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I live in Oakville, Ontario and have a detached home with an unfinished basement with concrete floor. I would like to put hardwood flooring in part of the basement. Instead of tongue and groove floors, can I lay down mortar and then solid wood planks (1 in. thickness, 8 ft. length) on top of the concrete to get the hardwood flooring?

What do I need to be aware of / careful about? Any tips / suggestions (moisture control, securing, home resale value) would be greatly appreciated.

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Yes, but.

There are so many issues with putting wood flooring at or below grade that I never like to see it done. The main issues are that wood swells with humidity, and humidity varies with seasons and other situations like rainfall. Most people think that their foundations are moisture-proof, but that is absolutely untrue with any masonry product, especially concrete. So the first thing you're going to need to do is a moisture content test on your concrete. These can be purchased at a hardware or flooring supply store, and you can send the test off for $10 US or so to a lab.

The next thing you have to determine is how to affix it. Around here in Texas, with slab-on-grade construction being most common and cellars being relatively uncommon, it's most likely to be affixed with construction or flooring adhesive. The main problem with affixing it this way is that it does not allow the wood to flex, expand, or contract without breaking loose from the adhesive or potentially cracking boards. I have seen some flooring installers in the Great White North (as we refer to the land you come from) who put down several inches of rigid foam insulation covered with a tongue and groove plywood product and affix the wood flooring to that. I would research that option -- I have no idea what it takes and if it's practical for your home, but I know that it would remove some of the height from your basement. With a father who's 6'4", and a best friend who's 6'7", that would be of concern to me.

The last and final thing you need to consider is what you're going to do if your basement ever floods. Wood floors are ruined by flooding. Rooms that are below grade are prone to flooding either due to rising water tables or infiltration from above, including from inside the home.

Instead of hardwood, I would strongly recommend that you look at ceramic tile that is designed to emulate hardwood flooring. It will provide the look that you're seeking without all of the problems. With an in-floor heating system, it could also provide the feel that you're going for at a lower end-cost than wood flooring.

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One thing that might be an issue in Oakville and not in Texas is melting snow entering the basement in the spring through a sliding door or a window. Try to avoid an installation technique that makes replacing a board very difficult. –  Kate Gregory Sep 5 '11 at 13:48
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Wood should not touch concrete. Concrete is a porous substance; it will absorb water and then release it into whatever it touches. If that is wood, the wood will mould and eventually rot. For this reason, your better contractors will advise against putting down hardwood directly over concrete. The hardwood floor suppliers will say there are ways to make it work, and there are, but none are ideal.

If you're going to do it anyway, here's the process. First, thoroughly level, clean and seal the concrete. Then, lay down a layer of breathable moisture barrier like Ty-Par or Tyvek. This barrier will prevent the transfer of liquid water, but will still allow air (and the water vapor it carries ) to permeate it, allowing the various strata to "breathe" and acclimate to changing temperature and humidity, which will prevent warpage. Then, lay down a layer of 3/4" plywood. This will be the base for the flooring nails, which are necessary to keep the floorboards tightly together to prevent squeaks. Secure the plywood to the slab with powder-actuated fasteners or concrete nails. Then, lay down another layer of breathable moisture barrier, and THEN lay down your floor, making sure to follow all the general guidelines for laying hardwood anywhere else (3/4" gap between edges and walls, nine flooring nails per board).

DO NOT put hardwood in a basement. Just don't. Tile it, carpet it even, but in a below-grade installation, it will simply be infeasible to ensure that the concrete will get and stay dry enough to not affect the hardwood in the long term. And if the basement floods, you have a lot of expensive flooring that has to be torn up and replaced.

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If the basement floods? Shouldn't that be when the basement floods? I've never met a basement that didn't flood at some point. –  Martha Sep 6 '11 at 21:42
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I just finished my basement (being no pro), and that is what I "should`ve" done: http://www.rona.ca/project/~building-subfloor-on-concrete-slab-1054_finish-basement_projects

Instead I put some DeltaFX membrane (which acts as a humidity barrier and a air gap) with floating floor, but by concrete slab was uneven and had some dips, which were noticable stepping on the floor. I had to pour concrete to even-out the floor, which helped greatly, but I still notice some minors dips today. Put a straight long level on the floor. If you see more than .5 inch, reconsider installing on concrete.

Starting again, I would do the sub-floor on concrete + insulation (I live in Montreal).

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