Large gaps in wood appear for many reasons. Some wood will bend and twist as it dries. This is especially common with treated lumber often used on decks and fences. When houses settle, occasionally I see large gaps develop between floor boards. There are a variety of methods to address these and similar issues by using wood filler for large gaps.
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Types of Wood Filler to Use for Large Gaps
There are numerous wood fillers on the market and each has their intended use. Before beginning to fill your large gap, take time to understand how each of the types of wood fillers work and how they can be finished.
Many of the strongest, most durable wood fillers cannot be stained and often will not blend with surrounding wood. Large gaps in painted wood have more wood filler options than stained or natural-finish woods.

Traditional Wood Fillers
By strict definition, there are two types of products called wood fillers. While many other liquids and materials can be used to fill wood, there are two primary wood fillers. These fillers are water-based wood fillers and oil-based wood fillers.
These two types of wood fillers will not provide or enhance structural strength to the gap being filled. Water-based and oil-based wood fillers do function as a glue. Using a traditional wood filler is a good option if filling your large gap is purely for aesthetics.
Water-Based Wood Filler
Water-based wood filler is a crumbly-texture paste that can be forced into nail and screw holes as well as gaps. Water-based wood fillers tend to shrink as they dry so filled holes need to be slightly overfilled.
Cleaning up tools after filling holes is also easy with this type of wood filler. Simply run the tool under warm running water and clean with a sponge or brush.
Water-based wood fillers also harden as water evaporates from the filler. This means that this type of filler is workable for longer and takes longer to harden than oil-based.
Oil-Based Wood Filler
Oil-based wood fillers do not shrink as the cure like water-based wood fillers. If your large gap is outdoors, this type of wood filler is highly preferable. Oil-based fillers cannot be stained but many major brands carry multiple shades of wood filler that can be matched to your project.
Cleaning up after you are done with oil-based filler requires using solvent-based cleaners like mineral spirits or acetone. Oil-based wood filler cannot hold nails or screws, but it likely will not crack as wood contracts and expands with the seasons.
Epoxy Wood Filler
If your finished project will be painted, epoxy wood filler is my most recommended large-gap filler. Epoxy wood filler also gives you the opportunity to use a colorful epoxy resin to artfully fill your large gap.

Epoxy will function as both a glue and filler. Epoxy will fill wood pores and bind pieces together.
In most cases, cured epoxy is actually harder and more durable than the wood in which it is embedded. Epoxy wood fillers are ideal for outdoor applications.
Latex Wood Filler
Commonly referred to as plastic wood, latex wood filler is made from a durable, water-based formula. This type of filler is great for indoor and outdoor applications.
Stain can be added to the latex wood filler in an attempt to match the wood filler to the surrounding material. Use the best stainable wood filler for a project like this.
Homemade Wood Filler
A combination of sawdust and wood glue can be a craftsman’s best friend. This simple gap filler requires around a three-to-one ratio of sawdust to wood glue. After mixing, it can be easily applied. It bonds wood pieces together.
Another awesome perk of this option is that if you use sawdust of the species of wood that you are filling, the homemade wood filler can camouflage the large gap it is filling.

How to Use Wood Filler for Large Gaps
Let’s walk step-by-step through filling large gaps using the wood fillers outlined above. Prior to filling your large gaps, set up a safe workstation.
Make sure the piece you are filling is secure and won’t move during the project. Proper ventilation will help move odors and fumes out of the work area. I always recommend safety glasses and gloves.
Using Traditional Wood Fillers
Applying wood fillers, whether oil-based or water-based, can be done with relatively few tools. I usually recommend using water-based wood fillers because they off gas less volatile organic compounds (VOCs), but many oil-based wood fillers have moved towards low VOC contents.
Remember, unless you buy wood filler that is specifically marked as “stainable,” wood fill cannot be stained. For the finished look desired by most DIYers, the wood filler either needs to be color matched beforehand or painted afterwards.
Tools Needed:
- Wood filler
- Putty knife
- Sandpaper
Method:
- Scoop a small amount of wood filler on the end of the putty knife.
- Press that filler into the large gap using the putty knife.
- Continue pressing small amounts of putty into the large gap until the large gap is completely filled.
- For water-based wood filler, I recommend mounding a little extra filler on top of the large gap to compensate for shrinkage as it dries.
Using Epoxy Wood Filler
Filling a large gap with epoxy wood filler opens you up to many enticing options. Epoxy resin can be vibrantly colored to accentuate your large gap. The epoxy can be wood-toned and matched to the color of the gap you are filling.
Regardless of how you opt to use the epoxy, if it is applied correctly, it will hold up indoors and out of doors. The filled large gap can be sanded, screwed, or nailed all while standing up to demanding conditions.
There are several methods for applying epoxy fillers. I will provide the method I think best for filling old screw holes.
Tools Needed:
- Wood filler epoxy
- Popsicle stick
- Sandpaper
Optional:
- Paint concentrate of your choice
Method:
- Following the manufacturer’s instructions to mix the wood epoxy filler. In most cases you will have a resin and a hardener that combined.
- If you opt to add color, make sure your epoxy is completely mixed before doing so.
- With your thoroughly mixed, work the epoxy into the large gap bit by bit until it is completely filled. Slightly overfilling the gap is preferable to underfilling..
- Let the epoxy set per manufacturer’s instructions.
- When the epoxy is dried, sand it flush.

Using Latex Wood Filler
Latex wood filler is excellent for indoor and outdoor use. Some versions of latex wood filler will accept stains. However, you should always do a test run on a scrap piece of wood with your latex wood filler to see if the outcome suits your desires.
Tools Needed:
- Putty knife
- Latex wood filler
Method:
- Clean the surface of all loose debris.
- Stir the wood filler prior to applying it to your large gap.
- Work wood filler firmly the gap with a putty knife.
- Overfill slightly, then sand flush after it has dried. For deep, large gaps wait as long as 36 hours or 2 to 6 hours for shallow, large gaps.
- Your wood can be painted immediately with latex paint or wait at least 12 hours to apply oil-based paint.
Using Homemade Wood Filler
Home wood filler is my most economic option. Try to match saw dust from the same species of wood as the large gap you are filling for best results.
Tools Needed:
- Popsicle stick
- Disposable cup
- Sawdust
- Wood glue
- Putty knife
Method:
- Put sawdust into your disposable cup.
- Add glue slowly, stirring periodically, until you get a putty-like consistency
- Work homemade wood filler into the large gap until slightly overfilled.
- Allow glue to dry for at least 24 hours.
- Sand flush.
Conclusion
Filling large gaps with wood filler is possible. Many wood filler options do not accept stains well, but all of my recommended wood fillers can be painted over after the wood filler has completely dried. There are creative, colorful, and economic options available to you to fill your large gap.