Engineered flooring over concrete


Old 11-15-16, 11:42 AM
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Engineered flooring over concrete

I'm planning to have engineered floor installed on top of concrete floor. The room is on the first floor, on the grade and there is no basement. It used to have carpeting which I ripped up and don't want to go back to. The concrete looks good, but there is a section by the patio door that I feel should be patched before the subfloor goes on. It's not part of the slab but what to me looks like the foundation. It's about 5 inches wide and is, at least in part, below the floor level. But by no more than half an inch. Still I wouldn't feel comfortable having the subfloor just hanging in the air above it. Now, there used to be a layer of, I don't know, maybe self leveling compound that I had to remove as it separated and broke into pieces when I was removing nails that fastened the carpet tack strips. So, what should I use to patch it? I was thinking maybe something flexible, elastomeric concrete? So that it doesn't shatter and/or separate when the nails are driven to fasten the subfloor. Would that work? Is there anything that shouldn't be used for that? I'm attaching a couple of pictures to hopefully illustrate what I described. Let me know if more information is needed.

Also there was a gap between the slab and the foundation that I filled in and plan on sealing with RedGuard to prevent any moisture from entering. Would that be OK?
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Last edited by tubino; 11-15-16 at 11:56 AM. Reason: Added info
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Old 11-15-16, 04:36 PM
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Use self leveling compound to level it out to the existing floor. What subfloor are you talking about? You aren't thinking of laying plywood directly on the concrete, surely . If the concrete is reasonably smooth and flat, you can lay down a good vapor barrier and install the flooring directly on top of it. You should do a moisture test to ensure you don't have undue moisture entering the concrete. Take a 3' x 3' piece of clear plastic and tape it securely to the concrete and leave it for a day or two. If it doesn't fog up, you are good to go. If it does, you may have problems down the road.
Old 11-15-16, 05:06 PM
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First warning sign I see is expanding foam under the threshold!
Is there a patio or deck even with the door on the outside?
Please post a picture from the outside.
At a minimum the door needs to come out completely before leveling the floor.
No way do you want to be using plywood as a subfloor.
Add a vapor barrier and install it as a floating floor.
Old 11-15-16, 06:29 PM
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Agree with others that a subfloor over concrete is a bad idea. You can float the void with a leveler patch material and then look to a floating engineered floor or even a click lock engineered floor that floats as well. Moisture test is an excellent idea which should prove negative as the room as been carpeted with not mention of mold issues.
Old 11-16-16, 03:10 PM
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Hmmmm... Thanks for all the input. I guess floating the floor could be an option, if I convince my wife. She doesn't like the idea that it, well, "floats" and is not solidly attached. As far as plywood directly on concrete I've seen it discussed in some other threads and didn't really see it being discouraged. Do you have any references as to why? What are the downsides?

The foam under the door: I just had it replaced and that's how it was installed. I don't think I can afford to have the door removed now. The patio (concrete) is about 6" below the floor level. Looks like it was poured separately from the foundation and there is a gap between it and the foundation.

Will do the moisture test but have a feeling it will come out negative as there was no issue with carpet, other than it was old.

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