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slow cure and low temperatures


Hirilonde
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I have been using fast cure exclusively this winter.  As some of you know I am working under less than desirable conditions where temperature is concerned.  I temporarily ran out of fast cure the other day and now I am learning a few things about slow cure:  (B&B epoxy)

 

1. It definitely is slower!  Nothing I have used is slow enough some times during the summer while assembling a complicated piece, but I have now discovered a new limit.

2. Just when I thought I had mixed my first bad batch of epoxy it finally started to cure.  Fast cure has been taking 24-48 hours to convince me it is safe to remove the clamps this winter.  It does however show signs of cure in 4-8 hours.  Slow cure had shown no sign of curing at all for 48 hours.  I almost considered this last application a bad mix and came close to cleaning it off.

3.  With enough heat and time I can report that the slow cure is working fine, but it sure does test my patience when used during winter in Rhode Island in a tent with poor heat that I am only willing to use under direct supervision.

 

Thank you Graham for ignoring my e-mail to take your time on my last order in lieu of Carla's situation.  You actually came close to matching Carla's speed and efficiency for handling orders.   :P    

 

I think I will now return to using fast cure, at least for a couple more weeks.

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Hi Dave,

 

Glad to hear that your epoxy cured.

 

When I first started using epoxy, I had read a posting that sometimes epoxy won't cure right when it's too cold.  I was paranoid about this and so I built little plastic tents and improvised with electric blankets and an old sleeping bag.     Later, I had an opportunity to talk to one of West System's reps and he reassured me that the epoxy will still cure at low temps, but it will just take longer.    The low temperatures just slow the epoxy chemistry down.   Now I just clamp it and leave it.  No fuss, no anxiety.

 

I suppose there could still be an issue whether the epoxy penetrates into the surface of the wood, but a longer cure would also give the epoxy more time to soak in.  Maybe it's a wash, but I'd like to hear the voice of experience on the strength of epoxied joints, or adhesion of sheathing when it's cold.  

 

My dad and I built a cedar-strip canoe when I was in high school, and it developed saucer-sized bubbles between the wood and the fiberglass sheathing.  The power went out the night we glassed the exterior and it got quite cold in our basement.  Dad always blamed the bubbles on the cold.    I can't actually swear that we used epoxy for that though.  I do remember that it had kind of gross sweet smell.

 

Cheers,

Bob

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Dave,

I dont know if you looked at my firefly thread, but it was 90 here the other day! Cooled down to the 80s today... And, no, I'm not rubbing it in. This is going to be another nasty fire year.

I had an assistant help with a strip/glass canoe once who mixed the epoxy backward, so the front half of the inside of the canoe had to be cleaned out. It took him three days. Glad your epoxy cured. : )

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I have used all the tricks:  heat lamps, tents and blankets etc..  My problem now is planking.  Each plank is 16 feet long and glued along its entire length.  But it is working, just not as fast as I would like.

 

I never see penetration as an issue.  Epoxy is extremely adhesive with very little penetration.  It water proofs by making a "thin candy shell" far more so than because it can penetrate.  I have glued teak and black locust with great success and there is very little penetration of either of these.  If I remove the surface oil, the surface is scuffed up and it is clean then even teak will glue well.  I clean with acetone just minutes before applying the epoxy.  I also always apply epoxy (or any glue) to both of the mating surfaces and work it with a brush, roller, scraper or what ever to assure no bubbles or voids.  I insist that this is a key to achieving constant success.

 

I have never found an issue with cold except that it slows down the cure.  I am not saying there are no issues, just that I am not aware of them nor have I suffered any failure because of it.  As long as I can get the work heated up some time after it seems to cure just fine. 

 

Mixed the epoxy backwards?  I have found epoxy works just fine whether I mix clock-wise or anti-clock-wise.  :P

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Dave-

Know what you mean about fast hardener. I used some today to fill holes in rudder for bushings, and couldn't believe how it heated up in my hand in minutes. Actually wasted a batch because it became useless very quick. I wanted to speed up cure time so I can drill holes before full cure but man it was kicked off quick!

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Working with epoxy isn't much different than other, previously favored adhesives. Using a fast cure hardener in cool weather makes sense, as you can always warm it up to affect a full cure, though you're pretty much screwed, if it's too warm to use a fast. I use a super slow and have about 50 minutes of working time in 90 degree heat. Of course, on days when it's not getting over 70 degrees (pretty rare around here), this super slow will not cure, but I have heaters and will tent an area or the whole boat if necessary. I can push a cure rate too, using these heaters. Inside an insulated box, I can keep a part at about 120+ degrees, which will cut the cure time about 75%. On a whole boat tenting, I can usually maintain at least 100 degrees which will half the usual cure time. So, there's no need to take a nap or hibernate off the season, just apply heat and use a goo that will give you lots of working time, instead of kicking off in the mixing cup.

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