How to Fix Gap in Hardwood Floor

Why Do Gaps Form in Hardwood Floors?

Hardwood is a natural material that expands and contracts with changes in humidity. Most gaps in hardwood floors are seasonal — they open in dry winter months when the wood shrinks, and close again in humid summer months when the wood expands. These gaps are normal and usually don't need repair.

Gaps that stay open year-round, or that are wider than 1/8 inch, may need to be filled.

Step 1: Determine If the Gap Is Seasonal

Before filling any gap, check your home's humidity. Use a Digital Moisture Meter to measure the floor's moisture content. If readings are below 6%, the gap is likely caused by low humidity — run a humidifier and check again in a few weeks. Many gaps close on their own once humidity is restored to the 35–55% range.

Method 1: Wood Filler (Best for Small Gaps)

For gaps up to about 1/8 inch that don't close seasonally:

1. Clean the gap thoroughly — remove all dust, debris, and old filler
2. Apply Gorilla Wood Filler into the gap using a putty knife, pressing firmly to fill completely
3. Slightly overfill — the filler will shrink as it dries
4. Allow to dry fully, then sand flush with 180–220 grit sandpaper
5. Wipe clean and apply matching stain or finish if needed

Note: Wood filler is rigid when dry. If the gap is seasonal, the filler will crack and pop out when the wood expands. Only use filler on gaps that stay open year-round.

Method 2: Rope or Cord Filler (Best for Wider Gaps)

For gaps wider than 1/8 inch, flexible rope filler (also called jute rope or hemp rope) is a better choice than rigid wood filler because it can flex with seasonal wood movement:

1. Cut a length of natural fiber rope slightly thicker than the gap
2. Press the rope into the gap using a putty knife until it sits just below the surface
3. Apply a thin layer of wood filler over the rope to seal the surface
4. Sand flush when dry

Method 3: Flexible Caulk (For Gaps Along Walls)

For gaps between the floor and baseboard (not between boards), use a flexible paintable wood caulk. Apply a thin bead, smooth with a wet finger, and allow to dry before painting or staining.

When to Call a Professional

If gaps are widespread across the floor, or if boards have shifted significantly out of alignment, the floor may need to be re-nailed or re-glued by a flooring professional. Widespread gapping can also indicate a serious moisture or subfloor problem that needs structural attention.

Products Used in This Guide

• Gorilla Wood Filler 16oz — fills small permanent gaps
• Putty Knife Set 5pcs — for applying and smoothing filler
• General Tools MMD4E Digital Moisture Meter — diagnose whether gaps are seasonal or permanent