From what I understand epoxy interlinks more completely at the molecular
level than polyester. Polyester links in long chains but the chains
themselves do not interlink like epoxy does so definitely epoxy will
give a stronger bond no matter what it is applied to.
The point that Payson makes in his build book, is that polyester bonded
well enough in his destruction tests that the outer wood plywood layer
gave way while the poly/glass connection remained intact. Obviously
because plywood is not linked together at the molecular level as
strongly as the resins are. The plywood did not separate at the plywood
glue line but just shredded off in splinters next to the polyester
My point has been when epoxy costs over 3 times as much as polyester,
then it might be strong enough for me. As mentioned, poly is $32/gal
epoxy $101 to $158/gal where I am. But I will still use epoxy where it's
gluing strength is required, but not for glassing or filleting.
The other issue often mentioned is that polyester is not as waterproof
as epoxy. I guess it to be more waterproof than the plywood and just as
waterproof as most exterior paints I know of. So in a boat mostly dry
stored and not left on the water all season it should last awhile. As
mentioned Payson had some boats over 20 years old and so does Jim. I
have one over 10 years old and a previous one as well and the joints
were solid but the water got in under the plywood where there was no
But if a builder feels the extra cost in using epoxy instead is felt
warranted then that is the best choice no doubt.
--- In Michalak@yahoogroups.com, Andres Espino wrote:
> Epoxy bonds well to Polyester but Polyester does not bond to
epoxy.Â This chemical bnd occurs while the catelatic action is
happening so i guess the chemicals in epoxy are more versitile or
> From: Steven sdantonio93@...
> To: Michalak@yahoogroups.com
> Sent: Thursday, July 25, 2013 6:41 PM
> Subject: [Michalak] Bolger Afterthoughts - like after Featherwind (Re:
Epoxy Vs: Polyester Resin.)
> Thank you all for the comments.
> One last question. How well does epoxy adhere to polyester? I assume
I would glass the bottom before putting on the skids, so I doubt I could
use tightbond III to glue the skids to polyester, which leaves only
epoxy to put them on.
> I can only assume glassing over a bottom with three skids would be a
> [Non-text portions of this message have been removed]
[Non-text portions of this message have been removed]