Rot Doctor


Subject: Stringer Rot
Date: Sunday, 19 April 1998

Please tell me your product can help. I have a 1986 Supra inboard ski boat. It is a fiberglass boat with wooden stringers encapsulated in fiberglass. There is dry rot on the stringers that support the engine (big block ) Some, not all of the motor mount bolts are loose and unable to tighten due to rot.

I know the obvious answer is to pull the engine and replace all stringers, but can your product give me a good temporary solution, if so how can it be applied. I suppose the best answer you can give me is to simply pour your product in the motor mount holes and replace bolts and let dry, but I doubt if it will be that easy.

Here’s hoping

Steve M.


I wish I could give you the answer you want, but I can’t.

Normally on rotten stringers we say that you can go in and if very careful reconstitiute the wood interior by using epoxy resin or a resin/substrate mix. If this is well bonded to the existing (remaining) wood then you have a fix, although it is 2nd best to replacing the wood. Ideally, you cut the top off the glass and replace the wood, after soaking it in the Clear Penetrating Epoxy Sealer (CPES) for future protection. Either way, what you end up with is a fix that will withstand the normal flexing loads placed on the stringers.

In your case, though, you are involved with the engine. To simply pour in epoxy to stabilize the engine is not likely to work. The engine bolts are metal and epoxy to metal bonds are not nearly as strong as epoxy to wood, glass cloth, etc. It’s doubtful that it would work. The engine would tourque the bolts loose, in all probability. You don’t know how far the rot goes or how bad it is, how wet it is, how to dry it out, or what will be needed to bring it back. Furthermore, your access is limited so it’s difficult to get these answers.

Sorry, but what you need to do is pull the engine, cut the tops of the stringers, replace the bad wood, make sure it is soaked in CPES and epoxy-bonded to the old wood remaining (we make some epoxy glues/adhesives that are especially for that), re-drill your engine mount holes and fasten the engine down again. You can re-glass the top of the stringer, but personally I wouldn’t do that. Just soak it in the CPES and then you’ll be able to see it and if there is any sign of future deterioration you can get right at it.

Come back if you have more questions.