Shrinkage cracks—and why filler won't help
Plank flooring expands and contracts with humidity
changes and may show some gaps. In fact, on old plank
floors, gaps are considered part of the “look.” To minimize
them, try keeping your home's relative humidity close to 50
percent. During dry seasons or heating periods, the humidity
often drops and you'll need to use humidifiers. During
periods of high humidity, you may have to dehumidify
(although air conditioning often takes care of it).
I don't recommend that you use a filler; it may look worse
than the shrinkage gaps. A non-hardening color putty will
fill the cracks, but it will dry and pop out within a year and
need redoing. A putty that sets hard can create larger gaps or
even buckle the floorboards by not leaving any expansion
space. Conversely, it will crack if the floor shrinks.
The real cure for cracks in a wood plank floor is to minimize
them in the first place. Here are the two main ways
excessive cracks develop.
1. The wood flooring has too much moisture content when
installed and then shrinks as it “dries out.” The solution is to
buy dry wood and to acclimate the flooring to the room you
want to lay it in. All work that introduces moisture (concrete
floors, drywall taping and texturing, painting) must be complete and dry. Then store the wood on location for at least
two weeks. A normal humidity level must be maintained
during this period (by heating or air conditioning).
2. The wood is too dry to start with and the flooring
absorbs excessive moisture after installation. As the wood
expands, the pressure will crush fibers at the edge of the
boards along tight joints. This is called compression set.
When the wood dries out again, it will shrink; the crushed
fibers won't completely rebound and a gap will form.
Again, the solution is to acclimate the wood to the space,
making sure the humidity is kept close to its normal level.
In all cases, put a coat of finish on new floors as soon as
possible, as this will slow down moisture movement into
and out of the wood floor planks.