[Alberg30] Resins

[George Dinwiddie]

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I don't know of a good source, but I can give you some info.  Both
epoxy and polyester resins are broad families, and the properties
can vary widely.  In general:

Epoxy resins are adhesive and polyester resins are not.  This means
that when you put new polyester on old cured polyester, you need a
rough surface for it to grab.  (If the old polyester is not completely
cured, a chemical bond will form.)  It also means that you can apply
epoxy to polyester, but not vice-versa.

Epoxy resins tend to be a bit more waterproof than polyester.

Epoxy resins must be mixed very accurately, or the resulting properties
may be completely undesirable.  This generally means measuring by weight,
but some manufacturers have calibrated pumps for their epoxy.  These
are not necessarily interchangeable between brands.

You can speed up or slow down the reaction of polyester resins by
adjusting the amount of hardener.  You can't do this with epoxy.
In some cases, you can get different hardeners for different 
reaction rates.  Both epoxy and polyester reaction rates are
sensitive to temperature.

Many fiberglass matts use a starch binder to hold the fibers
together.  This binder is soluable in polyester, but not in
epoxy.  This makes these matts unsuitable for use with epoxy.
Some filler materials (used to thicken the resin) are only
compatible with one or the other resin; others are compatible
with both.

Polyester is generally cheaper and easier to work with.  I tend
to use epoxy for small repairs, and polyester for larger things
like relaminating the deck.

 - George

> Peter Amos said:
> 
> I am looking for objective and unbiased information on a comparison =
> between polyester and epoxy resins.Does anyone know a good source or web =
> site?
> Peter Amos         Tait Tait #478
> p.a.amos at tesco.net

-- 
 ----------------------------------------------------------------------
  George Dinwiddie                                  gdinwiddie at min.net
  The gods do not deduct from man's allotted span those hours spent in
  sailing.                         NEW URL => http://www.Alberg30.org/
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