We have gaps in our wooden birch floors. Some quite large. We are told that the cause of this was due to nail spacing and inadequate glue. I'm baffled as to why nailing and glue would prevent hardwood floors from shrinking and staying shrunk. We live in CO and had the floors acclimatize for 30 days before installing. Are there reports/tests that show that floor shrinkage is caused by incorrect nail spacing and insufficient glue - I can't find any... seems to be caused by the manufacturer not drying the wood sufficiently before production.

  • What glue? Flooring type would be good information to have. You're probably right, though. This is due to moisture loss. How was it acclimated?
    – isherwood
    Commented Jul 9, 2019 at 17:34
  • The manufacturer may have dried the wood according to some standard, but if your location is drier then it will shrink further...
    – Solar Mike
    Commented Jul 9, 2019 at 17:35
  • Just a guess, but wood, over time, dries more and more, this causes shrinking of material. But also humidity causes expansion, so in essence the floor is always moving in expand/contract mode. Gaps form and the repair is not hard just manually intensive. If you pull boards out an reset you get a better fit, but the gaps could all return. Commented Jul 9, 2019 at 17:51

4 Answers 4


The flooring was probably mis-milled.

Wood flooring has to be cut, dried, accumulated, fit, nailed, etc. perfectly or you’ll have big gaps.

Often the manufacturers point the finger at installers, when actually it’s their problem.

The way to check is to hold two boards up and push them together. If one slips through then it’s too loose a fit between the tongue and groove. There’s no amount of acclimation or nailing that can fix that.

We’ve had many gymnasiums floors removed and replaced because it doesn’t meet grade. (You can see the manufacturers cry when it’s chainsawed out of there.)

Follow the Western Woods Use Flooring guise (National guide).

Hint: test a zillion boards to make sure all the tongues fit tight in the grooves and doesn’t slip...even if you shake the board while in the groove.


Wooden floor gaps are usually caused by the change of temperature. Wood has natural moisture so in the winter time, when the air is dry and homes are heated, it loses its moisture and shrinks. Thus, the gaps. Wait until the spring because they might expand back once they regain moisture. To avoid dirt and gunk going in those gaps put a rope (natural not synthetic) in between. If the gaps still show, you can apply wood fillers using your fingers or with a putty knife.

  • But beware that if you fill the gap, the filler will be spat out when the wood expands again. Commented Jul 9, 2019 at 19:22

Some of those floors are better left to 'float', meaning that each board is not attached to the floor joist. I have never glued tongue-and-groove flooring together. The boards will shrink and expand according to temp and humidity. The gaps will be larger when it is cold and when it is dry. They will get smaller when it is humid and when it is warm. If the gaps are too big when it is warm and humid, then I would loosen the nails, close the gaps, and just nail the perimeter.Sometimes i add finish screws to attach squeaky boards more tightly to the subfloor


If they are real wood planks, they may not have been installed tightly enough next to each other with an appropriate expansion gap along the walls. If they were installed in the summer after acclimating for 30 days, they probably needed to be installed tightly so when the humidity dropped in the winter and caused the wood to contract, the gaps would have been minimal. Vice versa if they were installed in the opposite season. Or the installer may have used incorrect fasteners to allow the wood to expand and contract with the grain of the wood. The wood will move more on the long side edges (assuming the wood was cut correctly in the direction of the grain).

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