# replacing plywood subfloor, please help



## crankbait09 (Mar 26, 2011)

I am in the process of replacing my existing particle board subfloor with plywood. I will be installing ceramic tile after all said and done.

I am getting mixed information and could use some more advice and see how it compares to what I have heard thus far.

I have been told that I need a 3/4" plywood subfloor. 
I only need the one layer of plywood subfloor. No need for two or more layers.
I can use 3/4" normal plywood.
I can use 3/4" tongue and groove plywood.
I do not need to seal the subfloor with a Kilz primer or something of the sort

I really don;t know what is right or wrong. Can anyone share their thoughts?

thank you


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## JazMan (Feb 17, 2007)

Hi Crank,



Crank said:


> I have been told that I need a 3/4" plywood subfloor.


¾" ply or OSB subfloor base is what I'd want as the minimum for ceramic tiles.



> I only need the one layer of plywood subfloor. No need for two or more layers.


One layer is good enough as long as the joists spacing is to specs. Of course more is better. 



> I can use 3/4" normal plywood.


If normal means square edge, no t&g, no you can't just use one layer. Subfloor-grade ply/OSB is always t&g, otherwise it's underlayment.



> I can use 3/4" tongue and groove plywood.


That's correctomundo.



> I do not need to seal the subfloor with a Kilz primer or something of the sort


That's right again.

Now tell me what you're gonna install directly over the subfloor? Concrete backer or a membrane? 

Has anyone mentioned the specs for the joists system? We should start with that, the framing.

Jaz


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## crankbait09 (Mar 26, 2011)

ok, i have a question about the T&G compared to regular 3/4" plywood.

lets say, i buy the T&G, and due to the shape/size of the area that i am flooring, I need to make specific cuts. Well the tongue and the groove are on one end of the board or the other. So if i leave the tongue in place on one end but have to cut the other end off due to needing a smaller size, i now have a normally cut piece of plywood, right? well, when i cut the next odd ball sized piece, there is no T or G for me to connect to. so at that point, im just butting one piece of plywood to the other with no T or G.

so, if I do that. what purpose is T & G if I ended up cutting them off?

why cant i just use normal plywood instead of the T &G?

am i making sense?

once the subfloor is in place, I will be placing a hardyboard (i think thats the name of it), on top of the subfloor, then ceramic tile on top of that.


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## ron45 (Feb 25, 2014)

Are you implying that your floor joist are not uniform and spaced properly.?


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## crankbait09 (Mar 26, 2011)

i wont know about the floor joist spacing till i remove the existing subfloor. but i need to make sure i have the right type of subfloor purchased and sitting here ready to go. I have dogs and i dont want the floor open. 

Prior to this thread, i did purchase 3/4" plywood, not T&G. I was going off the experience that my local big box store shared with me. Then I came home and googled how to do this project, then i started seeing the T&G type of subflooring.

I just want to make sure that I do in fact need to return the purchased ply and actually buy the T&G


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## TarheelTerp (Jan 6, 2009)

crankbait09 said:


> I am in the process of replacing my existing (T&G OSB) subfloor with plywood. I will be installing ceramic tile after all said and done.
> 
> i wont know about the floor joist spacing till i remove the existing subfloor.


*One more time:*
WHY do you believe that you need to remove the existing subfloor?


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## Bud Cline (Mar 12, 2006)

Let's take a step back for a minute.
You say you are replacing particle board. Is it (in fact) particle board, or is it oriented strand board you are taking out?
If you are removing the existing product and exposing the floor joists then YES you must use T&G. It should also be glued to the floor joists.

Once you begin the lay-in you will always want to have tongues and grooves interlocking in all cases. There is no instance where you need to remove a tongue or groove and dismiss the interlocking.

In some cases (corners) the cuts can be difficult to get into place when you have to interlock two sides of a panel at the same time. In this case the panels would have to be cut slightly short so that it can be slid into place effecting an interlock in both directions. This is where you will likely need to install some blocking/cleats to the floor joists to accommodate proper support and fastening of the new panels.

In no case would you have a square edge anywhere in the field.


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## crankbait09 (Mar 26, 2011)

TarheelTerp said:


> *One more time:*
> WHY do you believe that you need to remove the existing subfloor?


when I removed the existing sticky back tile, the particle board under the sticky back tile was chipping away and more than 3/4 of the tiles area was moldy (black mold).

So I was going to remove that double layer of particle board (like you find in walmart furniture), and replace it with 3/4" ply


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## crankbait09 (Mar 26, 2011)

Bud Cline said:


> Let's take a step back for a minute.
> You say you are replacing particle board. Is it (in fact) particle board, or is it oriented strand board you are taking out?


it is in fact particle board. It's the same type of material that you see in walmart furniture.




Bud Cline said:


> If you are removing the existing product and exposing the floor joists then YES you must use T&G. It should also be glued to the floor joists.


the floor joist will be exposed. I bought Liquid Nails subfloor adhesive (interior/exterior)



Bud Cline said:


> Once you begin the lay-in you will always want to have tongues and grooves interlocking in all cases. There is no instance where you need to remove a tongue or groove and dismiss the interlocking.


If I am not mistaken, there is a tongue on one edge, and the groove on the opposite end, right? Maybe I am over thinking that, but if I run out of room to place subfloor, I will have to cut the board in order to fit. therefor, losing the groove edge. no?

also, if i install the tongue and groove plywood (3/4"), Can I use 2-1/2" Galvanized screws (gray box at HD) to fasten it to the joists? Is that type/size ok?


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## MT Stringer (Oct 19, 2008)

Is this what you are talking about?
http://www.lowes.com/pd_12218-99899...URL=?Ntt=tongue+and+groove+plywood&facetInfo=

There is a tongue along one side and a groove on the other side, not the end. The board spans the joists so there is no need for tongue and groove on the ends. Cut to fit as needed.

Hope this helps.


