Floor slab OVER footing wall or not?
Streamline
| Posted in Construction Techniques on
I have a new construction foundation footing poured, with a 6″ stem wall on the footing for structural loading in the middle of the house (left of the stem wall is a room, right of the wall is another room connected by doorways). I plan on pouring a concrete slab to level with the top of stem wall (2″ styrofoam plus 4″ slab) so my top of floor is flat on either side of the stem wall, with the stem wall, so I can tile over the slab and stem wall. I am concerned that the slab and stem walls will separate over time and break the tiles above them. So I am going to drill in 1/2″ rebars into the stem walls at entryways and let the new slab bind to it. my question is whether this is the right concern or approach to remedy the concern.
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The slab and the stem wall may well separate over time due to settlement and the expansion and contraction of the slab. If you try to stop it by tying the two together with reinforcing, you have simply moved your problem elsewhere. I think you would do better to try and accommodate the movement in the doorways. How you do that with tile, I leave to more experienced posters.
In my own house I have several point loads that come down on the slab where I included an integral footing. ( thickened the slab). Tying the slab to the loadbearing structure in this way is asking for cracks, but my slab is saw cut into 3'-0" squares and can accommodate a lot of movement.
Edited 2/17/2007 8:45 pm ET by fingersandtoes
They will move, it will crack tile, you can't fight it with rebar. When and how bad depends on a million things nobody can even guesstimate at. You could be good for 20 years. It could crack in a couple of months. So I would say plan that the doorway will be a break and treat it like it will. Ditra the slab before tile, and at the door, I dunno. I'm not a tilesetter but first thing that comes to mind is make the tiles the same width as the doorway and either live with grout cracking or live with color matched caulk.
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how do the hotels and commercial buildings do their tiles so they don't crack? these places have expansive tiles (those massive hotels in Vegas) and I don't see cracks in them. What techniques are they appplying?
Stategically placed expansion joints[email protected]
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Eric,
What guidelines can you offer for use of expansion joints. My concrete guy says if I use stealth fiber, I won't need to put expansion joints in my 3-car garage slab. True?
The expansion joints I was referring to were for large expanses of tile on a floor.
There are others here who know way more than I about concrete.
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I would cut the stem wall out in the dorway area, poour the crete flush through with steel in it ( to keep it from shifting vertically) and then cut a control joint right there.
Then when doing the tile finish, use a flex caulk in a grout joint there and/or set a threshold to transition from room to room. It could even be a flush seet thresh of cultured marble with flex caulk on each side of it.
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On the stemwall/slab homes I have built the stemwall was "notched" to support the edge of the slab. Interior load bearing walls were supported by steel reinforced grade beams that were poured at the same time the slab was done. These slabs got wire and rebar and were tied to the perimeter masonry stemwalls with ladder wire.
Personally, I think pouring a slab inside stemwalls and unsupported by stemwalls is problematic, but at this point I'd recommend perfect compaction of any subgrade and filling with stone.
Matt,
My stem walls surround the entire living space where point loadings are. The subgrade is as follows: 4" quary spalls for underground drainage, 4" of pea gravel (capillary break), visqueen, 2" styrofoam, PEX tubes then 4" slab. The pea gravel is loose and can't be compacted effectively.
You suggested that I tie masonry stem walls with ladder wires. Could you elaborate? Is this a wire mesh in the slab and attached to stem walls somehow, or a different application? Some of the feedback suggests that it is not a good idea to attach stem walls to the slab. I think strategic expansion joints at the tile level is a great idea, placed on ditra membrane. Other thoughts on how I can stablize the slab from breaking tiles above?
Thx.