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Well????????
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As part of a remodeling project we are installing tile over a concrete slab. The area to be covered is about 350 sq.ft. The slab is three years old, has very minor cracks, and is quite uneven. There are high and low spots with up to a half inch in difference. We are going to use 12 inch tiles. I have seen installations on uneven surfaces and noted that the irregularities were amplified by the tiles. We are planning on filling in the dips and feathering out the humps, but we're not sure what to use. Can anyone recommend a product or procedure to do this? We are considering a skim coat of thinset troweled smooth, let to cure, and then applying a second layer of thinset to bed the tiles. Will the thinset work at this depth as a filler? I have read on bags of mortar that thinset is not a filler. How true is this, and are they talking about filling in the same manner that we are? Thanks in advance for any help offered!
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Question: is the unevenness of the slab caused by cracking or shoddy workmanship? I would not use thinset in such a manner as you describe.
Perhaps, you may consider a self-leveling cement. Pour just enough of the stuff to fill in the dips, to make the floor flat. This may present a problem at thresholds, cab elevations, etc.
I don't think a 12" tile will magnify the problem, a smaller tile will though. The problem you'll most likely run into with an uneven substrate is lippage. Especially with large tile, you'll find it very exasperating to get the entire face of a tile into the same plane as the neighboring tiles.
Fix that slab first!
*As Rich pointed out you need to determine if the slab is uneven from the cracking or from the workmanship. If its from cracking and still moving you'll end up in trouble no matter what you do. You can buy stuff in bags and buckets for leveling floors..dont know how good they work. A full float mortar bed is the best solution for correctingany uneven surface...horizontal or vertical. Dave
*Self leveling underlayments work quite well. I have used the one made by Customs on uneven slabs with great success. 1/2" would not be too much to fill. If there is more than that, aggregate can be added in the deep spots. The trick is to let the compound do its own leveling and not over-tool it. It will not isolate the cracks. That is another problem.
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Rich, the uneven slab is the result of shoddy workmanship. The concrete is solid and on well drained ground with a vapor barrier underneath. I appreciate your advice about the thinset as filler but what is the reason you wouldn't use it? I need to convince my co-workers because they are the ones who want to use the thinset. If we do use a self leveling compound, is 350sq.ft. too big to do by hand? Are leveling compounds expensive? Thanks for all responses.
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Dandan: Yes, the thinset mfg is talking about filling in the same manner as you are considering. Thinset at that thickness shrinks in volume as it cures. Moreso, it shrinks enevenly, so you get 'micro ridges'. Besides, it does not have the compressive strength, at that thickness.
350 sf is not too big an area for self-leveling. But, in my original post I meant to use the self-leveling only in the dips. If you want to go across the entire floor, fine; but since this will raise the elevation of the floor to that of the highest point you'll probably have problems at thresholds, etc. However, depending on the layout of the room, 1/2" may not be all that much of a problem.
I poured an area of approx. 650sf by myself, out of buckets, in one 10 hour day. You must stay on top of things, mix well, work fast, etc. Determine EVERYTHING before you start mixing. As Mike says, do not over tool. For the results I consistently achieve, I do not think this product too expensive. Consider the savings in labor, then, how much more is it than thinset, and the time to smear it?
*Rich and Mike:Im interested in trying this out when I get the opportunity....what product do you recommend??Thanks....Dave
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Hello Rich,
I have to level 2400 sf slab as much as 2" see my
post please need help
http://www.taunton.com/cgi-bin/WebX?13@@.ee6e07
< Obsolete Link > Lyle Popson "repairing concrete floors" 3/20/99 12:25am
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2 INCHES!!! In how many feet? Jeezs, while this is not too much for self-leveling, I would suggest you plan on removing the humped-up portion of the slab.
Let's see: if the grading was done correctly before the concrete pour, you would have an extra 2" of concrete in the center of the slab. That is, if the slab is 4" everywhere else, it is 6" in the middle.
I $&%#*@ can't believe anyone could get away with this. Was the inspector on drugs or paid off?
repour.
If you use self-leveling, what are you going to do; reset all the cabs 2" higher, cut the doors 2" shorter, raise the door headers 2", hang the base 2" higher????
The solution is not to go up to the highest point of the slab, but down to the lowest elevation of the slab. You have indicated this is at the walls. Saw cut the offending section(s) and repour. Sawcutting is easier than you think, faster, cheaper too.
You will now have a cold joint underfoot. Not a problem under carpet, but put down a crack suppression membrane under tile.