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## crankbait09 (Mar 26, 2011)

MT Stringer said:


> Is this what you are talking about?
> http://www.lowes.com/pd_12218-99899...URL=?Ntt=tongue+and+groove+plywood&facetInfo=
> 
> There is a tongue along one side and a groove on the other side, not the end. The board spans the joists so there is no need for tongue and groove on the ends. Cut to fit as needed.
> ...


yes, thats exactly what im talking about....other than the Lowes part


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## MT Stringer (Oct 19, 2008)

crankbait09 said:


> yes, thats exactly what im talking about....other than the Lowes part


Then I think your installation should go like these pics indicate.

Someone correct me if I am wrong. The purpose of the T&G is to support the subfloor between the joists. The ends should be cut to fit the center of the joists, thus no T&G needed.

I drew this quickly. Pics are far better than words, in my opinion.

Mike


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## hammerlane (Oct 6, 2011)

crankbait09 said:


> If I am not mistaken, there is a tongue on one edge, and the groove on the opposite end, right? Maybe I am over thinking that, but if I run out of room to place subfloor, I will have to cut the board in order to fit. therefor, losing the groove edge. no?


The edge that you would cut to fit would be because you are up against an edge like a wall. So you would not need the groove edge.


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## JazMan (Feb 17, 2007)

Crank,

Yes you are overthinking this. You will only cut the sheets where it goes against the wall. (be sure to leave the proper gap). You will not cut the part of the sheet that is in the middle of the room. 

Jaz


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## hammerlane (Oct 6, 2011)

JazMan said:


> Crank,
> 
> You will not cut the part of the sheet that is in the middle of the room.



I agree with JazMan...do nut cut sheets in the middle of the room and you'll be OK.


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## crankbait09 (Mar 26, 2011)

so the area that i am doing is an entry way. the entry way is 5' x 7', then there is a closet off of that that i will continue the tile work into, and thats 3' x 4'.

the T&G grain needs to go perpindicular to the joists, right?


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## ront02769 (Nov 28, 2008)

The narrow flT ends meet ON the joists, the tougue and groove sides go ACROSS the joists. Ron


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## MT Stringer (Oct 19, 2008)

crankbait09 said:


> so the area that i am doing is an entry way. the entry way is 5' x 7', then there is a closet off of that that i will continue the tile work into, and thats 3' x 4'.
> 
> the T&G grain needs to go perpindicular to the joists, right?


My drawing says it all. Did you take a close look at it?


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## crankbait09 (Mar 26, 2011)

ya, i saw that.

im nervous about cutting in to a joist. I am tapping on the floor, and hearing a little sound change from hollow/solid, but i am still nervous about exact location of the joists.

Is there a better way to determine exact location so i can make my first cut out to start piecing it apart?

When they made the house, they installed the register vent flush to the subflooring. so i cant even use that to determine thickness.

other than duct work, i cant imagine anything under this flooring (electrical/plumbing), but again, i dont really want to assume that.


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## HDS (Jun 21, 2014)

Try drilling some pilot holes to get a peek down. If after a short drill you haven't popped through, then you are probably on a joist. You should be able to see the nails too to help locate the joists.


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## crankbait09 (Mar 26, 2011)

i was hoping for the nail locations but there are ZERO nails in this particle board. im wondering if the previous owner used glue. which i think makes sense cause they had sticky back tile down. so no "craters" due to the nails would show when the tile was laid


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## crankbait09 (Mar 26, 2011)

ok, so after using the drill method, i was able to locate the joist locations. They seem to be on 16" centers. With that number determined. Will I be able to get by with 3/4 T&G as my subfloor? meaning ONE layer of subfloor? Then I will follow that with the hardyboard for the ceramic tile.


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## JazMan (Feb 17, 2007)

Crank,

Did you ever confirm that this particle board you're looking at is the subfloor and not a thin underlayment installed for the purpose of installing a vinyl floor? ¼" underlayment for vinyl would have been stapled and you won't see fasteners. Vinyl floors are not glued to the subfloor, that's why I think you're looking at ¼" particle board or similar stuff. 

I also asked about the joists & framing. Is any of this visible from below?

Jaz


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## crankbait09 (Mar 26, 2011)

Jazman,

After prying up what I'm calling subfloor, is actually what you are calling underlayment. So the underlayment is in fact 1/4" like you stated. i understand that now.

I can see the joists below in the crawl space. but what do you mean by framing??

I will be running a circ saw here shortly to pull up the existing subfloor/underlayment


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## TarheelTerp (Jan 6, 2009)

crankbait09 said:


> So the underlayment is in fact 1/4" like you stated.
> i understand that now.


I knew you didn't need a new subfloor.



> but what do you mean by framing??


 framing = structural lumber (like joists, wall studs, etc)



> I will be running a circ saw here shortly to pull up the underlayment


Get a long handled pry tool.


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## HDS (Jun 21, 2014)

Some pics would help.


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## JazMan (Feb 17, 2007)

OK, so, the subfloor is what? Probably plywood right?

Tell us about the house. How old, where is it? Tell us the size of the joists, the unsupported span and if at all possible the species and grade of the joists. (I won't hold my breath on that one). 

You don't need no stinking saw to remove ¼" stuff. One or two long crow-bars and maybe a small one. Other general tools like hammer etc. 

Subfloor = the material immediately on the joists. This is structural. Underlayment = the (usually) thinner material that is over the subfloor, a smooth, better grade to accept the floor covering. 

Jaz


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## crankbait09 (Mar 26, 2011)

Jazman

OK, now that I am back and the demolition has begun 

I will answer the questions before I ask more.

My home was built in 1994. It is located in Ohio. 
The joists are 2x9's. I was thinking that was an odd size and wasnt quite sure why they wernt 2x10's. But they are definitely 9" wide. They are mounted on 16" centers. As for the species/grade.....glad you wernt holding your breath for that one. I have no idea.

Now the questions........

In the main entry way, I removed all the subfloor as well as underlayment that was there. 3/4's of it was in pretty bad shape. The existing subfloor was 3/4" OSB T&G. So that was correctly done, right? 

