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Epoxy Working Time


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I have been using West Systems epoxy for a pretty good while with more than satisfactory working time. I use the 105 resin and 206 hardener. My current supply is about 3 years old and have the dispenser pumps. The last time I used it, a couple of months ago, I noticed what I thought was a quicker than normal setup time but scuffed it off as me just just dogging around. Today, I had a glue up with the WS and remembering last time, I watched the time and it started getting really gummy after 7 minutes and hard as a rock 15 minutes later. Luckily, I was able to mix a new batch and finished the assembly. The second mix did the exact same thing.  Does this stuff loose it’s working time as it gets older? 

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Great question!  I'll be honest in that I haven't really paid attention to the "working time" .   I will say that I've noticed it sets up a lot quicker in the cup than it does on the project.  I'll also add that the pumps don't seem to hold up compared to the lifespans of the epoxy in my shop.  

Very interested in what the others have to say!

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What was the temperature in your shop?  I notice a huge difference, based on the time of year.  If my shop temp is over 70 I  have to work much faster.  My current batch is over 6yrs old, and still going strong.  The only thing I do different now is give each pump a "waste" squirt if it has been several months since they have been used.  If I am mixing a large batch, I use a flat pan instead of a cup.  This also slows down the reaction.  Their web page has several tips for prolonging setup time.

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3 minutes ago, Bob said:

What was the temperature in your shop?  I notice a huge difference, based on the time of year.  If my shop temp is over 70 I  have to work much faster.  My current batch is over 6yrs old, and still going strong.  The only thing I do different now is give each pump a "waste" squirt if it has been several months since they have been used.  If I am mixing a large batch, I use a flat pan instead of a cup.  This also slows down the reaction.  Their web page has several tips for prolonging setup time.

Thanks Bob. I always use the same size drinking cups when mixing. Yeah, I have heard, contrary to belief, that the thinner the mix, the longer the work time. But mine has been constant.

Although this stuff is fairly expensive, compared to PVA, everything is relative, walnut to poplar. Perhaps I should just bite the bullet and buy all new. 

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I have decided that in the future I will buy the smaller container, not the gallon just so I get through it before it goes.

“If you don’t have time to do it right, when will you have time to do it over?”  John Wooden

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An update. I purchased a new qt. Of the 105 resin and a new set of pumps. I still had a half qt. of the 206 slow hardener so didn’t buy any more of that. I purged both new pumps and mixed a batch. Luckily I didn’t have much to glue up as the remainder started getting pretty hot and hardening in less than 15 minutes. We did have a rare 37% humidity and the temp was 93*. Not sure how much difference that made?

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