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West Wight Potter Mailing List maintainer
dfarrell@ridgecrest.ca.us
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And, to add to what Eric wrote, you wouldn't want to let the individual
layers of a repair cure individually. When you add layers to uncured epoxy,
the curing process creates cross-linked chemical bonds in the resin.
When you add a layer to a fully-cured surface of polyester or epoxy
laminate, the best you can get is "mechanical keying" of the new resin into
the imperfections in the old surface. That's the main reason you sand an
original surface with 50 or 100 grit before you put on new resin.
Chemical crosslinks are MUCH stronger than mechanically-keyed in resin. So
you want to finish repairs in one session, using the correct speed catalyst
for the ambient temp, before the resin cures fully.
Also, epoxy forms a stronger mechanical bond than polyester resin does to
cured laminates, which is why epoxy typically is the resin of choice for
most repairs. In short, epoxy has better mechanical adhesive properties
than polyester laminate on cured surfaces.
For initial layup of a laminate, the strength difference between epoxy vs
polyester resin is not as significant, and polyester has some other
technical advantages for initial layups (such as no amine blushing, etc)
Fair winds, Judy B
> -----Original Message-----
> From: etj@nwlink.com [mailto:etj@nwlink.com]
> Sent: Sunday, February 13, 2000 6:38 PM
> To: Judith Franklin Blumhorst; potter mail list
> Subject: RE: Repairing a broken stringer on the P19.
>
<<snipped>>
> Having just done this, I have a pretty good idea why. I has
> originally going
> to do it the other way until Judy suggested going biggest on the
> bottom. I'm
> glad I did it that way, because when you do it that way as you
> add layers, you
> still have some control over the lower layers. I think if i had
> put a small
> layer under a larger layer, i might have messed up the smaller
> lower one as
> I positioned the larger piece (assuming you're putting on these
> layers all at
> once, not letting them cure individually).
> http://www.nwlink.com
>
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