Polyester resin on 2 part epoxy

[Marcq]

Hi guys, , sorry for not posting more often, so far my questions has been answered using the search option.

I just finish(almost)fixing my 27gal ALU fuel tank by patching all the pin holes on it and recovering the tank with fiberglass mat and two part epoxy, one coat so far. But man that stuff is expensive. Can I do a second coat with polyester resin instead ?
Thanks, Marc..

 

[gcboat]

Re: Polyester resin on 2 part epoxy

Yes you can - just can't do it the other way around. Prep good, wipe clean with some acetone ( not saturated ) and apply your second coat.
Here's a nice guide : http://www.epoxy.com/install.htm

 

[Marcq]

Re: Polyester resin on 2 part epoxy

Thanks, just what I wanted to hear
Oh, and thanks for the link

Marc..

 

[gcboat]

Re: Polyester resin on 2 part epoxy

If you really get bored you can read through this link: http://en.wikipedia.org/wiki/Epoxy

 

[Mark42]

Re: Polyester resin on 2 part epoxy

Everything I have read on this forum indicates that epoxy sticks to poly, but poly does not stick to epoxy. I have read of people getting poly to stick to epoxy, but it requires roughing up the epoxy extensivelly to give the poly something to stick to.

With your situation dealing with a critical application (leaking gas tank) I would stay with epoxy. You probably wouldn't want to have to do it over if the poly came off.

When reading about gel coat finishes, all the info I found said not to apply gel coat (polyester/vinlyester based) to epoxy. There are special epoxy gel finishes available.

So I suggest you do some more research before using polyester over epoxy, just to be sure.

Good luck! And how about some pics of your work? We love pics here!

 

[Boomyal]

Re: Polyester resin on 2 part epoxy

Everything I have read on this forum indicates that epoxy sticks to poly, but poly does not stick to epoxy. I have read of people getting poly to stick to epoxy, but it requires roughing up the epoxy extensivelly to give the poly something to stick to.

With your situation dealing with a critical application (leaking gas tank) I would stay with epoxy. You probably wouldn't want to have to do it over if the poly came off.

When reading about gel coat finishes, all the info I found said not to apply gel coat (polyester/vinlyester based) to epoxy. There are special epoxy gel finishes available.

So I suggest you do some more research before using polyester over epoxy, just to be sure.

Good luck! And how about some pics of your work? We love pics here!

Ditto here. Maybe ondarvr will chime in here as well.

 

[Marcq]

Re: Polyester resin on 2 part epoxy

Damn, too late hope it will be alright. I knew there was some epoxy that won't accept polyester on top of them, that's why I asked. Guess I'll have to wait and see, I did rough up the surface good

Marc..

 

[ondarvr]

Re: Polyester resin on 2 part epoxy

Unless you did everything correctly it will almost just fall off, if you did do everything right, then it will stay in place until it gets stressed, then it will come off. When it gets hard see if you can pull it off, if it does peel off, then re-do it with epoxy. I wouldn't trust it on fuel tank though.

 

[gcboat]

Re: Polyester resin on 2 part epoxy

ondarvr - does this have any creedence at all : There are two main areas of marine use. Because of the higher mechanical properties relative to the more common polyester resins, epoxies are used for commercial manufacture of components where a high strength/weight ratio is required. The second area is that their strength, gap filling properties and excellent adhesion to many materials including timber have created a boom in amateur building projects including aircraft and boats.

Normal gel coats formulated for use with polyester resins and polyester resins won't adhere to epoxy surfaces, though epoxy adheres very well if applied to polyester resin surfaces. "Flocoat" that is normally used to coat the interior of polyester fibreglass yachts is also compatible with epoxies.

Polyester thermosets typically use a ratio of at least 10:1 of resin to hardener (or "catalyst"), while epoxy materials typically use a lower ratio of from 5:1 down to 1:1. Epoxy materials tend to harden somewhat more gradually, while polyester materials tend to harden

Hopefully I didn't steer Marcq off course too far. Oh, that little diddy came from Wikipedia.
O.K. marcq - if your project doesn't work out send me a PM and I'll gladly send you some epoxy resin for your trouble. It was definately my bad !!!

 

[BillP]

Re: Polyester resin on 2 part epoxy

There may be exceptions but every polyester resin mfg out there says NOT to use poly over epoxy. The only company that says it's ok to do polyester over epoxy is the WEST epoxy people...and they base their opinion only on one sampling. They also advise against using pressure treated wood...which goes against 20+ yrs of a well documented (and untarnished) history of pt use in the boating industry. My opinion is don't do poly over epoxy.

bp

 

[ondarvr]

Re: Polyester resin on 2 part epoxy

He said he used epoxy for the first coat, then he used polyester for the second layer. Polyester doesn't bond that well to epoxy, so the second layer could have problems. Even when the epoxy surface is prepared very well, the bond is poor, so if it was just done normally, as if he was bonding polyester to polyester, it will most likely fall off.

Polyesters use 1% to 2% MEKP to cure, not sure where they got the 10:1 ratio.

 

[Marcq]

Re: Polyester resin on 2 part epoxy

ondarvr - does this have any creedence at all : There are two main areas of marine use. Because of the higher mechanical properties relative to the more common polyester resins, epoxies are used for commercial manufacture of components where a high strength/weight ratio is required. The second area is that their strength, gap filling properties and excellent adhesion to many materials including timber have created a boom in amateur building projects including aircraft and boats.

Normal gel coats formulated for use with polyester resins and polyester resins won't adhere to epoxy surfaces, though epoxy adheres very well if applied to polyester resin surfaces. "Flocoat" that is normally used to coat the interior of polyester fibreglass yachts is also compatible with epoxies.

Polyester thermosets typically use a ratio of at least 10:1 of resin to hardener (or "catalyst"), while epoxy materials typically use a lower ratio of from 5:1 down to 1:1. Epoxy materials tend to harden somewhat more gradually, while polyester materials tend to harden

Hopefully I didn't steer Marcq off course too far. Oh, that little diddy came from Wikipedia.
O.K. marcq - if your project doesn't work out send me a PM and I'll gladly send you some epoxy resin for your trouble. It was definately my bad !!!

No worries man, it is only a temp fix until I find a used plastic tank with the same dimension or close 56''x20''x6'', if you see one let me know

Anyways, thanks guys, I'm learning stuff every day

Marc..