Ketchup style pumps are not very accurate, they are good enough when they are working correctly, but the only way to get a perfect mix is to use a scale. Or buy a $500 professional quality pump..... 

I have a (newbie) question about the "perfect mix."  My epoxy was kicking too soon it seemed, so I took to putting a little less hardener in (I am using the pump bottles that came with the Shearwater kit), e.g. 10 pumps of resin to 9+ pumps of hardener, which seems to work well.  But my experienced advisors told me that is not a good thing to do, so I intended to use measuring cups, and measure out 2 to one by using water measures to mark two lines on a single cup, then pump the resin and hardener one at a time using the lines as a guide.  I don't want to use two cups, since when I combine them, there will still be some liquid left in the cup that I pour into the other cup, again spoiling the "perfect ratio."  But then I worry they won't mix right if I don't use the "one pump of resin, one of hardener, one of resin...etc" process.

CY-you seem to be suggesting using a scale to weigh the two components.  Is that a better way to get the right mix than by volume?  If I weigh them in two cups, how do I get all the liquid out of the one cup and into the other?  Or can I weigh the resin in one cup, then add harderner to 1.5 times the weight?  Will they mix properly if I do that?

Thanks!

Alec

 does resin and hardner weigh the same 

   THE REASON MY BATCHES DID NOT CURE IS DUE TO ME NOT REALIZING THAT A CALIBRATED PUMP TAKES CARE OF THE 2 TO 1 RATIO AND ALL I HAVE TO DO IS 1 PUMP OF EACH. I READ MY POST AGAIN AND REALIZED THAT WHEN I PUMPED IT 2 TO 2 I WAS ADDING IT CORRECTLY AND NOT MAKING A HOT BATCH. WOW WHAT A LOAD OFF.

Guys,

Both MAS and System 3 are tolerant of slight mismatches in ratios. System 3 documentation says that you can be off by 15% and still get a good cure. I haven't read the MAS documentation, so I don't know their exact number.

The closer the better, of course, but these chemicals were designed for workshop use so you don't have to have laboratory precision. If I'm doing my math right, Alec was actually almost 10% off with his 10 to 9 pumping ratio and he's not reporting any problems curing.

I'm not promoting sloppiness in mixing, just pointing out that we don't need to be fixated on getting things perfect.

Have fun all,

Laszlo

   For very small (less than a pump each), or very large (more than 5 pumps each) batches, a sce is handy. The 2:1 resins I've measured are about .43:1 by weight. I write a little table of ratios on the wall above the scale. For example I'll pour 100g of resin then pour in hardener until the scale reads 143g. My written table has multiples of these numbers so I don't have to think while I pour- I'm always thinking about the next step and lose track easily it seems!