Are both suitable for board repairs with fibreglass?
Or one is better then another ?
I discovered recently that stuff I bought from Bunnings and used for crack and dent repairs on my boards was polyester not the epoxy as usual ...
Is that means that repairs done most likely to crack or drop off or should last as well ?
What I found by surprise only the that 'new' resin was effecting filler in the board and was melting polistyrene foam !!
Both are OK with fibreglass, epoxy is better with carbon.
Only epoxy with styrene foam!!!!
Also if they haven't completely cured it's not good to mix them, one stops the other from setting. (not sure which way round)
Polyester is harder but more brittle, epoxy is a bit softer but much tougher.
Does anyone here work at Bunnings and can send out a staff circular?
So the staff know that when somebody wants to repair a windsurf board, or SUP, or new school surfboard like NSP etc, don't just hand the customer a "fibreglass repair kit" ?
I love going in there (not) and asking for commonly used stuff that I know will confound them.
I asked if they sold vernier calipers and the 5 or so staff members on duty looked like they were going to implode with confusion as I explained what it looks like/does. 
Anyway off the soapbox now - Macro u can use epoxy on fibreglass surfboards no probs but the finished resin can be a bit more yellow so you need a clear hardender and not too much thickness (liek 2 layers glass).
But as you found out, you can not use polyester resin on styro core boards.
What decrepit said, also to add on, don't use rapid set epoxy in larger quantities on polyester/vinleyester resin surfaces, it heats up more than enough to re-soften the polyester, i discovered this the hard way 
^^^ nup. FIVE of them had no idea
Go in and ask for speedfile sheets, epoxy resin, or geez even a M6x40 socket head capscrew and they look like they will cry.
I don't know why but when I'm at bunnings people ask me for advice. Mark at a guess i would have to say your a fitter as i believe there the only people who actually call them socket headed cap screws like they are
I went in recently looking for some metal sheathed washing machine hose to stop my pipes banging.
I asked the guy where it was, he said "That won't stop the banging". I said "I know it will, as the banging stops when I turn the tap off at the wall". He flat out refused to tell me where it was, as he thought it wouldn't solve the problem.
So I eventually found what I was after, installed it, and bingo no more pipe banging.
I still give him the evil eye whenever I see him [}:)]
Hey can we start on Dick Smith now?
They could not sell me wire. Garden variety copper wire to solder onto a battery.
Used to have resistors, caps, diodes etc all loose, kilometres of wire in all gauges.
Now just gadgets and clueless sales assistants.
Yeah,I know,
back in my day when you went to a service station they ran out and filled it up for you.
Now the lazy mongrels just sit behind the cash registers.I mean ,its called a SERVICE station for a reason,,but now days you dont get any service.
I think I might write a letter to the government.
Oh stop ya whinging old boys.lol
Bunnings sell things cheap by paying 18 year olds , that have no building experience , next to nothing.
If they paid $60 an hour ,then they would get older experienced tradies that know a bit.
but then your rivits would cost $5 each.
As for Dick Smiths not selling resistors, caps, diodes etc,
they werent making money out of them anymore as most electronic stuff these days is not repairable, throw away, or all those bits are all inside one little chip the size of your thumb instead of a large circuit board.
I use to rewind pool pump motors for work, but its now cheaper to go buy a new one.
Such is life.
polyester wont stick to epoxy, it will peel of eventually, but epoxy will stick to polyester, to be safe use epoxy
If you go to the bunnings section where they have araldite, they will actually have Polyester resin AND epoxy resin AND a good range of epoxy glues and fillers.
They even sell some 2"glass tape that would suit the epoxy resin.
its all sold in horrendously small quantities and subsequently expensive prices, but they do have it.
try asking the stock fillerrs that are always wandering around ,rather than the regular assistants
its unlikely they can give advice on what to use on what though, i wouldnt give that kind of advice for that payrate 
