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Exterior beam wood filler/repair help!!

6 replies [Last post]
Joined: Nov 4 2003

I am hoping that some of you owners or contractors could help me regarding a filler material to repair rotted and cracked wood beams.

I saw on The Old House about 10 years ago a 2 part epoxy type material that I could never find. It came in tubes and had a special caulk like gun that dispenses the material so you can then mix it. After your apply this material into the void and it hardens, you can shape and sand it like other fillers. But it's supposed to stay flexible. I can't find it and I suspect it's only for contractors and expensive.

My need are the exposed beams in the atrium and roof pitched areas. The beams are cracked as they are painted in a dark color and one side is southern facing. Some of the cracks are pretty long, 12 to 24 inches by 1/4 to 1/2 inch wide at the worst part. Every couple of years I need to refill these cracks as the other fillers fail from the sun and heat exposure. The epoxy sounded like it could tolerate the sun exposure.

I also would like to repair a small amount of rot in the wood post that's framing the front door. Also southern facing and exposed to water as the water sheds off the pitched roof onto the ground and splashes onto the base of the door. (I have a later Claude Oakland Eichler with pitched roofs in front and back.)

Any recommendations are appreciated!


Joined: Apr 2 2003

Don't know about the This Old House caulking material you referenced?
(you can ask questions on their website

Wood rot
- you want to be thorough if you are dealing with dryrot, which is a fungus. Its spores spread out into the wood past where you see the damage. The spores re-activate with moisture. So I would recommend digging out as much as you can, treating with borate powder or liquid--which activates with moisture so supposedly will keep the spores in check--before attempting wood repair.

Read the last 2 sections of the following site for a little more explanation:

There's a product containing borates called Termite Prufe available in handspray or powder in the OSH garden section you might try. They promote it for termites (not sure I buy its effectiveness) but also for the wood decay problems.

Wood repair
- for the wood repair, you might want to try Abatron's WoodExpoxy (2 part expoxy), possibly in combination with their LiquidWood. They were recommended to me by others on this board and I was very pleased with the result when I used it on a wood beam. Its available through Builder's Supply (in San Mateo, I think). You can read about the products on Abatron's website at:

Beam Exposure
- I think my beam orientation is the same as yours. I had poor results from paint and fillers because of the sun issue. The paint was bubbling though it had been scraped down/sanded carefully prior to priming then painting. I actually think it was resin in the wood and so finally sanded the entire exposed beam face down to wood and sealed with 4 lb. yellow shellac--I think Zinsser market's it as BullsEye. (I used to use it to seal weaping knot holes in tall baseboards of my previous house). That seems to have done the trick for the bubbling on my beams.

As far as cracking, various fillers had been used and recommended by a house painter we know. He used some here, as did we. My take so far is that they all fail miserably. I actually don't think that flexible fillers aren't the way to go for these sun-exposed beams--the filler seems to expand in the heat and shrink in the cold so cracks are inevitable.

When I scrape out the painter's last attempt on one beam, I'm probably going to try some combination of the Abatron products recommended above.

Good luck.

eichfan at rawbw dot com

Joined: Nov 4 2003


Thanks for the information and tips!

I also have the bubbling paint issue on those same beams! I'll look into those filler products you suggested. I will definately be removing all rotted wood down to solid good wood. I then plan to place a metal flashing on top of the beams for added protection as a little rot has appeared on the tops of the beams.

Thanks again, Nelson

Joined: Jan 4 2004

Interesting links, Jake. One thing that I commonly encounter when treating wood destroying organisms such as Fungi, is that the building depts. and pest operators always have required removal of rotted wood. We have to be creative and bear in mind how the removal will impact the structural aspects of the building. Most pest operators allow a structural piece (such as 2x4's) to remain if there is over 70% intact and there is no dry rot present. We have done repairs/restorations to beams where a amount of rotted wood is removed down to healthy wood (usually in a shape that is easy to replicate), the new wood is glued, epoxied, or nailed in place, then the surface is floated out with a 2 part wood filler product. This is generally not allowed on repairs that must satisfy a pest report. (I have had a lot of success with a product made by Bondo called wood bondo, it hardens and adheres quickly, and remains workable for 15-20 minutes). Remember also not to remove much material from mid span of the beam, or the underside (or tension side) of the beam. It is really the best time of year to work on this type of condition. Good luck with your project.


Joined: Nov 4 2003


Thanks for your insights today. You mention you've glued, epoxy or nailed new wood to old to patch in rotted areas. Regarding the epoxy, is it anything special or regular 2 part adhesive type? I have another area of wood where the beam and fascia board meet in the atrium that needs a patch of new good wood to repair damage from rot. Do you use a special epoxy for exterior work?

Thanks, Nelson

Joined: Mar 24 2003

Read this past thread - i used Wood Epox and it was very successful.

Your Ultra Guide for Googie, Atomic Age and Mid Century Modern Living: OPEN 24/7!

Joined: Sep 11 2003

My husband is in the wood business and he says all his wood shops use auto body filler to fill voids in exterior wood (for exterior trim, columns, etc...)...basically, anything that is going to be painted. He just repaired one of the exterior beams in our atrium using this filler...after digging out all rot of course. Hope this is helpful.

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