Polyester vs Epoxy Resin?

Tim Good

Tim Good

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I'm setting sail south and want to stock up with some resin. Unless I stand correct am I right in saying that Epoxy resin is stronger but the downsides are:

- more expensive
- won't set correctly below 15c
- more hardener required / different to the catalyst for gelcoat and polyester resin.

If I was to hold one or the other on board for general purposes Repairs and, mouldings which would you choose?
 
northcave said:
1. - more expensive
2. - won't set correctly below 15c
3. - more hardener required / different to the catalyst for gelcoat and polyester resin.

4. If I was to hold one or the other on board for general purposes Repairs and, mouldings which would you choose?
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1. Yes
2. not necessarily: depends on the epoxy, of which there are thousands. Seek advice from a specialist supplier for low-temperature varieties. If you're heading to cold places, a directable heat source (hairdryer, electric paint-stripper etc) may be invaluable. (The latter are handy for heat-shrink, anyway.)
3. You answered your own question. Hardener is not catalyst.
4. Epoxy, but in various forms, including mouldable epoxy 'stick'.
 
I would have both as they have different properties and applications. Your assessment of epoxy is a bit wide of the mark. There are many different kinds of epoxy with different ratios of hardner, different curing times and temperature tolerance. For general purpose use one that has a 2:1 ratio is easier to mix and more tolerant of variations in ratio. You can usually get a slow and fast hardener for the same basic resin.

A visit to the Wessex resins website (West epoxies) is well worth it for explanations of using epoxy in different situations. although they obviously refer to West, the principles apply to other brands as well. I tend to use Blue Gee because they used to be based about a mile from where I live, but have used West extensively in the past.
 
Two different animals.. Polyester uses a bit of catalyst to get it going. More or less than the 2% changes the set off time related to the ambient temp, but it will go off.
Epoxy needs to get the mix exactly right. Wander off and it weakens. If it says 2:1 or 5:1, get it right. I use a scale that is good to 1 gm.
 
I agree with everything that has been said. Don't use epoxy resin with chopped strand mat (CSM) as epoxy won't break down the binder. I'll be taking a lightweight woven roving (glass cloth bends around corners easily)
When I set sail I'll be taking some epoxy resin and some talc to mix with it to make a glue. (If I thought the temperature was low I've use my wife's hair dryer to warm up the resin.)
Polyester won't stick to epoxy but epoxy will stick to polyester (roughen it up first to provide a "key" and to get rid of any wax)
Good luck
 
Over several years of long distance cruising we have never carried polyester. Epoxy will do everything polyester will do but not the other way around. Fast curing epoxy sticks are worth keeping onboard. A pal of mine stuck his boat on a reef. He used the sticks he had onboard for 15 years to do a temporary repair that kept the water out! We now carry a couple of sticks.
 
saab96 said:
I know from experience that you can buy both in France, Spain, Portugal and Trinidad. Of course it is worth carrying some for when you need it but it does go off so think of buying when you want it down "south". Enjoy going "south". The sailing gets so much better down there.
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Well technically we're heading "south" to end up in the "far south". For some reason we subscribe to the olde "attitude get better with latitude".
 
I've used epoxy with no trouble 12 months after I have bought it and had no trouble but on an extended cruise....? The supplier of polyester said as long as it is "runny" it can be used: no problem. But it does thicken up with time (12 months?)
 
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I keep some polyester resin, chopped strand mat and gelcoat onbaord. But i also have the epoxy putty sticks mentioned previously and some quick drying epoxy, same as Araldite but about £2.50 from Toolstation. All serve different purposes.
 
Gelcoat, or even just the correct pigment, can be worth carrying.
Other than that, araldite is always handy, but things like mat, you're probably better off sourcing from a dry shop than a damp boat.
 
lw395 said:
Gelcoat, or even just the correct pigment, can be worth carrying.
Other than that, araldite is always handy, but things like mat, you're probably better off sourcing from a dry shop than a damp boat.
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Plenty of ways to store things on a boat without having to worry about damp.
 
geem said:
Over several years of long distance cruising we have never carried polyester. Epoxy will do everything polyester will do but not the other way around. Fast curing epoxy sticks are worth keeping onboard. A pal of mine stuck his boat on a reef. He used the sticks he had onboard for 15 years to do a temporary repair that kept the water out! We now carry a couple of sticks.
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All very true. If you want a bit of polyester gelcoat for cosmetic repairs, I would take that. But if you're thinking about having something in hand for structural repairs then epoxy all the way, with some biax, finer cloth, colloidal silica and filleting blend. Add to that some form of mixing measures (volume or weight) and pots.

And don't worry about the longevity of stored epoxy. If the resin goes solid, warm it in a bucket of boiling water. If the hardener goes gunky brown, don't worry it still works a treat. West Epoxy say that if you mix a small batch and it cures then everything is working fine - there's no half measure of 'not working as well' etc.
 
Just take both. Use the epoxy for the important structural/strong stuff, the polyester for the less critical/cosmetic/temporary stuff. Also a selection of filler powders, box of gloves, box of doctors "tongue depressors" and big syringes for mixing. Take some cloth, although take 2x2 "twill" weave for it's ability to go into internal corners etc.
 
I tend to make stuff using polyester and fix stuff with epoxy.

Epoxy is a sophisticated glue whilst polyester is not good at sticking stuff together.
Laminating with polyester is cheap, forgiving and fast whilst epoxy laminating is expensive, trickier and slow.

If you want to keep your pride and joy looking good, get a 1ltr tin of colour matched gelcoat for scrapes and grazes.
 
Motor_Sailor said:
All very true. If you want a bit of polyester gelcoat for cosmetic repairs, I would take that. But if you're thinking about having something in hand for structural repairs then epoxy all the way, with some biax, finer cloth, colloidal silica and filleting blend. Add to that some form of mixing measures (volume or weight) and pots.

And don't worry about the longevity of stored epoxy. If the resin goes solid, warm it in a bucket of boiling water. If the hardener goes gunky brown, don't worry it still works a treat. West Epoxy say that if you mix a small batch and it cures then everything is working fine - there's no half measure of 'not working as well' etc.
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We carry 7oz cloth which is very light and some heavier cloth. The 7oz cloth will always bend around things and is easy to wet out. If you want it strong then lots of light cloth gives you strength so if you dont want to carry lots of different weight cloth take the lighter stuff cos it will do everything. We carry coloidal silica and micro baloons as thickening agents depending on the job. We dont have gelcoat as we are Awlgrip. We have some digital kitchen scales to measure the 1:1 and 2:1 epoxy out accurately.
 
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