Repairing rot in non-structural wood trim
I’ve repaired a lot of rotting trim in the past few years—mostly window sills, door framing trim, and garage door trim. I’ve used all of the commonly accepted practices—like cutting out and replacing the rotted piece and using structural repair epoxy—as well as not-so-accepted practices, like using Bondo. I’ve come to the conclusion that they all have their place in the hierarchy of repair options.
While simply cutting out and replacing the rotted material may be the preferred method, there are times when circumstances (or budget) just won’t allow for it. The same goes for the structural epoxy. It does a superb job, but at $5.00 a blob (that’s my unit of measurement for it; 1 blob = the size of a golf ball, @ 18 blobs per tube) you can quickly spend upwards of $100 for the epoxy alone. I’ve found that after explaining the cost-benefit analysis of epoxy vs. Bondo, most customers choose Bondo without a moment’s hesitation. And who can blame them? A 1-quart can of Bondo costs about $11, while the equivalent amount of epoxy is over $200.
A few months ago, I was doing a job as a sub for another service. The job consisted of putting up some PVC trim around a window to try to match all the other previously-finished windows. The job was a set price, so cost was definitely a consideration. There wasn’t money to do it right, but if it looked bad it would reflect badly on me.
The problem/opportunity was that, after replacing the old trim, there was a varying gap between the trim and the stucco wall of between 1/2 in. to more than 1 in. What to do?
While looking in the van for a solution, it hit me. I had a can of black expanding polyurethane foam from another job. I thought that, if controlled, it could be a very convincing stand-in for stucco. So I went back in and filled the gap. Here is where my accidental discovery came into play.
While impatiently waiting for the foam to cure, so I could begin cutting it away, I found that you could push it back in and compress it. You could actually rough-mold it to your desired shape. This was huge!
I shaped it to a reasonable facsimile of stucco and primed it. When it was all finished, you couldn’t see the repair.
I’ve since developed a new system of repairing rot in non-structural applications.
The Basic Components
The epoxy is an elastomeric wood repair epoxy. The brand I use is made by Advanced Repair Technology, called Flex-Tec HV. There are other brands, but this is stocked by my local Sherwin Williams.
The foam is basic expanding foam like Great Stuff or, in this case, Touch ‘n Seal.
The tools needed are a vacuum, drill with rotary rasps, 6-in-1 tool (not shown) and any other tools you may have to clean out the rotted wood fibers. I also keep a caddy handy with various consumables like paint sticks, epoxy resin, sandpaper, plastic flashing for shaping and mixing, rubber gloves, etc.
The procedure is quite similar to a dentist filling a cavity. Here are the basic steps:
|Find the decay. The homeowner will show you what needs to be fixed.
Determine the extent of decay by poking or digging with an awl, screwdriver, or 6-in-1 tool.
|Gouge out and vacuum all the debris until you hit sound wood.
|Grind away to rough out the interior, then vacuum.
|Seal the cavity with an epoxy resin.
|Fill the cavity with spray foam, then compress until it’s just shy of the surface.
You have a small window of opportunity to compress the foam (between 10 and 20 minutes). If you press it gently and it doesn’t stick to your fingers, you still have time.
Don’t rush curing the foam after you’ve compressed it. If you top-coat it too soon with the epoxy, it will blow out the epoxy like a big blister and dry like that.
|Smooth out exterior surface.
|After 24 hours, sand the high spots and prime.
The beauty of this system is that the foam is water-resistant (see “Spray Foam Waterproof Experiment” below) and rot proof. Also, unlike Bondo, the elastomeric epoxy will move with the wood, so it won’t be forced out over time.
The only drawback is that the upfront cost of the epoxy gun is between $60-$100. However, they do sell one-shot tubes that fit in a standard caulk gun for around $20. Most of us already have a foam gun—if you don’t, you really need to bite the bullet and get one. A cheap gun is around $40 and a can of foam is $20, but once you have it you’ll be amazed at how many tasks it can handle. It can be used to glue in nailers for drywall in places where a nail or screw can’t reach (like a closet under the stairs), glue up drywall, caulk and seal wide cracks, used in place of “caulk saver” foam bead, and for rot repair, just to name a few.
- Keep a few feet of 3/16-in. ID plastic tubing—cut into 1-in. to 2-in. pieces—for use as disposable tips. Not only will it allow you to get into hard-to-reach places, but it keeps you from constantly having to clean off the tip. Just pull off the old one and put on a new one.
- Keep a can or two of cleaner with you. If you have to change out a can you can quickly spray out the screw-on basket before you put on the new can.
- Keep a spare can of foam handy. If you run out, take off the old can, spray out the basket with cleaner and screw on the new can. This will keep you from having to clean the gun.
- Don’t leave the foam outside in the cold; bring it in at night with your batteries, caulk, and other weather-sensitive materials. It won’t freeze, but it will thicken to the point of uselessness.
- If you DO accidentally leave it out in the cold, fill a sink or bucket with hot water and soak the gun for a while,; or prop it over the defrost vent of your vehicle and turn the fan/heat on high.
