Moisture in GRP hull

Question
I have a 26' bilge-keel GRP yacht, some 30 years old, which spends the summer on a half-tide mooring and the winter ashore. I have used Danboline bilge paint on some of the inside surfaces. This spring I scraped off the antifouling paint and sanded the hull, intending to apply 2 coats of epoxy paint. I discovered that the hull had been painted many years ago with two coats of epoxy paint, although there were many small "holes" in the paint. The "yard" that did the work thought that the holes might be the first signs of pre-osmosis. (However the gel coat is not blistered, and I wondered whether the hull surface had been cleaned sufficiently before it was painted.). Of course, the existing epoxy paint has been eroded by my sanding, in places down to one coat, and in patches to the gel coat, therefore I am very keen to repaint the hull with 2 coats of epoxy. However, the "yard" advises against my applying a further 2 coats of epoxy because of the highish moisture content of the hull. The readings were about 7 above the waterline, and patches of above 15 below the waterline. The 搚ard?made no attempt to locate the source of the moisture in the areas with high moisture readings. I could purchase a moisture meter and make my own survey of the hull. They said that if they were asked to paint the hull, they would first have to dry the hull more, (which would be an expensive job). I think that I am disappointed that the original epoxy coating has not protected the hull better. I was advised by the 搚ard?that if I was to paint the hull, this would actually make matters worse, and that I would inevitable end up with osmosis. What do you think? Thanks

Answer
Hi Roger...Thank you for selecting the undersigned to reply to your question.

Although the boat was built around 1977, you didn't mention the name of the manufacturer. However, water can take its toll on gel coat and epoxy-painted surfaces, and fiberglass (GRP)is not immune to osmosis. In all probability, the moisture content above and below the waterline has existed for quite some time and internal delamination may be present.

Immediately after fall haul-out, determine where the highest readings of moisture are located, using a good quality moisture meter. Record the result, and circle all the identified area(s)above and below the waterline with  chalk or crayon. In a contrasting color, circle all areas where there appears to be any form of a surface distortion such as a blister.

It's important to store the boat in a well ventilated and heated facility, and make sure all hatches, etc. remain open for maximum air flow.

About a month or two after layup in a craddle or on a trailer, check the alignment of the keel. Is it warped? Does it deviate sideways? Or, is it hog-backed and go up and down? Either way, the backbone of the boat has been severely jeopardized and it's best to get rid of the boat before you go any farther.

Next spring, re-check and record the hull's moisture content, and compare with the results you obtained in the fall. Carefully examine the surface of the entire hull for distortions, and determine whether previously identified blisters have enlarged, shrunk or disappeared. Penetrate and drain the areas that are present or have enlarged, using an ice pick. Then grind down to below the delamination and rebuild with new material. It's a long and slow process, and if you do it yourself rather than pay a repairer or restorer, you will save a lot of money.

Keep in mind, you have determine from the out-set whether it will be economical to restore the vessel, based on your observations and findings of hull defects/deterioration.

Safe Boating
Ron Blanchet