Refinishing while seasonal gaps are in wood floor

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 ride 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%.

Similar Q: I am refinishing a Brazilian Cherry floor and after removing the existing wood finish, the floor started “popping” as small, approx 1mm gaps developed between some of the planks. From reading other responses, it looks like low humidity is the culprit. The RH outside the house is about 27%.

My question is what to do now, before I apply the new polyurethane finish? Should I try to increase the RH inside the house so that the gaps will disappear, or should I continue with the project and apply the polyurethane with the cracks present?

A: 27% RH outside is rather low. The idea is to try to maintain a somewhat stable humidity in the home year round. I would not let it get below 30 and would shoot for 40%. If you finish the floor as the cracks are opening, you may have trouble later when humidity rises and the still soft polyurethane in the cracks gets pushed to the surface.