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Fix a floor that has gaps

We'll confirm whether gaps are seasonal, try humidifying first, then fill small gaps with wood filler or rope—or tell you when to call a pro.

Troubleshooting · Home maintenance
30–90 min (plus 2–4 weeks if humidifying)
What you'll need
  • Hygrometer (to check humidity)
  • Humidifier (if humidity is low)
  • Wood filler, rope filler, or flexible floor filler (for small gaps)
  • Putty knife, vacuum or soft brush
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Steps

Goal: Confirm the gaps, try humidifying first, then fill small gaps or call a pro.

  • Check that gaps are between wood floor planks, not cracks in boards or separation from the wall.
  • Good: You see spaces between adjacent planks—proceed to Check if seasonal.
  • Bad: Different issue (cracks, lifting)—may need a different guide or a pro.

Check if seasonal

Goal: Determine whether gaps are seasonal (humidity) or year-round.

  • Note when gaps appeared or worsened. Seasonal gaps are worse in winter when heating dries the air; they often shrink in summer.
  • Good: Gaps are seasonal—proceed to Humidify.
  • Bad: Gaps stay the same year-round—proceed to Fill gaps if small, or When to get help if large.

Humidify

Goal: Raise indoor humidity to reduce or close seasonal gaps.

  • Use a hygrometer to check humidity. Aim for 35–45% for wood floors. In winter, heated air is often 20–30% or lower.
  • Run a humidifier in the room or use a central humidifier. Keep humidity at 35–45% for 2–4 weeks.
  • Good: Gaps shrink or close—you are done.
  • Bad: Humidity is already adequate or gaps persist—proceed to Fill gaps if gaps are small.

Determine floor type

Goal: Confirm solid hardwood vs engineered—affects which fixes are safe.

  • Solid hardwood is one piece of wood through its thickness. Engineered hardwood has a thin wood veneer over plywood or composite.
  • Glued-down or floating engineered floors may not tolerate some filler methods. When in doubt, call a pro.
  • Good: You know the floor type—proceed to Fill gaps if gaps are under 1/4 inch.

Fill gaps

Goal: Fill small gaps (under 1/4 inch) with wood filler, rope filler, or flexible filler.

  • Clean the gaps with a vacuum or soft brush.
  • For paste filler: apply with a putty knife, press into the gap, wipe excess, let dry, sand flush.
  • For rope filler: twist rope to fit, push into the gap with a putty knife, trim flush. Rope moves with seasonal expansion.
  • For flexible floor filler: follow product instructions.
  • Do not overfill. Excess can crack or look bad.
  • Good: Gaps are filled and the surface is flush.
  • Bad: Filler cracks or falls out—try a different filler type or call a pro for large gaps.

When to get help

Call a flooring pro or carpenter if:

  • Gaps are over 1/4 inch.
  • Gaps keep widening.
  • The floor is engineered and glued or floating.
  • The floor feels soft or bouncy (possible structural issue).
  • Humidifying and filling have not helped.

Do not force boards together or drill through engineered veneer—you can damage the floor. Confirm you have tried the steps above before calling.

Verification

  • Gaps have closed with humidity, or small gaps are filled and the surface is flush.
  • Indoor humidity is 35–45% if you are relying on humidifying.
  • Filler holds when you walk on the floor—no cracking or falling out.
  • No damage to the floor from overfilling or forcing boards.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Confirm gaps Check that gaps are between wood planks, not cracks or structural separation.
  2. Check humidity Measure indoor humidity; aim for 35–45% for wood floors.
  3. Humidify Run a humidifier for several weeks if humidity is low.
  4. Fill small gaps Use wood filler, rope filler, or flexible filler for gaps under 1/4 inch.
  5. Call a pro Large gaps, engineered or glued floor, structural concerns—call a flooring pro or carpenter.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Floor type (solid hardwood or engineered)
  • Indoor humidity reading
  • Whether gaps are seasonal or year-round
  • Gap width (approximate)
  • Steps already tried

Are there visible gaps between wood floor planks?

Gaps between planks are usually from wood shrinkage. Cracks in individual boards or separation from the wall are different.

Check that gaps are between adjacent wood planks. Yes: Proceed to check if seasonal. No: If no gaps or different issue, you may not need this guide.

Yes No

You can change your answer later.

Are gaps worse in winter and smaller in summer?

Seasonal gaps respond to humidity. Year-round gaps may need filling.

Note when gaps appear or worsen. Yes: Try humidifying first—run a humidifier to keep humidity at 35–45%. No: Gaps are year-round—check gap width.

Yes No

You can change your answer later.

Is indoor humidity below 35%?

Use a hygrometer. Wood shrinks when humidity is low.

Check humidity with a hygrometer. If below 35%, run a humidifier. Aim for 35–45%. Give it 2–4 weeks. Good: Gaps shrink or close. Bad: Humidity is already adequate or gaps persist—proceed to fill or call a pro.

Yes No

You can change your answer later.

Run humidifier and wait

Keep humidity at 35–45% for 2–4 weeks. Many seasonal gaps will close.

Run a humidifier. Keep humidity at 35–45%. Wait 2–4 weeks. Good: Gaps close or shrink—done. Bad: Gaps persist—proceed to fill small gaps or call a pro if large.

Done

Are gaps under 1/4 inch?

Small gaps can be filled. Large gaps often need a pro.

Measure or estimate gap width. Under 1/4 inch: Fill with wood filler, rope filler, or flexible floor filler. Over 1/4 inch: Call a flooring pro—large gaps may need board replacement or refinishing.

Yes No

You can change your answer later.

Fill gaps with wood filler or rope

Clean gaps, apply filler per product instructions. Do not overfill.

Clean gaps. Apply wood filler, rope filler, or flexible filler. For rope: twist to fit, push in with putty knife, trim flush. For paste: apply, wipe excess, sand when dry. Good: Gaps filled, floor stable. Bad: Filler cracks or falls out—try flexible filler or call a pro.

Yes No

You can change your answer later.

Gaps are reduced or filled

Gaps have closed with humidity or been filled. No further action needed. Seasonal gaps may open slightly in dry periods—that is normal.

Done

Call a flooring pro or carpenter

Call a flooring pro or carpenter if: gaps are over 1/4 inch; gaps keep widening; the floor is engineered hardwood and glued or floating; the floor feels soft or bouncy (structural issue); or humidifying and filling have not helped. Do not force boards together.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why do wood floors develop gaps?
Wood expands with moisture and shrinks when dry. In winter, heating dries the air and wood shrinks, creating gaps between planks. In summer, higher humidity often closes them. This is normal for solid hardwood.
Will a humidifier fix floor gaps?
Often yes. If gaps are seasonal (worse in winter), running a humidifier to keep indoor humidity at 35–45% can reduce or close them. Give it a few weeks. Gaps that persist year-round may need filler or a pro.
When should I call a pro for floor gaps?
Call a flooring pro or carpenter if gaps are wide (over 1/4 inch), getting worse, or the floor is engineered or glued-down; if the floor feels soft or bouncy (structural issue); or if you have tried humidifying and filling and gaps persist.

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