Poly or Epoxy

[RobK1971]

Hi all,

How can I tell if a previous fiberglass repair was made using Poly or Epoxy resin? If I understand correctly, Epoxy sticks to Poly but not the other way around? Is this correct? This is why I ask, because the repair in question needs to be redone.

Thanks!

 

[erikgreen]

Re: Poly or Epoxy

Well, one way is that epoxy yellows when exposed to UV. Is the resin in question an amber yellow color or darker?

If not exposed to UV it can be tricky. It's much easier to ask whoever had the repair done what it is.

You can in fact make poly bond to epoxy, it's just that the bond is very weak without a tie coat, which is a special layer meant to help a polyester chemistry resin tie to an epoxy resin.

When it doubt, you could always use epoxy too. I take it you're avoiding it because of the price? If you buy from US Composites, it's cheaper by far than West Marine or similar.

Erik

 

[RobK1971]

Re: Poly or Epoxy

Thanks for the reply Erik. A bit of background on this: I have decided to restore a 16' flatback canoe that I picked up very cheap.

The transom is rotten but the overall condition of the canoe is quite good. I decided to give it a once over if for no other reason than to learn how to work with fiberglass and gelcoat.

I want to redo the gelcoat and have begun to sand the canoe. While sanding, I uncovered an old repair near the front. The canoe was once painted covering up the patch. It is very lumpy as it was never sanded out properly but somewhat smoothed out with white gelcoat.

Well, one way is that epoxy yellows when exposed to UV. Is the resin in question an amber yellow color or darker?

It's definately not yellow an not dark.

You can in fact make poly bond to epoxy, it's just that the bond is very weak without a tie coat, which is a special layer meant to help a polyester chemistry resin tie to an epoxy resin.

Interesting. What would you use for a tie coat? I assume it's a chemical on it's own?

...I take it you're avoiding it because of the price?

Erik

Being a canoe as I now mentioned, it's not a price issue. I guess I just rather keep everything the same, but that's probably just because it's my first attempt at this sort of thing and would just rather keep things straight forward.

 

[Bondo]

Re: Poly or Epoxy

I want to redo the gelcoat and have begun to sand the canoe.

Ayuh,... If your going to go through the ridiculous amount of Labor to regelcoat it,...
You've GOT to use poly resins...
Gelcoat is a poly resin,...

If you just Paint it instead,... You can use any resin you want...

 

[fish_on_the_deck]

Re: Poly or Epoxy

I've never done it myself, but have been told you can lay a rag soaked with styrine or other poly thinner on the spot... if it it becomes tacky after a couple hours that means the thinner is effecting it, and it is poly... if there is no effect... epoxy.

hopefully somone who has more experiance than me will back me up here.

 

[Yacht Dr.]

Re: Poly or Epoxy

Hi Rob and welcome to Iboats..

Over analizing things is a direct result of No pictures

If its a repair then it could be a red spot or ?? you only mentioned that its not yellow..or dark..

Its only a canoe

Is the whole thing "painted" or gelcoated ?

YD.

 

[RobK1971]

Re: Poly or Epoxy

Hi Rob and welcome to Iboats..
Over analizing things is a direct result of No pictures

Thank you! I agree, the lack of pics is absolutely unacceptable indeed I will get on that shortly!

If its a repair then it could be a red spot or ?? you only mentioned that its not yellow..or dark..

I will search through my pics. Hopefully I have a good one of the repair. It is reasonably small and has white gelcoat in it.

Its only a canoe

Exactly why I chose it as my first project. If I completely mess it up....well....as you say, "It's only a canoe" and not something bigger that I paid more $'s for. I knew that recoating it with gelcoat would be a pile of work but the size of this canoe, I can handle. I may never want to do it again after, but I figure it will give me a good feel for working with gelcoat.

Is the whole thing "painted" or gelcoated ?

YD.

It's been painted over the gelcoat. I assume to cover the patch.

I'll get to figuring how to post those pics now....

 

[jonesg]

Re: Poly or Epoxy

Hit it with a sander, you can smell the difference if you know what the different resins smell like.

 

[RobK1971]

Re: Poly or Epoxy

I'll try this again. Here is a pic of the transom before I removed the trim. Two pictures of the transom while being torn appart. The picture of the patch up front shows a high spot right in the middle. It doesn't look to be of any different color like yellow or anything else. The last pic is after three hours of sanding.

 

[Yacht Dr.]

Re: Poly or Epoxy

Prep with 80g.. mask and go with gel.

Its IMO very ez and forgiving.

You want to be a Dino.. good.. its so simple..but FAST m8.

Gel Is not Paint.. you mix and GO ! over coating isnt the problem..its gettin gel kicked off in your gun. But its not as hard as Paint.

Your going to sand it down to 600g or 1k then buff.

you will also have no worries after its done ( it can be fixed ez ) .

Gel IS best IMHO

Paint is a real PITA .. again IMO....

Gel is polishable primer LOL...you cant mess it up too much as long as you Know from the start ( same with paint though..but paint is one shot chancorama ) .

YD.

 

[RobK1971]

Re: Poly or Epoxy

Hit it with a sander, you can smell the difference if you know what the different resins smell like.

Not sure what the different resins smell like; at least not yet, but I do know what it smells like when I hit this fiberglass with the sander as opposed to just gelcoat. I have to say I prefer the smell of the stuff in it's uncured liquid form. I'll have to find something made of Epoxy and sand it down to learn it's smell Thanks for the tip Jonesg!

 

[RobK1971]

Re: Poly or Epoxy

Prep with 80g.. mask and go with gel.

Its IMO very ez and forgiving.

You want to be a Dino.. good.. its so simple..but FAST m8.

Gel Is not Paint.. you mix and GO ! over coating isnt the problem..its gettin gel kicked off in your gun. But its not as hard as Paint.

Your going to sand it down to 600g or 1k then buff.

you will also have no worries after its done ( it can be fixed ez ) .

Gel IS best IMHO

Paint is a real PITA .. again IMO....

Gel is polishable primer LOL...you cant mess it up too much as long as you Know from the start ( same with paint though..but paint is one shot chancorama ) .

YD.

Thanks for the advice Dr.! I will be going at it some more this weekend and hope to have it all sanded. Then I'll do the transom before coating the outside.