Dover Projects Repair Wood Rot Epoxy Wood Filler
Posted on 28 March 2012 | 5:16 am
After scraping old paint off our exterior door, I noticed something that wasn't good. Some of the trim around the bottom of the door was rotted out. So I pried off the middle board shown above, and found that matters were even worse than I thought. The sill beam below the door had rotted as well! Oh boy...
Here's what the sill beam looked like with most of the worst rot removed. But you can see that in order to repair the sill beam (the 6"x6" beam on top of the foundation shown above), I'll have to remove the left exterior door trim to get at the beam. Note: I don't have the sill beam repair article done yet, but I will soon.
What follows is only about making a cosmetic fix to the bottom section of the left door trim. That bottom section, although it doesn't look too bad in this photo, was very rotted (mostly on the back side) and very soft up a few inches from the bottom. This is what happens when wood is in contact moist surfaces (the steps, during rain and snow). Also the wood grain at the end of the boards is particularly good at sucking up moisture. Note: You can click on any photo to enlarge them.
Rather than remove the whole piece of left door trim, it seemed easier in this case just to cut the lower few inches off with a sawzall, make the rot repair with wood epoxy, and then reattach it later. I could have manufactured a new matching piece of wood, but it would have been quite a bit of work, as the piece was unique in size and notched out in the back, and also was not an available trim piece from home stores. I remembered seeing an article online about repairing rot with epoxy, so it was off to Google to research "rotten wood repair", as I was also eager to learn about rot repair for the fun of it as well!
After researching it was time to repair the rot. Here's what I did, using 2 products:
1. Liquid wood hardener (resin that penetrates soft wood, making it hard again)
2. Epoxy Wood Filler (2 part epoxy to rebuild/replace the rotted wood)
Here's the bottom of the door trim. You can see the rot from the front doesn't look too bad, but much of it was so brittle it just came loose in my hands, after this photo was taken.
The wood rot was worse on the back. The rotted wood was completely dry, but very soft and crumbly. Note: I'm in these photos as I was using the laptop as my camera here, and had to see what I was shooting. Please excuse my large nose!
Step 1: Remove Unstable Rotten Wood
The first step to repair wood rot with epoxy wood filler, is to remove any rotted wood that is loose, crumbly or very soft. You want to get down to reasonably stable wood. It can be a bit soft though. I used a screw driver, like a dentist removing tooth decay. Wire brushes work well for other flatter surfaces. The wood should also be completely dry, or as dry as possible before going further. This might mean using a heater, or fan, or whatever to dry the piece out. Or if it's an exterior piece you might need to cover the area with a trap for a while to thoroughly dry it out. Less than 20% moisture content is the recommended level, but who has a moisture meter? Just use common sense and get it as dry as possible.
Step 2: Drill Holes in and Around the Affected Area
Drilling holes helps the liquid wood hardener penetrate deeper into the wood. I should have drilled hole a bit bigger. 1/4" is recommended. Don't drill all the way through!
Step 3: Apply Liquid Wood Hardener
There are a number of brands out there. I just happened to have quick access to this one (Minwax, High Performance, Wood Hardener). This can was about $9.50 at Home Depot.
Lather on a few quick coats with a cheap disposable bristle brush. Be sure to get every nook and cranny. Then let it dry for 2-3 hours. When dry, the resin that has penetrated the soft wood will make it hard and stable again. My glove here looks weird as the lower half ripped off, so it's not some special fingers only glove, ha!
Step 4: Add Screws for Strength as an Extra Measure.
The screws are optional, but are not a bad idea, as they act like rebar (reinforcing bars used in concrete). The screws give the epoxy wood filler something to grab on to and will add strength to the repair. I used exterior deck screws.
Step 5: Mix up a Batch of Epoxy Wood Filler
This just happens to be Bondo epoxy wood filler. Many people have used regular Bondo for fixing wood rot before with no issues, but a quick Google search will also turn up just as many people saying that the traditional Bondo (used for auto body repair) isn't a good idea to use on wood rot repair, as it does not expand and contract with temperature changes and that a dedicated epoxy wood filler, made for wood rot does. The product above is from Bondo and say it's a "wood filler". I've never seen it before (might be the same as the auto Bondo, who knows). Anyway the photo on the front looked convincing so I figured I give it a go, as other epoxies I found online were more expensive. I'll give follow up, updates as to how it holds up in our harsh New England winters and humid summers.
