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I am in the process of installing solid wood flooring in the living room and I have just removed the existing laminate flooring and underlay to find the concrete subfloor is in great condition except for near the sliding door. I am planning to glue the hardwood flooring to the concrete and I am getting a moisture detector tomorrow to check the subfloor is not damp. The house is approx 1980s in the UK.

From the small holes in a line, it looks like there were carpet grippers and an internal wooden sill for the old sliding door before the laminate flooring. But the concrete in this internal sill area is damaged in the photos shown.

Will this be OK to continue with gluing the boards down? Perhaps if I do not glue them to this cracked only. If this cracked area is damp, can I put over a DPM just over this area plus 10cm.

I had opted in for gluing the boards down, as we have a tile hearth that is going to be level with the floor boards and I did not want excess movement between the two.

If it is recommended that this might be an issue, what would be the next best method to fix tongue and groove solid wood flooring?

In the closeup on the second picture, the grey under the cracked concrete looks like slate.

Cracked internal sill area

closeup of damaged concrete with what appears to be slate or other stone underneath

Hole on the right hand side

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  • This is for sure not the type of floor you would install solid wood flooring. My answer is pick another flooring type.
    – DMoore
    Sep 19, 2021 at 18:17
  • @DMoore - it is not your answer, just a comment. But I would be interested in seeing it as an answer with an explanation of why.
    – Willk
    Sep 19, 2021 at 18:51

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Solid wood flooring is not recommended to be glued to concrete subfloors or installed directly on concrete. Many things can go wrong: 1) wood expands and contracts with humidity, seasons, etc., 2) moisture can seep in between the wood and concrete subfloor, 3) Wood expands greatest in the long direction (with the grain)

The organization that controls solid wood flooring is MFMA. They are a national organization and highly respected. You can Google them, but be prepared for some long reading.

Btw, a critical check on your acclimated wood is to get some boards that are fairly long (over 5’) and insert the tongue into the groove and see if they stay together when you hold them vertically and grab only one board and let the other board loose. If the loose board slides out, it’s not acceptable.

Do it on many many boards. If they slip out you’ll notice clicking when walking on the boards because the tongue doesn’t fit tight enough.

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  • While reading online there are lots of posts suggesting that glueing is the professional and prefered method. There are also lots of products for glueing wood to concrete that allows flexibility. So I have tongue and groove solid flooring, how should it be installed without an additional subfloor?
    – IamOnStage
    Sep 20, 2021 at 7:16
  • Your point 3: Wood will expand in length (with the grain) but this is negligible and is basically ignored in woodworking, but the greatest amount of expansion is across the grain. I do 100% agree with not putting solid wood directly on concrete.
    – FreeMan
    Sep 20, 2021 at 12:15
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    @FreeMan Oops, yes you are correct about expansion. I had it backwards. Fixing solid wood flooring to concrete will create problems. I’d test quality as per my suggestion to insure the tongue fits correctly in groove. I’d also follow instructions established by MFMA.
    – Lee Sam
    Sep 20, 2021 at 16:49
  • Agreed that gluing wood to concrete is a bad idea either way the wood should choose to expand.
    – FreeMan
    Sep 20, 2021 at 17:46
  • Isn't MFMA just for maple flooring, not necessarily all wood flooring?
    – Glen Yates
    Sep 20, 2021 at 18:25

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