This post was updated on June 14, 2024
Hi, I am Scott Paul. I have been staining new and old decks for over 30 years. My Wood Filler help tips for decking are based on my history as a wood restoration contractor and actual hands-on testing. See here for more info about me.
Wood 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. However, as the Internet’s top authority on wood deck restoration, I do not recommend using wood filler or caulk for your decking projects. However, we are always interested in hearing about your deck restoration experiences. If you’ve tried using wood crack filler on your deck or are thinking about doing so, please leave me a comment or question below.
See Below For Commons Question on Deck Wood Fillers
What Is the Best Exterior Wood Filler for Decks?
My Pro Tip: There isn’t one.
We can’t recommend caulk and wood filler products to fill cracks in a deck. Using wood filler for decks will not yield a good result. Decking stains that show the wood grain will not blend with a wood filler. The filler will stand out and look like “white” blotches over your deck.
Should I Fill Cracks in Deck Boards?
No, it’s best to leave cracks as they are. They won’t harm 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 it is used in when used on wooden decking. This is especially true in an area with 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 have 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, 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 stain over wood filler, use a solid stain. A semi-transparent stain will not hide it, and no stain will do a perfect job of covering it, but a solid stain will work best.
What Can I Do About Deck Cracks?
My Pro Tip: Leave them alone. They are normal and will not harm the deck.
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 or turning the boards over may be the best option. But cracks aren’t detrimental to the deck in many cases, 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 Ranger Patch by Gulf Synthetics. That’s probably your best bet. But rather than using wood filler to repair rotted wood, it would be better to replace the wood in most cases.
Can I Use Wood Filler on Pressure-Treated Wood?
Pressure-treated wood is full of preservatives that prevent severe cracks and damage, so cracking that’s bad enough to need filling is unlikely. However, we don’t recommend using wood crack filler on any type of wooden deck, including one made with pressure-treated wood.
I have Cracks in My Deck Support Posts. Should I Repair?
It’s not an issue! Deck support posts are made of pressure-treated pine, and pine wood generally shows cracks after a few years outside. This is completely normal, and your deck support structure will not have any issues.
Need Help? Wood Filler Deck Questions?
Want Help? Please ask me below if you have questions about my deck tips with a wood filler or need help choosing a stain. Just post a comment below and include as much information as possible.
I am so grateful for this website and for your frank, clear answers to questions I’ve had for years. I’ve tried wood filler before- epic fail. You are spot on. I will say that I used Gorrilla Glue for a huge, deck splinter a few years ago and, while not ‘pretty’, most people don’t notice and it is still working fine.
Have large chips at eyes. Big enough if you catch right barefooted can cut you. What can I use to fill? Or should deck company replace any boards like this?
Replace the boards.
the 2×8 top rail on my exterior deck has separated about a1/4″, what can i use to fill it in?
Fillers will not work or exterior decking.
Love your page Scott and thank you for this service!
OK so we have painted deck and the last time it was painted they did a terrible job and painted way too thick and didn’t allow proper drying time, etc. We are redoing it and looking to make it decent – not perfect.
We rented this sander and it’s going an OK job – we wish it could get more off but I think that if it were more intense then the exposed nails (or like all of the nails) would be an issue so doesn’t seem feasible. Also we have no problem replacing bad boards – they are pressure treated and we even have some left over from the last time ~3 years ago and they are ready to go
Anything else to keep in mind?
When reapplying a solid stain or paint, you want to remove all loose and peeling coatings. You do not have to remove the intact coating that is not failing fully: https://www.deckstainhelp.com/how-to-reapply-a-solid-color-deck-stain/
For sanding tips, see here: https://www.deckstainhelp.com/how-to-sand-your-wood-deck/
Use deck screws. We do not suggest wood fillers on decks. We never use primer on decks. We do not ever use paint on decks but solid color stains. Paints will have a stonger chance of peeling.
I’m planning to repaint my moms wood deck, but should I treat it with something after a thorough cleaning and sanding?
No need.
I’m redoing our deck. The wood, under 3-4 layers of paint, doesn’t look to bad to me. My wife really likes the look with the paint partly on the wood too. My question is what would be my best option for keeping the paint partly on and treating it. I am leaning toward Penofin oil for treated wood. It’s a covered deck but still gets a little wet. Please tell me what you think
Thanks,
Lee
It will not work to have the paint partially on. The paint has to fully come off if you want to use any semi-transparent stain or any treatment other than a paint coating.
FYI, Penofin has issues turning dark or even black.
https://www.deckstainhelp.com/?s=penofin+reviews&post_type=post
Does drylok work with wooden deck? Our deck is 10 years old with deep cracks on the supporting columns. Our contractor suggested 1 layer coating of drylok to fill the cracks and waterproof them from further water damage. The deck is solid dark brown color now. Thank you!
No, this will not work.
my deck has splinters
,i was wondering if i could sand it and seal it,rather than replace it
Depends on the wood condition and whether it can be salvaged or not.
Attached is a picture from my previous question
I am replacing old wood on my deck. The joists have some splits about 1/2″ deep and small old holes that are soft/turning black. Before replacing planks – I am thinking of spraying some boric acid to prevent any rot; and filling cracks and old holes with a loctite PL MAX construction adhesive to keep water from pooling in the voids. The loctite product appears to be very strong and used in marine applications. Any thoughts?
Not sure how it will work it will not “stain” to blend, if that matters. The boric acid will not stop the rotting where it has already occurred, so replace those joists or posts as needed.
Hi
I have wood beams on my front and back porch. Some of the beams have long cracks in them
Im not sire if they are natural of have been caused over time by the weather.
Someone suggested i fill in these cracks with wood filler. Before doing so i wanted to ask your opinion. I have attached a pic
No, do not fill them. They are not an issue and they will not stain to blend.
Thank you in advance.
1) 45 yr old deck exposed to extreme temperatures and snow and apparently multiple attempts painting it. Most has peeled from floor but posts have cracking and peeling paint. Want to remove rest of paint and protect wood. What is best approach? Sealing it? Waterbased or oil based stains best? Want to insure against future peeling!
2) Paint has peeled from very old, dry wood exterior window trim. Would solid stains work better than frequently re-painting? If so, waterbased or oil?
Thank you in advance. Have received many suggestions with little agreement.
1. Post pictures for prep advice.
2. Not sure on paint for windows, we only work on decking.
Painting contractor here. In answer to your second question: If you can avoid painting anything outside, do it. Yes, stripping the paint from your exterior window trim and coating it with a solid stain (oil base or water-miscible oil) will make future maintenance much easier. The stain will not peel.
Have a screens in deck . The screening is framed, there is a gap between one of the uprights and the screening. Just had the deck refinished and the new contractor says that he can’t recaulk the space. Any suggestions?
You can caulk it. Not sure why he would say otherwise.