbuilder said:


> Or you could use Advantech. It's actually an OSB product that has been impregnated :vs_OMG:with a waterproof adhesive. It won't delaminate, is 3/4" thick, might save you a couple bucks, and it's tongue and groove.
> 
> just a thought.........:vs_cool::vs_coffee:





123pugsy said:


> I used this for my sub floors.
> At first I thought it was just OSB but it's much more than that.
> It weighs a ton and is very strong.


Yep! This was the plan for sure was to use this stuff for my subfloor. I've worked with it before and it's a great product.

It definitely weighs a TON! lain:

Thanks guys! I appreciate the input here. I know this is an older thread, but I'm finally in the thick of it and am doing final planning now.


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## jbfan (Jul 1, 2004)

I can't add anything to the discussion about how to do the floor, but I thought I was slow when it came to projects.
A bit over 4 years for this one!!

Just couldn't help myself.


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## scootermcrad (Jul 23, 2012)

jbfan said:


> I can't add anything to the discussion about how to do the floor, but I thought I was slow when it came to projects.
> A bit over 4 years for this one!!
> 
> Just couldn't help myself.


HAHA! Yep! There's a lot going on around here. I have a car project that's been going for 10 and the house had to become the priority, so that will end up being a 12 project, probably! :biggrin2:


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## 123pugsy (Oct 6, 2012)

scootermcrad said:


> HAHA! Yep! There's a lot going on around here. I have a car project that's been going for 10 and the house had to become the priority, so that will end up being a 12 project, probably! :biggrin2:


Don't feel bad.

I started drawing my house about seven or eight years ago. Just started the house last August finally.

I'm in the same boat......I haven't touched the hot rod in two years.....getting the eebie jeebies.....


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## scootermcrad (Jul 23, 2012)

123pugsy said:


> Don't feel bad.
> 
> I started drawing my house about seven or eight years ago. Just started the house last August finally.
> 
> I'm in the same boat......I haven't touched the hot rod in two years.....getting the eebie jeebies.....


Yeah! Exactly! I'm anxious to be done with all this so I can get back to the regularly scheduled programs... :vs_OMG:


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## scootermcrad (Jul 23, 2012)

Materials on-hand and things are about to get started. I have a last minute question, before getting started. Any reason I can't build in sort of a rim joist around the perimeter walls to help with the process? It would obviously be wedged shaped from end to end, and basically non-existent at the short end, but seems like it would help the leveling process.

I have a spray foam guy coming out today or early next week to chat with me about insulating between the sleepers, once they're installed. He said the foam itself will seal the slab, so no vapor barrier will be required on the slab. The sleepers are pressure treated and based on the response here will be glued and Tapcon'd to the floor.


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## scootermcrad (Jul 23, 2012)

Okay. I started laying out sleepers last night. I want to revisit some questions though, before I start screwing this stuff down.

*Insulation* - I won't be able to have everything spray foamed, because of how shallow the sleepers are at the high part of the slab. I was thinking foam board here. I feel like the 6 mil VB should go down first in these areas and the sleepers over top. Correct assumption?

Also, can I use Roxul bats in the deeper areas and use a spray foam to seal off gaps where insulation cannot be installed?

*Vapor Barrier* - Seems like majority says vapor barrier direct to slab, unless spray foam is used. Since the spray foam is starting to look like a logistical nightmare, I'm probably going to end up just putting the 6 mil VB straight on the slab with sleepers over and I'll make sure there is some kind of sealer where Tapcon's penetrate the VB. So how do I handle the edge perimeter? Dimensionally I have enough to cover the entire slab and roll it up the surrounding walls (like a tub), if I need to. Would that be advisable?

Ready to get this done!!! Electrical is going in and I'm going to be ready for a floor soon! Woohoo!

Thanks guys!


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## Gary in WA (Mar 11, 2009)

https://buildingscience.com/documen...g-the-plank?searchterm=slab%20vapor%20barrier

http://www.fortifiber.com/pdf/data_sheets/DS_aquabar_b.pdf

Gary


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## scootermcrad (Jul 23, 2012)

Gary in WA said:


> https://buildingscience.com/documen...g-the-plank?searchterm=slab%20vapor%20barrier
> 
> http://www.fortifiber.com/pdf/data_sheets/DS_aquabar_b.pdf
> 
> Gary


Okay. So I looked through all that. UHG! So now a standard 6 mil VB isn't going to be enough, huh?

