The Rot Doctor


Subject: Cored hull moisture
Date: Sun, 11 Jan 2004

I have emailed you before on other issues on the 24' Olympic I am rebuilding. I have all the structure removed now, including the transom. This boat has a balsa cored hull bottom & there is some wetness in areas of the core. The glass covering the core appears to be adhering well. Once I determine the extent of wet core I will likely employ the hole drilling method to dry it.

The core material is end grain & about 3" x 1" pcs. On this project, I have the following questions.

1- will CPES™ flow to adjacent balsa squares adequately enough to saturate entire core if holes are drilled on 4" or 6" centers? It's certainly not feasible to drill each piece of balsa.

Applied to dry, rotted wood, CPES™ will flow a long way in all directions. I would expect CPES™ to flow the 3" from each hole if they were drilled on 6" centers, and the balsa was rotted and dry.

In dry, non rotted wood, CPES™ will penetrate many inches WITH the grain of the wood, but only 2-4 millimeters ACROSS the grain of the wood. If the wood is saturated with moisture, the CPES™ will not penetrate much in any direction.

If the core is rotted, CPES™ is quite useful. If the core is wet and delaminated from the fiberglass, CPES™ can be used to rebond the core to the glass but best results are achieved after the core has been dried. If the core is wet but not delaminated, your main goal is to dry out the core, with CPES™ used after the drying process to rebuild the areas where you exposed the core during the drying procedure.

2- Can the solvents in CPES™ affect the existing bond of the glass / resin above or below the core, or break down any of the resin holding the laminates together?

The solvents in CPES™ will not cause any problem with any properly cured fiberglass structure.

3- If I drill holes, how big should they be?

At least big enough to allow the tools used to work on the core proper access to the balsa. Generally speaking, bigger is better, but it really depends on exactly what you are trying to do to the core. Most procedures call for holes somewhere in the 1/2" to 3/4" range.

4- Is it advisable to cut out panel sections on a hull bottom if I find that I can get the cap off without pulling balsa with it?

It depends on the core damage. For core that is wet but not delaminated, I would not recommend this. If the core is largely rotted and you intend to replace sections of the core, this can definitely be the way to go.

Thanks for your help
Russ L.

You are quite welcome and let me know if I can answer any further questions.