Gaps in wood floor over the winter

A: We moved into our new house last fall. Over the winter our floors started gapping. I contacted the home builder and he talked with the flooring guys and they said it was due to low humidity in the home. I installed a humidifier but by then the cold weather was almost over. I also bought a humidity gauge and it reads over 40% most of the time.

The floor guys claimed the gaps would close by themselves but it’s now July and we have noticed little if any improvement. Our warranty on the home will be over in November so I was wondering how long it normally takes these boards to fix themselves.

Q: Difficult to answer. Several winters back, we had snow from November to March, so it was a long heating season. I saw gaps in my 70-year-old strip floor which I never saw before. I fixed the humidifier on the furnace and the gaps closed soon after.

I would say that some slight gapping here and there can be expected with any floor. I am talking no wider than a dime. Depending on the time of year and the climate in the house at the time of installation, an effect can be felt on a floor. I am faced with that right now. If the humidity inside the house is very high, say for example 70% or higher at installation, then drops to 30x in winter, you could get more gapping. Or if wet trades had not finished while a house was being built and the floors were installed in this environment, or if the wood was, in fact, itself holding higher than normal moisture content of 7-9% at time of installation, then it will shrink considerably during winter months, and because it was above normal when installing, may never completely close up.

Gaps appear in winter and disappear in summer

Q imported from our old site, Face Lift Floors: By 1994 I noticed gaps between some of the blanks, obviously due to shrinking. They appear in the winter and disappear somewhat in the summer. They may have appeared sooner but I did not notice. I measured 28 gaps, along with a 30-foot stretch, using some old IBM punched cards which are about .007 in thick (? .018 cm, .178 mm). Gaps ranged from 3 cards to 12 cards. The total number of cards in all the gaps was 195 cards. I measured the gaps a year ago, in March of 2003. The total number of cards is 143, down from the original 1994 number. I measured the gaps at the end of last summer, in early September. No change from March. Today I measured the gaps –  the total number of cards is 104.

Maybe the humidity has started to increase, even though the furnace still goes on once in a while. I should have probably measured the gaps in January or February.

Would it make sense to fill the largest gaps with real cherry strips, leave the others alone, and then see what happens over the next year or two? If I fill some gaps with nonhardening Dura Seal and then the wood expands some during the summer, will that squeeze some of the Dura-Seal out of the gap?

A: I love my computer but don’t have any experience with IBM punch cards, and since I am old school, I am not metric but inches and feet. Could you tell me how big the gaps are in those dimensions?

I also wonder if you live near the lake since it has taken some time for this floor to find its place. I would not be inserting cherry strips or anything else until I knew this floor was really stable. Any floor can expand and contract with weather extremes. Large gapping is another issue.

If you have large gaps, I would think the floor was not dried properly before installation and was not acclimated to the house before installation. If you have a lot of movement between boards, as far as expansion and contraction, I would not even put in a filler.

From your description, however, it took over 4 years for these gaps to appear. So, something has changed in the house during that time to cause a dry or dryer environment. Perhaps you need to add some humidity to the house during the winter. We really only have so much control over that, don’t we? I mean, if you read the literature, and depending who you read, the relative humidity which is ideal for hardwood should be kept between 45-55% or 30-50%. That is confusing. I can tell you for sure that if your home has 45% relative humidity in winter, you will have water running down your windows. Just keep it above 30% in winter, and don’t let it skyrocket up to 90% in summer. In that case, you are in a sauna, and your floor will swell and cup.

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