BTW: How old is the house? What state is it located? How long ago did you buy it? Was it disclosed to you? Can you say L-suit?
"Honey, will you come here to calm me down?"
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Howdy Rich,
We are in the process of buying this DIYS house in
the country at about 50% of the appraised value.
It needs all new flooring any way.Only 3 doors are
affected more than 1". Yes the Kitchen cabinets will
be raised. the house was framed to adjust for the
crown .it is in the center of the slab. The slab is
38 x64. I do believe Raising the floor with some
type of material is the way to go, all roomes are
affected to some extent.Go Plywood or ce
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"Go plywood or ce"...Lyle, what is ce?
On another note: I am interested in hearing how you proceed with this project of leveling your floors. Seems to me you are going about it the hard way. Let me/us know.
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Ce=Cement/Concrete/Sandmix? Don't know? Need Ideas
It is to large of an area to cut out.
LP
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So, Lyle, than what would you use the plywood for? to raise the floor? Not advised if floor is slab on grade. Okay, for wood subfloors. Use minimum 3/4".
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I've been following this discussion with interest. Here is my situation:
I just bought a house in Seattle. It's 75 years old and in great condition, and the previous owners already started on finishing the basement. The walls and some ceiling are finished; there's a bathroom with vinyl on the slab for a floor but the kitchen and rec room are still unfinished floor-wise.
The cement was poured such that one end of the slab has a drain in it and if any water were spilled it would run towards that drain. Therefore, it's sorta rough and uneven. I'd really like to level it out and do the floor right; probably hardwood since I have access to a bunch of it for free. However, the walls are already in, which sorta complicates things, but here's my plan so far from what I've read and heard:
1) Make a very thin form along the base of the existing walls - like 1/4 inch wood, fastened temporarily to the walls. I'll caulk (?? - or something) the gap between the bottom of the wood and the rough/bumpy existing floors. Once I remove this wood, the new cement will have a small gap between where it ends and the cement starts, but it seems like the easiest solution (maybe I could fill that gap with something?) Is this too picky? Could I just assume the existing drywall will act as a form just fine?
2) Pour self-leveling cement onto the old floor, until it's all leveled out. (do you have to trowel this stuff? When you say "keep on top of it", what do you have to watch for?) The old floor is painted; is this a problem?
3) Once this is dry and cured, I'll lay a plastic sheet down as a vapor barrier and then a subfloor of plywood or furring strips.
How does this sound to you professionals? I'm just an amateur, and I'm not aware of the potential pitfalls of this sort of endevour.
Thanks in advance for any input!
Eli Smith
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Ahem..., Eli, we WERE talking about concrete and tile! Now, if you wanna' change it to wood, go right ahead. But, don't say I didn't warn ya'. c/:^)
Seriously, if I follow you, you want to lay down a wood floor on top of the slab. But the existing slab is sloped to a drain and its rough in texture. So, you want to level out the slab so you can get on with your wood floor. But, you are not certain how to proceed. Is this right?
To level slab, you have several options.
1) Set temporary screed edges at perimeter of floor(basically, at all walls). They can be nailed or shimmed into place. Delete drain and pipe. Pour new concrete. Where it comes to a feather edge at upslope side, cut concrete back at around 2" thickness mark and fill feather edge with pourstone. Broom finish.
2) Set rim joists against all walls. Build joist grid to support your new wood floor. (think of interior deck)
3) Pour the basement full of self-leveling. Mix, pour, and walk away. Be sure to plug the drain first so all your expensive mud doesn't go down the...
Now, I do have a question: since the room in question is the basement. And the former owners had installed a drain in the floor, are you sure wood--even if free--is the right choice? What about it guys?
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Hey, Rich, thanks for the feedback. It sure is great to be able to get answers from people with some clue and experience.
I think I'm going to go with the self-leveling cement. And while there is a drain in the basement, it was made that way 75 years ago, and I've seen some nasty rains come and go with no water. I am going to test for moisture down there though.
One last question: do I have to use forms along the walls with self-leveling? or could I just pour it against the existing drywall?
Thanks again!
Eli
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If you use self-leveling, you do not need any forms. You can allow it to run right up againstthe drywall. (Just don't splash against the drywall. When you come back the splatter will take the drywall paper right up with it. And you don't want to stop in the middle of a pour to wipe splatters.)
Before you pour, look around for any likely looking hole that may allow the self-leveling to leak.