How to Identify and Repair Rotting Wood | Ask This Old House

In this video, Ask This Old House general contractor Tom Silva takes host Kevin O'Connor through the causes of wood rot, how to avoid it, and what to do when it occurs.

Host Kevin O'Connor and general contractor Tom Silva discuss identifying wood rot and what to do about it. After discussing some of the key ways to keep wood from rotting, like flashing and avoiding ground contact, the two discuss the signs of wood rot.

Prevention is Key
For the most part, rotting wood is preventable, but it requires keeping water away from the house as much as possible. This means installing gutters and maintaining them, preventing the wood from coming in contact with the ground, and properly flashing any openings that water could sneak into. Also, seal any outdoor wood surfaces like fascia, window sills, and trim with a sealer or primer—don't forget the backs!

Signs of Rot
It's important to know what to look for when identifying wood rot.

First, look for peeling paint on wood surfaces. This indicates that water is penetrating the wood. As the sun dries the board, it pulls the water through the wood and separates the paint from the surface.

Also, look for soft, punky wood that flakes off. This is advanced rot and can be a sign of carpenter ants.

Replace or Repair?
If you can replace the rotting wood easily, you should. This could be the case for window and door trim, fascia boards, decking, and other wood that's easily accessible and readily available. Just be sure to seal and flash the board so the rot doesn't come back.

But, replacing a board isn't always easy. In the case of window or door sills, replacing the rotted wood can be a big job-one that's not necessary if enough good wood still exists. In that case, it's better to remove as much of the rotten, compromised wood as possible by scraping, cutting, or sanding before repairing.

Fixing Rotten Wood in Place
Once the rotten wood is removed, you can repair it in place with products explicitly meant for the job. A rotted wood restorer can be applied to the damaged wood to restore its strength before repairing it. You can then apply a high-quality wood filler to the surface with a putty knife. Most of these wood fillers are two-part formulas, and it's a good idea to go light on the hardener, not heavy.

When the filler dries, sand it to a smooth, even finish to hide repair before priming and painting.

Where to find it?

About Ask This Old House TV:
From the makers of This Old House, America’s first and most trusted home improvement show, Ask This Old House answers the steady stream of home improvement questions asked by viewers across the United States. Covering topics from landscaping to electrical to HVAC and plumbing to painting and more. Ask This Old House features the experts from This Old House, including general contractor Tom Silva, plumbing and heating expert Richard Trethewey, landscape contractor Jenn Nawada, master carpenter Norm Abram, and host Kevin O’Connor. Ask This Old House helps you protect and preserve your greatest investment—your home.

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How to Identify and Repair Rotting Wood | Ask This Old House

[psergiu]

Finally, you guys started putting up link for the products used in the description ! It was always annoying seeing "this new and improved magical thing" that was exactly what you needed but you had to freeze frame and zoom in to guess what it is.

[jeffthewhiff]

I just completed a project for a customer where it was necessary to remove quite a lot of rotted wood from under several window sills and the epoxy wood filler did a great job. Incidentally, I replaced the old wood trim with PVC, so it will never rot. Good video!

[Mike__B]

I love how he opens the can and his first instinct is to sniff it "... there's a lot of solvents in it..."

[christophergoc]

I’m in dental school and when we mix a putty to make a mold of the teeth we are taught to measure the same way- make a little circle of the base and run a bead of activator across it. Really cool to see that technique applied here!

[Mr.Pop]

I swear to god bondo is my fav tool. Ive repaired so many doors that were rotting out at the bottom using the wood restore and bondo.

[MojoPup]

Thanks for another great video guys! I first used that stuff to rebuild a door jamb in a 100 year old prairie house. Worked great, lasted the 12 years I was there.

[lasinmt]

