Floor both cupping and gapping

Q: I have 2 year old maple 3/4 inch floor with varying widths. It has had cupping in some areas and ugly cracks between the wider boards.

Humidity always checks out at about 45. First floor rooms with finished heated basement below. 15 Year old house. Floors over vinyl flooring in one room and particle board in two others. Moisture Barrier in all rooms. Installer will come back to refinish for free in driest time of year: Feb-March. Will this solve the problem? Advice on type of finish? Would a filler pop out in summer months (in Wisconsin)? Would staining the maple make cracks less noticeable? Does maple stain okay? Thanks for your response.

A: Strange, you seem to have two opposite conditions occurring in different areas. Cupping usually indicates moisture imbalance from beneath the floor, ie too much moisture movement through the boards from bottom side toward top. Gapping indicates shrinkage or lack of moisture. What isn’t known is whether the flooring was acclimated to the house before installation and if both the sub floor and maple were checked with a moisture meter first to make sure the difference was not more than 4%. I wouldn’t be concerned if the sub floor was more than 4% drier than the maple but if it is more than 4% higher that could be a problem. In the areas where there are gaps, is it possible you have heating ducts running along the ceiling in the basement between the floor joists?

I wouldn’t have an issue installing over vinyl flooring provided it isn’t the thick, old ‘cushion’ floor which could allow movement and flex of the floor and loosening of the fasteners. When you say particle board do you mean chip board or OSB? Not a great fan of installing on this because it tends not to do a real good job of holding the flooring down near as well as plywood. Not saying this is the cause of any issues, only that it doesn’t hold cleats and nails very securely. If you have any movement between boards any wood filler applied will crack out.

Maple can be stained of course. I’ve done my share. It would help to make the cracks less noticeable I think because maple is generally so light coloured with such tight, pencil thin grain that any imperfections in the floor surface are immediately apparent. It isn’t the nicest wood to stain however. It can tend to look somewhat mottled or blotchy because of the wide swings in density from one spot on a board to the next. As long as you are aware of this beforehand and can live with that then there is no issue. I prefer sating polyurethane and Poloplaz Primero is the best I’ve ever used. It does smell while drying.

Follow-up Q: Thank you for your prompt reply.

The man who installed the wood has agreed to come back and refinish it. As we are now in the winter the cracks are large all over not and just one area. I think the problem may be that we have different widths. The wider crack, the narrowest cup. Perhaps they were not properly acclimated when installed. At this point I am rather weary of dealing with this floor. It is only two years old and started having issues within the days of the install. I was thinking of just pulling it out and replacing it with something else. Is that crazy?

A: It would be a shame and a waste to rip out and discard what is basically a new, 3/4″ thick floor. I assume this is factory finished maple so they are going to have a major job sanding it and dealing with the micro bevels. I’d have them do that or if you don’t want to deal with it, if you can arrange for a payment to cover the sanding, take the money and live with the floor for now. Give it a year or so to see if these gaps close and it flattens out at all. I went to look at a maple floor installed in a new house in Welland, Ontario several years ago. Very much like your situation. Maple installed on chip board. Fairly bad cupping so guaranteed once the moisture content stabilized they would have significant gapping too. The builder and someone from the warranty company said this was considered normal. Wow, I couldn’t disagree more. New construction is particularly risky because at one point the entire structure was open to the elements and was wet. This takes time to dry out. So installing hardwood floors until the building is dry is not a good idea. But they do it anyway as if it is an assembly line house and they have to throw it up and sell it fast.

Follow-up Q: Thank you for being so helpful. Our wood was unfinished / finished on site. I do think there was a problem with the wood since we had trouble right away. If we sand where it is cupping will it appear concave later when it dries out? Can the gaps be corrected? From what I read, filler, etc. is only a temporary fix.

A: The guy doing the sanding should take multiple samples with a moisture meter to make sure the wood is within specifications before sanding it. Once he sands it the edges of the boards will be a bit thinner than the center and if it isn’t dry the boards would then likely crown where the center is raised up higher than the edges. I’ve never found a filler that can never crack out. Thinking it through though, you don’t really want anything between gaps that might be an impediment to the wood swelling slightly under higher humidity conditions because then you would likely end up with cupping again because of stress on the board edges. Normal gaps are usually considered to be about as wide as a dime. If there are any that are much larger than that a few of those could be filled, here and there. A polyurethane adhesive such as gorilla glue could be used first. It expands as it dries but is easy to sand off the floor surface. After it is dry it won’t pop out and it can be cut back to just below floor level and a wood filler applied over top of it. I would only do this in random, large gaps. Not over the entire floor.

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