So it answered some of my questions, but it still isn't EXACTLY providing a solution. Remember, I don't have a VB under the slab. And if I use the "Aquabar B" underlayment, how does that protect my subfloor material from collecting moisture?

So. Here's the direct question, while restating I don't have a VB or insulation under my slab:

What underlayment/vapor retarder product do I want to buy given my situation and does it go straight to the slab or not? And how should I insulate the floor cavity between the sleepers?

I've heard so many answers here, that now I'm just confused. The article linked to above (on the internet) says don't believe what the internet says and do something different. I definitely can see how mildew under a plastic sheet could be an issue if the air gap can't be completely eliminated.


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## scootermcrad (Jul 23, 2012)

Reached out to Fortifiber. Sounds like Moistop Ultra 10 is what they recommend for the application.

http://www.fortifiber.com/moistop_ultra_10.html


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## scootermcrad (Jul 23, 2012)

Any reason I couldn't use an adhesive to glue the poly down like Henry's, or something? Even a standard Mastic tile adhesive? That would ensure no air bubbles, if I took my time and laid it out.


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## Gary in WA (Mar 11, 2009)

Try it (poly).... let us know the outcome later.

You could use a surface applied epoxy coating Fig. 2= $$$; https://buildingscience.com/documents/insights/bsi-003-concrete-floor-problems?full_view=1

IMHO, I'd use either Forti- product (my link is only 0.87 perms and seals around the fastener penetration somewhat) before poly (my last choice)... yes, run it up the concrete walls some for complete air seal with mastic at perimeters. Your link is made for this application at 1/8 the perms; http://www.fortifiber.com/pdf/data_sheets/DS_moistop_ultra_10.pdf. 

Gary


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## scootermcrad (Jul 23, 2012)

Gary in WA said:


> Try it (poly).... let us know the outcome later.
> 
> You could use a surface applied epoxy coating Fig. 2= $$$; https://buildingscience.com/documents/insights/bsi-003-concrete-floor-problems?full_view=1
> 
> ...


I contacted my rep for the Moistop Ultra 10 and the prices were actually very good! A 4'x25' roll is only $22. 4 rolls of that and a roll of their tape, and we're all set! They say asphalt mastic can be used for additional adhesion where needed. This seems like a smart way to go.

I will use my monster roll of Poly under the house to fill in the voids.

Thanks for the help!


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## Gary in WA (Mar 11, 2009)

You are welcome, that is why we are here!

Glad to hear that price... so many things are inflated these days. 

Good to go...

Gary


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## jackislost (Jun 21, 2015)

scootermcrad

Just checking up on this project. See how it turned out and if you have had any issues. Your past situation sounds like my current one. I have a 32' x 13' room with 2.75" slope over the 32" portion on a slab. I recently decided to redo the shower in the back part of the room due to water leaking. Tore out the shower to discover the entire back part of my house (an addition after house was built sometime in the '50's) was built on 2x4's on edge with 2x 3/4" plywood with carpet on top. The entire bathroom was ripped up do to shower leaking for however many years. Once that was ripped up I decided to rip out the rest of the addition because it seemed liked there was more wrong. So I did and I found cracks spanning the width (13') of the slab. Have water damage where a door use to be that is covered by a piece of plywood outside, and the entire room on the inside had paneling. Of course the 2.75" slope in the slab, and no insulation behind panelling. 

I had planned on pouring concrete to make it level, but just a few hours ago I decided to go back with sleepers like they had (after a construction numbers crunching guy stopped by). Except, I will do 2x6 ripped to fit the slope, 16" oc, with shims to boot. Rigid insulation between the "joist". Then will do 1/2" to 3/4" OSB on top of 2x6 (joist/sleepers). Topping it off with some type of laminate or similar flooring. 

