Epoxy curing times/temps

[pcatterall]

I understand that I really need to apply most epoxies at 10 degrees and have read up on the various specs to determine overcoat and full cure times.
For planning purposes and to work out how soon I can coat my hull I would like to understand what happens if I apply a coat when the temp is above 10 but then it drops ( overnight say) to below this, will the curing just stop and start again when the temp gets back up? will there be any adverse affects on the curing?
Assuming that we have 'normal' weather this year would an April or May application be possible?

 

[sailorman]

I understand that I really need to apply most epoxies at 10 degrees and have read up on the various specs to determine overcoat and full cure times.
For planning purposes and to work out how soon I can coat my hull I would like to understand what happens if I apply a coat when the temp is above 10 but then it drops ( overnight say) to below this, will the curing just stop and start again when the temp gets back up? will there be any adverse affects on the curing?
Assuming that we have 'normal' weather this year would an April or May application be possible?

affix a plastic tent around the hull & leave electric heaters on 24/7

 

[Boathook]

As far as I'm aware with epoxy, the curing stops / slows down when it gets cold and then restarts / speeds up when it warms back up. If another layer of epoxy is required the epoxy will require good cleaning, etc to remove the 'greasy' surface which is a by-product of the epoxy curing.

 

[prv]

In a joint or fillet, once it starts going the heat from the exothermic reaction tends to keep it going. I suppose you won't get such a strong effect with it spread in a thin film, but perhaps some?

Pete

 

[Avocet]

A lot depends on the epoxy being used. If this is an osmosis treatment, I think some manufacturers allow application as low as 5 degrees.

If it is some other application, I have had some experience of cold weather use. I was told by the manufacturer of the resin I was using that cure would all but be suspended if the temperature dropped much below 10 degrees, and would re-commence as soon as the temperature rose again. HOWEVER, I was also warned that the curing agent tends to be more willing to react with atmospheric moisture than with the resin, so for all the time that cure is not taking place, some of the hardener will be "used up" in reacting with any atmospheric moisture - potentially resulting in an incomplete cure when the temperature rises again. I don't know how profound this effect would be and depending on the application, it might not be a big issue, but I guess it's best avoided.

 

[electrosys]

Last year I conducted something of an experiment regarding the low temperature curing of epoxy, although I really hadn't planned to.
I'd mixed too much and decided to place the excess in the fridge, in the hope that I could still use it the next day - so I put the sealed container of mixed epoxy into the freezer section of the fridge for half an hour to drop it's temperature rapidly, and then transferred it to the salad storage area. It set after 3 hours.

So - the only way to know for certain the characteristics of the epoxy you're using - is to 'suck it and see'.

 

[macd]

if I apply a coat when the temp is above 10 but then it drops ( overnight say) to below this, will the curing just stop and start again when the temp gets back up? will there be any adverse affects on the curing?

Most manufacturer's spec sheets are notably coy about this, partly, perhaps, because the variables are infinite. Frankly, I don't know the precise chemistry of the answer, but suspect (from having used epoxy a lot) that humidity is at least as important. I know that mixes applied in, say 12C, but reducing close to freezing before fully cured have gone off OK (i.e. as well as I can tell without resort to high-tech testing.)
Note also that boathook's "greasy" surface is probably with West resin. I hate the bloody stuff. Easy to buy, a pain in the butt to use.

 

[Avocet]

That's interesting. I've been using SP resins for the last few years and although I've been warned about a waxy / greasy surface film, I've never actually managed to witness it. In conditions of high humidity it can go a bit milky as it cures, but as far as I can tell, there are no other ill effects.

 

[gjgm]

I understand that I really need to apply most epoxies at 10 degrees and have read up on the various specs to determine overcoat and full cure times.
For planning purposes and to work out how soon I can coat my hull I would like to understand what happens if I apply a coat when the temp is above 10 but then it drops ( overnight say) to below this, will the curing just stop and start again when the temp gets back up? will there be any adverse affects on the curing?
Assuming that we have 'normal' weather this year would an April or May application be possible?

West System probably have some reading for you on the web somewhere, but I dont think you get the same bond strength if the temp drops/rises if its a long cure time.
I think they say tee-shirt temp, which is more like 20+.
Hence the tent technique mentioned above.
I have heard suggested using a domestic electric blanket; no idea how safe that is!

 

[oldsaltoz]

A safe base kine for most 'standard' epoxy resins is more like 20*c minimum and humidity less then 74%.

A sudden drop in temperature or due point being reached can effect the surface finish, ranging from Amine blush, waxy surface or milky appearance.

In marginal conditions I completed repairs using a high powered light (tungsten globe) on the inside of the boat, the heat from lamp prevents problems with high humidity and low temperatures, however too much heat will cause the resin to flow on vertical surfaces.

The simple and reliable test for surface contamination after epoxy resin has cured is to run fresh water over the area with a garden hose and look for water beads.

To remove the contamination just keep the hose running and rub the area working from the top down with scotch-brite plastic kitchen sourer.

Hope this helps.

 

[macd]

I have heard suggested using a domestic electric blanket; no idea how safe that is!

Now that's an idea: if they made electric blankets out of woven rovings, you could lay-up in almost any temp and just snip off the cable after curing.

Seriously, if mains electricity is available, a cheap fan heater is just the ticket for all but very big jobs. For whole-hull work in marginal temperatures, tenting and heating is the best answer, laborious though it is.