I noticed that only certain spots of the subfloor were actually glued to the joist. Why would they not run adhesive the whole length of the joist? Once I peeled away the subfloor, there is residue remaining along with pieces of OSB that stuck to it. How do I clean off the joist so the new subfloor will lay perfectly?

As I was removing the subfloor, I got close to the wall, and noticed that the next joist was in fact under the wall. now, obviously I couldnt cut under the wall so i am not exactly sure how im going to fasten the new subfloor to the joist under the wall. I am attaching a photo that i hope is good enough for you to see what im dealing with. If its not clear, let me know, and i will take another.

next question. i have an existing register that is floor mounted. the register is nailed to the subfloor using galvanized roofing nails. The duct leading to the register is just hanging below. From what I can tell, if I remove the duct/connection to the plywood, what problems could I possibly run in to when installing new floor and register back in same location? I am also sending a photo of that area, but not close up. if you need a close up photo, i will get another one for you.

As for the closet that is off the entry way, that floor was perfecto!! Since there is zero foot traffic in that closet, I was able to pull off the particle underlayment and it exposed the plywood underneath. I may need to fill in a couple of gouges that were there already, but besides that, I should be able to add the cement board and tile that as planned. subfloor will remain!!! I am attaching a photo of the closet too. (There are still a crap ton of staples in the subfloor, but I know I need to remove them.

In front of the closet, there is a joist. How exactly do i cut the existing subfloor, so the cut is straight and cut perfectly in the middle of the joist so I have a joist to screw the new subfloor on to? In other words I have to share the joist. Little to no room for error when cutting


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## JazMan (Feb 17, 2007)

Crank,

2x10's measure 1.5 x 9.25" you've got 2x10" joists. That's very common.

¾" OSB subfloor is fine. There should be a continuos bead of construction adhesive bonding the sub to the joists, plus fasteners of course. Remove the old with chisel point putty knife or plane or ? Residue film is ok, but not anything thicker than a dime. 

Now is the time to check that the joists are all in plane with each other. You didn't answer my question asking for the unsupported span of the joists. Now would also be a good time to sister them to stiffen the joists. But since the house was built in '94 it should meet min. standards for ceramic. How did the floor feel before? I think it would be a good thing to do if you wanna take the time to improve the structure.

You do NOT wanna remove the subfloor from under the walls, (it's kinda hard to do anyway). The walls were put up after the subfloor and therefore rest on it. Cut the old a few inches from the wall if the joists go perpendicular to the wall, then install 2x10" blocking to support the new sheets. If the wall is parallel to the joists, you may have messed up and will need to install another joists, or get hangers and install shorts every 16" in the opposite direction. Looks like that's the situation in pic #1.

Let's deal with the other issues later.

Jaz


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## crankbait09 (Mar 26, 2011)

I'll ask these couple questions before I leave, but I will read the responses later........

So since I removed the ply from under that wall in one small section, do i continue all the way down doing the same or should I make my cut a couple inches away from the wall like you stated and worry about that one corner later? Once I hit a corcner, What can i use to finish the cut to remove the remaining plywood? I'm thinking jigsaw?

I will measure the unsupported span (length wise) and get back to you. 

When installing the mini joists in the opposite directions, how do you install them? Just nails? any specific length/type?

thank you for your help on this!


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## JazMan (Feb 17, 2007)

Crank said:


> So since I removed the ply from under that wall in one small section, do i continue all the way down doing the same or should I make my cut a couple inches away from the wall like you stated and worry about that one corner later? Once I hit a corcner, What can i use to finish the cut to remove the remaining plywood? I'm thinking jigsaw?


Leave as much of the old subfloor as you feel comfy with to make it as easy to install the new joist. Remember the edges of both the old and new must be supported. Also remember that when you piece in a small piece of subfloor, it should be supported by 3 joists, 2 can cause the edges to peak when a load is applied to the space between the joists. 

Another solution in your case might be to add an underlayment to give you a nice flat uniform base. If you do that it will have to be over the entire areas and needs to be installed in the same direction as the sub & min. ⅜" thick. 

Jigsaw, circular, whatever will fit and make a straight cut. 

The new joist (s) needs to be the same size as the old, 2x10". Use joist hangers available everywhere. 

Jaz


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## crankbait09 (Mar 26, 2011)

ok, so if i were to hang small joists as braces, perpendicular to the existing joists, do i need joist hangers with a span that small? If I do need them, i was looking at HD and say tons of options. how do i know what hangers to use? what type of nails/screws do i use to hang these joist hangers/joists? I will be taking measurements of the span that you requested tonight or tomorrow. (i have to get down in the crawl space for that)


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## JazMan (Feb 17, 2007)

Hangers make the job easier and better. They make nails for the job, but it's not critical in your case. They should be 1.5" long. Screws using a magnetic bit might be a good idea for this. Use good screws, not drywall screws.

Jaz


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## crankbait09 (Mar 26, 2011)

I'm back now. I finally got all of the old subfloor/underlayment pulled up. I still need to clean off the old OSB/adhesive from each joist. 

I am posting a picture of the status thus far. 

I was going to stop at HD tomorrow or the next day and purchase the 2x10 joists and hangers so I have them at the house when it comes to the point of installing them. 

If my calculations are right, i will need (5) 2x10 joist that will lay perpendicular to the existing joists, which will be spaced 16" o.c.. I will run 5 of them in the first row on the left. then i will do the same layout for the row on the far right. each row of little joists will have a total of (10) joist hangers (2 per mini joist, 5 joists in each row). I was looking at the HD website and they have 3 different types of joist hangers, ranging from $1.50-$5.00 each. since that is a considerable price difference, can you help me in determining which one will work for my needs? As for the screws to mount the joist hangers, you mentioned not using drywall screws, can i used the galvanized screws that HD sells (gray boxes)? Or should I be thinking of something else? 

in the photo attached, you will see in the lower left corner, the area that i screwed up. Should I just notch that area out and clean it up? How can I go about fixing that? 

other than that, i think it looks good. (but thats a total rookies thoughts  ).


