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Comments from:
Osmosis & Glassfibre Yacht Construction - 2nd
Edition (1995)
By Tony Staton-Bevan
Published by Sheridan House ($19.95) telephone: 914-693-2410
We have found an excellent book on boat blisters and are quoting below some passages from that book.
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page 26 -- Protecting the underwater portion of a fiberglass
hull
At present epoxy based paints seem to offer the best protection, due to
their superior adhesive qualities and resistance to water penetration. Although in the past solvent-based epoxy
paints have proved fairly reliable, to achieve an effective water barrier requires a build up of at least four
coats of paint. In doing this it is possible for solvents to be trapped within the coating, or even in the hull
itself, which can result in the epoxy remaining soft and being less waterproof.....
Further research and development by paint companies led to the production of solvent-free epoxy paints. These products
have many advantages. They can be applied up to 8/1000 of an inch (8 mils) per coat and since they contain no solvent,
they wet and dry film thicknesses are virtually the same. Many solvent-based epoxy paints have a dry film thickness
of less than half that when wet."
COMMENTS FROM PROGRESSIVE EPOXY POLYMERS, INC.:
ROLLERS COMMONLY ALLOW A PERSON TO APPLY ABOUT 8-11 MILS OF A SOLVENT FREE EPOXY PAINT. ON ROUGH SURFACES (AND/OR
WITH A BRUSH OR PAINT PAD) IS IT OFTEN POSSIBLE TO APPLY THESE COATINGS AT UP TO 16 MILS. AT 16 MILS COVERAGE IS
100 SQUARE FEET PER GALLON, AT 8 MILS IT IS 200 SQUARE FEET PER GALLON.
WE HAVE NEVER HAD ANYONE APPLY 4 COATS OF EPOXY PAINT AS A BARRIER COAT.
page 28 -- Barrier coat thickness
In my experience a total build-up of something like 16/1000 inch (16 mils)
is needed, and anything thinner than this is less likely to be successful.
COMMENTS FROM PROGRESSIVE EPOXY POLYMERS, INC.:
WE COMMONLY SEE THE FIGURE OF 10 MILS AS A SUITABLE THICKNESS.
page 30 -- More on barrier coat thickness
My experience and that of others, is that a solvent-free epoxy coating
of at least 16/1000 (16 mils) is required for protection and at least 24/1000 (24 mils) for treatment, after the
gel coat is removed, and these are proving to be very effective.
COMMENTS FROM PROGRESSIVE EPOXY POLYMERS, INC.:
WE GENERALLY SEE ONE COAT OF A SOLVENT FREE EPOXY (GENERALLY OUR WATER GARD 300 EPOXY) ROLLED ON (AT ABOUT 8-11
MILS), OR TWO COATS IF THE GEL COAT HAS BEEN REMOVED.
SOMETIMES A SOLVENT BASED EPOXY PRIMER, OR A SOLVENT THINNED COAT OF THE WATER GUARD EPOXY IS APPLIED AS A PRIMER
UNDER THE BARRIER COAT. THIS IS DONE TO IMPROVE ADHESION OF THE SOLVENT FREE EPOXY TO AN OLDER OR WORN FIBERGLASS
HULL.
page 38 -- Regarding hull blister repair with epoxy
The first coat is worked well into the exposed laminate. Following this,
the hull is reprofiled with epoxy filler. When smooth and fair, sufficient coats of epoxy paint are applied to
give a total dry film thickness of about 24/1000 inch (24 mils)....
Having protected the outside of the hull, what about the inside? Although I have no firm evidence of blistering
caused by water working it way through from the inside of the hull, it is important to seal the bilges, and again,
epoxy paint is the ideal coating. I have seen water in the bilges cause slow disintegration of the laminate by
hydrolysis.
COMMENTS FROM PROGRESSIVE EPOXY POLYMERS, INC.:
THIS IS VERY SIMILAR TO OUR METHOD OF FLUSHING THE OPENED BLISTER THEN SEALING IT WITH A THIN EPOXY, THEN USING
EPOXY PUTTY TO FAIR AND SMOOTH.
I HAVE SEEN AN ARTICLE OR TWO SHOWING WATER DAMAGE TO FIBERGLASS HULLS ON THE INSIDE SIDE OF THE HULL.
Knowledge is Power - We like informed consumers!
Learn the basics of epoxy at our educational EPOXY 101 page - Click Here.
Finally, email us back with your questions or comments before you buy - EMAIL HERE
Progressive Epoxy Polymers, Inc. (homepage-click here)
web site on hull blisters - click here
web site on marine barrier coats - click here
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