Mixing epoxy by weight

[bymiller]

I am using Marinepoxy and have been mixing it by weight instead of volume. Can someone tell me the correct ratio?

[tech_support]

We do not recommend mixing by weight. 2/1 by volume is difficult to mess up. Mixing by weight, especially small batches, can lead to bad batches.

How have you been mixing by weight if you do not know the correct ratio?

What scale do you use? Unless its an expensive/accurate scale, you may be further off than if you mixed by volume.

[bymiller]

I have been using the 2:1 ratio but I can see that the two containers are not emptying at the same rate. I have a Taylor scale which weighs down to tenths of an ounce. I have not had a batch that has not seemed to cure properly. I can switch back to the pumps but that seemed less accurate to me.

[Lon]

Although close, I know it's NOT 2:1 by weight.
I use the pumps to dispense only, not measure.
Measure with any variety of small containers - I use 6 oz plastic yogurt cups the wife saves.
You can creatively pre-mark container(s).

[tech_support]

pumps can be inaccurate, they can create a vacuum in the bottle. I do not use them unless we are doing a lot of 3 oz batches. We have always recommended pouring into a graduated cups as the least error prone way to measure.

[Larry B]

Here is how I do it:
I place a cup on the scale, then place another cup inside that cup. 0 your scale, pour in WATER until scale shows 2oz, draw a line around that cup, place it back on the scale and pour in WATER until your scale says 3oz, draw a line around that cup and now you have a premeasured cup for 3 oz of epoxy. using water gives you a perfect volume ratio. Then just place a cup into the premeasured cup, pour in the epoxy to the first line, then hardner to the second line. Mix it up and go. I've never had a bad batch and going on 30 gallons.

[Lon]

Larry, doesn't your method actually measure by weight, not volume?

You can put an ink mark anywhere on your see through cup:
(1) fill to the line with hardner and dump into your mixing cup
(2) fill twice with resin and dump into your mixing cup

I do scrape the sides and bottom of the measuring cup.

But, what works, works, right?

[Larry B]

Larry, doesn't your method actually measure by weight, not volume?

Yes, but I'm weighing water not epoxy so it don't matter. It comes out 2:1 ratio by volume with the epoxy because the water weighs the same and the epoxy and hardner does not weigh the same. Confusing

[jacquesmm]

Larry's method is very accurate and explains it well, thank you.

[wadestep]

I like Larry's method, sounds like it would work well. However, I'm now 6-8 gallons of epoxy down using the pumps. I occasionally check their calibration in graduated measuring cups, but only check them about 1/4 of the time.

So far, there's been only one bad batch: 4 pumps of hardner and 2 pumps of resin. Otherwise, my pumps are batting 1000. I do be carefull to get full pumps each time, and never let the liquid level in the jugs fall below 1/3.

wade