"Lew Hodgett" wrote in message
...
wrote:

What are the relative merits of polyester resin vs epoxy resin?

Trying to compare polyester and woven roving to epoxy and knitted
glass is like trying to compare oranges and apples.

Both are "fiberglass" laminates, but the similarity ends there.

About the best you get is 35%glass/65%resin using woven roving, mat,
and polyester.

OTOH, it is quite common to get a 50%glass/50%resin using knitted
glass and epoxy. This laminate does not require any mat.

Bottom line....................

Polyester/roving produces a rather brittle, heavy laminate.

Epoxy/knitted glass produces a more ductile, lighter weight laminate.

Pound for pound, polyester and woven roving cost less per pound, but
you use more pounds, so the cost differences tend to disappear.

Epoxy, knitted glass and a 1/2" Airex foam core would produce a very
light weight, bullet proof, dinghy or kayak.

Just remember three things.

1)You will buy a commercial dinghy for less money than you will spend
to build one.

2)You build one because you want to do it.

3)Once you use epoxy and knitted glass, you will never consider
polyester again.

I have never actually built anything with fg, but have done numerous
repairs.
I have always used woven cloth with epoxy, and haven't heard the term
"knitted" before.
A google search showed it was the same as unidirection fabric. Is that
correct, or is knitted something else?

"Toller" wrote:

I have never actually built anything with fg, but have done numerous
repairs.
I have always used woven cloth with epoxy, and haven't heard the
term
"knitted" before.
A google search showed it was the same as unidirection fabric. Is
that
correct, or is knitted something else?

Woven fabric looks like a burlap bag, a very coarse weave.

Knitted fabric looks like suit fabric, very fine, tightly knitted
fabric.

Do a Google for Knytex, then DB170.

That will get you to a double bias (+/-45), 17 oz/sq yard material.

It is about all I use these days.

There are also what are known as "Uni" fabrics which have the fiber
oriented either 0 or 90 degrees to the run of the roll.


Lew

Knitted glass consists of two or more layers of unidirectional glass which
are knitted together. It's available with the glass at 0 and 90 degrees and
with the glass at +-45 degrees. It is less expensive per pound than glasss
fabric. Because the fibers are not crimped by weaving, it's stronger and,
for a given glass content, thinner and therefore it needs less epoxy to
fill. So, for structural purposes, it's superior to mat & roving and to
cloth. It often does not finish as smooth as cloth, so a top laminate of
cloth is a good way to finish .


"Toller" wrote in message
...

"Lew Hodgett" wrote in message
...
wrote:

What are the relative merits of polyester resin vs epoxy resin?

Trying to compare polyester and woven roving to epoxy and knitted
glass is like trying to compare oranges and apples.

Both are "fiberglass" laminates, but the similarity ends there.

About the best you get is 35%glass/65%resin using woven roving, mat,
and polyester.

OTOH, it is quite common to get a 50%glass/50%resin using knitted
glass and epoxy. This laminate does not require any mat.

Bottom line....................

Polyester/roving produces a rather brittle, heavy laminate.

Epoxy/knitted glass produces a more ductile, lighter weight laminate.

Pound for pound, polyester and woven roving cost less per pound, but
you use more pounds, so the cost differences tend to disappear.

Epoxy, knitted glass and a 1/2" Airex foam core would produce a very
light weight, bullet proof, dinghy or kayak.

Just remember three things.

1)You will buy a commercial dinghy for less money than you will spend
to build one.

2)You build one because you want to do it.

3)Once you use epoxy and knitted glass, you will never consider
polyester again.

I have never actually built anything with fg, but have done numerous
repairs.
I have always used woven cloth with epoxy, and haven't heard the term
"knitted" before.
A google search showed it was the same as unidirection fabric. Is that
correct, or is knitted something else?