Refinishing during the season boards shrink and gaps develop

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Q: I have 3-4-5 inch wide red oak floors installed over radiant heat. Each year when the heat is turned on the boards shrink and gaps between the boards develop. I am planing on refinishing the floors. How can I get rid of the seasonal gaps?

Will Timber Mate work as a solution for my problem? I would like to finish the floors with gloss finish.

A: The worrisome thing about this is: if you fill these gaps, what will happen when the floor expands? You may also face another issue if the floors are finished now. Polyurethane can seep between the boards, where, robbed of oxygen, it doesn’t really harden. then when the boards expand, this finish can get squeezed out and appear as poly balls on board edges. I think I would wait until spring or summer when they have closed up before sanding. Or, run a humidifier to get the RH up closer to 40%.

Follow-up Q: Thank you for your reply. Just a little more information: The floors were installed and finished in 1994, with a water base finish. When the floor was installed it was tight, with no seams or gaps. I was planning on sanding the floors with a random orbital sander, filling the gaps with Timbermate, then coating the floors with Waterlox, two coats of original sealer and two or three coats of the gloss finish.

A: You still have the expansion/contraction issue and I don’t think it would be wise to fill the floors under those conditions. Waterlox would be fine.

I’ve never had this much shrinkage

Related Q: I had new hardwoods installed and refinished with a water based matt finish. I noticed after my cleaners wiped the floors down with a wet cloth to clean the dust off, that crevices between the boards became evident. A different contractor I had at the house noticed it and said he thought the refinisher didn’t vacuum out the floor well enough after they sanded, so dust filled the crevices and then came up when the floors were wiped down. The floor refinisher, based on a photo I sent him, said its the normal shrinking and expanding of hardwoods. I have had hardwoods before and never had this much shrinkage.

I was thinking – if the finish went over the dust in the cracks, wouldn’t it be finished into the floor, so it wouldn’t be able to be washed out? I don’t see dust particles in the finish, so I would think if it the dust wasn’t properly cleaned out that it would show up in the finish. Help!

A: A small amount of shrinkage during heating season (about the thickness of a dime) would be considered normal and expected.  Keep in mind also that some species of wood exhibit a more severe reaction to changes in humidity.  I’m thinking in particular of Hickory and Pine.  Expecting the floor to behave as if it was one solid piece of wood is not possible.  Otherwise, I don’t know any other details to offer a comment.

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