How to Fill Cracks in Floorboards

Updated April 17, 2017

It is common for the wooden floorboards of an older home to have cracks and gaps in them. Wood floors are affected by weather, humidity and ageing. Many cracks are caused by the wood swelling and shrinking with changes in the temperature. There is a way to fill the cracks with a flexible filling material that can endure the seasonal changes in the wood.

Create your own flexible wood filler. Mix sawdust together with shellac, varnish or white glue in a container.

Fill the crack with the homemade filler. Use a putty knife to press the filler down into the crack.

Soak a small piece of hemp rope in linseed oil or glue. Pack the hemp rope into the crack.

Pack more wood filler on top of the hemp rope. Allow the filler to dry.

Place masking tape around the edges of the crack. The tape protects the floorboards during the caulking process.

Fill the cracks with a flexible marine or silicone caulk. Caulk is available at hardware, paint and home supply stores. Cut the tip of the caulk tube off about one-quarter of an inch from the top. Cut the tip at a slight angle. Place the caulk tube in a caulk gun. Lay a bead of caulk into the cracks. If the cracks are deep, insert a piece of cloth into the crack before applying the caulk.

Wipe the tip of your finger across the caulk. Gently press down and smooth the caulk line out. Clean the tip of your finger with a damp cloth.

Measure the length and width of the cracks. Make or purchase wood shims. Purchase wood shims at hardware stores, home supply stores or a lumber yard.

Glue the backs of the shims with wood glue. Insert the shims into the cracks. Allow the glue to completely dry.

Sand the top of the shims with sandpaper or a hand-plane. The tops of the shims may be slightly higher than the surrounding floorboard. Sand or hand-place the shims until they are smooth and level with the floorboard.

Things You'll Need

  • Sawdust
  • Shellac/varnish/glue
  • Container
  • Putty knife
  • Hemp rope
  • Lind seed oil
  • Masking tape
  • Silicone or marine caulk
  • Caulk gun
  • Utility knife
  • Wood shims
  • Sandpaper
  • Hand-plane
  • Rags
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About the Author

Robert Russell began writing online professionally in 2010. He holds a Ph.D. in philosophy and is currently working on a book project exploring the relationship between art, entertainment and culture. He is the guitar player for the nationally touring cajun/zydeco band Creole Stomp. Russell travels with his laptop and writes many of his articles on the road between gigs.