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## HDS (Jun 21, 2014)

Could you slide in a full 2x10 and just add a couple of new joists? How far do the joists go until they are supported by a beam?


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## crankbait09 (Mar 26, 2011)

I forgot to get the span that Jaz asked me for. I'll get that answer tomorrow


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## HDS (Jun 21, 2014)

On the left side, does the wall sit flush with the joist? if you sistered in a 2x10 and removed the plywood, you might be able to support the new subfloor.


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## JazMan (Feb 17, 2007)

Thanks for the pics, they help. The pics show something a little different from what I thought.

HDS is right, you need to add, (sister) two long joists on the right and left, the 1st and 5th joists. Also install blocking on the other two sides. You can use hangers for these short joists, 4 near the door and the same on the opposite end. 

It's best to glue and bolt, or at least screw, the two joists to the old. The two new joists don't have to rest on the center beam or the outer wall for support, but can if you can do it. 

Jaz


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## crankbait09 (Mar 26, 2011)

so the little perpendicular joists are not an option at this point???? that is easier for me to do by myself. without measuring, i poked my head through the crawl space and noticed there was no end in the joist run. or if there was, it was blocked with insulation. SO i will need to get down there and determine exactly how long the run is. I will figure out the span exactly. Why exactly is it critical to know the existing span?

so right now, i need to be set on which joist option i go with. little perps, or new long runs. not comfortable with the thought of long runs, but i will do what i need to do. please advise


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## crankbait09 (Mar 26, 2011)

HDS said:


> On the left side, does the wall sit flush with the joist? if you sistered in a 2x10 and removed the plywood, you might be able to support the new subfloor.


onthe left, the wall sticks out maybe 1/4" from the existing joist underneath. so not exactly flush


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## HDS (Jun 21, 2014)

crankbait09 said:


> onthe left, the wall sticks out maybe 1/4" from the existing joist underneath. so not exactly flush


If that is the case, you should be able to sister in a second 2x10 the entire length (even supporting it on the foundation wall) and still have a good inch sticking out for your subfloor to sit on.

Cut back the old subfloor flush to the wall on the left side.
Add blocking at the opposite end of the door where the old subfloor will meet the new subfloor. You want to support the edges.

If you can, add a piece of scrap wood to the bottom of the floor joist where the blocking is going. You can use this as a shelf to hold the 2x10 you are going to sister in. Measure the distance from the blocking to the foundation pocket/rim joist to get the length of your sister joist. Cut the 2x10 a bit short, say 1/2 to 1" so you can slide it in easier and still have room to rest on the sill plate.

Take your 2x10, notch the top slightly (1/2" deep by 4-5") so it'll slide into the foundation pocket. Get some construction adhesive and put a bead on the old joist. 

Slide in the new 2x10 in and up against the old floor joist. Using 3" decking screws, screw it in place. Don't use drywall screws. 

You can use nails, but it is going to be hard to swing a hammer between floor joists. If you don't have one, get or borrow an impact driver for putting in the screws.


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## crankbait09 (Mar 26, 2011)

Can you please explain to me what this blocking is? I don't understand what that is/means.


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## JazMan (Feb 17, 2007)

Crank,

The two long joists would be better and should be easier too. They don't have to go all the way to the supports if that's too hard. All they're for is to support and fasten the new ply to. They don't even have to be the same width. 

The span of the joists info is to make sure they're stiff enough for ceramic tile. I don't recall a mention of when the house was built. Modern specs should be good enough for ceramic/porcelain, just making sure. 

Blocking in your case would be the short joists, (14.5") that you will fasten between the joists at both ends. North and South as we look at the pic.

Jaz


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## crankbait09 (Mar 26, 2011)

JazMan said:


> Crank,
> 
> The two long joists would be better and should be easier too. They don't have to go all the way to the supports if that's too hard. All they're for is to support and fasten the new ply to. They don't even have to be the same width.
> 
> ...


I am attaching another image of what i was thinking and also what i was imagining from what you said. lets clear that up first.........


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## HDS (Jun 21, 2014)

crankbait09 said:


> I am attaching another image of what i was thinking and also what i was imagining from what you said. lets clear that up first.........


You'll still need the 'New Perp Joists' aka blocking, at the ends where the old subfloor meets the new subfloor. You'll need it between all 4 of your joists openings. Half will be under the old subfloor, and half under the new subfloor to give added strength.

On your interpretation, you are spot on (plus adding the blocking across the width to support where the old and new subfloors meet.) The question is, on the right side when facing the door. how close is that joist to the edge of the wall. If you remove the extra subfloor and sister a joist to it, will it stick out enough to support the subfloor?


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## HDS (Jun 21, 2014)

Sorry it isn't to scale, but the red would be the new joists you'd add.


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## JazMan (Feb 17, 2007)

HDS,

You need blocking between the joists on the fourth side too.

Jaz


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## crankbait09 (Mar 26, 2011)

ok........so if i am finally understanding this right....i am only placing a perp joist or full span joist wherever the existing/new will meet at the ends. i can run a full length joist parallel next to the existing joist. screw them together so they now would be doubled up to make two. so i could use (3" decking) screws to screw them together. then I could lay the new sub floor on top and only use the new joists as a screwing point. so essentially im doubling up the joist to make it thicker.

right? am i finally making sense of all this? 

does this nix the joist hangers since I am using screws to double up the existing?


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## crankbait09 (Mar 26, 2011)

HDS said:


> The question is, on the right side when facing the door. how close is that joist to the edge of the wall. If you remove the extra subfloor and sister a joist to it, will it stick out enough to support the subfloor?


I am not sure on this. I'd like to leave it alone if i could. this just leaves more room for error and something else i create more work for myself in attempting.


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## crankbait09 (Mar 26, 2011)

HDS said:


> Sorry it isn't to scale, but the red would be the new joists you'd add.


this is what i was picturing!!

thank you for the patience and teaching!!!


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## JazMan (Feb 17, 2007)

Your interpretation is right xcept for the 8 pieces of blocking on the north & south ends of the pic.

