Think of it this way:-
Polyester is a bonding resin, which means that it binds a material, I.E.
fibreglass by surrounding the fibres on both sides and through the fine
glass filaments. If you use it on ply then it cannot soak into the surface
and through to the other side to bind the plywood fibres.
Epoxy is basically a very strong glue which binds two surfaces together.
The costs will be negligible if you just put a lightweight coat of epoxy and
glass onto the hull, instead of coating it over a polyester surface.


"not-it.org" wrote in message
...
If this is not a "troll", then read on:

I would have a problem with you mixing the two types of resins - I
wouldn't buy the boat. It's not because of the epoxy - I'm not
convinced that the poly should be next to the hull.

I have had great luck with epoxy staying stuck to wood. Not so with
poly - it's designed to stick to itself and fiberglass, and f/glass,
and itself. I've had delaminations occur on my tests in using poly to
stick f/g to a wood hull. It may take a few years to happen, but thats
why I wouldn't buy a used boat constructed that way.

It may work wonderfully for years, and I hope it will for you,
However, do a lot of reading on the chemistry and bonding
characteristics before you sacrifice sweat and wallet-padding.
It will be cheaper to build it only once (duh... but true).

I have spent *months* in the past going over it, and over it again, to
eventually "bite the bullet" and get epoxy, and so far am still glad.

litmus test:
If it's a boat to be proud of, its worth the epoxy.

If it's a boat to :
try a new design - poly
take care of for 20 years - epoxy
beat up, and become a 'planter' in 4 years - poly.
make a f/g mold for a one-off - poly
annoy others with fumes - poly

- - -
Why not slap together a cheap-ply row boat, and test this out, first.

make itunder 8ft and you can build it out of 1 or 2 sheets of
plywood, ~4mm. Then glass it - the poly wont be all that much for one
gallon, thats the premise, here. Maybe buy the glass for both all at
once, n save a few bucks.



On Sat, 27 Sep 2003 23:43:21 +0100, "carlp" wrote:

Anyone have suggestions or problems resulting from the use of polyester
for
the bulk of construction and epoxy to seal the polyester, say a 85
gm.glass
woven cloth impregnated with epoxy .
Only the cost saving would be large, considering the difference in the
price
of the two resins.
I have started on the frames of a 23 ft. WL. sailboat, strong back is in
place.
cheers
Carl.

"AB" ) writes:
Think of it this way:-
Polyester is a bonding resin, which means that it binds a material, I.E.
fibreglass by surrounding the fibres on both sides and through the fine
glass filaments. If you use it on ply then it cannot soak into the surface
and through to the other side to bind the plywood fibres.

Polyester does "soak into" the plywood, especially if given time by
lightening up on the catalyst and temperature. I've spread uncatalized
polyester resin on plywood and let it "soak in" before applying a second
layer with catalyst. I didn't put any fibreglass on the hull, just painted
over the cured polyester. Not scientific though. The small boat is only in
its second season so I'm not sure how successful it was yet. I've also
drilled lots of holes in wood to help polyester get a bite. I remember my
father doing the same thing when patching rust spots in an old car. I've
also done the same on the 14 year old car I have now.

I found the following reference in a book I read this afternoon
"How to Fibreglass Boats" by Ken Hanikson, published by Glen-L Marine in
1974 (Glen L Witt's company. Perahps email to Glen-L or Devlin would get
information they might have on the conditions under which polyester can be
succesfully used to cover a plywood boat.)

I found the above reference in "How to Beat the High Cost of Sailing" by
Richard Lyttle (1976). I also like "Frugal Yachting" by Larry Brown (1994)
although its not as informative. Brown sails a Potter 15 with his wife,
and the book is mostly about pocket cruisers that can be towed around on a
trailer. Since the original poster in this thread has already started to
build his boat these books are of limited interest, but I like them anyway
because they address the subject of sailing at least cost. Both books are
available from the Ottawa public library.


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