First you fill the supplied cup with the wood filler. Forgot to put my gloves on here.
Then you squeeze out a bead of epoxy hardener to a length of the diameter of the cup (see your product for specific directions).
Mix the Bondo and the hardener up well with a disposable plastic putty knife.
Step 6: Apply the Epoxy Wood Filler to the Rotted Wood
Be sure to goop it into the nooks and crannies. I used plastic putty knife and screw driver to work it into the pockets of the rotted wood. Bondo suggest that you build up layers no greater than 1/2 inch thick at a time.
Bondo sets up quickly, so you'll be mixing up a few batches and applying it in layers if you have to build up a large section as I did. I'm sure there's a neater way to do this (you can build a form out of plastic), and I'm sure some people are better skilled with their putty knifes (you can wet your putty knife with lacquer thinner to keep the wood filler from sticking to it). I didn't bother much with neatness and it shows, but it didn't seem to matter. All this extra bulk will be sanded away. Let it cure for 30 minutes. It'll get warm, as the chemicals do their thing.
After about 15 minutes with a 5" orbital sander, I was able to craft a very close replica of the original trim piece, complete with notched cut out on the back side (the house siding goes behind that notch). No more wood rot here. And once primed, painted and reattached, this piece will be rot resistant, as it's epoxy, not wood.
More photos and story coming shortly of the piece being reinstalled.--Peter
Products/Tools
Minwax, High Performance, Wood Hardener
Bondo Home Solutions Wood Filler (No info. on 3M's website, they make the stuff)
Popular alternative: Abatron LiquidWood, and Abatron WoodEpox
Another alternative: Conserv Epoxy
Another alternative: PC Products
Wire brush, screw driver or whatever to remove the rot
Drill
Disposable bristle brush
Plastic putty knife
Shaping tools: Rasp, sandpaper, sander, etc.
Resources
The Family Handyman: How to Repair Wood Rot with Epoxy
This Old House: How to Repair Rotted Trim with Epoxy
Abatron.com: Wood rot repair information and products
PC Products: Product video
My Standard Disclaimer: This is what I did. This does not mean this is the best way, the right way, to building code, or even safe for your needs. So you are on your own with your project. I make no promises about the information presented here. I'm just a do-it-yourselfer, not a professional at all, sharing my story. So if something goes wrong with your project, you are on your own. Good luck, and have fun!
All content and photos, copyright 2009, Dover Projects.
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My Other Articles
automobile metal repair and panel welding Wakefield s Classic
Posted on 8 March 2012 | 1:18 pm
I was talking to a nice gentlemen recently who had read my rust article. He wanted to know if the guys who had redone his Camaro did it correctly. I asked him if he had any photos of the resto process. Well in fact he didn’t. But he described what he had seen when he visited the restoration process. I had a few follow up questions that he couldn’t answer, bottom line I can not stress enough how important progress photos of your restoration or car build are. Photos are the only way to document what was done to your car.
Moving forward I think this guy has some interesting questions about how to properly repair or restore the body on any car.
Let me start this explanation by saying that I was learning the body trade in the late 50s. This was an interesting time in the evolution of automotive metal work in the new car construction. Going back to the early beginning of car construction on assembly lines The sheet metal used in body panel stampings was much thicker than it is today. Since the late 20’s and early 30’s where it was not uncommon to see sheet metal on cars that was 10 and 12 gauge metal. Most body panels were 14 gauge. Connecting body panels was achieved by fixing the steel panels to a wooden body skeleton with nails and or screws. Accident damage was repaired by hammering out the dent and metal working the area until it could be filed smooth. The addition of Lead applied to the metal provided another way to smooth the panel before painting. Lead soon became an accepted repair method. Experienced leaders also became body artists in customizing metal bodies. When I came on to the car scene in the late 50’s sheet metal was much thinner so the hammer and dolly technique was an art, too much was a bad thing. Wood skeletons were gone. Body panels were welded together and exterior seams were leaded. The practice of attaching panels was being done by the form of “spot welding” Somewhere along in the late 40’s fiberglass car bodies were “experimental” In the early 50’s “Bondo” a plastic body filler was making it’s debut, and has been misused ever since.
