[Public-list] Epoxy Vs. Polyester resin

[George Dinwiddie]

Patty J wrote:
> Katrina took my cap rail off and ripped some of my deck to hull joint.
> Does any one know what I should use to make my repairs...epoxy or
> polyester resin with the fiberglass.  I've already read Don Casey's book
> on the subject and I'm ready to start grinding but want to use the
> correct materials.  The only part that was ripped off is the deck part
> just under the cap rail and it looks to me like they used fiberglass
> mess and sheeting sandwiched together, so I suspect they used polyester
> resin, but not sure.

Yes, Whitby used polyester resin.  Personally, I recommend using 
polyester resin for the repairs.  Epoxy has advantages and 
disadvantages.  It is chemically adhesive, where polyester depends on a 
physical bond (which you get by grinding an 8-to-1 scarf).  It's also 
unstable in UV and will break down much faster than polyester if not 
kept painted.  And, the chemistry requires a much more careful mix.  You 
can adjust the working time of polyester by using more or less hardener 
(to a point), but epoxy will become brittle or lose its strength if not 
mixed right.  I think epoxy takes more skill to layup than polyester, 
also.  Also, you can apply epoxy to polyester, but not the other way 
around.  So an epoxy patch will require epoxy in the future, or a bigger 
grinding job.

Except for small repairs where the adhesiveness of epoxy was a 
significant advantage, I use polyester.

I do recommend using a respiration mask and nitrile gloves.

  - George

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   When I remember bygone days                         George Dinwiddie
   I think how evening follows morn;            gdinwiddie at alberg30.org
   So many I loved were not yet dead,           http://www.Alberg30.org
   So many I love were not yet born.
                                             'The Middle' by Ogden Nash
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