This post was updated on November 1, 2022
fillDecks 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.
For this 40-year-old, no maintenance
de ck should I use oil base primer?
And oil base stain and paint?
I am new to all these. Thank you for your help.
Do not use a primer with deck stains.
Best website ever.
My deck is 40 years old, lack of maintenance. Lots of rotten wood. But base is good. Have rotten knots too and big holes. What to do?
Use wood hardener?
Can I use primer over some leftover paint from five six years ago?
Please recommend brands too.
Appreciate your advice and time.
Post pics in the comments for prep help and advice.
Attached are four. More to come
You should replace all our bad wood and rotting boards now as they cannot be fixed. Let the new wood weather until Fall after install. Prep and restain all with a solid color stain.
Permafill by Gulf Synthetics is discontinued. No longer available.
MANY EPOXY FILLERS STATE THEY ARE STAINABLE. ARE YOU SAYING THIS IS A LIE?
Yes. They will stain to blend with interior stains but not exterior transparent or semi-transparent stains.
I have pressured wood on my deck. The previous owner had painted the deck and it has peeled off, there is also algae and some mold.
1.Can I just sand the deck?
2 I want to use a black solid stain, is a brightener needed?
3. There are some stains that have sealants, can I use that or do I need to use a specific waterproof sealant first and then stain it?
4.In one of the panels, the end is lifted, just used a screw?
Thank you for your time.
1. You can sand off the paint.
2. Clean and brighten for final prep after.
3. You cannot apply a sealer before applying a solid color deck stain.
4. Not sure what you are asking.
So Bondo and or pro bond by Elmer’s you claim is not needed for deck repairs do nothing is your opinion. Their claims are what false?
Their filler will not stain to blend with a transparent or semi-transparent deck stain. It will look like white blotches all over your deck under the stain where you use it. They also have a tendency to crack and break out if used in a state where it freezes.
Regarding filling knot holes etc., the guy at the store suggested epoxy. No disrespect; but I had to ask.
Epoxy will not stain to blend. You can find a caulk that is similar in color to your stain and use that.
I read the same thing youtube
In one breath you say you can’t recommend a filler in the article, In the next breath you’re recommending Permafill by Gulf Synthetics (which they no longer sold BTW) in the comments. Sounds like you trying to sell a service to me.
Huh? Feel free to go elsewhere for advice. Thanks
I have used woodfiller for last three years on my deck and I have found the woodfiller has lasted for a year or more,I have painted the deck after I did any scrapping and sanded it .
I have a new deck that has cedar posts and beams that were assembled with Simpson “concealed” connectors. But those require 5/8″ holes where the steel pins are driven into the internal connectors. My plan was to use a plug cutter to make plugs out of the same wood to cover the holes, but the holes don’t have pristine edges. I was thinking about filling them and sanding them flush until I found this article. Any suggestions? Unfortunately, the stain we’re using is oil-based and transparent.
Fillers will not work to blend when stained. Maybe a pre-tinted filler or caulk that is similar in color to your stain will work.
Thanks for the reply.
Right this second, I’m trying an experiment of the old trick of glue mixed with wood sawdust.
Perhaps the thing that will help is that the holes in question are either 9′ in the air or down by my ankles.
Hi there. This is all really helpful, especially seeing that the vertical cracks are normal. Here’s where I need some reassurance: I live in a place where we get ice in the winter. I kept thinking I needed to fill the variety of cracks so that the expansion of frozen water within those cracks would not worsen the condition of the wood. Is that a concern or are you saying no, it either won’t do much damage or it will do damage but there’s not much to be done about it and eventually replacement would just have to happen? I appreciate your time. Thanks so much.
Cracks are normal so just leave them as is.
We had a new deck installed in November 2021 (we live in Georgia). The wood is pressure treated and it now has long cracks down the posts some of them look deep. There are some cracks on the deck boards as well. What should we do?
Nothing. Cracks are normal in decks. Just leave it as is. See here about new wood and staining: https://www.deckstainhelp.com/how-long-should-you-wait-to-stain-a-new-deck/
Even when it looks like this?
Yes, that is normal.
how can I restore this deck?
HI there, May I ask what you mean that the wood filler will fail? Does fail mean cause rot of the boards? Or does it mean the filler will get dry and come out? Is the concern that using wood filler to repair cracks will look “ugly” under transparent stain or that using wood filler would actually damage either the boards (rot?) or make the paint job look bad or peel? Thank you!
All wood fillers will fail on exterior wood. It will “crack” or fall out after a year or less. It also will not blend at all with any deck stains that are transparent or semi-transparent.
