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Resin type

NYTOM

Well Known Member
Would anyone know the type of resin compatible with the green cowls as opposed to the older pink models. Polyester, vinyl ester or epoxy ? :confused:
 
Use Epoxy

My understanding is that you can use epoxy resin with polyester parts, but not polyester resin with epoxy parts. I could be wrong about that, but my friend, who's a fiberglass guru, told me to use an epoxy based system, so I did. I've used the West Systems epoxy resin for all my fiberglass work so far. If you get the slow hardener (but not the super slow), it has a great working time.
 
My understanding is that you can use epoxy resin with polyester parts, but not polyester resin with epoxy parts. I could be wrong about that, but my friend, who's a fiberglass guru, told me to use an epoxy based system, so I did. I've used the West Systems epoxy resin for all my fiberglass work so far. If you get the slow hardener (but not the super slow), it has a great working time.

+1

Polyester resin layups over epoxy is a no no. Adhesion is poor. However, polyester fillers will adhere just fine to fully cured epoxy layups.

Larry
 
..Alchemy?
Apparently . .
West testing.

West: "Because of the difference in curing chemistry, it is not possible to achieve a chemical bond between epoxy and polyester gelcoat."

They go on to say the adhesion is mechanical. The final conclusion is that the bonding is fine for gelcoat (I assume not as a structural bond).

Pretty much covers polyester fillers too.
 
..Alchemy?

Not sure I understand your meaning by that.

A decent amount of research taught me that polyester resin (as in peroxide activated for layups) does not adhere that well to epoxy, though it adheres well to cured polyester.

Not saying that it will fall off, but does not create the bond level expected for a layup andt is considered a bad practice by those in that business.

I am admittedly not a "fiberglass guy" just passing along learnings.

Larry
 
Apparently . .
West testing.

West: "Because of the difference in curing chemistry, it is not possible to achieve a chemical bond between epoxy and polyester gelcoat."

They go on to say the adhesion is mechanical. The final conclusion is that the bonding is fine for gelcoat (I assume not as a structural bond).

Pretty much covers polyester fillers too.

This relates to epoxies ability to bond to polyester which isn't really relevant to polyesters ability to bond with epoxy. The cured epoxy or gel coat on the OP's cowl has reached a full cured state and therefore cannot chemically bond with anything (epoxies can only chemically bond prior to reaching a full cured state). Epoxy is known to have a much stronger mechanical bond than polyester resin. Epoxy is much more flexible in what it will form a relatively strong mechanical bond with. This is one of it's main advantages. Polyester is not as flexible in this regard and doesn't grip very strong, mechanically, as epoxy even in its most favorable environment.

If I remember correctly, polyesters chemical bonding window never closes, which is why polyesters resins can be so successfully applied over cured polyester; In this case, it is not rely upon it's poor mechanical adhesion, but forming a strong chemical bond. As West mentions, polyester cannot even chemically bond with epoxy, even if the epoxies window was open, due to different chhemistries.

Larry
 
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Not sure I understand your meaning by that.

I am merely amused with the notion that polyester resin is bad, but polyester filler is good. Must be some alchemy taking place when fillers are added to resin.
 
If I remember correctly, polyesters chemical bonding window never closes, which is why polyesters resins can be so successfully applied over cured polyester; In this case, it is not rely upon it's poor mechanical adhesion, but forming a strong chemical bond. As West mentions, polyester cannot even chemically bond with epoxy, even if the epoxies window was open, due to different chhemistries.

Larry

Isn't that true for laminating resins/gelcoats only? Once you add the wax or apply PVA the polyester fully cures and has to be sanded for further coats.
 
This relates to epoxies ability to bond to polyester which isn't really relevant to polyesters ability to bond with epoxy. The cured epoxy or gel coat on the OP's cowl has reached a full cured state and therefore cannot chemically bond with anything (epoxies can only chemically bond prior to reaching a full cured state). Epoxy is known to have a much stronger mechanical bond than polyester resin. Epoxy is much more flexible in what it will form a relatively strong mechanical bond with. This is one of it's main advantages. Polyester is not as flexible in this regard and doesn't grip very strong, mechanically, as epoxy even in its most favorable environment.

If I remember correctly, polyesters chemical bonding window never closes, which is why polyesters resins can be so successfully applied over cured polyester; In this case, it is not rely upon it's poor mechanical adhesion, but forming a strong chemical bond. As West mentions, polyester cannot even chemically bond with epoxy, even if the epoxies window was open, due to different chhemistries.

Larry

Larry my friend, read the report. :) The basis was West reporting on an epoxy repair over a polyester boat material, FOLLOWED by a polyester gel coat covering over the epoxy under the water line. The testing showed even the mechanical bond of polyester-over-epoxy was adequate for a coating. Just like your comment of body filler - Bondo, exactly what we were discussing.

Regardless of this specific report, a structural repair should be researched carefully and polyester-over-epoxy structural repairs would seem to be lacking.
 
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