1. ABNORMAL GAPS
Not all gaps are bad, but these are. The gaps pictured here are too big and irregular. They take away from the overall look of the floor, which should be relatively uniform across its surface.
Wood floors are prone to movement. Installed correctly, floorboards hold tight to one another during humid times of the year and might reveal gaps during drier times. Abnormal gaps are generally the result of flooring that’s too wet when it is installed (sidebar p. 80), but they also can be the consequence of installing flooring in areas of excessive dryness. I’ve worked on floors that had abnormal gaps because floorboards were installed directly over heating ducts, in areas that received a lot of sunlight, and in homes heated with woodstoves, which creates a dry interior environment.
Gaps are an aesthetic issue and should be repaired when they disrupt the overall look of a floor, not when they measure a particular width. I repair abnormal gaps during the most humid time of year, when they are at their smallest. If I repair gaps when they are at their widest, I might not leave sufficient clearance between floorboards and create a floor that buckles when it expands.
Also, I never use wood filler to repair gaps. Instead, I make a patch by gluing slivers of wood to the edges of the floorboards. I’m careful to apply glue to only one side of the sliver so that I don’t glue any boards together.