I need to lay a plywood sub-floor (ready for engineered hardwood to go on
top) over a concrete floor in my first floor family room. What is the best
way to fix it to concrete? I have never done anything like this before, but
I understand there are nails that will drive themselves down into
concrete....is that right? Are they easy to use?
Would this method be better than some kind of thinset/mortar etc?
There's many options:
1) Concrete nails (what you asked about). Drive with a sledge hammer
(full size 10lb or a hand sledge). This gets old very fast if you're
trying to drive a lot of nails, which you do. USE PROTECTIVE GEAR!
2) Tapcons (screws you drive into predrilled holes). Relatively easy on
the system, but the drilling is a pain.
3) Remmington power drivers. These are .22 shell powered nailers. Easy.
Requires care you don't shoot yourself. USE PROTECTIVE GEAR!
4) Construction adhesive (caulking gun application). Trick is getting
the ply to stay flat while it's drying.
5) Use sleepers instead of ply, using (1) and/or (4) to fasten them.
6) Combination of above.
I think what I'd specifically suggest is to use (4) and (1) to hold the
ply down for set. You won't have to drive so many nails - they're just to
keep the ply flat while the adhesive dries.
The adhesive is best overall because it'll do the best job of preventing
the plywood from "slapping".
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
Find out what the manufacturer of the hardwood requires. They should
have some very specific requirements for concrete floors. Hardwood and
concrete (moisture) don't generally get along well.
If it were me and the manufacturer did not have any thing to say and
suggested that installation over concrete was ok, I would want to make sure
I had a solid vapor barrier and then sleepers then the new subfloor of
materials that can handle potential moisture.
The best plan is to use a membrane between concrete and plywood, and again
between plywood and engineered hardwood. Because of that, I 'm not sure
adhesive will work for the concrete/ply joint.
Any ideas anyone?
I am not sure I would want to fix it to the concrete. I would rather
put it on sleepers. I don't think you want it in direct contact with the
concrete that can and will bring in moisture. Concrete is NOT waterproof.
I would not want a trapped space between two membranes. I suggest one
barrier on the concrete and then use sleepers treated for moisture. Frankly
I would not worry about "attaching" the sleepers to the concrete, I would
tend to let the floor float.
However before I made any decisions, I would get back to the
manufacturer and find out exactly what they recommend for your situation.
Somehow I suspect they are going to tell you not to use their product on
concrete, without special prep that they spell out.
BTW is this above or below grade?
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