The benefits of wood filler are greatly exaggerated

It is an unavoidable truth of hardwood floors that gaps will eventually open up between the boards, parallel to their long sides. Keeping the humidity constant in your home can help to limit the swelling and shrinking of your boards, but in older homes, those seasonal gaps may have become permanent. How do you cope with those?

Wood filler is advertised as the answer to all wood floor voids, but that is a dirty lie!

The problem with the gaps between floor boards is that, even when the gaps are permanent, they aren’t stable. The boards on either side still shrink and swell with the seasons. Which means that anything we put in that gap is still going to be constantly pummeled and stretched. But floor fillers aren’t stretchy like caulk. They dry hard and brittle.

Which means that any boards adjacent to the filler, when filled to bursting with the humidity of August, will squeeze that filler until it cracks. Don’t be impressed when wood filler claims it won’t shrink. Even if that is true, it is not helpful if the width of the opening into which you press the filler is constantly changing.

Filler, is not wood.

It is ugly, flat and poorly colored. When you’re painting over filler, it is a marvelous product.  But if you need the surrounding wood to show and coat over your filled areas with a clear coat, the sheer hideousness of filler is revealed.

So what do you do?

Filling gaps in hardwood floors

  • Don’t use filler on the longitudinal gaps of older floors because it will turn into cracky fill in the course of a season. Open, honest, clean gaps are always more attractive than gaps with broken fill. Learn to love them.
  • Filling nail holes, short-end gaps, and small chips is a correct and honorable use of wood floor filler. Be sure to use a hardening fill that matches the background color of your wood and be sure to do this as part of a re-sanding of your floor. Hardening fill needs to be aggressively sanded to make it flush with the surrounding wood and to remove the residue that you push into the wood surrounding the void you just filled. We always use filler after we have finished with the 36grit pass, but before we start 60grit.

TIP: always buy filler by looking at the actual color of the product, rather than going by the name on the jar. Sometimes filler labeled “red oak” is a better color match for old maple that the filler labeled “maple.”

If you have individual gaps that are so wide that small objects or childen will be lost in them, it is better to fix them with wood than with filler.

The most permanent fix is to remove the offending board and replace it with a larger board that you have ripped down to the exact width of the old board plus the gap width. If you are going to just fill the gap with wood, use a wood shim in the matching species and pound it, slender end down, into the gap. Use a small amount of wood glue to hold it in place and use a block plane or a pull saw to bring it flush to the surrounding floor.

Takeaway: don’t believe the false claims of wood filler products. Learn to love your gaps. Fix long gaps with wood. Reserve wood filler for nail holes and small chips. And choose your filler by looking at the color of the actual product, not by the color listed on the jar.