You should glue & screw/bolt. Give us the span just in case you should sister all those joists. How did the floor feel before. Did you ever tell us the age of your house?

Jaz


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## crankbait09 (Mar 26, 2011)

as for the span, i will get that for you tonight (PROMISE!!) when measuring the span, i am just measuring how long the joist goes before it hits the end or the beginning of the next run, right?

the floor was NEVER squishy/springy. It was solid. at least the main traffic area. never really walked on the edges.

the house was built in 1994.


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## crankbait09 (Mar 26, 2011)

screwing and adhesive - check.

no joist hangers needed now????


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## JazMan (Feb 17, 2007)

A house built in '94 should meet min. specs of L360 deflection. 

You might want hangers for the blocking. How were you planning to install those? I guess you could toe-nail/screw, but it's easy for the joist to move ⅛" and mess things up. 

You're installing ceramic tiles right?

Jaz


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## crankbait09 (Mar 26, 2011)

So if the end joists that are the perps are called "blocking", what are the added joists that are running side by side to the existing joists called?

Ok, so if i need joist hangers, what ones do i get? There were a few options. No clue what one is used for over the other.

i thought everything was going to be hung using decking screws


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## crankbait09 (Mar 26, 2011)

yes, i will be installing ceramic tiles after this mess is over with


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## JazMan (Feb 17, 2007)

Crank said:


> what are the added joists that are running side by side to the existing joists called?


They're still "joists". But since it's attached to the other, it's called a "sister", thus you are "sistering". 



Crank said:


> Ok, so if i need joist hangers, what ones do i get?


Heck if I know specifically which one. I don't even know what choices you have. Will you use 2x10's" You don't have to. It's not critical in this case, you're not holding up a joists just blocking to stiffen the ply between the joists. * http://www.strongtie.com/products/connectors/lus-hus.asp 

Jaz


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## crankbait09 (Mar 26, 2011)

ok, so what i am gathering, i am not adding any structural support at all, right? but rather i am just adding boards to screw the subfloor to, right?

so the sister boards, will be screwed into each other, no hangers needed.
the blocking will need joist hangers that go from inside to the inside of existing joist....right?

i think id rather use 2x10's for the sisters/blocking to keep it uniform


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## JazMan (Feb 17, 2007)

Crank,

I'm gonna need your address or email so I can send you an invoice.:laughing:

The sisters make that joist stiffer therefore sturdier. Why would you need hangers?



> the blocking will need joist hangers that go from inside to the inside of existing joist....right?


Yes, unless the rim-board is close enough to sister into that. Hard to tell how far out the subfloor comes on the door/wall side. Can't see the near side.

Jaz


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## crankbait09 (Mar 26, 2011)

don't you regret tapping in to this thread!!?? i certainly regret deciding to tile the floor!!

im actually thinking.....if i were to place a sistering joist for the rim-board and it does stick out far enough to support the new subfloor, then i wont need joist hangers. hmmmmm

im checking that tonight.

i will be getting back to you with:

1. the span of the existing joists
2. how much the rim board hangs out to where i can double it up


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## crankbait09 (Mar 26, 2011)

ok, here are my findings............

1. see attachment for existing joist layout, the 9'-4" span is the entry way. then it ends at 9'-4 and starts the new run of 16'. the two joists meet like shown below. they are mounted to the center brace as shown.

2.if i were to double up the rim-board all the way around, the only side that would benefit from that would be the right side by the closet door. all other three sides wouldnt even touch the sister joist. 

so. where do i go from here with the info i just gave you?


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## JazMan (Feb 17, 2007)

If you can sister direct to the rim, do it. It's better and very easy. 

1. 9'4" is a good span. 16' is very marginal. I'd have to know the species and grade too. Are you tiling the whole area? 

2. I'm not understanding what you're saying about rim boards. I thought you had only one side with rim board. On the north side where that door is shown in post #34. But fasten to rim or joists if at all possible. Then of course you don't use hangers.

Jaz


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## crankbait09 (Mar 26, 2011)

JazMan said:


> If you can sister direct to the rim, do it. It's better and very easy.
> 
> 1. 9'4" is a good span. 16' is very marginal. I'd have to know the species and grade too. Are you tiling the whole area?
> 
> ...


1. the only area being tiled is the entry way, which is on the 9'-4" span. the 16' span is running towards the back of the house, which im not touching. it's remaining carpeted. I may do the kitchen at a later date but after this project, i may boycott that all together!!

2. when you guys mentioned a "rim board", i thought that meant any board running along the edge. so any existing plywood i left behind, i thought that was rim board. guess not . again, terminology that i know nothing about.

so yes, the only rim board i have, is on the north side (as you stated).

3. so since i am not close enough to existing joists to just use "sistering", what should i do now?


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## JazMan (Feb 17, 2007)

1. Boycott if you want. If you're married, how comfy is the couch?

2. Rim boards are the "joists size" pieces at the outer "rim" of the house or over other concrete walls. 

3. You can fasten several 2x10's to bring the last one out far enough. Or you could toe-nail most and just use a hanger for the last bay. Or? Just put something there to support the ply.

Jaz


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## crankbait09 (Mar 26, 2011)

to me it seems as if i were to do the (5) perpendicular joists like i was thinking, would be the easiest and would be the most support i could get. no?

ok, it sounds like it i am now at the point where I need to decide how to support the subfloor. It sounds like there really isnt a right or wrong way to do this, as long as the ply is supported.

correct?

i will see what i come up with. then after that, it is time to begin the tile process!!


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## JazMan (Feb 17, 2007)

Well...........do it any way you want, but it'll be wrong cuz since there is no t&g you're recreating the same situation as on the north/south sides. You'd have to install 5 with hangers and then also install blocking to support the ends. 

Got some paper handy to draw it so you can picture it?

Jaz


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## crankbait09 (Mar 26, 2011)

sigh............

