Epoxy cure in cold weather

My garage averages around 55 degrees most of the time. I have a small electric heater that kicks in if it goes below 50.

The strange thing is that at this temperature the epoxy still hardens up nicely in less than 24 hours. I epoxied Skerry stem joints yesterday at around noon, went in to check this morning at 8:30 and the epoxy was quite hard--passed the "thumbnail" test. I pressed pretty hard with my thumbnail and did dot get a discernable dent. The temperature was about 58 degrees.

In a way this has me worried that I am not doing things properly. I am using MAS epoxy with the slow catalyst.  Using the attached pumps to mix it--one pump epoxy to one pump catalyst.  And yes, I have the correct pumps on each container--I get twice as much epoxy as hardener per pump.  (MAS's literature states that adding extra catalyst will not shorten the cure time anyway.)

As I said the epoxy is hardened, but I suppose it is not actually cured. The reason I say this is that because according to MAS's literature a full cure at 59 degrees would take 10 days. This is also confusing because their lit states that a cure at 77 degrees would take 5 days, whereas CLC states that it takes 24 hours at 75 degrees!  What is going on here?

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RE: Epoxy cure in cold weather

You are doing things right. 

By "full cure" MAS means that the epoxy has reached full strength.  The epoxy will be hard long before it is fully cured.  Here's a page from the MAS epoxy site that has more detailed information on film set vs. full cure times:


You can (and should) re-coat as soon as soon as the epoxy surface is tacky; the epoxy will be quite strong (joints will be stable) as long as it is hard enough passes the thumbnail test, but it will not reach full strength for many days. 

In a way, this is similar to paint - you can recoat a wall after an hour or so, but the paint manufacturers always say to wait several weeks or a month before washing or subjecting it to hard use - same kind of exponential cure process (quickly skins over, gets pretty hard in a day or so, but full cure to maximum durability takes a long time). 

RE: Epoxy cure in cold weather

Never used MAs but WESt resin will kick at 50 deg. Fast hardener works best at low temps. Like MAS epoxy, WEST kicks and gets hard but the total cure to full stength takes several days. One caution is wait at least 4 days (cold temp more like a week) before sanding. At full cure the sanding dust is inert RE breathing it, before full cure it can cause an adverse reaction.  Of course wearing a good dust mask anytime you grind wood or resin is an excellant idea.

Do not add extra hardener. Epoxy should alweays be mixed at the proper ratio. The cure of old school polyester resin could be accelerated by jacking up the catalyist, but epoxy hardener is not a catalyist but part #2 of a chemical linking mixture and exact mix ratio must be done.

One more thing - do not let the "full cure" deal scare you. Based on my 25+ years of fiddling with epoxy, I would guess the strength difference between can't dent with fingernail to full cure is less than 10%. So when it feels hard, continue to march through the building process.

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