Mix epoxy and hardener by weight?

For mixing larger amounts of MAS epoxy and hardener, can the 2:1 ratio be figured with weights instead of using the calibrated pumps?

This seems pretty simple but I do not want to make a drastic mistake so your opinion will be helpful.

I'll assume the weight of one pump of expoxy is not 2x one pump hardener, so I thought I could weigh one pump of each and multiply accordingly.

For example if 1 pump expoxy is 3 ounces, and 1 pump hardener is 1 ounce, then by weight my ratio would be 3:1. Does that seem sound?


8 replies:

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RE: Mix epoxy and hardener by weight?

Watch it.  The hardner pump only dispenses half as much.  In your example, the ratio by weight is 3:2.  If you are using larger amounts best to use calibrated cups and get a weight ratio from the epoxy manufacturer.


RE: Mix epoxy and hardener by weight?

Hello PAG, thanks for the reply.

The pump dispenses half as much by "volume" not by weight. Therefore I think my ratio is correct if using weight. I don't see the 3:2 ratio you describe, but then again, this is why I posted here.

I agree on your point to use graduated cups, but I trust weight much more. Maybe the cups are accurate by +/- a certain percentage, but I don't know what that percentage is. Maybe it is a non-issue?


RE: Mix epoxy and hardener by weight?

I mix all my epoxies and two part products by weight.  I use a small Weight Watchers electronic scale.  I have it set on grams versus ounces. All of my epoxies and linear polyurethane paints catalyze perfectly.  Grams or ounces, doesnt matter so long as you use the correct ratio for your particular product.

All of the pumps fail after time.  On the suction stroke they don't always fill properly

I used to use calibrated measuring cups, throw away types but then went to measuring by weight.  Now I can use cat food and yogurt containers.  Almost all electronic scales have a "zero" feature.

Some of the ratios are tricky such as West 105 catalyized with 207.  The ratio is 1 to 3.7 so I made up a table.


For linear polyurethane paint I know that the coverage is about one square foot per 10 grams (.3 oz.)

You will love measuring by weight.

RE: Mix epoxy and hardener by weight?

I must add the measuring by weight assumes that both components have the same spacific gravity.  The can be checked by measuring out equal volumes of each and checking their weights.

You will also find that some product manufactures specify measuring by weight but settle on their customers measure by volume because a scale is frequently not available.

RE: Mix epoxy and hardener by weight?


WCGW is right on his weight ratio.  It really does not matter what the relative specific gravities are either.  If one calibrated pump of resin is 3 oz. (weight) and one pump of hardner is 1 oz (weight)  Then the volumes are correct:  2:1 due to pump calibration and the same ratio by weight is 3 oz : 1 oz.  This has very little to do with which is the best method but at least we now have the arithmatic right.

RE: Mix epoxy and hardener by weight?

Totally off topic:  Would Catalina Charlie be a resident of Catalina Island who attended the University of Michigan in the 60's?


RE: Mix epoxy and hardener by weight?

Ok thank you all for the input. John Harris answered the question for me in response to a tech question I entered on the web site. He says that the weight is basically going to work out as 2:1 so that works for me!

Just for kicks I'll weigh a few pumps of each when I get my new epoxy supply and new pumps. Thanks again!

...and further off topic, Catalina Island is my sailing goal this summer in my MKII sailrig/kayak. I'll buy Cat C. a beer at Eric's if he's there when I make port..

RE: Mix epoxy and hardener by weight?

PAG and WCGW, I hope the moderator does not nix this.  Yes, I did go to the Univ. of Michigan in the 60's (Naval Architecture and Marine Engineering 1969). And when you get to Catalina give me a call.  If I am not in Avalon I will be at Rippers camping and paddling my Kaholo.  Go up to the Harbor Master's Office and ask for me.  

Give me a call at 310-809-0661  any time or cccanby@ hotmail.com.  Love to chat.  PAG, how do you know me?  Please call.  Charlie Canby

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