Did you run a VB on the concrete? Did you go with the Moistop material and if so does it seem to have done what it says it can do? Also any advice you would like to share so that I might be aware of any pitfalls or mistakes that can or could happen. I have ripped everything up and am currently making my materials list to order in the next day or two. Would love your feedback so that I can be just a bit more knowledgeable about what I am about to undertake. Hell I got through the tear out which was brutal considering people back in them days like to use 4 inch nails to nail everything down with. I don't swing a hammer if I ain't got to. 

Anyway any advice would be great, hope your project went well and that you were able to move on the hot rod or whatever was next. I am in the same boat mine is just not a hot rod, its the other 10 or so major projects that I have going. But hey got to stay busy somehow. Thanks

Jack


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## MI-Roger (Aug 8, 2009)

> I had planned on pouring concrete to make it level, but just a few hours ago I decided to go back with sleepers like they had (after a construction numbers crunching guy stopped by). Except, I will do 2x6 ripped to fit the slope, 16" oc, with shims to boot. Rigid insulation between the "joist". Then will do 1/2" to 3/4" OSB on top of 2x6 (joist/sleepers). Topping it off with some type of laminate or similar flooring.


Remember that the spacing of your sleepers is the same as standard joists so you must select your sub-floor material/thickness as if the room was conventionally framed. I would also anchor your shims so they do not move over time. Since I envision these being driven between the sleepers and the slab your only anchor method may be construction adhesive. There are also rigid insulation boards, Homasote is one, that can be installed to insulate the floors.

Your plan of using taper cut sleepers/joists sounds great.


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## jackislost (Jun 21, 2015)

MI-Roger said:


> Remember that the spacing of your sleepers is the same as standard joists so you must select your sub-floor material/thickness as if the room was conventionally framed. I would also anchor your shims so they do not move over time. Since I envision these being driven between the sleepers and the slab your only anchor method may be construction adhesive. There are also rigid insulation boards, Homasote is one, that can be installed to insulate the floors.
> 
> Your plan of using taper cut sleepers/joists sounds great.


Thanks MI-Roger,

I actually am planning (may sound odd) to add 2x6's around the perimeter of the room, then attach the sleepers (joist) with a 2x6 hanger on each end. As of now the plan is 23/32 OSB T&G (is this an overkill?) for the sub floor. Was also looking at sealing the concrete before the vapor barrier, would this be acceptable? Yes rigid insulation will be cut to fit between sleepers, while also will be running plumbing and electrical under the subfloor. Going with plastic shims, and then the rigid insulation is of the pink variety that is common in these parts (Arkansas). 

I didn't state earlier about the walls but they are cinder block walls that I will add blue 6mil sheeting to blocks then styrofoam (blue color 1"), then 1x3 furring strips 16"oc and the same type of pink rigid insulation between the strips. Then drywall to finish it off. Im just hoping that all this will work and there will be no issues. About to spend several dollars on this and would like to only do it once instead of having to come back in a few years and do it all again. Any previous water issues from outside I believe will be corrected once I put the French drain in by the old door frame and the rest of that wall. I feel about 85% confident that I have a solid plan in place. 

Thanks for replying and hopefully no one gets upset for jacking the thread. Not my intentions, but gotta get help wherever you can find it especially when one doesn't like to admit they need it..... Have a great day.

Jack


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## SeniorSitizen (Sep 10, 2012)

The house has a history of being fine moisture wise except for a couple of areas, plumbing/shower and a poor choice with a door. 

What there no history of is the vapor barrier and insulation approach. I wish you well cutting off the ambient room conditions from the concrete that never was wet because of water soaking up through for all those years. If condensation decides to rear it's ugly head at the concrete surface, which will more than likely happen on an outside wall perimeter, what will the plan be for that. I frequently read the word "_sealing_" room air from the concrete surface. In my estimation a lot of folks are lost when they use that word.


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## jackislost (Jun 21, 2015)

SeniorSitizen said:


> The house has a history of being fine moisture wise except for a couple of areas, plumbing/shower and a poor choice with a door.
> 
> What there no history of is the vapor barrier and insulation approach. I wish you well cutting off the ambient room conditions from the concrete that never was wet because of water soaking up through for all those years. If condensation decides to rear it's ugly head at the concrete surface, which will more than likely happen on an outside wall perimeter, what will the plan be for that. I frequently read the word "_sealing_" room air from the concrete surface. In my estimation a lot of folks are lost when they use that word.


