The Rot Doctor


Subject: Drying wet deck core
Date: Fri, 26 Jul 2002

Hi Doc: I've been reading through your Q&A's and I see reference to getting wet cores "reasonably dry" before using epoxy saturation. What is the technique for drying a wet core so that it can be reinforced?

Opening the surface with drilled holes is the most common method. It works, but takes time and requires that some sort of rain protection be provided. Other people have rigged plastic tubing to shop vacs and use that to suck out moisture. This definitely accelerates the process.

I have a fiberglass deck with a plywood core which is wet over a significant area. Rot has started in at least one part, and there is some delamination. Can I get it dry enough to work on?

You can, but it will take a little time and you will need to either have the boat under cover, or provide some sort of tarping to keep the water off the area. CPES will work in wood that is slightly damp (meaning if you squeeze it no wetness is evident), and our fillers and resins will cure in this environment.

In tracing this problem, I have found a way to detect and measure wetness in my deck core. An ordinary ohmmeter (multimeter) can be used to measure the electrical resistance between bolts and screws driven into the core. Where there are no fasteners, small holes can be drilled into the underside of the deck and small finishing nails driven into the plywood.

Where the core is very wet, the resistance between any two points is in the 10,000 ohm range. Dry areas show resistance's over 1,000,000 ohms. A resistance of 350,000 ohms corresponded to a moisture test of 14%.

What you have done is fabricate your own moisture meter! Nice going, and thanks for sharing this with us.


Geoff M.

Hope this is some help, and come on back if you have additional questions.