Rot Doctor


Subject: moisture in transom
Date: Sat, 08 Apr 2006

I recently purchased a 2003 Baja 302 from a private individual. I had it surveyed and the surveyor detected no moisture in the transom. I was pulling the through-hull exhaust off and found moisture trapped between the fiberglass resin they used to seal the 4 inch holes and the mufflers themselves. Basically the rubber gasket they had used failed. So I thought no big deal, I’ll let it air out and dry then install again with some 3M 5200.

Well upon further investigation I saw water stains coming from the bolts from my stern eyes as well as my K plane trim tabs. So I pulled the stern eyes and noticed that there was minimal if any sealant, causing water intrusion into the plywood cores of the transom. When I pulled the cables and bolts for the K planes (trim tabs) I noticed the core looked like wet sawdust. I could take a small screwdriver (electronics screwdriver) and push it into the wood approximately 1/2 inch. I don’t know how far this water intrusion has occurred as I’ve only investigated it this far. My concern is that from other Q&A posts I’ve read, dry rot occurs. I don’t want this on a 3 yr old boat.

I have a 5 yr hull warranty, but I don’t know if they are going to cover this under the warranty and I want to make sure its sealed correctly as to not have this problem again in the future. So will your product work in this scenario? I can’t get to the complete transom to see how far this water intrusion has effected the transom other than drilling holes which will definitely void my warranty. Could you please advise if your product is what I need to properly eliminate this problem in the future? Thanks for you time and help.

David S.


It’s likely, although not a certainty, that the moisture is local to the through-glass fitting holes. The only way to know for sure is to tear all the glass off the transom, and of course this is not very practical. I would certainly do a tap-test inside and outside the transom, using something hard to tap and listen to the sound. If there is wood deterioration inside there will be large variations in the sound, from solid raps to a more hollow thud. Extensive transom rot would be unlikely in a 3-year old boat, although the local beginnings of rot are quite possible.

For the local areas you have discovered, our CPES (Clear Penetrating Epoxy Sealer) should be sufficient to stop the deterioration process and solidify the wood. The wood should be reasonably dry (use a hair dryer if required) and then with something like the syringe from our CPES Injection Kit, or a kitchen baster, squirt the entire interior around the hole with the CPES, allowing the wood to absorb all that it will. If there is additional filling to be done, our Fill-It Epoxy Filler can be used. This can be applied with a putty knife or it can be pumped in with our reusable caulking tubes.

Re-sealing the holes is best done with a 100% polyurethane caulk, such as 3M™ 4200. This is applied to a dry, clean surface and then the fitting base is screwed into it to about 50–75%. Wait for a couple of days (or longer) and then come back and screw down tightly. You have basically formed a watertight gasket.

How far you go in protecting the rest of the wood core in your boat is pretty much your choice. Certainly every bit of exposed wood should be CPES-treated, including all drilled holes through the transom, stringers, floor supports. It’s possible also to inject CPES into the top of the transom through opened seams or drilled holes and have it seep down over the wood. This does offer some protection.

I hope this is some help. Feel free to come back if you have additional questions. If you wish to order you can do so via phone or our secure on-line order form. We have warehouses on both coasts so shipping time is three to four days or less to just about any point in the US.