Not sure I am tracking what you are getting at. If your speaking about my situation then, first there was no insulation whatsoever in the area that I am redoing. As far as a vapor barrier, there is none to my knowledge whether under the pad or on top of the pad. The house was built by the grand-dad of the person I bought it from which has had water issues for knows how long. After I bought it I went under the crawl space 3 months or so after purchasing it. We had just had a decent rain and I go in the crawl space and find about 8 inches of water standing against a load bearing thats within the last 5 feet or so of the house. Well I know that didn't just start happening after I moved in. So there has been a water issue with the house up until I moved in. I began correcting the issue with French drains, gutter drains and now the last part of it, the addition built on the slab. 

So the question is if condensation rears its ugly head.... whats the plan...???? I have no clue. First, what are the ramifications of condensation on the outside perimeter of the wall? I truly don't know. And is it wrong to seal of put a vapor barrier like I have planned on doing? I am learning as I go so please do tell me because I don't want to make a mistake. I am about to drop some big change to purchase the materials and I would like to only do that once and not have to come back in a couple of years and have to revisit the same situation. Thanks for your time.

Jack


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## SeniorSitizen (Sep 10, 2012)

jackislost said:


> Not sure I am tracking what you are getting at. If your speaking about my situation then, first there was no insulation whatsoever in the area that I am redoing. As far as a vapor barrier, there is none to my knowledge whether under the pad or on top of the pad. The house was built by the grand-dad of the person I bought it from which has had water issues for knows how long. After I bought it I went under the crawl space 3 months or so after purchasing it. We had just had a decent rain and I go in the crawl space and find about 8 inches of water standing against a load bearing thats within the last 5 feet or so of the house. Well I know that didn't just start happening after I moved in. So there has been a water issue with the house up until I moved in. I began correcting the issue with French drains, gutter drains and now the last part of it, the addition built on the slab.
> 
> So the question is if condensation rears its ugly head.... whats the plan...???? I have no clue. First, what are the ramifications of condensation on the outside perimeter of the wall? I truly don't know. And is it wrong to seal of put a vapor barrier like I have planned on doing? I am learning as I go so please do tell me because I don't want to make a mistake. I am about to drop some big change to purchase the materials and I would like to only do that once and not have to come back in a couple of years and have to revisit the same situation. Thanks for your time.
> 
> Jack


Ok, I'll state another way. The proposed insulation will make the concrete colder than it was before because there was never insulation between the concrete and it's heat source before. The room air was previously the heat source for the concrete.

Example: With the insulating / vapor barrier plan, with the room air being 75 degrees with a relative humidity of 48 percent, if any of that room air reaches the concrete that should cool to 54 degrees or below, condensation will form on the concrete and you will probably never know it happened until the strange musty smell is emitted because of mold.

Can you seal the two separate areas so room air never reaches the cool concrete surface. There are a lot of people that think it can be done and if they can I'm all for it. 

But it reminds me of the crawl encapsulating plan. Has anyone gone back in 5 or 10 years and reported the mess they find after they were sure their job was perfect?


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## jackislost (Jun 21, 2015)

SeniorSitizen said:


> Ok, I'll state another way. The proposed insulation will make the concrete colder than it was before because there was never insulation between the concrete and it's heat source before. The room air was previously the heat source for the concrete.
> 
> Example: With the insulating / vapor barrier plan, with the room air being 75 degrees with a relative humidity of 48 percent, if any of that room air reaches the concrete that should cool to 54 degrees or below, condensation will form on the concrete and you will probably never know it happened until the strange musty smell is emitted because of mold.
> 
> ...


So sounds like I could get rid of the 6mil plastic (visqueen) and just got with the rigid insulation. At least thats the way I perceive it. You are truly far more knowledgeable about this type of stuff than I am and I can't even keep up with what you are trying to tell me. I understand that when warm air and cool air meet then condensation happens. In my pea sized brain I saw the rigid insulation as the barrier right under the sub floor, whereas the 6mil visquene placed on the concrete would serve as the barrier from anything below that. Hence creating a dead space, if you may, between the bottom of the sub floor to the concrete.... 

