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The floor of my customers kitchen/breakfast room is half on a slab and half on trusses. The floor on the slab has been replaced twice by previous contractors due to condensation causing the tile/linoleum to curl and turn loose. I do not know what is under the slab. It now has plastic with 3/4 pressure treated plywood as the base which has to come up. It is damp now although the area around the exterior walls is not. The slab does go to the outside and is about half above the grade level. What is the best way to put a stop to the condensation problem for my customer and give them peace of mind that this will not come back to haunt them again? They are receptive to raising the floor as much as 1 1/2″.
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RON,
Your concrete floor is wicking up ground moisture, which is prevalent enough to do the damage you have related.
Contact the Canadian based company, Xypex. They have a wonderful product known by the same name which consists of a powdered crystalline.
In penetrates the slab via the natural capillaries inherent to concrete and will not allow the water to move through them.
It does permit vapor and air transmission, allowing the slab to breath.
It is non-toxic and will literally use the floors water content as a migratory vehicle to slip deep into the slab.
You may contact Xypex at: Xypex.com; or: 1.800.961.4477.
Sincerely,
Brian T. Chaffee
Architectural Concrete Services
1.732.237.0301
*I'm real curious as to HOW the concrete is passing this moisture to the finish floor if there is a plastic vapor barrier installed. Ron mentions that the current floor that has to come up is plastic over the concrete, then treated plywood. How did the moisture get past the barrier?If the plastic didn't stop it, the Xypex won't either. It has got to be coming from another source, or making its way around the barrier somehow.James DuHamel
*Plastic under a concrete slab is minimal protection from ground level moisture at best. How many times have you seen a mason (or contractor)puncture the plastic prior to the pour to release extra moisture from the fresh concrete (around here, northeast, it seems to common practice). The seams are simply lap joints with no tape, and just the act of pouring the slab and working the pour can damage an already incomplete vapor seal. Xypex (although I have never had reason to use it, I have checked it out) bonds chemically with the concrete to prevent capillary action, check it out, get the warranty, talk to people who have used it...it is not a vulnerable thin sheet of plastic laid under a pour.
*Regardless of what else you do, a thorough inspection of grade and runnoff during rain are in order. Wearing a raincoat while swimming won't kleep one dry.
*He's talking about plastic laid OVER the concrete floor, sleepers in place, and a treated plywood subfloor/underlayment with vinyl on top of that. If it was installed correctly, I cannot see how that much moisture penetrated through it all, and did that much damage. I would be looking for another moisture source, and cure that first. Otherwise, this job will wind up like all the others. I am just curious how enough moisture penetrated all of this, and damaged the vinyl on the top. I have used Xypex before, but a cheaper, and in my opinion more effective barrier is #30 felt paper on top of the slab, with seams glued. I leave about 8-10 inches hanging out past the sole plates, and then when the walls are in place, I tack the overhang to the bottom section of the stud wall. When finished, it looks like I made a shallow box out of felt, and installed the walls and sole plates inside it. When I apply felt on the exterior walls, I let it go down about 1/2" or so below the sole plate. This overlaps the overhang. Has served me well for many, many years. I have seen way too many slabs with NO vapor barrier. I do not trust the vapor barriers used by concrete contractors for the very reasons you stated. James DuHamel
*Here's my opinion ...for what it's worth.1) if you put down plastic on a slab that has a history of moisture problems the slab will never dry out ..you are only attemting to 'cover up 'the problem.2)why was pressure treated plywood used?Pressure treated plywood,like pressure treated lumber is pumped full of water as part of the treating process and should never be used on interior applications.Was the tile/linoleum laid directly on the plywood? 3) Was the slab originally part of the exterior of the house? If so ,how long has it been a part of the interior? Long enough to have acclimated to the inside temps before being sealed off with plastic and plywood? 4) Could the moisture be coming from a source such as outside runoff or possibly a broken drain on the inside? Just some rambling thoughts ....J.H.
*Jerry,We use kiln dried treated plywood (BC grade) all the time for bathroom floors. It is dry, smooth, and takes vinyl flooring adhesive as well as any non treated plywood. As for the use of treated wood indoors, that is a matter of opinion. Some will use it, some won't. The sole plates on a house on slab are treated, and part of them could be considered "indoor". They may be covered up, but they are still inside the house. Plastic poly over a wet slab is protection from the migrating moisture. Covering up the problem is exactly what you are doing, and for a reason. The plastic barrier prevents the moisture from migrating into the structure. It seals off the slab, and keeps the moisture outside of the structure. We use them all the time on garage conversions where the garage had no vapor barrier installed when the slab was poured. We then install sleepers, shimmed level cause a lot of garages here have slightly sloped slabs to help water drain out, and then install solid foam insulation, subfloor, and usually an underlayment. The whole purpose of all this is to KEEP the moisture from getting into the new conversion. I guess different regions do different things. Just a thought...James DuHamel
*James,You may have found thier problem. You insulate with foam on top of the poly in garage conversion.From the post, this is just a slab area that abutts an exsiting wood frame construction. More like a garage, and it is in a high moisture area(kitchen). With say three sides of the slab exposed to outside air temperatures, couldn't it get cold enough to condense water vapor from inside the room?Another way to think of it is that the poly vapor barrier is on the cold side of the floor(frame construction. He did say that the sleepers and plywood above the poly were wet and rotted out.The solution could be to add rigid foam insulation between the new sleepers, and also go outside and insulate the edge of the slab.Years ago I believe I read that most of the heat loss for a slab on grade occurred at the edge of the slab. Insulating two or three feet under the perimeter was pretty common in the late 70s, and then we started adding edge insulation to act as a thermal break in the 80s. At least in commercial work.This is just a stab in the dark, but I would try James's insulating method.Dave
*I was reading the information on floor condensation and my question is what can be done to an existing slab with 6mil plastic as the vapor barrior that still sweats?A.D. Banks