"3. You can fasten several 2x10's to bring the last one out far enough. Or you could toe-nail most and just use a hanger for the last bay. Or? Just put something there to support the ply."

ok, so if i were to build the 2x10's (4) thick along the north side, that would give me enough to mount the plywood. I wouldnt need 4 thick along the east and west walls, more like (2) thick. how do i handle the south section? i have no perp running joists to connect to

i feel like anything i thought i understood, was not as clear as crystal as i thought


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## JazMan (Feb 17, 2007)

My suggestion in "3" is for the north wall only. You should sister the east & west joists. You will probably need to block the south side, but I'm taking a WAG cuz there is no pic of that side.

Who's gonna do this work anyway? Got help?

Jaz


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## crankbait09 (Mar 26, 2011)

i can sister the east/west wall as many deep as i need as well??? (I need one maybe two deep on the west, and one deep on the east). the west wall has the HVAC duct I need to hook back up. so I'd have to cut that out.........so the sistering of the joist would be in the way

I will post a pic of the south wall tomorrow. but it is nothing more than the existing plywood, only mounted on the existing joists. no perp joists either.

i saw the prices of these 2x10's. that will add up quickly as well. can i get by with a 2x4, or 2x6?

this work is all me. which is why i am asking so many questions. I know no one that does this type of work or is knowledgeable with it.


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## JazMan (Feb 17, 2007)

> i can sister the east/west wall as many deep as i need as well??? (I need one maybe two deep on the west, and one deep on the east). the west wall has the HVAC duct I need to hook back up. so I'd have to cut that out.........so the sistering of the joist would be in the way


You could shim out as you stated, or how about trimming the subfloor a bit more. I have no way to tell you what to do with the HVAC.



> I will post a pic of the south wall tomorrow. but it is nothing more than the existing plywood, only mounted on the existing joists. no perp joists either.


That's what I'm expecting to see. How far away is the beam? You will block the south side too.

You can use smaller dimensional lumber as I stated before.

Jaz


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## crankbait09 (Mar 26, 2011)

i thought about trimming the plywood closer to the wall (west wall). only have the jig saw to use for that. just gotta make sure its square though. 
so the east/west walls will be the easiest to run the joists along. only have to go one deep

the north side is a little trickier since the joist is a little further under the door way.

the closest beam for the south side is about 3 ft away. (no where close) i guess the joist hangers would be best for this side.


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## HDS (Jun 21, 2014)

I photoshopped your pic to hopefully clarify. The first pick shows where you should put blocking in red. You'll need to support where the old subfloor (by the door and by the carpet) meet. Those will be 2x10's.

In pic 2 is how you would sister to the one joist by the HVAC. In green, you could probably get away with just using a 2x4 and cutting the old sufloor flush to the wall. 

On the other side, in purple would be a new 2x10, 9'4" long that supports the edge of the old and new subfloors. Half will be under the old, and the other half will be for the new.

Now if you have a joist that is relatively close (pic 3, black line), you could cut the subfloor back to it, and then use a 2x4 sistered to it like the green in pic 2. 

In either case, you'll still need to add blocking where there is no T&G and or the old and new subfloor meet up.


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## crankbait09 (Mar 26, 2011)

ok, a little up date on to where i am on this subfloor

i have gotten all my blocking and sister joists in place. that was much easier than i originally thought it was going to be. I was way over thinking that whole process as well as thinking how difficult it was. eh, wrong 

i now need to clean the top of the joists off then i should be ready to lay the subfloor.

here is a picture of the current status


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## HDS (Jun 21, 2014)

Looks good!


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## crankbait09 (Mar 26, 2011)

thank you!!


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## JazMan (Feb 17, 2007)

OK, looks fine. Did you put a straight edge across the joists to verify one isn't low?

Jaz


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## crankbait09 (Mar 26, 2011)

No. I eye balled.
I will throw a straight edge on it tomorrow and refasten


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## crankbait09 (Mar 26, 2011)

Hey all,

hope everyone had a good christmas/holiday..........

Last night, I decided to just jump in to the deep end and lay the subfloor down on top of the new blocking and sister joists. (yes i made sure the blocking was even with the existing joists).

I measured along each each side in increments of 6". so that way i could get every miscut and uneven edge measured out and cut accordingly. Once I got the subfloor in place, I had to do a little bit of trimming using my multi tool. That is my new hero. 

They plywood slid in to place perfectly and all is strong and no sags or creaks are to be heard.

So now I am going to prepare my mind to start laying the cement board and tile. ANOTHER project Iv'e never done..........

now, i will need to cut out an opening for the HVAC register. Is there a secret to doing this? I will have the cement board in place as well as ceramic tile. With the cement and tile adding additional thickness, how do i go about mounting the duct opening? when pulling it up, i noticed the vent opening was nailed to the subfloor edge. wasnt a tight fasten but it held it there. should i do the same?

here is a pic of the current condition


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## JazMan (Feb 17, 2007)

Merry Christmas to you too.

Just for accuracy, your Truflor is OSB, not plywood. I think you laid it upside down, but shouldn't really matter. The stamping go down, unless there's stampings on both side in your case.

Which concrete backer board will you be using? which thinset mortar? 

You leave the duct work as is, why do you wanna raise it? 

Jaz


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## crankbait09 (Mar 26, 2011)

i put the writing upwards due to the black lines that were on it. they marked the locations of the joists . they actually lined right up with it. figured they made those markings for that reason.

as for backerboard, I am using 1/4" hardiebacker EZ GRID. (that what you wanted to know?)

thinset mortar - I am using Versabond white blanco

as for the vent , since I am adding cement board and tile, that will raise the height of the floor from where the original flooring was. so wouldnt the HVAC register opening have to rise as well to meet the upper surface of the tile?

one more thing......If I have a minimal elevation change from existing to new subfloor, how can I fill that in?? I'm talking minimal height change. there are a couple spots where the joist/sisterjoist made the surface not exact. so it dips in certain spots. SO how can I fill that height difference in? Are you following what im asking??? and yes it is along the sisterjoist runs


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## JazMan (Feb 17, 2007)

crank said:


> as for the vent , since I am adding cement board and tile, that will raise the height of the floor from where the original flooring was. so wouldnt the HVAC register opening have to rise as well to meet the upper surface of the tile?