I will add that the room in question has never had more than a window unit in it to provide heat and air. It doesn't get ran very much because the son of a gun is will raise my electric cost by way to much. So when its super cold, we will turn the heat on a few hours at a time. A) to keep office equipment safe, and B) we let the dogs in when it gets real cold and they sleep in that room. In the summer the AC would be turned on for a hour or two a day when I come in from working but that would generally be it. 

I wish that I could wrap my brain around your previous suggestion, but I am more lost now then when we first started this banter. But thats ok, I have yet to buy my materials list and hopefully I will ge able to grasp the idea b4 I do that. Thanks


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## Homerepairguy (Aug 1, 2010)

jackislost said:


> I have yet to buy my materials list and hopefully I will ge able to grasp the idea b4 I do that. Thanks


With all of the mold possibilities that have been discussed, maybe reconsider leveling with sand mortar mix. If the surface does not end up being flat and level enough, then use some self leveling floor compound to finish.


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## 123pugsy (Oct 6, 2012)

Homerepairguy said:


> With all of the mold possibilities that have been discussed, maybe reconsider leveling with sand mortar mix. If the surface does not end up being flat and level enough, then use some self leveling floor compound to finish.


This sounds good.

Dricore panels on top of the level floor and done.

http://dricore.com/nw/subfloor_installation_videos.php


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## jackislost (Jun 21, 2015)

Ive got a 3" difference in slope in some places. And I do like the idea of the Dricore panels or something similar to that. What were you thinking "Homerepairguy" that one should do after using your purposed method? Just lay subfloor down and get after it? Would like to know what you would do after that.... I do appreciate everyone chiming in with some advice. Thankfully I am under the weather and not feeling well or I would have probably already bought my materials. Which I would have probably already regretted, so again I am sincere when I say thanks. I appreciate it.


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## Homerepairguy (Aug 1, 2010)

jackislost said:


> Ive got a 3" difference in slope in some places. And I do like the idea of the Dricore panels or something similar to that. *What were you thinking "Homerepairguy" that one should do after using your purposed method? *Just lay subfloor down and get after it? Would like to know what you would do after that....


I would fill in with concrete (rock & sand) where thickness allows finishing the top, and use a sand mortar mix for the rest to taper to zero. Because it's hard to finish to zero with a sand mix, maybe consider a self leveling floor compound to finish the top. Then I would abandon the wood floor preference and install vinyl floor tiles on top. (Sometimes gotta go with the situation that one's got)

Actually I did this on our home. There was about a 1.5 inch drop in one corner of a back bedroom due to a retaining wall buckling. I had a new retaining wall built and that stopped the ground settling.

I leveled that bedroom floor using a sand mortar mix, tapering to zero. I installed floor tiles (asphalt or vinyl, I can't remember) on top. Installed new baseboards around the perimeter. (Electrical wires were lifted to accommodate the new baseboards.)That was 40+ years ago and we have not had a single problem with that floor.

Hope things work out well,
HRG


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## jackislost (Jun 21, 2015)

HRG

Any thoughts of insulating the concrete floor before putting the vinyl down???? Thanks

Jack


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## Homerepairguy (Aug 1, 2010)

jackislost said:


> HRG
> 
> Any thoughts of insulating the concrete floor before putting the vinyl down???? Thanks
> Jack


Ah no. I must admit that living in Hawaii, insulating the floor never crossed my mind. That said, I couldn't figure out how to do it when leveling an existing concrete floor that goes from zero to a 3" drop.

As far as installing in floor heating, I guess one could jack hammer grooves in the existing concrete where necessary to lay pex tubing. Research shows that pex tubing should be 1 to 2 inches below the surface for optimal results. Also that one must insure that there are no chemical additives in the concrete that will react with the pex tubing.

In spite of the high cost of living in Hawaii, I guess there are a lot of pluses when it comes to home construction ... :wink:.

HRG


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## scootermcrad (Jul 23, 2012)

Oh wow. I just saw this was bumped up. Sorry to be late on the response!

I have been in the middle of a mess with permits, thanks to the contractor I hired, but that's a whole different story and a different part of the house.