Great advice and discussion on how to approach and use these wood repair products. I bought a 22 year old RV in Feb in Bend OR. Probably sold below freezing to hide the rotting mildew smell. OH boy once we warmed up it got worse & worse. Thought I'd fixed it when just at the end of that fix I discovered another source in another part of the RV. First was in the floor under the fresh water tank. Knew how to prevent the problem in the future. BUT the next one was in the wall. I'm in the throes of fixing the wall as we speak which goes into the edge of floor meet wall too. I finished scraping all black and dark spots out along with rotting wood today. Removed a vinyl wall paper that was probably part of the wall product to begin with not applied after the wall was installed. Clearly the window above this wall area was the source of the leak. So of course that's on the agenda to fix asap but first the wall and I've put in place strong plastic cover and duct tape to prevent leakage while I repair the wall. So my only complaint to date including this video ... is they are all vertical repairs or tutorials and I have to work about a 30 x 60" area across the wall where the dinette and bench seats are placed. I've removed all the wall paper and the strange wood underneath is super thin layers pressed together probably with some wood type of glue and some layers came with the wall paper vinyl when stripped off. Any that was dry and still stuck well and smooth I left. My plan is to treat the entire area where the vinyl is removed with a form of wood hardener. I'm in a steep learning curve having never owned an RV in my life and I'm in my 70's. So yes it is crystal clear the seller knew about the problem. Even added hard flooring to hide some of it. I've removed those boards and actually scraped away all the bad areas and hit with three of my favorite moldicide products. Make that 4 I found another one I like. I'm not a fan of perfumed products. My favorite is Oxine not activated and made into a strong dilution. Also Moldex with out bleach formula, and Odorban lemon and lemon lysol along with Microban all purpose cleaner that seems to do an amazing job on foam and fabric mildew scented products but also this punky wood. And the ply wood that provides the seat for the bench cushions also had picked up the scent and sure enough the Microban 24 hour bacteria killing Multi Purpose Fresh Scent spray has done wonders over all my other products even the stronger dilutions. But I tend to use all over a few days drying each time well. Then I wipe clean with alcohol 71-89% bought at the store since sometimes these products can leave a residue that might effect painting or wood filler etc. from doing it's job. My plan now is to run a strong fan on the wall 24 hours for about 3-4 days. Making sure it's definitely dried out. Treat with wood hardener. With no experience I play to see what 4 layers looks like up to 6 even 7 if need be. Then I also have the wood filler like you demonstrated probably same brand but does have the hardner. And cover the entire area plus right over the areas that wall paper still clings as it would not release without damage to the wall so I need a smooth sanded surface when done. I intend to apply a heavy duty self adhesive vinyl wall cover over the entire area under the window right over original bits I could not remove and smooth it out. Then add trim probably a wood trim strip to hide the seams where the old vinyl paper ends and the new begins. Color scheme should match well enough. I'm not looking for a high end job just one that comes out decent and fools the eye or the casual eye thinking everything looks good. I don't intend to sell this unit I got myself into this mess and I searched 2 years for this RV without landing one so I'm hanging in there with it. However it was neglected all her life and in that neglect itself it was abused. But low miles and good engine and bones she just needs some TLC and updated technology and deep deep deep cleaning inside and out. So far she's got a new bath faucet, shower head, toilet, sky light, dome vent fan, also added new TV antenna and fancy MaxxAir fan that replaced the original just 14x14" vent in the coach. The new fan moves air both ways at 10 settings.I've got it set to exhaust at 40% speed all day and night with the large fan running to dry out the wood wall now. As of yesterday through today I smell zero mildew. No signs of trouble like this anywhere else. My husband installed the back up camera today which works really well and new tow mirrors as the originals were frozen and couldn't be adjusted. My hopes it would be road ready by next weekend is more like with luck by end of July. I'm upholstering the dinette, fabric trim and sofa because though photos showed a clean looking RV it was far from it. Instead of shampooing and living with it knowing the dirt was really still there I had to remove and replace foam etc. too. Far more work than ever I had in mind. The windows are my most difficult challenge. I did identify the main glaze rubbers in their two sizes for the three windows but there's a damaged area for rubber on the horizontal T that I can not ID and it rarely is replaced but because there's 4-5 inches damaged I suspect we need to. U;n watching all the videos on using both wood hardeners and fillers as I can. So far all are for wood that's horizontal not a wall or vertical. We are expected heavy rains over the next 3 days so I'm waiting to apply the wood hardener until our humidity goes down. But I'd love to take advantage of our cooler temps as a low weather cycle moves through. July in NW MT can bring very high temps with it's drier weather.

[ALAPINO]

Always makes me smile a little seeing Kevin's Momentum watch.

[brocktonma.]

He’s using all purpose bondo. Works amazing dries fast. If the hole is deep do it in stages.

[StoneE]

Most hosts advise viewers to use respiratory protection when using volatile chemicals. Kevin just huffs it. 🤣

[Guardducks]

I have mixed up bondo in high heat and it never made it to the wood, it set that fast.

[azianchick]

Thank you so much for this video!! I have a shed and part of the wood looks like it is rotting. Just a small section so I feel confident I can save it after watching this video. I want to get into the trades so bad but I feel so inadequate and not "handy" enough. But maybe after doing small projects like this, I'll gain more knowledge and confidence.

[donaldlewis]

You have to respect the integrity of Tommy and Kevin. The only two guys on the internet who actually wear thier wedding rings.

[johnroberts]

HI TOH, that's a sweet dollhouse Tommy, I know a lot of little girls would love too have one like that !!! 😊🛠

[pklemm]

Tommy! Nice running into you today at Home Depot.

[denisemorgan]

How do you ask for help on your house? Is there a way to contact you?

[Bremend]

Anyone recognize the container right away from the bondo chronicles?

[LIOTBs]

I Love this Old House you guys are amazing!

[michaelgreer]

I've always wondered what was wrong with wood when it's soft and spongy.

[charlyrodzz]

Wood swells when humid, does that product cracks when wood expands?