Polyester on top of epoxy

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hmm

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Hi, I have a small repair job to do on a very cheap and nasty boat (most of my boats are!)

Started off with Epoxy.

Run out

Skin flint and miser.

Lots of polyester resin, so I want to use this.

Do I have to wipe over the epoxy with acetone (whatever that is - nail varnish remover? - I haven't got any - got meths, white spirit - brake cleaner) and then apply the poly?

Or can I just slap the poly on? I did the epoxy Sat night - want to finish job Sunday Morn.

Thanks.
 
You mean te poly won't adhere to the epoxy?

I laid some over it on a test zone - will wait til morning to check.

Or do you mean poly wont stick to the original boat substrate?

As a mate of mine says - boats are made of poly - why not repair with poly - I told him, epoxy is stronger, stickier, more flexible - he says tosh
 
Polyester does not stick to a smooth epoxy finish. If the epoxy is roughed up, you can get a mechanical bond, but this is not as good as a chemical bond. However if you leave epoxy until it is fully cured - the time depends on temperature-, then you are still depending on a mechanical bond, where you have to rough up the surface, and there are plenty of boats built like this. What ever you do, it is also necessary to remove the waxy finish called the epoxy bloom from the old surface, probably with detergent and water, before any treatment.
I have to say that I would prefer use epoxy.
It is so forgiving compared to polyester.
 
Scrub it with soap and water then sand it ,the polyester will stick like $h-t-----to a blanket.
 
That's interesting. I used to work with fibreglass cars and we made some of the moulds out of epoxy. Our experience was that polyester would never stick satisfactorily to cured epoxy. Abrading it would make things a bit better but sooner or later it would always come off again leaving the epoxy pretty much intact.
 
............so again I say "I'd rather have a repair that sticks. "

It's a no brainer. If you laid epoxy on already, you've got to carry on with it.
 
G'day Hmm,

Standard wax / poly resins will stick to epoxy but I would not rely on it if it's structural. Epoxy can be made more ridged or flexible than standard poly resin layups so will want to delaminate.

Before you do anything to the existing epoxy coat it must be cleaned, you don't need any harmful chemicals, just a running hose and a plastic kitchen scourer, Scotchbrite will do; start at the top or high spot and work down, rub till the water no longer forms beads.

If you must apply poly resin over an epoxy the only bonding will be mechanical not chemical, so use a 40 or 60 grit to get a good key.

Also note: Poly resins do not stick to raw timber for long periods, so if you must apply poly to timber make sure the timber is only used to form the shape of a rib, never apply poly to a sheet of raw ply. Epoxy will do a far better job and last many years.


Personally I would never apply poly over epoxy if I could avoid it.

Avagoodweekend......
 
It would have been much better if you had filled with polyester and then given an epoxy coat to finish !!

Epoxy - then Polyester is not advised ... it will fail eventually.
 
Once again I am relieved when my opinion is validated by Old Salt Oz.
Is there some other site where you -O S O - give life style advice, solve questions on the third world debt problem, and so on? I would be willing to pay for practical advice.
 
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G'day Hmm,

If you must apply poly resin over an epoxy the only bonding will be mechanical not chemical, so use a 40 or 60 grit to get a good key.



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Once the resin has gone off, any bonding of fresh resin will be mechanical whether its epoxy or poly. But the mechanical bond with epoxy will be much stronger.
 
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