epoxy curing??

graham

graham

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Helped a mate today using epoxy resin and glass cloth to patch some holes left by redundant fittings in the hull.

The resin was bought from Robbins only this week.It was quite warm (15 or 16°) We mixed it accurately and stirred thoroughly. All the surfaces were ground back to clean glass first . Despite all this we still needed to use a heat gun to get it to go off.

Is this unusual?
 
Thanks for the quick response. We left it over 2 hrs ,still completely liquid.It was measured using the pumps on the containers .We did another test sample later double checking the ratio and this also needed heat.

I think it was West System but not 100% sure on that.
After a good bit of heat from the heat gun it then set quite quickly and is now solid as a rock so we arent too concerned.
 
Maybe that was the only problem then.Its solid now anyway so no real problems.Perhaps the hull itself was colder than the surrounding air.
 
Even in warm 20degree plus ambient temp epoxy can take a long time to set. I have typically found even during summer it has needed 24hrs before sanding and even then can be prone to clogging the paper.

Glad it set with heat. At least you have the finished the day without the worry.
 
Using a heat gun can actually be a bad thing, too much heat and the epoxy becomes liqued again.
This why you cant have epoxy boats in dark colours, they can breakdown , you can see this as print through from the glass layer on the paint finish.
 
epoxy will always clogg the sandpaper unless you scrub it first with a scothbrite or something similar. They cure with a waxy residue on the surface, and this is what clogs the paper.
 
Hi all, it was my boat that Graham was helping on (and very grateful I am too!). What surprised me was that it took more than just warming the epoxy, it took real heating! After the first job didn't go off I mixed another pot. That only started to set after I heated the cup until it started to scorch! Gently warming the mix had virtually no effect. It is West system and I used the mini pumps with the A kit. Once it started to go it went with a rush. When I left the boat tonight the temp' was 12 degrees. If I have to wait for it to go much higher it'll probably be august bank holiday.............

Is this one of those compounds where adding some part set mix can start a reaction in a fresh mix?
 
I think I saw you with the heat gun this afternoon! I use an SP Systems epoxy coating grade and that comes with slow and fast curing agent. The slower one can take two hours to solidfy. I assume this is a) to allow it be painted like a varnish, and b) to allow it's use in hotter climates (25C and above). So maybe there's nothing wrong here. What was the product number? Have a look on the West website and check the cure characteristics of the base / curing agent combination you used.
 
Don't know about West, but SP Systems have a fast and slow hardeners for some of their resins. Even using fast hardener, at 15 C you're at the bottom end of the allowable temperature range, and 2 hours is not really long enough to start noticeably curing. Slow hardener will be, um, slower.
Check the dispenser nozzles - if they've been sitting around on part-used containers for a week or so sometimes the nozzles can partially clog giving incomplete delivery - epoxy is very sensitive to the mix ratio.
 
My gut feeling is that you expected it to cure rather more quickly than it wanted to. 2hrs at 15 degrees is a big ask. I would suggest that gentle warming to about 30 degrees and much more patience (like overnight) would be in order. Having said this I am not familiar with the epoxies you have available for colder conditions. Certainly be wary of overheating the layup. Excessive heat is a way to remove (destroy) epoxy.
I would worry if temp was below 23 degrees or so. But then perhaps I am spoilt. olewill
 
Using 205 ( fast ) hardener the minimum cure to solid time at 20deg C is 6-8 hours, minimum useage temperature is a high 16 degrees.
Using 206 hardener its 9 - 12 hours and the minimum useage temperature is a high 16 degrees.
With 209 hardener the cure to hard time is 20 to 24 hours with minimum use at 21 degrees.

Time to maximum strength is 1 to 9 days!

Cooler than 20 degrees = longer cures and the curve is exponential get below the minimum use temp and it may not cure, ever!

Get it too hot and you will destroy the epoxy making those patches into weak spots, you will also have heated the surrounding polyester matrix to the same temperature - not healthy!

The West literature has a big "'CAUTION' do not exceed 60 deg C" written into it.

RTFM!
 
[ QUOTE ]
Using a heat gun can actually be a bad thing, too much heat and the epoxy becomes liqued again.
This why you cant have epoxy boats in dark colours, they can breakdown , you can see this as print through from the glass layer on the paint finish.

[/ QUOTE ]

Another old wives tale, IMHO.
Thousands and thousands of dark gelcoat or painted expoxy yachts produced annually (including mine).
And if you can see cloth weave through gelcoat, then its either shrinkage on an older polyester boat, or more usually a result of a less than professional layup, ie where they've not used fine enough cloth inside the gelcoat. Its certainly not a sign of any epoxy breaking down.
JOHN
 
RTFM - absolutely right. I thought I had, I've been planning this weekend for ages. Seems that even though I read the manual, not all of it sunk in. I think I was more foccused on what I was going to do than how I was going to do it. (As a colleague of mine is very fond of saying "assume makeas an ass of u and me - smug git).

Of course, reading the manual again, with the benefit of the "Oh my God, why isn't this working?" feeling in my giblets makes everything clear. So, from the manual.

There is a graphic that shows 205 hardener with a core working temprature of 25C.
Gel time at 25C , 20 to 25 minutes
Cure to solid (thin film) at 20c, 10 - 15 hours(!)

Even the 206 hardener is much slower than I'd anticipated with a core working temperature (from the graphic) of about 19C.

The manual does say however that if the tempearature is too low you can "Apply heat to maintain the chemical reaction and speed the cure."

There is also another part which says that the minimum recommended working temperature for the 205 hardener is 5C, so I reckon that even in sunny Cardiff it would set eventually.

At the moment, it seems that the epoxy (after warming) has cured. I shall be giving it a good testing before the boat goes back in the water.

I think if I were doing this sort of thing again (almost inevitable with my boat) I would regard the fast hardener as normal for my local conditions. And still think of applying some warmth if I wanted to do a job in a short period of time.

I am of course, left with the residual doubt that after launching I'm going to hear the merry pop of an epoxy plug detaching itself followed by the musical tinkling of an indoor water feature or that my injudicious application of heat will have damaged the structure of my boat to such an extent that it will fold in half on first meeting the testing conditions of Cardiff Bay.

Just have to add those worries to all the others, going bald, beer belly, global warming, kids, slugs, work, house etc etc etc......
 
Now here's a strange thing. Last night I plugged a couple of small holes with the same mix I'd used before and left it. The outside temperature per my car ambient temperature gauge was 12C. I've been down there today and its cold and wetter than a fish's wotsit. But the epoxy is rock hard.
 
Hi I have often successfully repaired outside in the winter by gently raising the temperature of the resin and the hull prior to
application and then fixing a polythene sheet looselyaround and over the repair with masking tape and then lifting one end and inserting my wifes hairdryer and hey presto you have a central heated tent over the repair.
depending on the strength of the hairdryer you may need a airhole outlet the oter end /forums/images/graemlins/smirk.gif
 
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