Is there a difference?
It's to use as a bonding agent.
epoxy is much stronger, but its nasty stuff if you get it on your skin, so wear PPE. It also stinks.
As to which is best, it depends on the application its being used in
If you think epoxy stinks, you haven't smelled polyester. epoxy is the low odour alternative.
epoxy is generally thought of as better. I believe it is less brittle. It costs more and smells less. It is more sensitive to mixing the right
quantities as the two parts react with each other to form the polymer.
polyester is fully mixed bar the catalyst. 2 - 3 % is needed to cure but it is not too sensitive. slightly less than 2% catalyst but will mixed will
probably still cure but more slowly. a bit over 3% might cure too quick;y but will still go off. It can be bought almost anywhere (Halfords etc).
quote:
Originally posted by balideyIt also stinks.
As balidey says, keep epoxy off your skin. It may not affect you, or may not for a very long time, or you might get a reaction almost immediately.
Once you're sensitised to it, you may be unable to touch anything made from, or containing, epoxy resin ever again (even hardened stuff).
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Eeek... think I'll be doing this with a pair of welding gloves and a wet suit on!
unless youre laying up CSM bound with emulsion, or youre only interested in cost, use epoxy
as said tho, with BOTH of them wear gloves and a boilersuit, dont get it in your eyes, avoid breathing fumes as much as possible and have a hot shower
afterwards. (especially if you are/have been grinding)
Epoxy is bad for your skin (free radicals and all that) but it isn't based upon volatile solvents.
Polyester meanwhile gives off tons of fumes and (unless you've got good ventilation) will quickly gas you (or at the very least give you a
stonking headache and severely drop your sperm count for a few weeks!!)...
Polyester isn't very strong structurally compared to epoxy (e.g. if you get two laminates of same thickness but one is epoxy and one polyester
it's possible to tell which is which)...
Epoxy is expensive. Polyester is cheap.
From a bonding point of view it also depends what you're bonding to what... some things are more compatible with one than the other...
quote:
Originally posted by alistairolsen
unless youre laying up CSM bound with emulsion, or youre only interested in cost, use epoxy
as said tho, with BOTH of them wear gloves and a boilersuit, dont get it in your eyes, avoid breathing fumes as much as possible and have a hot shower afterwards. (especially if you are/have been grinding)
Depends what you're bonding....
It's NOT a good idea to use polyester as a bonding agent. Why? Well, when it cures there's a few% shrinkage in volume. This will pre-stress
the bond. To some extent, it's this loss in volume that makes getting your finished article out of a plug less trouble than it would otherwise
be.
Bonding to wood, or general bonding to substrates with polyester can be helped with a polyurethane primer, try 'G4'
Back to epoxy, great as a bonding agent, final characteristics (brittleness, etc.) depend on amount of cross-lnking. Yep, the amines will sensitise
your skin, but let's be a little rational on the exposure you're actually going to get? Styrene (polyester) isn't exactly the best
thing to breath or contact for heavy periods either...
Epoxy isn't too good with UV exposure, doesn't do too well when wet all the time.
If you're bonding (panels, what?) how about a PU product (Sikaflex) or somesuch.
Anyway, ignore all this, I'm a Chemist. Go play.
It's a fixed wing (spoiler). It's GRP and is quite large / heavy. It will have quite a lot of pressure on it.
From my limited experiences with both, use EPOXY for the reasons above. No headaches. That was enough for me.
quote:
Originally posted by motorcycle_mayhem
Epoxy doesn't do too well when wet all the time.
If you're bonding (panels, what?) how about a PU product (Sikaflex) or somesuch.
Anyway, ignore all this, I'm a Chemist. Go play.
I would look at something like Sikalfex. They have some very good products for structural bonding of GRP. Where I used to work, it was used to stick
the two halves of a boat together, so it really is strong stuff.
Alternatively, depending upon the exact application, you could bond the pieces togther (PU or similar), then layup more CSM over the bond. Again, this
works wonders. We used to pick up an entire hull, on nothing more than carborad tubes with a few layers of CSM/polyester over the top.
quote:
Originally posted by alistairolsen
not arguing, just curious, we use epoxy paints to protect conventional polyester grp from osmosis (water ingress beneath the gelcoat) and the resin in many cases as a finished surface for yacht hulls....
quote:
Originally posted by twybrow
quote:
Originally posted by alistairolsen
not arguing, just curious, we use epoxy paints to protect conventional polyester grp from osmosis (water ingress beneath the gelcoat) and the resin in many cases as a finished surface for yacht hulls....
Why not just use isophthalic resins/gelcoats instead?