Okay! The update! I had actually purchase some heavy VP barrier ($$$!!) and ended up returning it and bought the Moistop product. Not only was it CHEAPER, but it's actually designed for this application. Four 25-foot rolls will get the job done for me, taping the seams with their tape. I purchased a hefty pile of pressure treated lumber, Tapcon screws, and a new hammer drill for the job (which is definitely recommended for the installation). I'll be shimming with plastic shims and cutting to match the contour of the floor where needed. Bought a nice laser to get all my markings.

The plan is to put down the Moistop barrier, then the floor structure will be built over that and secured with Tapcons. Floor joists will be 16" OC, like normal. I also plan to use a perimeter structure, as mentioned by others. Once the floor structure is down and leveled out and every little nook and cranny is sealed, I'm having the insulation guys come in. They will be doing open cell in the roof structure and closed cell in the floor to seal up every last little air pocket that could be present. Once the floor is insulated I have the option of puting 15 or 30 pound felt paper over that, or just go right to a proper subflooring like 3/4" Advantech. Then I'm ready to finish up the rest of the room.

Does anyone see a reason to go the extra mile and put the tar/felt paper down before the subfloor goes down, or is this a waste with the closed cell insulation, since in theory nothing should be getting through?

This has been a hell of a project, and it doesn't help that there's a million opinions on the subject. This project also has to be my focus in the next few months in order to show progress for my permits. So updates will be coming soon! At least the plan is in place, finally.


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## 123pugsy (Oct 6, 2012)

No need for felt paper.

Open cell for the roof? Is this just for sound?


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## scootermcrad (Jul 23, 2012)

123pugsy said:


> No need for felt paper.
> 
> Open cell for the roof? Is this just for sound?


Yeah, I agree. I'm thinking I gain nothing with felt paper. 

Yes, open cell in a 2x10 cathedral roof structure for insulation and sound. Seems to be common practice here. Anything "on-slab" or grade level is recommended closed cell. They will come in and do both at the same time.


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## 123pugsy (Oct 6, 2012)

I understand the open cell is a lower r value.
Am I mistaken?


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## scootermcrad (Jul 23, 2012)

123pugsy said:


> I understand the open cell is a lower r value.
> Am I mistaken?


That is correct. Lower R value. It takes more open cell to achieve the same R value as closed cell, per volume. The flip side is, closed cell is much more expensive per volume. Because I have 2x10 rafters, I can achieve the R value I'm after for still less money than the closed cell with room to spare. The other part of this is the argument of "closed cell versus open cell" in a leak situation, etc., which we'll save for another thread.

Closed cell for the floor structure is ideal (and recommended by the installer). Low volume (height of structure will range from 1.5" to 5.0" between joists), and the closed cell won't absorb any moisture. The price will probably still be somewhat hefty, but that floor will be toasty in the winter and from a sound standpoint, great for this room, since this is where I'll have a nice audio system.


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## scootermcrad (Jul 23, 2012)

Small update... I need some input.

Prepping the slab floor for the vapor barrier to go down. Starting to realize I have a lot of work to do to this slab, or so it seems. I have a low spot where an old drain was (now filled) and I have some exposed brick embedded in the slab where a wing wall used to be. Also a couple cracks I should seal. (Pictures attached)

The low spot for the drain is about 1-1/2" deep (or less) and is about 3-4 feet in diameter. Can I fill this with Quickcrete or something similar, or is there a SLC I can mix up that I'll be able to fasten to that won't crack?

What should I used for the exposed brick to make sure it's not wicking moisture up through the slab and under my barrier? Seems like I need something I can trowel over it and smooth out.

What about sealing the cracks? I'm assuming something like Sakrete "Concrete Repair" in a caulking tube is okay for something like this?

Pictures attached of the areas. So about the rotation on a couple of the pictures. :glasses:

Thanks!


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## scootermcrad (Jul 23, 2012)

Can I use a general non-shrink grout like Quickrete or Sakrete for the majority of this?


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## Nealtw (Jun 22, 2017)

Do what ever you want to the floor cracks and brick there will be no such thing as stopping the wicking.
The low spot is best served with matching shims slid in from both sides about ever 16" where it is low. Plastic or sill gasket between wood and concrete sealed or not.


