Gaps in Hardwood Floor, Between Planks, How to Fill Them

It is common to have gaps in hardwood floors after installation or when the floor gets old. This happens when wood loses its moisture content.

Gaps in a wood floor are influenced by factors such as indoor humidity levels, weather changes, radiant heat below, and just negligibly by installation or milling errors.

Wood is a natural material that responds to changes in humidity and temperatures. Higher levels of humidity during the summer or rainy season causes wood to absorb moisture and expand.

If not controlled, floor boards will swell and your wood floor will start cupping and buckling.

The opposite happens during colder weather and dry winter seasons when indoor humidity is low. The wood loses moisture and starts to shrink as gaps form between boards.

This expanding and shrinking due to moisture changes will take place even on high quality and properly installed hardwood floors.

Gaps in Hardwood Floor, Between Planks, How to Fill Them

Gaps in hardwood floors resulting from weather changes can be ignored or be minimized by controlling indoor humidity levels by investing in a humidifier.

Condition your home to 30%-50% humidity levels and temperatures of 60°- 80° Fahrenheit.

Although rare, milling and installation errors can cause hardwood floor gaps. During manufacturing, wood planks are made with precisely-measured tongue and groove, as well as standardized height and width.

Manufacturers also conduct moisture testing and weight sampling. This is to meet the standard requirements set by governing bodies such as NWFA.

Nevertheless, the structural component of the wood can be affected during storage, shipping, or acclimation leading to bending, split ends, or planks with different widths that may affect the flooring outcome.

High temperatures from the sun or under-floor heating from furnaces can lead to separation lines forming between the floor boards.

Excessive heat makes wood lose moisture, dry up, and shrink. In the long run, locking joints and seams are also weakened, leading to an unfortunately all-too-familiar squeaky wooden floor.

Large gaps in both new and old hardwood floors should not be ignored. Dust and debris settle in those gaps and make cleaning to be difficult.

Such matter resting in the gaps absorbs moisture and begins to decompose. In the long run, mold will start to grow or wood will decompose along with the gunk in the gaps.

Gaps can also be also a tripping hazard. You can stumble or fall when you unknowingly hit a raised area of the floor.

In addition, separation lines can mar the aesthetic value of your hardwood floor. A smooth and intact floor is usually beautiful, durable, and valuable.

How to Fix Gaps in Hardwood Floors

Fixing a gapped floor promptly is the right initiative for caring and maintaining a wooden floor. Methods for filling them depend on the gaps’  size, number, and the nature of the floor itself.

Too many or wide gaps may require extensive repair by a professional wood worker, while few or small ones can be a DIY task.

A floor with too many gaps requiring extensive repairs should be replaced completely to maintain the floor’s beauty. In such cases, the cost of repairing the floor is often similar to replacing it entirely.

Filling gaps in a hardwood floor can be done using a stained rope, wood putty, or with wood strips.

Filling floorboard gaps with stained rope

A natural rope is a commonly used for filling gaps in hardwood floors found in many old homes.

The rope has to be stained so that it looks exactly like the color of the floor. How to do it:

  • Clean the gaps to remove debris and all dirt. If there is old putty, remove it using a paint scraper carefully to avoid damaging the wood. Vacuum or use a brush to ensure the gaps are clean and clear.
  • Obtain a rope that is slightly larger in diameter than the gap and soak it in a wood stain. Remove the rope after it has saturated and carefully place it on cardboard so that it can air dry.
  • String out the rope along the gap line and press it using a putty knife so that it can perfectly fit.

Using wood putty to fill gaps in wood floor

Wood putty or fillers can be used on small, stable openings that are not caused by changes in humidity.

Unfortunately, this method is not permanent if you are dealing with floors affected by humidity. When the boards expand or contract, the putty or filler also separates.

How to use the putty:

  • Clean the floor boards and make the gaps clear.
  • Take the wood putty and fill it into the gaps using your finger.
  • Remove excess putty or filler using a putty knife, avoiding scratching the finish.
  • Smooth out the putty by wiping a damp cloth along the gap line.
  • Let the putty dry, and then apply a stain to match the color of your wood.

Fixing gaps in hardwood floor with wood strips

This method works best for wider gaps.

Shape a strip of wood from spare floor boards or any of the same wood species and proceed as follows:

  • Apply some glue around the wood strip and fit it gently into the gap using a hammer.
  • After the glue has dried, sand the wood strip to the same level of the floor, avoiding damaging the finish.
  • Apply a wood stain on the strip to match the rest of the floor.

Filling gaps in hardwood floor with sawdust

Fine saw dust mixed with wood glue or polyurethane is a quick fix for gaps in a wooden floor.

What to do:

  • Get saw dust, preferably from your sanding pad or miter saw, and mix it with wood glue or sealant.
  • Apply the paste into the gaps and let it dry for 10 minutes.
  • Apply some finish or marker so that it can match the rest of the floor.

How to prevent gaps in hardwood floors

To avoid gaps and cracks in hardwood floors caused by expansion and contraction, we recommend the following:

  1. Acclimate the wood to the new environment for 10 days or more before installation.
  2. Use a hardwood floor underlayment paper to prevent moisture migration up through the subfloor from wet or damp basements.
  3. Invest in a digital hygrometer for daily monitoring of relative humidity; maintain humidity between 30 -50% using a humidifier.
  4. Use engineered hardwood for flooring in hot and humid areas.
  5. Properly seal and finish hardwood floors to avoid moisture absorption.
  6. Use quality wood with higher Janka ratings for flooring.

The Bottom Line

While gaps in hardwood floors may be normal, they should be prevented or be fixed as soon as they are discovered.

Do not let them ruin the beauty and value of your investment — a well maintained wooden floor will remain attractive for decades to come.

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