Hi all, AGAIN !
Gelcoat versus Expancell / Eurathane ?
Polyester gelcoat is just fine when used on thick polyester layup's.
Most boats are made from polyester [ it is cheap]. the Gelcoat is applied to the
inside of a female mould [ mold in the U.S.] ,when it reaches the ''tacky to
touch'' cure stage, the resin / lay up is applied. The bond is chemical, it
becomes
effectively, a single lay up, no adhesion concerns.
Polyester gel coat applied onto epoxy substrate [ as in the Europa construction]
will not adhere too well. As I mentioned before, do a test token of epoxy lay
up, skinned with Polyester Gelcoat,
and one skinned with Expancell / epoxy, then bend them back and forth, the
Polyester
will fail first every time. First the Gel will crack [ polyester Gelcoat
is brittle in comparison to Expancell / epoxy] so then you have effectively a''
hinge line'' which will cause the lay up to fail where local bending occurs.
The Gelcoat will also be able to be peeled off without too much trouble.
Gelcoat is far heavier than Expancell [ it has to be, it is the finnished coat,
much denser / harder] it WILL YELLOW [no matter how good / expensive it is ]
and it does not really protect the substrate from UV.
WHICHEVER topcoat you chose, ensure it has a high UV block in it. Most
autopaints,
even expensive ones, only have enough UV block in them to stop the pigment
fading, we need something above 90% UV block to prevent damage to the structure.
The marine paint suppliers will be able to help with that one.
Other tips ?........
I had very many years in the boat building / repair trade, believe me Gelcoat is
not the way to go, a fair proportion of our work was fixing Gelcoat problems
!
Cheers,
Nev.
>>> <TELEDYNMCS@aol.com> 01/26/04 02:04am >>>
In a message dated 1/25/2004 7:04:06 PM Eastern Standard Time,
garrys@tampabay.rr.com writes:
> How come my boat isn't cracking, crazing and yellowing?
Simple. Because you boats skin is very thick compared to the skin of an
airplane and doesn't flex near as much. The hull is facing down, not up, so the
UV
exposure is minimal. Go to any gliderport and look at any 10 year old or older
gel coat finished airplane, particuarly around the tail wheel, corners of the
canopy and edges of the gear doors and you will see what I'm talking about. I
have yet to see one that doesn't have cracks and I see lots of gliders being
that we run a gliderport here in Tennessee. You won't notice the yellowing
unless you put it beside a new airplane, but when you do it's obvious.
And, you're right. Gel coat is 30+ year old technology. 30+ year old
technology that has been surpassed by a better product.
Regards,
John Lawton
Dunlap, TN
A-245
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