Thank you so very much. If there was 1 coat of primer and 2 coats of paint on the wood, would you see the cracked wood filler? A company proposed filling the cracks with wood filler and then priming plus 2 coats of solid color paint on the deck (we also have three new boards that are clearly a different color). I am wondering why they would say that? Unless it makes the boards looks the most smooth and we would never see the cracked filler under all of the layers of paint? Is there ANY advantage to using a filler?
Eventually, if it comes out then yes, you will see it with gaps. BTW, you should never prime and paint an outside deck. This is a recipe for peeling.
Oh my goodness! Thank you! You mean skip the primer part??? Or do you mean do not use paint, just use stain??
No primer or paint. Use a deck stain. Solid color if you want the opaque look.
Any way to fill or hide those pressure-treated incisions? I plan on using a solid color stain. I just hate those marks!
Sorry but not really.
If I will be applying a solid stain (RAD) which type of product for filling cracks/voids is best (mainly for longevity)
Noticed a few answers here saying it’d be ok if using a Solid stain. Epoxy. Filler. Exterior caulk.
Would you apply prior to strip or after?
I have cracks as well as splintering on our 15 yr old PT pine deck.
If using a solid stain then use a flexible caulk to fill. After stripping.
We had a new deck constructed this summer. The contractor placed caulking in the joints of the rail top. Now I read that it should not be done! How do I get that off? sigh……
You probably cannot remove it. Stain the deck and if the caulk shows, you may need to redo the caulk over the current with a color that blends with the stain color you picked.
Found this website too late. Just used some wood filler on big cracks, stained deck with semi transparent product. Colour difference between filler and deck boards is atrocious. In two years, when I re stain, will switching to a solid stain mask it better? I could also just reverse the boards too I guess.
Solid stain will mask it.
Thank you for your feedback!
What can I use on the old boards before the solid stain is applied to fill in the weathered cracks? The replaced boards are obviously new and solid and I want them to blend better than they will as is; I’ve already purchased the solid stain it was mixed at Sherwin Williams.
It will not work. The filler will fail and crack out on exterior wood.
So, if not a filler, which was more a descriptive word I chose than product, is there anything that can be applied to bridge the visual gap between the 2?
Sorry but no.
What about a epoxy filler?
It will not stain to blend. If using a solid stain, then you should be okay.
My deck posts are showing such cracks as in the pic. My contractor recommended to apply this exterior coating before painting/staining. Will this help for cracks to stabilize and not propogate faster and is it generally recommended to apply on the floor of deck before paint/stain?
Deckover peels and cracks are normal in wood. Just leave as is.
Thank you v much.
I have one more followup: on this solid stained deck (6+ years old), I dont want to go through the hassle of sanding the entire deck to remove old stain. If the stain can be removed with a stain remover, I will go for a semi transparent stain, otherwise I will go for a solid stain.
Are the below recommended steps to follow before I pressure wash and start staining
Please advise if above are recommended or should I skip these two steps and move to pressure wash and staining.
You cannot strip this olid stain off so your options are to power sand it all off or cover it with another solid stain.
Thank you. I will go ahead and do another solid stain then.
This means that using the stripper has no value, correct?
Is wood cleaner recommended generally (even if there is no mold/mildew), before applying solid stain?
In this scenario, you do not need a striper. Just give it a good pressure wash.
And no wood cleaner as well? Thanks much!!
I have a main Cedar post on my deck that’s in concrete. It’s older and one side is chewed up due to a gate that was on it & pulled out over time. Can I add a thin cedar board over it? I notice some that are a 1/2 inch thick or less for indoor use.
Was thinking it might protect the holes from the weather?
Yes, you can wrap the post with cedar boards. This is very normal.
Thank you so much for your quick response! I have a follow up question…
Will any cedar board work or I’d there indoor & outdoor cedar? Is there a recommended thickness to use?
Use exterior cedar wood. 1″ is normal. They look like this when wrapped.
Do you recommend a particular brand of stain for a transparent or semi transparent stain? The deck has pressure treated flooring & cedar rails. It suffers from extreme sun during the day & weather exposure. Temps in the area range from high 90s to just below zero in the winter. The frame & posts are older. The railing & floor are brand new green lumber.
One of these brands: https://www.deckstainhelp.com/best-semi-transparent-deck-stain-reviews/
Great Help article. I was just about to attempt to fill small cracks in my deck boards with a wood filler. Glad I read this article first. I am just going to lightly sand the deck and re-stain with my transparent stain.
I completely sanded my 2 year old deck that had no paint or stain. I used Sansin wood stain and it turned out great.
It will be 2 years this summer since I stained, and there is like no peeling at all.
