Grahame,
Years ago, polyester resin was the matrix of choice when wet lay-ups were
the typical building method. However, 'poly' was way too soft. Hulls would
flex considerably, thereby ruining the airfoil shape of the sails as the
rigging sagged. 'Poly' was also prone to wicking salt water into the
laminate structure causing structural delamination and blisters on the hulls
that sometimes reached the size of dinner plates. Those blisters were very
expensive to repair and not a great favorite of anyone charged with keeping
the hulls looking good. 'Poly' also ex-gasifies under the paint causing
bubbles to be trapped lifting the paint membrane. Hulls were/are commonly
treated with an epoxy undercoat before painting, even if the topcoat was/is
Imron or Awlgrip.
Epoxies such as the West System
http://www.westsystem.com/webpages/userinfo/moreinfo/composite.htm
and the SP lines
http://www3.gurit.com/pdfs/adhesive/PSG_Epoxy_Adhesive.pdf
have been more commonly used for building over the past 25 years. They
produce a better and more durable laminate structure. They are used almost
exclusively when constructing a matrix with carbon. In fact, I can't
remember when I last used 'poly' on a boat.
The catalytic component in any resin mix has always been colloquially
referred to as the 'catalyst' or 'hardener' in boat building yards. Mea
culpa, mea culpa, mea maxima culpa. I'm old enough to have gotten into the
habit of using the word 'catalyst' when referring to any hardener. Be that
as it may, the process remains the same.
1.) Mix the resin thoroughly before blending in the filler material.
2.) Once the filler is thoroughly incorporated into the (reacting) resin, it
has a pot life determined by several factors.
3.) Screed the resin/filler mix onto the surface to be faired before the
resin/filler mix hardens in the pot.
As to the mix ratio being critical, I couldn't agree more. That is why I
suggested using a calibrated metering pump system supplied by the resin
manufacturer.
(Our discussion might be over-engineering a simple fairing job. I was just
lurking on the list and thought I'd share a tip that made our lives a bit
easier when sanding in various boatyards over the years.)
Regards,
Jack
----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Graham
Singleton
Sent: Tuesday, November 21, 2006 12:35 PM
Subject: Re: Europa-List: To Those That Have Sanded Before Me... :)
<grahamsingleton@btinternet.com>
Jack
Boat people tend to use polyester materials we use epoxy so it isn't
catalyst it's reagent. Any variation in hardener /resin ratio will be
disastrous, it won't cure properly and unreacted resin or hardener will
prevent adhesion of the next layer, paint or whatever.
Graham
Jack Hilditch wrote:
>
>Graham,
>
>Agreed. A Filler depth should be quite thin (1/8" or less) so, while
>sanding a catalyst-rich filler mix
>Jack
>
>
>
>
>
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9:20 PM
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