How to check if a repair has been made with polyester or epoxy resin.

[Concerto]

This will become a more frequent question over the coming years. With epoxy being recommended as it is stronger and has better adhesion than polyester, but how does a boat owner know what may have been used by a previous owner or repairer?

It seems the hardness of the epoxy is the first indicator,as it is more difficult to sand than polyester. However if fillers like micro balloons have been added, then this may not be the case. The smell of the dust is a better clue as a polyester will smell like a new glassfibre boat, where as epoxy is a totally different smell. The problem is that epoxy can bond to polyester, but polyester does not bond as well to epoxy.

Do you know of a better way to check out whether polyester or epoxy have been used for a repair?

 

[CAPTAIN FANTASTIC]

As you are suggesting, smell will be the easiest and good way to determine.

 

[Hacker]

I’ve just asked a colleague who is a FRP wizard. If you grind or scrape it then polyester smells sweet and epoxy smells more like burnt plastic. Other trick is if you can see the underlying grp. CSM (chopped strand mat) or combi mat aren’t used with epoxy as it doesn‘t melt the binder.

 

[dankilb]

Yup - immediate difference in the smell when sanded/machined.

Don’t forget that CSM is now available with epoxy appropriate binders, although it’s unlikely to be as widely/commercial used as it is/was with poly.

 

[geem]

Does it really matter? If you are doing further repairs wouldn't you be using epoxy anyway?

 

[Tradewinds]

Hot air gun - softening. Epoxy softens at a lower temperature.

Obviously you need to be careful and do a small an area as possible.

Agree with Geem - If you are using epoxy for the repair I don't really see that it matters if it's polyester or epoxy. If you're using polyester resin for the repair then it's handy to know.

 

[Concerto]

I am not doing any repairs, but raised the matter for those less informed.