If you still have some foam left after a job, store the can upside down, attached to the gun (see photo, right). My supplier told me about this. There is a bladder inside the can, and, after use, air can get trapped in the bottom and render the can useless, no matter how much you shake it. I ruined two almost-new cans by leaving them in the upright position, but after taking this advice, I haven’t lost another one.
Foam spray gun cleaning
Before I ever bought my first spray foam gun, I read all the pros and cons I could find to be sure it would be worth the investment.
I decided that it would be a worthwhile investment, as long as I could stay vigilant about closing the valve—otherwise you could wind up with $45 (or more, depending on which model you bought) of useless junk. One error by you or one of your crew and you would have a gun with hardened foam in the tube.
Well as it turns out, it is almost impossible to always remember to shut down the mechanism. It’s like that truism about windows…there are two kinds of windows, those that leak and those that will leak.
The first time I accidentally left the feed tube open I had had the gun for about a year, so I felt like I’d already gotten my money’s worth. When I did it again a couple weeks later, I wasn’t feeling as unbothered.
I figured that the gun was already ruined, so taking it apart to attempt a salvage could be no worse than a waste of time. If, on the other hand, I succeeded, I would no longer have to buy a new gun every time someone (no need to point fingers here) carelessly left the feed tube open.
My motivation came from cleaning an M16 rifle. Anyone who has been in the military has spent countless hours disassembling, cleaning, and reassembling an M16. The first time you do it, it may seem daunting, but after the umpteenth time you can do it in your sleep. There’s really no trick to it: you take the gun apart in a logical sequence, laying all the parts in order, clean all the individual pieces, and re-assemble it. Eventually the parts don’t need to be in order because you know what each part does and where it fits into the over-all assembly. These foam guns are no different, and they’re easier because they have fewer parts. Also, with today’s digital cameras you can take pictures as you go, much like leaving a trail of bread crumbs.
To begin, we have a dirty, filthy foam-clogged spray gun.
Here’s a list of the tools I use to clean the guns:
- Lacquer thinner
- A sealable plastic that fits all the parts
- A pair of adjustable pliers and two wrenches
- An M16 cleaning kit.
You don’t need the M16 cleaning kit, but if you have something like it, it helps. The brush fits well enough to clean the inside of the tube, and you can even put a patch soaked with lacquer thinner on the end of the eyelet to clean the tube. Again, you don’t need this, you just need to be creative as far as finding things around the shop to scrub and scrape away the debris.
To begin, disassemble the gun down to its component pieces, being careful not to lose any of the smaller pieces (such as the “C” clip, or the shut-off valve bearing). If you’re not sure about the order, start taking photos for your re-assembly.
Scrape as much of the foam off as you can, and place the parts into the lacquer thinner to soak. Periodically remove the pieces and clean as necessary. This requires an investment of time, since different parts will take longer than others to get clean. So take your time and be thorough.
Be aware that in addition to the steel bearing (not shown)—on which the shut-off valve spring rides—there is a plastic bearing inside the brass screw-on can adapter. This plastic bearing does not come out for cleaning, but it needs to be clean enough that it can freely move in and out as you push on it with a tool. If it doesn’t move freely, it’s not clean enough.
Below are the individual (cleaned) components of this particular gun.
And the original gun after re-assembly…
Spray Foam Waterproof Experiment
After I stumbled onto this new procedure, I began wondering how waterproof the foam really was. After reading about the differences between open-celled foam and closed-cell foam, the major difference seemed to be density. If you are spraying the underside of a roof deck, you would use closed-cell foam because of the higher Perm Rating, which basically equates to “waterproof.” Open-celled foam is merely water-resistant. My theory was that by compressing the foam before it set, I was making it denser, thereby making open-celled foam more like close-celled foam.
I’m sure that in a laboratory it’s much more technical than that, but I’m working out in the field, not in a lab, so for my purposes this theory would suffice. All I needed was an experiment to confirm or dispel my hypothesis. So I filled the middle section of an empty drink bottle with foam. Since I couldn’t compress it the experiment would be done with open-celled foam.
In the picture (see photo, right), the foam appears glossy against the sides as if it is leaking down, but that is how it looked when I sprayed it in, before putting any water into it. Also, even though it has a cap on it, the cap is not tightened. I left the cap loose so the water wasn’t being held up in a vacuum—that way, it wouldn’t spill or evaporate quickly.
I started this experiment on Oct. 27, 2010. Today is Dec. 3, 2010; so far there has been no leakage.
Update: By Dec. 21, there were drops of water visible in the bottom of the bottle…
To take the experiment one step further I somehow needed to compress the foam in the water bottle. After some thought, I came up with a way to do it.
I took another bottle and sawed off the bottom. This allowed me to compress the foam from the top and the bottom. I hot-melt-glued the bottom back in place and filled the bottle with water.
I have to say I didn’t expect the results I got. Within an hour there were signs of water leaking through, and within a day, all the water was in the bottom of the bottle. I was pretty confident that it would easily outlast the original experiment, but I’ve come to the the conclusion that the expanding foam is NOT waterproof, merely water-resistant. This doesn’t mean that the foam rot repair technique is no good, it’s just something to keep in mind when you consider using it.