The only spots it has is where the boards end against a 2×10 on a ramp for wheelchair.
Is there anything I could put in the board end to prevent this from getting worse. Like an outdoor caulking etc ???? Thanks
It will not work well or stain to blend with the deck stain.
I have a moderately large treated pine deck , originally painted with a dark brown Wattyl Decking Paint (Weatherguard – I think). Probably painted about 5 years back. For some time now it is showing major cracking – some cracks quite long but none wider than 1 to 1 1/2 millimetres. Further painting does not cover the cracks which apparently need some type of a filler. External position with temperatures ranging from minus 7degrees C to about 34 degrees C. I would appreciate your advice as to the how and what with to fill the cracks.
Crack fillers will not work for outside decking.
I have some deep screw holes and joints that separated on my deck in Maryland. Anything recommended to fill and take a transparent or semi transparent stain?
It will not work as the article above explains.
I did read the article, but was hoping for something…….
I bought all weather silicone that takes on paint, was hoping that would work. Guess I’ll take it back and live with the issues.
Hi, My 87 year old dad just finished putting in a new deck. He’s very meticulous and does good work. He sanded all sides of each pressure treated, heat cured board. Then he applied 1 layer of semi-transparent outdoor stain to all sides. He then applied a 2nd coat to the top of the board. 1 year later the boards are getting cracking that runs longitudinally. The cracks are about 1/4 in wide and some are up to 3 ft long. The knots are also splitting and cracking. He lives we in the Pacific Northwest with plenty of rain and snow.
So, is there anything he can use to fill these cracks so that they don’t worsen? Preferably the fix wouldn’t take back breaking work to accomplish. Thank you much!
No, it will not work or blend with the semi-transparent stains.
Hi my pool deck has slight cracks what should i use?
Just leave alone as is. A filler will not work.
Can I seal around base of my summer house/bar. With exterior silicone it’s on a slab base thanks
Not sure if that will work or if it is needed.
Should I fill screw holes in new summer house / bar with exterior wood filler before using clear stain
No, it will not work.
We have just installed a new deck with pressure treated wood. Should I wait until next year to stain, to let the wood weather, or would it be better to stain it this season?
See here for new wood tips: https://www.deckstainhelp.com/how-long-should-you-wait-to-stain-a-new-deck/
Very helpful info on this site. Thank you!
I am planning to use Defy Extreme Solid Stain on my deck. I have some cracks that are unsightly and wanted to ask about filling those. Since I am using a solid stain I will not have the color matching issues of transparent stains. Would filling work intros case?
A solid stain will cover the wood filler.
Thanks. Any particular type that would be better for the job? Wood putty? Exterior painter’s caulk? etc.?
Exterior caulk is much more flexible.
I have a deck project were there are some severe cracks on the main support posts. They are long and deep. Since fillers and caulk are not recommended, what can I do to prevent these cracks from getting any larger over time after I redo the deck…?? As of now, the deck will be re-stained with a dark brown colored stain. Also, I have read that you should not use colored stain on the floor of a deck but instead you should use a semi transparent. Is this correct…?? The homeowner wants the deck all the same. What is the best way to stain the floor so it lasts for several years….??
You cannot prevent cracks from getting any worse. If they are bad, then replace those boards. If you want a semi-transparent dark brown then look at TWP in Dark Oak or Armstrong Clark in Rustic Brown. Penetrating stains like those will not be prone to peeling like a solid stain. Just clean and recoat every 2-3 years,
Unfortunately the cracking is on the main posts and not the floor boards. The deck has a lattice roof and would be virtually impossible to replace without excessive cost involved.
Thanks for the reply and info on the semi transparent
I have a deck board with removed splinters from a chisel. Would it be ideal to sand, then stain over those parts? Wood filler them? Or replace the boards? Climate is harsh winters.
Never use a wood filler on a deck when using a semi-transparent stain. Spot sand the areas, then strip all the deck down, brighten the wood, then stain.
I’m prepping a newer deck for eventual stain and have noticed what I would consider done deep or wide cracks especially in the 4×4 posts I installed. I know you mentioned no filler, leave as is and replace only if bad enough
What’s consider bad enough to replace? I’ve read 1/4” deep or wide…
That is not an issue. Just leave as is.
Thanks for the quick response. This is about 3 weeks after being built…looks ok?
First time staining 1 year old redwood deck. Do I do anything with the knots, some are cracking and some small ones have fallen out. Is there something I can do to keep them from falling out? Will be using RAD cleaner and brightener and semi transparent stain. Thank you.
Wood filler will not work on a deck and it will not stain to blend. It will look terrible.
