The Rot Doctor


Subject: (Dory Damage)
Date: Thu, 15 Jan 2004

Dear Dr. Rot,
I'm happy to have run across your website. I'm getting ready to start some long needed boat repair on a boat that I built 20 years ago with much love, but sadly, have let it deteriorate. Most all of the rot has happened in the past year because of a foolish decision to keep the boat covered with a blue tarp while I decided to get around to repairing it. The tarp, I realize now, was only holding the moisture and condensation in next to the already affected areas. Consequently, as you can see from the photo, the rot has advanced and my project has grown enormously. I intend to cut out all the areas that are not sound and scarf in new wood as needed. I plan to use a few of your products to accomplish this. Before I begin, would you please advise me on the following? My boat is constructed with southern yellow pine planks over white oak laminated frames.

1) Once I cut out all the obviously rotted areas, do you recommend cutting back into the seemingly sound wood further to ensure that most of the active rot fungus is removed. How far can you expect the rot to have progressed?

Cutting out the bad wood is only necessary as required to make a good or easy repair. CPES™ will soak as far as the rot has progressed, if given enough soak time. Since you have to be sure that all the rotted area is thoroughly soaked, it is usually quicker to cut out most of the bad wood, use the CPES to treat the old wood, and any rotted areas that you don't want to remove for any reason, and then put in the new wood. It would be hard to even guess how far the rot has progressed past the missing wood. What we usually do is take a wire brush to the rotted area and scrub until we start to get to good wood, then stop with the wire brush and treat the rest with CPES.

2) In the past I reinforced the bottom of the dory with fiberglass and overlapped it about 4" up on the garboard planks. Is this always a recipe for future problems or if finish is sanded back to bare wood and then treated with CPES, will this enable you to use fiberglass reinforcement safely?

There are two main problems when fiberglassing over wood. One, will the resin stick. Polyester resins do not stick to anything well, and so are a bad choice when doing this type of work. Epoxy resins are much stronger, and more flexible when cured. Especially our epoxies. Getting a good bonding surface is critical. Clean, dry, bare wood is the key here. Especially the dry part. Dry wood gets us to the other problem. When you seal in the wood with fiberglass cloth and epoxy resin, any moisture that might get into the wood tends to stay in the wood. Bang a rock or a dock and make a micro crack, and moisture can wick in, but not easily get out. Sooner or later you will have rot, if enough moisture gets in.

As long as you bond to clean dry wood, and no significant amount of moisture gets in behind the fiberglass, you can be successful with this.

3) I read on your website about different types of polyurethanes. The green finish you see on by boat is a linear polyurethane made by Sterling Lacquers. I have found it to be incredibly indestructible, retains it's color, and lasts for years without any touch-up (I trailer my boat when I use it - doesn't stay in the water for great lengths of time). Are any of the urethanes you are describing linear polyurethanes. Is there any reason you would recommend not continuing to use this product?

Sterling makes industrial strength products. They cost a lot, and you MUST follow the directions EXACTLY to get good results, but as you are aware, it can be worth the trouble. Our resins are either aromatic or aliphatic polyurethanes depending on which one you are talking about. As with any well made polyurethane our products can achieve a very long life span. The Sterling products are designed for a harder, high gloss finish typically desired for boat hulls. Our polys are more of a flexible, lower gloss finish, although plenty of people use them on their boats. Which one I would recommend would depend on the type of finish you were after.

I realize this is a whole lot to respond to, but I would appreciated any information you can give me.

Thank you,
Paul K.
St Louis, Mo.

We are happy to answer all emails. Please let me know if you have further questions.