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## scootermcrad (Jul 23, 2012)

Nealtw said:


> Do what ever you want to the floor cracks and brick there will be no such thing as stopping the wicking.
> The low spot is best served with matching shims slid in from both sides about ever 16" where it is low. Plastic or sill gasket between wood and concrete sealed or not.


There is sill gasket between all wood framing and concrete, currently.

My vapor barrier is not flexible enough to push down in that large dip for the drain, so I'll need to bring it up reasonably close to level with the surrounding floor. I'm mostly trying to prevent air pockets wherever possible. The Fortifibre barrier has some good weight to it, but anywhere I can prevent pockets the better.


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## F250 (Feb 13, 2018)

Since the fill around the drain doesn't need to be structural, I would use the cheapest concrete mix I could find (sand-mix only).

Also, on your ceiling insulation... in addition to your open cell bats, you can add a skin under the rafters with something like 3/4" closed cell panels and buy yourself another jump in R.


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## scootermcrad (Jul 23, 2012)

F250 said:


> Since the fill around the drain doesn't need to be structural, I would use the cheapest concrete mix I could find (sand-mix only).
> 
> Also, on your ceiling insulation... in addition to your open cell bats, you can add a skin under the rafters with something like 3/4" closed cell panels and buy yourself another jump in R.


Thanks! Seems to make sense. It's really just filling a void and needs to hold a couple Tapcons for the structure.

For the ceiling insulation, decided to just leave it to the pros for the sake of installation logistics (scaffolding will be required). They will be spray foaming it.


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## F250 (Feb 13, 2018)

Unless you use some sort of epoxy concrete fill, I would not shoot Tapcons into that low spot fill area at all because it will get shattered by the impact. 

You might just need to drill and drive some longer concrete screws through the fill and down into the original concrete... just in the low spot fill areas.


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## scootermcrad (Jul 23, 2012)

F250 said:


> Unless you use some sort of epoxy concrete fill, I would not shoot Tapcons into that low spot fill area at all because it will get shattered by the impact.
> 
> You might just need to drill and drive some longer concrete screws through the fill and down into the original concrete... just in the low spot fill areas.


I guess in reality, I probably don't NEED to put Tapcons in smack-dap in the middle of that area. Lord knows there will be plenty of weight. I'll keep the patch as small as possible so that I don't have to span more than about 24-inches without a screw. I think that is very doable. Good point!


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## Canarywood1 (May 5, 2012)

I see this thread was started in 2012, are you saying you still don't have it complete after almost 6 years???, i think someone is pulling someones leg.


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## F250 (Feb 13, 2018)

Canarywood1 said:


> I see this thread was started in 2012, are you saying you still don't have it complete after almost 6 years???, i think someone is pulling someones leg.


Sharp eye, Canary!! Look back at Post #17 where the OP picked up the thread again after a letting the project sit for, what? Yes, about 6 years.


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## scootermcrad (Jul 23, 2012)

Canarywood1 said:


> I see this thread was started in 2012, are you saying you still don't have it complete after almost 6 years???, i think someone is pulling someones leg.





F250 said:


> Sharp eye, Canary!! Look back at Post #17 where the OP picked up the thread again after a letting the project sit for, what? Yes, about 6 years.


Yep! Almost 6 years! I have a car I've been building for over 11 years. I just have a busy life with work and family. I work on things when I can. Definitely takes the fun out of it, sometimes.


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## scootermcrad (Jul 23, 2012)

Made a little progress this weekend prepping the floor for my Moistop VB to go down. I have a question.

There are three wall sections in this room that have PT sill plates sitting on foam barrier strips/gaskets. The Moistop barrier will get taped right up on these sole plates. I assume I want to apply sealer between the slab and the sole plate to prevent moisture from finding it's way through that barrier strip, correct?

Couple more details to wrap up and the Moistop is going down so I can start building a structure! FINALLY! I just don't get to work on this very often.

On a side note, before the siding and flashing was installed on the exterior of the building, water had a tendancy to get in through the gasket when we had bad rain storms. Once all that was installed, dry as a bone, but it tells me that moisture does have the ability to move through the gasket at some level.


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