Subject: Rot in trailer top
Date: Fri, 05 Jun 1998

Hello Dr. Rot,

I was very happy to find your website. I have a rot situation involving a 19' travel trailer and I have attached some JPEG photos so you can get an idea what I am faced with.
The trailer has a "pop-top" roof that fits on the trailer as a lid would fit on a shoe box. The roof has an aluminum skin and on the vertical edges on the perimeter of the roof, plywood is epoxied to the aluminum. The plywood strips are 1" thick, 3 1/2" tall, and are continuous in length for each of the four sides of the trailer. To finish off the roof, an aluminum type of "C" channel, is fitted to the bottom edge of the roof, enveloping the outside of the aluminum roof skin, the bottom of the plywood, and about 3/4" of the plywood on the inside. I have removed this "C" channel on the rear of the trailer, but it is still on the left side of the trailer at this time and is partially visible in the photos. I will probably have to remove the left side "C" channel, as I notice some rot at the end where it meets the rear "C" channel (this is a lot of work as it is about 15' long).
The problem occurred because there was a void in the sealant where the "C" channel laps up on the exterior aluminum surface. This allowed water to lay in the "C" channel and rot the wood about 3/4" up in the worst spots.
This fungus looks like it has little white fingers that stretch out to infect new wood. In one place on the inner surface there was a bulbous mound of this fungus. After removal of the rear "C" channel, I found the wood to be slightly damp, but it is drying out very quickly.
Despite how ugly the wood looks, I believe I am still basically in good shape. However, I need to put a halt to any further damage. In the T1 photo, you can see the heads of two carriage bolts, just to the right of the roof "corner cap". This is the attachment point of the roof raising system, and the wood there seems to be tough and in good shape, however right below the mount, the wood isn't well off.
The "C" channel is attached to the roof by 2" screws from the bottom and 1" screws on the inside edge. All screws were holding firmly and the "C" channel was secure, however I believe only the last one inch of the 2" screws were holding in the worst spots.
In the worst spots the plywood is rather crumbly (like in the corner), and then goes to where the plywood is still firm but the plies are separated, and then to the point where it is good.
My situation is this, I think it will be difficult to work on this wood, due to its position, and the fact that I don't have a lot of room between the exposed inner plywood surface and the "naugahyde tent" part of the trailer. I can make a little room by lowering the roof about halfway to give slack to "tent" part of the trailer, and I did this to make removing the side "C" channel screws easier (I would have room to apply products by brush in this manner). Removing the whole roof and flipping the roof upside down to work on it would be a very major project, and I hope not necessary.

My questions are these:

1. How would you approach this problem? Which products and how much?

Well, I think I'd approach it about the same way you are. I'd remove the "C" channels and then saturate the wood with our Clear Penetrating Epoxy Sealer (CPES). I would use a brush and probably a syringe to "inject" as much of the CPES as possible on the upper surface of the wood. Plywood is pretty absorbent when dry, and I don't believe drilling access holes here would be worth the extra time it would take.

The wood must be reasonably dry -- the drier the better. I would probably apply two applications of the CPES. On the second pass the wood will accept much less of the CPES than on the first application. Give the first application a couple of days to cure-out before starting with the second.

After the second application of CPES has had time to cure, I would review the entire ply structure. If there were missing gaps/pieces, I'd probably go back with our Epoxy Filler and smooth things out. The filler will bond molecularly with the CPES and make a strong structure. When everything feels solid, replace the "C" Channel.

2. Would the rot stop progressing as long as the wood stayed dry? (Even if it did, I still want to treat this wood, as I can't afford one more unnoticed leakage problem.)

Yes, wood won't rot when dry. But the fungal spores are still there and the slightest moisture will get them going again. Coating all the wood you can get at with CPES will help resist future rot.

3. I would like to pre-treat the unaffected areas of the perimeter of theroof without having to remove the "C" channel (as it would be a major project, and I already have one major project). How well would the CPES penetrate good 1" thick plywood, considering the lip of the "C" channel goes up about 3/4" on the inside? Would the CPES penetrate to the bottom of the plywood where water could possibly lie in the event of a bad seal on the exterior of the "C" channel?

Yes, the CPES will penetrate good plywood, especially at end-grain or broken points. You need to flood-in the CPES from the top. You'll probably need a syringe and needle to do it right. These we supply in our Epoxy Injection Kit. What will happen is the CPES will migrate down the sides of the ply and then run along the bottom of the "C" channel. The wood will absorb what it can, more in porous areas and less in the non-porous areas. The bottom of the ply piece is likely to be fairly open, so a good amount of CPES will be wicked up

4. Do you remove the crumbly wood and use filler, or do you treat the crumbly wood to make it good again?

I'd suggest leaving the crumbly wood in place for the CPES applications. Afterwards, during your review, you can give it a tug and see how well it seems to be staying in place. It is often surprising how well CPES can solidify bad wood.

Thank you for your time, if it would be easier for you to address my problems over the phone I will gladly give you a call.

Steve S.


Some answers above. Thanks for the j-peg images, very helpful!

Obviously, the short answer here is flood everything with the CPES when it is dry and then go back and use the putty to fill vacancies. I think this will do the job for you. How much? I'd suggest two of the 2-quart CPES units, one injection kit, and one 2-pint kit of the Epoxy Filler. You're looking at about $150.00 here w/shipping. I do think this will be enough material, unless you lose a lot of CPES on the ground. You can always re-order if necessary.

You're going to need to reseal the "C" channel where required. My strong recommendation is to use a polyurethane sealant, one in the 10oz gun-tubes. I'm not really sure what is available at the local home stores, but the big popular one now in the boating world is the 3-M 4200 (mild adhesive) and 3-M 5200 (strong adhesive). The discount marine stores sell this for around $10-12 per tube. There may be another poly sealant available at your home store. You get a better bond with the poly and the CPES than you will with any other sealant.

I hope I've given you some help. Come back to be with additional questions. You're a thorough guy going about this in a practical manner.


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