Not to say that new technology hasn’t improved many aspect of automotive body work, but if we take a look at the old school methods we might get an understanding of what works and why. Going on the premise that back in the 50’s a body repair was done to be permanent. Today insurance companies consider an auto body repair permanent if it lasts 3.5 years. Dissimilar materials rarely stick to each other forever. Plastic body filler isn’t permanent, over time it lifts, puckers, shrinks, or peels. When was the last time you saw lead crack chip or peel on an auto repair. Enough said about smoothing body work techniques, remember “less is best.”
That brings us to the last tidbit of metal body work, or the art of welding and panel fitment or replacement. There should be no argument that the best repair to a metal car body is the exact body panel replacement attached in the exact method done by the factory. Lets say you have a rusted out quarter panel on a 1965 Mustang Coupe. In my opinion the best way to fix the rust is to remove the complete quarter panel, call the factory and order a OEM quarter panel and attached it with spot welds following the factory weld map, the roof seam gets lead and the trunk seams get a touch of sealer. Well you and I know that there are a few flaws in that procedure, primarily it is next to impossible to get OEM panels for older cars. So we are stuck with aftermarket panels that may not be the same gauge or of the same stamping quality of OEM panels. Even when working with complete aftermarket panels they can be still be attached just like the factory did it. Often we find that a lot of shops don’t have the same spot welding equipment as the factory. Consequently, other welding methods are and can be used. Bear in mind that the more heat that is applied to a metal panel the more “oxidation” occurs. Yep heat causes metal to oxidize. Isn’t the rust or “oxidation” the reason we are doing this in the first place? Remember in the welding repair process you will need to assure yourself that where heat was applied to weld the metal, you are able to clean up the metal and treat it so that the oxidation process is stopped or slowed as much as possible.
What if you have to repair metal and no complete panels are available, what then? Well this is where many opinions enter into the “what’s right, what’s wrong” arena. Many body guys think that butt welding replacement panels in is the only proper way to go. Others still use a “lap” seam to put partial panels on existing sheet metal. First let me say that butt welding eliminates the pocket between two panels that traps moisture and creates rust. But I must say it takes a very skillful welder to butt weld a big patch panel into existing sheet metal without causing a lot of distortion. The more distortion, the more body filler is needed, now you have a whole different set of problems. Remember when it comes to any filler “less is best” As an alternative is the overlay of panels, as we discussed this method put two pieces one on top of the other using a 1/2 inch lap seam. The lap seam gives moisture a place to start oxidation. If you can seal both sides of the seams you will slow the possibility of oxidation occurring. Don’t forget that the factory uses a type of “lap joint” when they spot weld panels together. When performing a lap weld on an external panels I will always sweat the seam with lead when the welding is complete. Lead goes a long way to “seal” the lap joint. Bottom line either method can work well, both methods have pluses and minuses, sometimes you just have to trust the advice of the guy doing your work. Document it with photos.
Well we have looked at spot welds and the types of welds but we haven’t discussed the type of welding equipment. Whether it is electric stick or wire feed, Mig or Tig, or gas and stick, good results can be had by any experienced welder with any choice of welding process. One thing to be mindful of in the “good old days” we worked on body panels with the “less heat” approach. Braze was one such method that used less heat than arc or gas welding. When we were finished brazing a panel it was most always smoothed with lead before painting. I don’t ever remember problems when doing this type of repair. In recent work we notice that the plastic fillers have a tendency to “lift” or separate from braze material over time. This mystery of separation, seems to be due to the flux residue in the brazing process. So don’t use plastic filler over a brazed seam or joint. If you lead the braze first then apply the plastic filler I don’t think you will have a problem with “lifting”
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