No. The plenum doesn't meet anything, make the cut outs and the register sits on the floor as it did before. The register is not attached to anything, just fills the hole. 



crank said:


> one more thing......If I have a minimal elevation change from existing to new subfloor, how can I fill that in?? I'm talking minimal height change. there are a couple spots where the joist/sisterjoist made the surface not exact. so it dips in certain spots. SO how can I fill that height difference in? *Are you following what im asking???* and yes it is along the sisterjoist runs


No, not exactly. Are you saying the sisters you added are not flush with the original joists? Are they too low, too high? If too low and the old one is the one that is in plane, fasten only to the one in plane. No need to fasten to the low one, it's just there to stiffen the other. If any are too high and it's making the joists out of plane, get your plane, (the tool) and plane away. The sheets need to be within 1/32" of each other. 

How many square feet of area is it again? You can use the cheaper grey thinset under the Hardie if it's a sizable area.

Jaz


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## crankbait09 (Mar 26, 2011)

understood, thank you

the area im doing id about 35 sq ft, not including the little closet to the right

i hear two different direction on the thin set under the backer board. some say yes do it, some say no need. i still go back and forth on that part in my mind


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## JazMan (Feb 17, 2007)

> i hear two different direction on the thin set under the backer board. some say yes do it, some say no need. i still go back and forth on that part in my mind


You have never read directions from any knowledgable person or company to not apply thinset under any CBU. Those who say not to, have no clue and are looking to cut corners. I guarantee hairline cracks within a few years if not done according to directions. Usually the hairline cracks are not easily visible though. How about the tape for the seams, what have you heard about that? 

Jaz


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## crankbait09 (Mar 26, 2011)

to back up a couple of posts........as for my uneven seams from existing to new........the "lip" is actually being caused by the new subfloor being lower than the existing floors. but only in certain spots.

as for the tape....I heard that it was not needed. 

so what i heard was, subfloor down, cement board fastened in place, thinset, tile, grout with sealer.......done. ( i think that was everything)

i might as well ask another question. do i need to primer the subfloor with like a KILZ primer? Is the primer needed?


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## Bud Cline (Mar 12, 2006)

I heard this", "I heard that", "I heard", "I heard", "I heard". Where on earth do you people go to "hear" all the crap you do? 

All cement board comes with (or has available) instructions - READ THE INSTRUCTIONS.

When "sistering" floor joists it only stands to reason that the floor joists should be flat and plane. If they are not, make them so.

I realize a first timer can get confused but this really isn't that difficult if you think things through. :thumbup:

"do i need to primer the subfloor with like a KILZ primer? Is the primer needed?"

KILZ isn't any kind of a primer for this purpose. KILZ is basically a stain killer/sealer. There is no need for KILZ in any of this.


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## JazMan (Feb 17, 2007)

crank said:


> as for the tape....I heard that it was not needed.


You need to stop asking your barber (or who ever), how to install a floor.:wink:

Jaz


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## crankbait09 (Mar 26, 2011)

this may be my first problem..........I asked the associate at home depot when i was buying all the flooring needs to do this project. :bangin:


ok, so lets back up. if kilz is not needed, is any sealer needed at this point?

what tape should be bought? assuming this tape goes over the cement board seams where the boards meet, right?

would you mind posting a reliable source internet link that would tell me step by step instructions how to do this process??


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## HDS (Jun 21, 2014)

Your best bet is to go to the cement board manufacturer's website and download the directions.


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## rusty baker (Feb 13, 2009)

crankbait09 said:


> this may be my first problem..........I asked the associate at home depot when i was buying all the flooring needs to do this project. :bangin:
> 
> 
> ok, so lets back up. if kilz is not needed, is any sealer needed at this point?
> ...


Don't ask an associate at HD anything except maybe where to find the bathroom. :whistling2:


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## crankbait09 (Mar 26, 2011)

well, i did ask a contractor at HD in the flooring section about the thin set underneath the cement board. he said that he does it for the customers since he does not know what kind of load will be ont he floor after all said and done. but for his own home, he did not do the thinset under the cement board. he said it was overkill and not really needed. but for his job they do it to protect them due to warranties and what not.

make sense to anyone?

i will download that info from the manufacturers site. right now, after looking at my cement board, there are no instructions anywhere on it......so off to the manufacturer's site i go

this is the video i found
http://landing.jameshardie.com/homeowner/landing-hardiebacker.shtml#

if i wanted to ever install ceramic tile on the walls, i would use the cement boards. can those be fastened to walls with drywall already in place or does the drywall need to come off first, and the cement board fastened to the studs?


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## JazMan (Feb 17, 2007)

> well, i did ask a contractor at HD in the flooring section about the thin set underneath the cement board. he said that he does it for the customers since he does not know what kind of load will be ont he floor after all said and done. but for his own home, he did not do the thinset under the cement board. he said it was overkill and not really needed. but for his job they do it to protect them due to warranties and what not.


Just stay away from this contractor, he's a hack. What type of work does he normally do? No, makes no sense. Apparently he knows it's better with the thinset under the panels, but he thinks some homes don't need it. :huh: That's it, aim for minimum you think you can get away with. 

That video is fine from what I saw. I don't like the mock-up, but it'll work.



> if i wanted to ever install ceramic tile on the walls, i would use the cement boards. can those be fastened to walls with drywall already in place or does the drywall need to come off first, and the cement board fastened to the studs?


Years ago many of us did it both ways depending on what was there and if a double board was needed for mud bullnose trims to finish the edges. But we've learned the wallboard should be removed otherwise vapor can damage the paper & gypsum. 

Jaz


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## crankbait09 (Mar 26, 2011)

ok, thanks for the response on the wall tiling.