How. Do you repatr brick that the deck is joined to
I have no idea what you mean?
Have stripped and brightened a cedar deck, replaced some rotten boards, do those boards need to be left uncovered to weather or can they covered with clear plastic along with old boards until they can be stained? Is there a recommended stain to match CWF-UV cedar, don’t want to use CWF-UV again, was looking at TWP 1501.
Leave uncovered. TWP 1500 is much better.
Any suggestions for splinters on the deck? From the day it was built there seemed to be numerous amounts.
Try a solid stain: https://www.deckstainhelp.com/what-are-the-best-solid-color-deck-stains/
Hi, We have a pressure treated wood deck about 10 years old now and beginning to show its age with some minor weather cracking and discoloration. I pressure wash it (fan tip only) with detergent every spring so it is “clean” but there are still plenty of stains in the wood. I’d like to put on some kind of sealer to prolong its life and hopefully improve the look a bit. The wood is expose to extreme cold and lots of snow and ice so I am concerned it will just chip and flake and make things much worse. I’d be grateful for any suggestions and advice!
Try one of these stains: https://www.deckstainhelp.com/the-5-best-deck-stain-reviews-and-ratings/
What about taking elmors wood glue and mixing in saw dust of the type of wood you are trying to fill a crack, and making a putty to fill cracks or say spaces in shrunk treated deck wood?
Do you think that would hold up to the elements and possibly be able to be stained with the rest of my deck come the fall?
What we use is construction adhesive mix with sawdust rub in cracks sand it
i have 4 x 6 supporting posts on my wood awning that have developed surface splitting( not all the way thru). what do you suggest to use on these splitting surfaces?. I want to stop any further progress of this condition. the posts and awning are about 9 yrs. old.
Splits are normal for exterior wood. Just leave them as is. No harm will happen.
What do you recommend for a knot that has started to rot? I see you don’t recommend fillers but worried to just stain this area like the rest of the deck.
Any help would be greatly appreciated!
See Permafill by Gulf Synthetics. It is not stainable with a semi-transparent stain but it will work to fill your issues with your stair stringer.
What stainable product would you use to fill cracks on a deck in Maine that is exposed to extreme heat & cold?
Nothing will work like the article states. Leave the cracks as is. It is normal.
The top rail in this photo has been curing for 8 months and we are now ready to stain deck- photos show what happened to board over winter. If filler is not suggested, do you have any suggestions as to what should be done? Thanks for your time and great website!
Just leave alone or if really bad, replace the board.
Thanks 4 your response, hoping pics went thru. If we replace board do we wait several months to stain or stain now with the rest of the deck? Thanks again!
You could stain the new board now and then apply another coat to the new boards in the Fall.
my contractor filled screw holes on the deck and railing with wood filler then sanded the areas. I wanted to stain it natural, but now not sure what to do as I’m concerned these wood fill sections will be very noticeable. Should I sand the whole deck and railing to even it out then prep treat it before I stain? Would changing the stain color to a darker shade help?
It will be noticeable and it will not blend with the stain. Sanding will not help Doesn’t matter the color. He should not have done it and there is not an easy way to fix it.
Building a new deck. Should anything be done to the knots in the wood before staining deck?
Nope. Just leave them as is.
We have an old (likely since the house was built in 1990) untreated cedar deck, with some rot and/or softer spots on its boards.
1.) Would I be able to use PC-Petrifier Wood Hardener on some of its boards and railings? (I wouldn’t mind using on all of it.)
2.) If so, should I use it after I would clean and brighten it?
3.) I’d like to just seal it afterwards (and yearly from now on). What would you recommend as the best sealer for this type (age & condition) of deck? We live in Seattle, and even though the deck is facing west, it gets max 3hrs/day of sunlight.
Thank you very much!
1. Never used this before but it seems like you can.
2. Prep first.
3. TWP 100 series in clear for a sealer of the Defy Extreme Clear.
I just put new decking boards on my deck, Looks really good but a lot of nail holes, I would like to fill them and stain the deck clear, question is there any filler that would look like treated wood ? so when I put the thompsons clear on my eyes won’t go right to them ? Thanks Glenn
No, it will not work on outside wood.
I know that wood filler and caulk aren’t good options for filling cracks on deck but, I have a toddler and I’m concerned about splinters. My deck was in bad shape when we moved to this house and I have sanded it down so it’s a flush surface again. I still have cracks and some deep chips. If I just paint my deck is there anything I could use to fill the bad areas? I would replace some of the boards but it would end up being more than half the deck and I can’t get into that big of a project. Please any help you can offer would be greatly appreciated
Try Permafill by Gulf Synthetics.