The Rot Doctor


Subject: Fastener question
Date: Sun, 05 Dec 1999

Doc: Have been having fun with your epoxy products. As you suggested, all new wood is getting a good slathering of CPES (changing out the motor,so lot's of new motor mount wood).

We talked about hull fastener replacement when I stopped over to your place. Wanted to ask your opinion of my process. I have been unable to remove any existing fasteners so far. I've tried hammering on the end of a huge screwdriver, impact hammer, screw extractor (two different types), all of which resulted in several choice expletives, but no screws removed.

One thing I noticed was when drilling a pilot hole in the fastener for an extraction attempt, the screw appeared to have only a very thin coating of rust on head of the fastener. The surrounding wood appears to be sound. Made the decision to use Phosphoric acid to lock the fastener's visible rust, apply CPES, with a subsequent application of lay-up epoxy, and then filler.

What do you think? Should I "get a bigger hammer" and get the old fasteners out at all cost, or carry on. I have only done 4 fasteners this way, and have maybe 30 or so more that are bleeding through.

Hope to get some digital photos of "Teasel" next week.


Mark V.


I've been where you are, with an old sailboat with iron fasteners. What I found out was that if you hammer, attempt extraction, etc. etc. and the screw won't move or break then the screw is basically in good shape. I gave it all up, polished the heads with a Dremel-type tool, did the Phosphoric acid business, and then sealed them with epoxy putty. These were the days before CPES was developed, but had it been around I would have done exactly what you are suggesting.

I would use two coats of the CPES, a day apart each screw head, and allowing the surrounding wood to absorb all the CPES that it will. Then the L&L Resin and the Epoxy Filler. You can't do better than this, and it will take care of 90% of the bleeding, but not all of it. Iron is iron, and if the water gets to it by whatever means then you get the rust.

The only downside to all this is any later extraction of the screw is almost impossible because of the epoxy. The purist would just use the acid and a standard hull putty, which may be pure but will result in the whole rusting process all over again -- and it won't take long. I hoped my solution would last quite awhile, and it did. With the CPES it will last even longer.