With older tongue-and-groove hardwood or even wide-plank floors, gaps inevitably develop between the boards, mostly because the wood shrinks over time as it dries out and loses moisture content. The problem is magnified when the boards were not tightly laid in the first place. Another exacerbating condition is water damage. Water-logged wood will first swell then shrink as it dries out. Floors that are subjected to dry heat from below—such as when they are installed above a furnace room—are particularly prone to developing gaps.
Although some gapping is inevitable, severe gaps become more than just unsightly. Wide gaps between boards can become dirt magnets, and the floor may even become a tripping hazard if the boards begin to cup or curl, a common occurrence with old wood flooring.
Should You Fill Flooring Gaps?
It's important to keep in mind that all wood expands and contracts with seasonal humidity changes. If you're bothered by gaps in the dry winter months but don't seem to notice them much during the relatively humid seasons, it's probably best to leave the gaps alone, as filling them when they're at their widest will create problems when the wood expands again and the gaps naturally close up. In extreme cases, floorboards can buckle if you have left no room for them to expand.
On the other hand, old flooring can develop gaps that are more or less permanent, although they still may get slightly wider and narrower with humidity changes. Check your flooring during the humid season, when the wood is most swollen and the boards are at their tightest. If you find that the gaps are large enough so that a nickel standing upright can slide into the gaps, then you have a problem that needs correction.
If you're certain the gaps are there year-round, it's probably safe to fill them. It's best to do this during the humid season, when the gaps are most narrow. Of course, this means you might see slight gaps appear when the wood shrinks again next winter, but this is better than a floor that buckles during the next humid season when the boards expand.
Before You Begin
We've provided instructions for a few different methods of fixing the gaps in your wood floor. Depending upon the option you choose, you might not need all of the supplies on our lists. Read through the instructions carefully, then gather the supplies and tools appropriate for your chosen method.
Equipment / Tools
- Tape measure
- Table saw
- Miter saw or handsaw
- Sandpaper or planer
- 5-in-1 tool or flathead screwdriver
- Utility knife
- Shop vacuum
- Putty knife
- Wood floor boards or matching hardwood
- Wood glue
- Wood stain or other finish
- Jute rope
- Wood stain
- Wood putty
- Clear varnish or polyurethane
How to Fill Floorboard Gaps With Wood Strips
This method involves using a table saw to rip-cut narrow strips from spare floor boards. If you have no leftover flooring boards lying around, then you may be able to buy new or salvaged boards of the same species or simply use pieces of matching hardwood lumber.
Cut the Strips
Measure the width and length of each gap between floorboards. Set up a table saw to rip-cut strips to the measured width. Cut the strips as needed for the length of the gap to fill, using a miter saw or handsaw. Try to cut the strips from the grooved side of the spare floor board. That way the depth of the piece will be correct when it touches the tongue of the existing floor board.
Ripping thin strips of wood on a table saw can be hazardous and requires specific safety precautions. Get expert help if you need it.
Glue the Strips in Place
Apply wood glue to the sides of each strip and gently tap it into the gap, using a mallet or hammer. Try to get the strip flush with the adjoining boards. Wipe away excess glue with a damp cloth, then let the glue dry.
Sand and Stain the Strips
Sand or plane down any high spots in the strips, being careful not to damage the surrounding finish or boards. Stain and/or finish the strips to match the rest of the floor.
How to Fill Floorboard Gaps With Rope
Filling large gaps with natural-fiber rope is a traditional method commonly used on wide plank floorboards in very old homes. While the rope doesn't look like wood, you can stain it to blend with the floorboards, and the filled gaps will be much less noticeable than the dark, empty gaps. Be sure to use natural rope, such as jute or cotton, because synthetic rope won't accept a stain.
Clean Out the Gaps
Scrape out the gaps with a painter's 5-in-1 tool or flathead screwdriver, removing all dirt and old putty from the gaps. Be careful not to damage the edges of the adjoining floorboards. Vacuum the loose debris from the gaps with a shop vacuum. Repeat scraping and vacuuming until the gaps are clear.
Stain the Rope
Select a rope with a diameter that is slightly larger than the gap. Pour wood stain chosen to match the tone of your floorboards into a small bucket. Dunk the rope into the stain so it is saturated. Carefully pull out the rope, letting the excess stain drip back into the bucket. Stretch the stained rope out on clean cardboard and let it dry completely.
Do not expose the rope to direct sunlight or intense heat, as there is the potential for the rope to spontaneously ignite if you are using an oil-based stain.
Fill the Gaps
String out the rope along the gap, then force it into the gap with the 5-in-1 tool or a putty knife, stopping when the rope is flush with (or slightly below) the wood surface. Trim the rope as needed with a sharp utility knife.
To help secure the rope, apply a bead of wood glue in the crack prior to placing the rope. After the glue has dried and rope has been trimmed, brush with a clear varnish or urethane to give the rope a hardened surface.
How to Fill Floorboard Gaps With Wood Putty
Filling gaps with wood putty is a quick and easy method that works on small, relatively stable gaps. However, there's a good chance the gaps will open up again during the dry season, and they may crack inconsistently.
Clean the Floor
Clean the floorboards on both sides of the gap, using a slightly dampened cloth.
Apply the Wood Putty
Apply a fine bead of wood putty to the gap, then work it into the gap with your finger, using circular motions to force the putty down into the gap. Remove excess putty from the wood surface using a putty knife. Be careful not to scratch the floor's finish.
Choose a wood putty that is similar in color to the floor boards. If you can't find a single color that matches, there are kits with different colors that you can blend to create a custom color.
Clean Up and Let the Putty Dry
Let the putty set up, then wipe gently along the filled gap with a slightly dampened cloth to remove putty residue from the adjoining boards. Take care not to pull putty out of the gap. Let the putty dry completely before walking on the floor. To give the surface more strength, apply a coating of varnish or urethane. This also will likely help it blend better with existing flooring.
Coatings and Colors Manual. United States Department of Homeland Security.