Q: I live in Alberta, and have had solid maple hardwood flooring installed over a new sub floor of 5/8″ plywood on my main floor. The strips were nailed securely and tightly by a carpenter friend who has done this before, and his floors always looked great for years after, so I know that he is doing it correctly.

By the way, this flooring was reclaimed from a 55 year old house about to be demolished. The flooring was acclimatized in my house for a period of approximately six weeks before being installed.

I did bring in a professional hardwood floor sander/refinisher to finish the floor. It was only after the sanding and two coats of oil-based urethane were applied that I noticed and became concerned about the gaps between hardwood strips. I obviously had not checked closely before the refinishing began, so my mistake. I can only guess that being in this part of the province during the heating season, the humidity level was so low that the hardwood shrank appreciably.

My new furnace is equipped with a Generalaire by-pass humidifier, but unfortunately it was not connected during this whole process.

So, now I have halted the final finish coat on the floor, and have the humidifier working at a maximum setting.

It has now been three weeks with the humidifier working at a high setting, and I’ve been hoping that I would see a reduction in the gaps between some of the hardwood strips, but my close inspection reveals no change whatsoever.

I expect that the person I contracted to sand and finish my floor should have asked me prior to starting the job about humidity, but all he asked was whether the material had spent some time in the new environment before being nailed down, which of course it had.

What is my best strategy for getting this flooring to swell back to what it was when laid? My understanding is that finished and sealed solid hardwood floors will swell and contract with humidity changes, so is it not reasonable to expect that raising my relative humidity level will have this effect on the wood? Or should I just have the gaps filled, more urethane applied, and then hope that it will not expand later and cause me grief with the filler material breaking up?

I have considered getting a hygrometer to see what my humidity level is, and try to ensure that is 40% to 50%, but have not done so yet. I would very much appreciate any advice or thoughts you may have on this situation.

A: Interesting situation. First, I really don’t think you can blame the floor sanding company. They really have nothing to do with the gapping. If anything, applying a polyurethane coating to a floor would slow moisture movement from beneath the floor and cause the floor to expand if there was to much moisture, for example, coming from the basement. I do not think we can keep the humidity levels at 50% in the colder parts of Canada in winter without having moisture problems all over the house. You might want to check the environment below the floor to see what the readings are there.

2 thoughts on “Gaps”

  1. His response: I used the instructions found here I used the top off a small spice container. When they say a few drops, all they mean is to have wet salt that is kind of ‘caked’ but not a liquid-like solution. Popped it inside one freezer bag, then another and waited. After 12 hours, I found my $20 el-cheapo hygrometer was reading on the low side by 7%. (Checked the Internet and it seems a ‘real’ scientific-grade instrument is upwards of $750, but units like that are guaranteed to err no more than 2%).
    Of course, if a hygrometer is actually faulty and does not read high or low consistently by the same amount, you could get fooled. But, I’ll give it the benefit of the doubt and this is close enough for what I need.
    The area where my hardwood floor is now reads around 38-40%, so I’m going to try to get it a bit higher and check the gaps between strips later. I’m moving on with finishing the reno and revisit these little gaps later, no sense in getting bent out of shape. Just another learning process!

  2. Follow-up Comment: Thanks for the reply. I certainly do not blame the finisher. His work looks just fine to me, and I think he is quite ethical. I only mentioned the situation because I wish I would have known more about the importance of knowing the moisture content of the material before installing. I’m a pretty logical-thinking guy and realize that a good contractor would know how to look ahead and avoid this type of thing; well, I’m my own contractor and he wasn’t so smart 🙂

    Anyway, I’m sure the floor will slowly expand to its former dimensions. I bought a hygrometer (cheap, but I calibrated it) and things are on the dry side. Good point about the polyurethane coating’s effect.

    Wood Flooring Guy Q: You mentioned that you calibrated your hygrometer. I have to ask you how you did that. I have 2 of them, and I could set them side by side and get 2 different readings! Not a huge difference, but one or both are not dead on accurate.

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