Andy Dingley wrote:

I'd suggest that you're unusual in this, being significantly more
experienced than most. Maybe boatbuilders are fussier.

Naw, just set in their ways and scared to death of $$ signs.

Just look at initial price of materials, not finished cost of laminate.

OTOH, you tend to get a little fussy when you are building for
yourself, which is what I did.

Certainly here in the UK, for "hobby" levels of work or even small
dinghy makers, polyester is _far_ more common than epoxy. Just the
price
of resins is enough to swing it.

Again, got to look at finished laminate cost.

Yes, epoxy is more costly than polyester.

Yes, knitted glass used with epoxy is more expensive than 1/2 OZ mat
and woven roving.

That said, you use less epoxy by weight and about the same amount of
glass, thus the total laminate cost is about the same.

It is also far easier to wet out knitted glass with epoxy than it is
to wet out mat and roving with polyester, thus there is some labor
savings once you ramp up the learning curve.

I've never used epoxy that didn't need vacuum and controlled moderate
heat. This has been with either prepreg carbon, or Kevlar.

Different world.

Never worked with either one, but understand they are a bear compared
to knitted glass.

I've never
used a grade of epoxy that wasn't fussy enough to require this -- when
I've been working at that level, with glass, or 20-30 years ago it was
always just polyester. There are certainly such epoxies around that
aren't so fussy (I use West System for general gluing), although I've
never used it seriously for fibreglass.

Standard WEST is laminating resin.

There are only 4-5 base resin (Part A) manufacturers world wide.

Shell, Dow, Ciba come to mind.

Lots of formulators for the hardener (Part B) like WEST.


If you have the skill to achieve that sort of wetting out. "Typical" UK
amateur skill levels (I'm coming to this from the kitcar world) are
often distinctly heavyweight, certainly on the first projects.

It's a basic problem with polyester, mat and woven roving.

Roving doesn't wet out easily, thus the mat is used to hold the resin.

OTOH, epoxy readily wets out knitted glass so it is easy to squeegee
out excess resin.

The trick is the knitted glass.

What do you mean by "mat" ? I'm referring to weaves, as well as choped
strand. Maybe this is a local terminology issue?

"Mat and roving" describes a glass that consists typically of a layer
of 24 OZ woven roving with a 1/2 OZ stranded mat stitched to it.

Been the backbone of the polyester boat building industry for years.

BTW, chopper guns in the USA are a thing of the past. Changes in the
environmental laws have turned them into antiques.

It's only been the last 10-15 years that knitted glass has started to
see some acceptance.

Old habits die hard.

Incidentally, there's an epoxy thread in rec.knives at the moment. How
do you best attach scales to a metal frame ?

What does the term "scales" mean in the above?

Lew