Short answer: it depends on the crack
There isn’t one best filler. The right choice depends on four things: the size of the crack, whether it moves with the seasons, whether the wood is bare or finished, and whether you’ll stain or paint over the repair.
Fillers and what they’re good for
- Ready-mixed wood filler. Good for small cracks and nail holes before finishing. It’s easy to use and cleans up with water, but most types shrink slightly as they dry.
- Two-part polyester filler. Hard, with little shrinkage, and it sets in roughly 15 to 30 minutes. It suits work under paint. It releases styrene fumes, so ventilate.
- Two-part epoxy. The strongest option. It suits structural, rot and exterior repairs, and large voids.
- Epoxy putty. Good for small cracks, screw holes and chips. It shapes well and can be sanded once it cures.
- Latex or water-based filler. Low odor and easy cleanup, but more shrinkage. Some are sold as “stainable.”
- Clear casting epoxy. Used for decorative or live-edge cracks in some projects. Thick pours need a deep-pour formula, and the maximum depth varies by product.
Caulk isn’t a wood filler. It stays soft, won’t sand well, and won’t take stain, so keep it out of visible repairs.
Small cracks before finishing
For a small crack before a finish goes on, a ready-mixed wood filler is usually enough. Overfill slightly, since most one-part fillers shrink as they dry. For a deeper crack, build the fill in layers, following the product’s maximum depth per layer, which is often about 1/4 inch.
Test the color on a scrap or a hidden spot first. “Stainable” fillers don’t absorb stain the way real wood does. They usually end up lighter or blotchy, so color them separately, or pick a filler that suits the finish you plan to use.
Sawdust mixed with shellac, lacquer or epoxy blends better than sawdust mixed with wood glue, which tends to dry darker and weaker.
Structural and outdoor repairs
For a crack that has to carry weight, or for a repair outdoors, epoxy is the strongest choice. It bonds to sound wood and can be shaped, drilled or painted. It costs more than a standard filler, and it’s a skin sensitizer, so wear gloves. For oily outdoor wood, see how to repair cracks in teak furniture.
A wide crack in solid wood can also be fixed with a glued-in sliver of matching wood, which is often the least visible fix. See will wood glue fix split wood.
Cracks in an existing finish
For a crack in a finished surface, use a filler designed for finished wood. Wax fill sticks are easy to use and suit sides and legs. Burn-in sticks are melted in and last longer on heavily used surfaces. Neither is a structural fill. How to repair deep scratches in wood furniture explains both methods.
What a long-term outdoor test showed
One blogger left several fillers and epoxies unpainted on a horizontal piece of rough-sawn cypress outdoors in Florida for five years. The results were mixed:
- The epoxy-based products held up well, with some hairline cracks but no structural problems.
- A spackle-type filler shrank early and separated from the edges. By year five it could be pulled out with a fingernail.
- A styrene-based filler stayed in place but developed cracks around its edges.
- A water-based wood filler held up well, which surprised the tester.
This was one tester in one climate, and the products weren’t painted, which the manufacturers recommend. Treat it as one data point rather than a ranking, and test your own repair in your own conditions where you can.
Cracks that move with the seasons
A crack that opens and closes with humidity means the wood is working. Rigid fillers can crack or pop out in that situation. If the crack is stable and cosmetic, you may choose to leave it. If it keeps moving, look for the cause, such as a top that’s held too tightly to its frame. Caulk isn’t a substitute for a proper fill.
Color and sheen
Test the color on a scrap, and let the test dry before you judge it. Open-pored woods such as oak and walnut need a grain filler for a smooth finish. Grain filler is a different product from crack filler, made for open pores rather than cracks.
After the fill has cured, match the sheen with an aerosol finish of the right sheen, such as satin, semi-gloss or gloss.