# Slab on slab to raise floor



## stadry (Jun 20, 2009)

either a bonded OR unbonded overlay will work,,, see that jnt down the middle ? make certain you reference that jnt & cut it in even tho its unlikely ( due to home's fairly constant temp/humidity ) there will be much expansion orcontraction of the new conc o'lay

if it were ours, i'd also form another jnt bisecting both halves :yes: just in case,,, wouldn't bother w/fiber OR wire mesh, either :no:

not going to incl attn to level as you're bright enough to know that part, right ?


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## gling (Jun 29, 2011)

Thanks for the tips.
The wire mesh vs fiber were a couple of the options I was considering although having the new slab bond to the existing is something that I wasn't sure how important would be. The fact that it's enclosed on all sides lets me not worry about moving horizontally and we will use expansion board around the edges as three sides are masonry foundation with wood frame above.
Also, there is another joint in the existing slab as seen in attached photo.


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## joecaption (Nov 30, 2011)

My biggest concern would be having it in contact with the sheetrock.
If it was mine I would use pressure treated 1X's as sort of a form along the outside walls. I's one of them as a guide and mark the wall and use my ossilating saw to cut the sheetock so the 1X's could be nailed directly to the bottom plate and the wall studs.
This is going to be a one shot deal, I'd never suggest a first time DIY do this job. Hire a real concrete finisher. Done wrong and this will be a night mare real quick.


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## Canarywood1 (May 5, 2012)

gling said:


> My brother has a 16'x16' entry slab that is 3" lower than the finished tile floor in the main area of the home. He now wants to raise it in order to tile it to match the existing floor. It is enclosed on all sides with existing stem walls so the question is, would 2 1/4" +/- of concrete be OK to pour on an existing slab?(it's in good shape).
> I've thought of doing it with treated 2x4's laying flat with plywood and Hardi Board but the height variance doesn't quite work out so concrete seems to give better control of the height we need. The price works out about the same either way but I'm just concerned with the depth of the slab (cracking) and it bonding to the existing.
> Thanks in advance for any help.


 


As Joe said,this is a one shot deal with concrete, but why not set your sleepers on edge instead of flat to get to your required height,just rip them to whatever size you need.


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## joecaption (Nov 30, 2011)

Also what's going to happen with that door opening?
Sure the bottom of the doors not going to drag on the floor once the tiles in?


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## Duckweather (Mar 26, 2012)

Just one more thought. Was the room a garage, or open once? It may have a pitch to the floor.


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## paintdrying (Jul 13, 2012)

You are going to need a pump truck, that will add about 1000 dollars to that job. As said, ripe the boards to needed height and move on.


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## gling (Jun 29, 2011)

The room was originally to be sort of an open air entry/sitting room (there's four operable skylights in the room) with plants, sound system etc, and had a large sliding glass door where the big opening now is. You would come in through the front door but actually enter the house (living space) through the sliding doors. The house is built on a hill side so the front rooms and garage are the only ones on grade and the rest of the house is on floor joist.
The existing slab is level but not necessarily real flat with a few humps and dips which is why I'm hesitating using lumber. Using 2x4's flat or ripped with T&G and Hardi Board brings it up to a point where there would only be approx 1/8" +/- left for thinset under the Travertine. Plus the humps and dips would transfer to the new floor unless the existing slab was ground flat or I ripped each of the 2x's allowing for the uneven slab.
I'm just thinking a concrete product would be easier and cleaner to achieve a flat level surface for the tile if it's enough coverage to avoid cracking.
The two side walls are masonry up about 6" before the framing starts and I have planned to cut the drywall all of the way around before the concrete gets poured (which I am hiring a concrete guy to install/finish). The main concerns are the cracking and how it would bond to the existing.


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## AndyGump (Sep 26, 2010)

Hey, I think I know your area.
Lake Forest?

Andy


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## joed (Mar 13, 2005)

2.5 inches should plenty thick enough for new layer of concrete.


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## oh'mike (Sep 18, 2009)

Tile setters frequently build up an area like that using deck mud---trowel down a fresh bed of modified thinset to ensure a good bond--then start packing it with deck mud---

I lost my book marks a while back--this one explains mixing deck mud--but contains a lot of extra info before you get to the mud--How to build a shower - Building a shower pan with pre-sloped mortar bed, liner and curb.


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## gling (Jun 29, 2011)

AndyGump said:


> Hey, I think I know your area.
> Lake Forest?
> 
> Andy


Close, I'm Aliso Viejo, brother's house is San Clemente.


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## gling (Jun 29, 2011)

oh'mike said:


> Tile setters frequently build up an area like that using deck mud---trowel down a fresh bed of modified thinset to ensure a good bond--then start packing it with deck mud---
> 
> I lost my book marks a while back--this one explains mixing deck mud--but contains a lot of extra info before you get to the mud--How to build a shower - Building a shower pan with pre-sloped mortar bed, liner and curb.


That's an interesting idea and I'd heard it before but dismissed it as impractical. I guess it wouldn't be any different than the way I used to see marble floors installed, floating "deck mud" over slabs throughout the house to keep the marble perfectly level. I just thought that 256 sqft at 2+ inches thick would be a little much. Haven't seen it done for awhile, probably why I've forgotten it.


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## stadry (Jun 20, 2009)

w/o the membrane, its the same method we use when overlaying exterior wood steps.formica c-tops, & hardwood floors w/polymer-modified concrete


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## Duckweather (Mar 26, 2012)

There is a bonding agent you can paint on just before you pour. Ever try to get concrete off your tools, or the foundation wall, when someone doesn't clean it off right away? Or is the floor painted? I do like those drains at the valleys though.


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## jomama45 (Nov 13, 2008)

You'll be fine with the 2 1/4" concrete as long as the existing slab shows now sigh of movement. We do it all the time, and don't attempt to bond the two together. If you want to tile directly to the concrete though, I would suggest allowing the concrete to cure a few weeks minimum to ensure that the majority of the shrinkage has taken place BEFORE tile is placed over it. You may want to discuss use of admixtures with the contractor as well, as these mixes generally need to be placed wetter which in turn creates the risk of more shrinkage. There's plenty of admixtures to overcome this though, and get it to cure & shrink faster.........


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