If you watch that video again, or fast forward to minute 4:17, they start talking about how to lay the board down. does it matter which board is in what orientation with the joist? is there a correct way to start it? should i lay the cement board at doors edge perpendicular to the joists to start? if i have to lay the first board perp to the joist then i will have a very small sliver that i would need to completely cover the ply. can i not just lay all the cement boards parallel to the wall since its such a small area?

in the video around the same time mark, they say that it is not good to place the cent board edge to edge especially at a 4 way intersection cause it "weakens" it. how is that possible. Isnt the more cement board with no gaps stronger? can someone please explain that to me.


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## JazMan (Feb 17, 2007)

> does it matter which board is in what orientation with the joist? is there a correct way to start it?


Concrete backers do not have "grain", they do not add structural strength. You orient the sheets in the most convenient way. 



> in the video around the same time mark, they say that it is not good to place the cent board edge to edge especially at a 4 way intersection cause it "weakens" it. how is that possible. Isnt the more cement board with no gaps stronger? can someone please explain that to me.


I think doing "T" intersections strengthens the seamed joints. That layout also helps keep the boards going straighter. Plywood and drywall is also installed this way. 

Jaz


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## crankbait09 (Mar 26, 2011)

ok, so lets say i start laying thin set, then cement board. then i find im running out of time and dont complete tiling all at the same time, which leaves the cement board exposed. can the cement board be walked on or does the area have to be avoided till tile is placed?


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## JazMan (Feb 17, 2007)

Concrete boards are not a walking surface, but obviously you can walk on them while doing the work. If you have to leave it for a while, why not lay down some cardboard or a rug? 

Is this an only bathroom or are you just asking? Normally there isn't much you can do in an empty bathroom, plus you can't walk of the just installed tiles for min. overnight if you're careful and not a big person. 

Jaz


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## crankbait09 (Mar 26, 2011)

remember this is an entry way.....not a bathroom. obviously we have more than one entrance to the house but just needed to know if i need to keep it blocked off till tiling was done and set


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## crankbait09 (Mar 26, 2011)

i have the tape now for cement board joints, and i have the instruction video. i will check back in once completed or if i run into a problem. off i go...


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## JazMan (Feb 17, 2007)

> remember this is an entry way.....not a bathroom.


Oh yes sorry, got your project confused with another. Yikes, we're at 98 posts?:wink:

Yes, it's best to not walk over the CBU and make dust and track debris into the grout joints.

Tape the seams; Tip: don't use that silly tool they show in the video. Use a flex 6" wide putty knife instead, press hard. Do not create speed bumps. Otherwise tape as you set the tiles. 

Jaz


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## crankbait09 (Mar 26, 2011)

getting ready to cut/lay cement board. one question before i start. i see that i need to mix 6 quarts of water with a 50lb bag of thin set. let's say i start and have to come back later to finish. instructions say that i can use the material in the bucket for up to 4 hours. i can almost garuntee that it will take me longer than 4 hours to do all this. is there any way to salvage the mixture if i wanted to continue later? I do have a lid for the bucket if that matters.


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## crankbait09 (Mar 26, 2011)

so what did i do or not do right here? I scored the edges of the hole i needed to cut out, i smaked it with a hammer and the board ripped. I had wooden 2x4's under neath for support.


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## crankbait09 (Mar 26, 2011)

i redid the cutout with a new cement board. this time i pretty much cut all the way through by using the carbide scorer. went all the way through and lightly tapped the board with a hammer and it popped right out. i guess i didnt go deep enough the first time. phew. that was a lot of work


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## JazMan (Feb 17, 2007)

No, you can not save mixed thinset by covering it. Portland products do not need air to set up. Makes good bucket anchors for your rowboat though. 

You don't wanna mix the entire 50 lb at once, even when doing a large open area. Plus you only need about 12-15 lb to set about 40 sq. ft. of Hardie. Remember the mix is looser for the Hardie than it should be for setting the tiles. 



> so what did i do or not do right here? I scored the edges of the hole i needed to cut out, i smaked it with a hammer and the board ripped. I had wooden 2x4's under neath for support.


You didn't score the "X's" in the cutout, kiddy-corner to kiddy-corner as the video showed. One 2x4 for support isn't enough. You do not score through it, 2-3 scores is enough. You still coulda used that piece, nothing wrong with it.

Jaz


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## crankbait09 (Mar 26, 2011)

thanks again for all of your help on this project.

I have dreaded this since the start. Now that it's all done (minus the grout), and I look back. I don't think I care for tile work to much. Too much rides on whether a tile job, when completed, is "perfect". Although I do have some imperfections and slight rises in certain spots, It turned out nice. For my first tile job, I am happy with it. 

Out of all the tile I cut and layed..........I ended breaking 1 piece. That's not bad at all. I wouldnt have broke any but when I was fitting the tile under the door jamb of the closet, I layed it in and couldnt get it back out for a slight modification. as I lifted up on it, it got caught on the door frame and snapped. 

I will post a picture of the finished product when grout and wall trim are in place. please stay tuned.

thanks again!


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## crankbait09 (Mar 26, 2011)

I completely forgot to come back after all said and done, to post some final pictures of the project. sorry, the closet picture is upside down. hopefully you dont get a kink in your neck trying to view it 

I do have some final touch up to do on the trim work (paint) as well as lay the trim in the closet.

Whoevers idea it was to lay white tile, with whitish grout in an entry way, where there are dogs coming in and out, needs shot!! 

Not a good idea!!! I am constantly mopping it trying to keep it white. The grout is getting dirty with mud and getting harder and harder to clean. But the battle goes on 

thank you again for all the help, and i look forward to the next SMALL project you can help me complete :thumbup:


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## HDS (Jun 21, 2014)

Nice job, now cover it with a rug and keep it clean!


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## crankbait09 (Mar 26, 2011)

have that thing covered as well as i can. dogs find a way to slide it off.................sigh


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## ron45 (Feb 25, 2014)

Johnson non slip floor wax.?
Or....
http://www.amazon.com/dp/B00S3OIADO?psc=1


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## Carpenter76 (Feb 16, 2015)

Awesome Information!! Thank you all for sharing!!

Respectfully,

Leo


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