Polyester resin curing

[TBarCYa]

I've read that gelcoat will not cure in the presence of air but what about polyester resin? Since gelcoat is polyester based I would think that they would behave the same but I really don't know. If I've already applied polyester resin but didn't cover it to prevent contact with the air, is there something that can be done to get it to cure? After a couple hours it was still tacky which I thought was because of the humidity but after what I've read, now I'm not sure.

Thanks.

 

[TBarCYa]

Re: Polyester resin curing

Okay, I found the answer... The resin I'm using (Evercoat Boatyard Resin) has wax and doesn't need catalyst or to be covered like gelcoat. Most likely cause of the slow cure is the high humidity here in the Northeast. Now for my next question...

I used this resin to repair some cracks and chips in my gelcoat and I'm planning to use anti-fouling paint on the bottom so do I need to cover the repair with gelcoat or can I sand it and prep for paint? My understanding is that gelcoat is cosmetic only so there would be no need to gelcoat before applying paint.

Thanks again.

 

[ondarvr]

Re: Polyester resin curing

Yes your resin does need catalyst, if you didn't add any/or enough you'll need to remove what you put on and start over.

If you didn't use any glass, and just painted resin on the surface to fill and cover the cracks, then you need to start over even if you did catalyze it. Resin has little or no strenght by itself, the glass is where you get the strength.

If you catalyzed it, ground out the cracks and used glass, then pay no attention to what I just said.

 

[TBarCYa]

Re: Polyester resin curing

For the most part, what I was covering are hairline spider cracks that I could easily have just painted over except in one area along the keel where the previous owner's repair had failed. The spider cracks were just painted over with thickened resin but the keel repair was done with thickened resin and glass then covered with just thickened resin to give me something I can sand smooth. Strength isn't as much of a concern smoothing over spider cracks as it is along the keel which is why I didn't use glass. Those cracks are barely wide enough to catch a fingernail in but I didn't want it to compromise the bottom paint.

Thanks.

 

[BillP]

Re: Polyester resin curing

If you didn't add catalyst to the poly resin it can stay soft for a long time. I have some that leaked out of a container in an obscure location under my workbench around 1985. I only wiped it up with a dry rag back then and the spot is STILL tacky. The house may be sold before I find out how long it takes to fully dry.

 

[TBarCYa]

Re: Polyester resin curing

I mixed it with hardener per the instructions on the container but apparently there is some sort of catalyst for non-waxed resins that rises to the surface and keeps air out of the resin while it cures.

 

[gcboat]

Re: Polyester resin curing

It's called amine blush - it is a waxy substance that rises to the top of most resins. It can be safely removed when all has cooked off. There are resins that do not produce this by-product but they are a little hard to find in the 'big box' stores. A competant glass shop should be able to get you what you need.

Read through this : http://www.epoxyproducts.com/blush4u.html

 

[BillP]

Re: Polyester resin curing

It isn't a catalyst but is a liquid wax. It used to be called "Modifer C" from our supplier and was added to laminating resin to make it have a dry surface instead of a tacky one. I don't know what they call it now but thats what causes the blush in polyester resin.

 

[ondarvr]

Re: Polyester resin curing

Polyesters don't blush, only some epoxies do.

There is no special catalyst for waxed or non waxed resin, but wax additive can be added at any time before use, you can buy it at most places that sell resin.

 

[TBarCYa]

Re: Polyester resin curing

Ok so if I had unwaxed resin then I would have to add the wax additive to get it to cure but since I have a waxed resin there is no need. Cool.

I checked on it this morning and it appears to be cured (hard and not tacky) so sometime this afternoon I'm off to sand it smooth before my first float since I tore up the drive last August. I can't wait!!

 

[BillP]

Re: Polyester resin curing

Polyesters don't blush, only some epoxies do.

There is no special catalyst for waxed or non waxed resin, but wax additive can be added at any time before use, you can buy it at most places that sell resin.

Respectfully, in a long ago previous life I worked glassing/sanding/finishing surfboards commercially. We added mod c (liquid wax) to laminating resin and it produced what looked like a blush on the surface...every time for 1000s of boards. It looked exactly like the blush on epoxy and had to be removed for anything to stick to it. We used it for a hot coat to fill the weave and give a high build resin layer for sanding. I never tried washing it off but don't think that would work with this stuff. But regardless of terminology, people need to know adding wax to laminating resin will result in wax on the surface and it has to be removed if you want to coat over it.

bp