This post was updated on March 7, 2022
Decks can crack and split as the wood ages, leaving large voids on the surface, and it can be tempting to fill these voids with an outdoor wood filler. But as the Internet’s top authority on wood deck restoration, we do not recommend that you use wood filler or caulk for your decking projects. However, we are always interested in hearing about your experiences with deck restoration as well: If you’ve tried using wood crack filler on your deck or are thinking about doing so, feel free to leave us a comment or question below.
What Is the Best Exterior Wood Filler for Decks?
We can’t recommend any caulk and wood filler products to fill cracks in a deck: Using wood filler for decks will not give you a good result.
Should I Fill Cracks in Deck Boards?
No, it’s best to leave cracks be. They won’t be detrimental to the deck, and any wood filler product will eventually fail anyway.
What’s Wrong With Using Exterior Wood Putty on a Deck?
One of the biggest problems with using wood filler or caulk on a deck or wood surface is the instability of the filler. Wood putty tends to crack or break out of the voids you put it in when you use it on wooden decking. This is especially true in an area that gets wintry weather: The natural freezing and thawing processes will quickly cause wood filler and caulk to fail. Also, outdoor wood filler doesn’t look natural on a deck.
Can You Stain Wood Filler?
In general, it’s challenging to put stain over wood filler, and we don’t recommend doing this. Many homeowners have asked about using wood filler or caulk with stain, but it usually looks unsightly because you end up with an uneven color pattern. The wood filler does not stain to match the deck finish. This can be frustrating for someone staining a deck: No matter how hard you try, the caulk or putty will not look like the rest of the stained surface. It’s going to stick out like a sore thumb.
If you want to try staining wood filler anyway, make sure to sand down your exterior wood putty so it’s smooth, clean off the dust completely, and apply the stain in thin layers for the best results.
What Stain Covers Wood Filler?
If you are going to stain over wood filler, make sure to use a solid stain. A semi-transparent stain will not hide it; no stain will do a perfect job of covering wood filler, but solid stain will work best.
What Can I Do About Deck Cracks?
The best way to deal with cracks and voids is to sand around the area to lessen the size of the gap. In extreme cases, replacing the boards or turning them over may be the best option. But in many cases, cracks aren’t detrimental to the deck, so you don’t have to do anything. Some small cracks and splits will not hurt the deck’s performance.
What to Use to Fill Holes in a Wood Deck
For severe damage, like a rotted knot, you can try Perma Fill by Gulf Synthetics: That’s probably your best bet. But rather than use wood filler to repair rotted wood, in most cases, it would be better to replace the wood.
Can I Use Wood Filler on Pressure-Treated Wood?
Pressure-treated wood is full of preservatives that prevent severe cracks and damage, so you’re not likely to have cracking that’s bad enough to need filling. But we don’t recommend using wood crack filler on any type of wooden deck, including one made with pressure-treated wood.
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As an article and comment contributor to the site, Scott has been around the pressure washing industry since attending college. In 1993 he started his first company called Oakland Pressure Wash specializing in exterior pressure washing and deck staining. That company evolved into OPW L.L.C. shortly thereafter concentrating more on exterior wood and deck restoration. Scott and his Deck Cleaning Michigan company have restored over 10,000 decks in the Metro Detroit area since the early years. He has become an authority in the deck restoration industry and has contributed to numerous wood restoration forums and informative sites.
All the products he suggests through this site are sold through online sites and in retail stores, allowing the consumer to choose their own means of purchase. Scott’s eCommerce sites do sell many top brands he endorses and if you appreciate any of the help he has offered then feel free to purchase from one of them.