/Q. I have heard that gel coat will not adhere well to epoxy
<http://www.cruisersforum.com/forums/tags/epoxy.html>. Can you confirm
this?/
A. There is a common misconception, fueled by some gelcoat
<http://www.cruisersforum.com/forums/tags/gelcoat.html> manufacturers
and by some expensive failures in the field, that gelcoat will not bond
to epoxy. Polyester resin bonds poorly in a secondary (mechanical)
bonding situation which consequently makes epoxy the resin of choice for
repairs <http://www.cruisersforum.com/forums/tags/repairs.html>. How can
one be squared with the other?
The answer is surprisingly simple - *gelcoat does bond to a properly
cured and prepared epoxy surface*. There are a couple issues to be aware
of to have success making this repair. There are three situations that
cause gelcoat to not cure over epoxy... all related to the hardener
chemistry. Epoxy hardeners are basically a blend of amines, which can
terminate the chain reaction of the radical molecule that is the basis
of polyester (and vinylester) cure chemistry. So by carefully mixing,
curing, and preparing of the epoxy so that there are no unreacted amines
to interfere with the gelcoat cure, gelcoat bonds quite well to epoxy.
The first situation is _undercured epoxy_. Gelcoat applied to undercured
epoxy will be in contact with unreacted amines and the cure will be halted.
The second situation is if the epoxy is mixed _off ratio_ so that it is
hardener rich, again leaving unreacted amines free to interfere.
Third is the issue of _amine blush_, commonly called blush. Blush is a
surface phenomena that is a reaction of the amine molecules at the
surface with the carbon dioxide in the air. It forms easiest in the
presence of moisture, so working in cool, humid environments will
maximize the formation of blush. Any amine hardener has the potential to
blush, but it can be minimized by careful choices of amines in the
formulation. In fact, WEST SYSTEM 207 Special coating hardener is one of
the lowest blushing hardeners on the market and still maintains
structural properties on par with our other hardeners. Regardless of
chemistry, blush is very easily dealt with because it is water
<http://www.cruisersforum.com/forums/tags/water.html> soluble. A simple
wash with clear water
<http://www.cruisersforum.com/forums/tags/water.html> removes the blush.
No soap, no solvents. Then sand that washed surface with 80 grit paper
to provide the gelcoat with sufficient key so it won't run. Be sure to
use non-air inhibited gelcoat that has a paraffin wax added. Gelcoat is
applied over epoxy on a routine basis everyday in boatyards
<http://www.cruisersforum.com/forums/tags/boatyards.html> that are aware
of these issues.
*Bruce Niederer*, Technical Services West System Inc.
http://www.westsystem.com/
<http://www.cruisersforum.com/forums/misc.php?postid=52038&threadid=5794&external_page=http%3A%2F%2Fwww.westsystem.com%2F>
See also the articles at:
http://www.epoxyworks.com/indexprojects.html
<http://www.cruisersforum.com/forums/misc.php?postid=52038&threadid=5794&external_page=http%3A%2F%2Fwww.epoxyworks.com%2Findexprojects.html>
On 7/6/2015 11:42 AM, Bill Coleman via CnC-List wrote:
Polyester resin doesn’t stick too well to anything except uncured
polyester resin.
That’s why Gougeon’s recommend epoxy for fiberglass repair. Well,
that, and they sell it, of course.
https://www.youtube.com/watch?v=tMVCwhz_hY4
Bill Coleman
C&C 39
Erie PA
*From:*CnC-List [mailto:cnc-list-boun...@cnc-list.com] *On Behalf Of
*Fred Hazzard via CnC-List
*Sent:* Sunday, July 05, 2015 1:57 PM
*To:* cnc-list@cnc-list.com
*Cc:* Fred Hazzard
*Subject:* Stus-List Damage to fibreglas
I put a hole in several layers of fibreglas about a foot above the
waterline in the side of my boat. As it may take some time before
repairs are made, Â should I seal the glass to prevent water from
getting in the layup? If so what should I use?
Fred Hazzard
S/V Fury
Portland, Or
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