Polyester Resin Properties?

[Dougal]

Anyone ever found a way to maximize the shelf life of either opened or unopened Polyester resin and MEKP? Also, which in your opinion, is worse for going off - the resin or the MEKP?

I mostly use epoxy resins for most small jobs and repairs, even if using CSM and cloth, so that's not usually such an issue. Sometimes though, its just easier, more sensible or more applicable to use poly resins, but having to buy yet another Kilo, as the last lot has perished (yet again), after using just a little from the can, is sooooooo frustrating.

Even unopened, the shelf life can be pretty short, and some suppliers are a little reluctant to tell us that without being pressed. Some retailers don't even appear to understand the problem.

 

[TQA]

My current boat came with some West System epoxy slow and extra slow hardener . It behaved normally and cured hard when at least 5 years old and stored at ambient temp in the tropics.

The hardener had gone from clear to dark brown translucent colour but worked fine.

 

[Lon nan Gruagach]

No sympathy!!
You know all the data sheets and specifications... All the bit with "West Systems" vs cheap stuff.
If you throw all their time, effort an lab testing out the window, then why bother.?
Buy smaller batches and throw it away when out of date.

Just how far off the recommended mix ratio are you prepared to go? Personally I am sick an tired of "it has to be precise"..,. Nothing, but nothing this world is precise, proper engineering has tolerances!

But, for the sake of something you can know exactly, as in the use by date, stick to it or just be guessing how strong your fix is.

 

[Dougal]

Put your rattle away sir. The word i used was "polyester".
Have no probs with Epoxy as I believe i stated?
And i dont believe i actually asked for "sympathy" ;-)

 

[Lon nan Gruagach]

Put your rattle away sir. The word i used was "polyester".
Have no probs with Epoxy as I believe i stated?
And i dont believe i actually asked for "sympathy" ;-)

Your funeral. Epoxy, polyester, cement, whatever. These chemicals are engineered and tested to specifications such that if you wanted to know for sure that your fix will work. Just because the tin is sealed does not mean that the contents are stable.

Sympathy? dont bleat about having to throw away excess that you bought knowing full well that the is a time limit on its efficacy.

 

[Graham376]

Anyone ever found a way to maximize the shelf life of either opened or unopened Polyester resin and MEKP? Also, which in your opinion, is worse for going off - the resin or the MEKP?

Keeping polyester in the fridge will extend it's life but SWMBO may shorten yours.

 

[lw395]

For a bit of filler or bodging the tender, I've got away with using any polyester that still pours.
For anything that matters, I buy new. It's cheap and readily available.
I've not noticed old MEKP failing to work.

I have colour-matched bits of gelcoat. I think once I've mixed a batch, its life stored in a glass jar with lots of air space is short. Maybe the air gets to it during mixing and stirring? It lasts about a month or two, not six?
I've bought colour matched gelcoat from various places, the stuff in tins (like small paint tins) has lasted better than that in plastic pots. But for filling scratches on the bottom of my dinghy, I'd expect the stuff I bought last winter to be OK.

I keep resin in the workshop, which is never that cold, neither is it ever very hot.

 

[Dougal]

Thanks for the more sensible replies guys That exactly the kind of info I was after. We're often offshore, or at least a long way from anywhere to purchase new stock, so maximising the life of all my onboard supplies is extremely important.

 

[Birdseye]

Keeping polyester in the fridge will extend it's life but SWMBO may shorten yours.

Better still, stick it in the freezer. Thats what I do and I have not noticed any issue at all using the resin afterwards having allowed it to warm up first. Had some resin in the freezer for at least 5 years so far.

 

[Motor_Sailor]

Polyester resin has all the reactive parts already mixed when you buy it.
It only needs a tiny bit of catalyst to get those parts to react together at a reasonable speed to be handy. More catalyst, more speed.
But they are already reacting when you buy it, if very, very slowly. But like all reactions, it doubles in speed every 10 degrees you raise the temperature.
Hence limits on it's shelf life and the benefits of keeping it cold / frozen.

With epoxy, the two parts it needs for reaction are in the two separate containers. They have a very long shelf life and this is direct from the West Epoxy's own horses mouth: 'if it cures, it is as good as the day you bought it. There is no loss of strength - hard epoxy is hard epoxy whatever it's age".
But the hardener will go brown and the resin can solidify, but warming it up will return it to liquid, again with no loss of performance.

 

[Mistroma]

For a bit of filler or bodging the tender, I've got away with using any polyester that still pours.
For anything that matters, I buy new. It's cheap and readily available.
I've not noticed old MEKP failing to work.

I have colour-matched bits of gelcoat. I think once I've mixed a batch, its life stored in a glass jar with lots of air space is short. Maybe the air gets to it during mixing and stirring? It lasts about a month or two, not six?
I've bought colour matched gelcoat from various places, the stuff in tins (like small paint tins) has lasted better than that in plastic pots. But for filling scratches on the bottom of my dinghy, I'd expect the stuff I bought last winter to be OK.

I keep resin in the workshop, which is never that cold, neither is it ever very hot.

Ditto, though mine is probably 10-15 years old . Catalyst obviously goes off pretty quickly but I have used quite old catalyst when I couldn't get hold of new stuff easily (middle of nowhere at the time). I keep it in a locker below the waterline, the container is rarely opened, well sealed and wrapped in polythene with a silica gel pack. I guess that this keeps much of the moisture away and extends storage life.

I used it a couple of years ago to bond in a backing pad for an anode and it still looks fine. A small test went well and didn't show any problems. I needed a tiny amount last year and was mildly surprised to find it was still OK when tested.

I'd buy new if planning to do big job but stuff I have on board has been fine. I have things to plug leaks when afloat and only run into the odd GRP job during the season, not worth buying some new stuff and leaving 95% of that lying around for another 10 years.

 

[Birdseye]

dinner now finished.

As Motor Sailor says, epoxy is a different matter. The resin seems to store at room temperature for years without problem. The catalyst is a different matter - it degrades starting to smell stronlgly of ammonia and turning yellow. I have used it in that state for not critical repairs like to a fridge drawer but I am unsure how well the catalysed resin using old yellow catalyst would work in a high strength application. And personally, when I want high strength I always use epoxy.

So keep the resin but buy new catalyst after a couple of years

 

[Motor_Sailor]

. . . but I am unsure how well the catalysed resin using old yellow catalyst would work in a high strength application. . . .

Well, it's worth repeating what I was told by one of the West Epoxy guys in the States- "if it cures, the result will be as strong as it was intended" .
The hardener can go deep brown and still work. You will know when epoxy hasn't cured to it's full strength because it will be a soft sticky, uncured mess, but if it's gone hard, it is at full strength.

I have used and tested West Epoxy for over 30 years in the tropical heat in Florida and the cold of the UK, and I don't think I have ever had some not work, however old it is.
You can't be sloppy with your technique when it comes to mixing and its application, but as to its shelf life, it does seem to be quite stable.