View Full Version : Epoxy ratio by weight

03-24-2007, 12:49 PM
I need to mix some epoxy and for the life of me I can't remember the ratio by weight. It is U.S. Composite 635 resin and the 4:1 hardener. I've always mixed by weight . Is it 100 parts resin to 26 parts hardener (I think)? Or, 100 parts resin to 46 parts hardener( I think)? The former sounds more like it but the latter keeps sounding correct too. My impending dotage looms closer! U.S. Composite is closed today.

Dave Fleming
03-24-2007, 12:55 PM


03-24-2007, 01:10 PM
that is by volume. That would work if the resin and hardener weighed the same. I'm not sure they do. Or, I could be wrong

03-24-2007, 04:52 PM
I believe system 3 is 100 to 44.


03-25-2007, 01:47 AM
one "pump" of resin will not weigh the same as one "pump" of hardener.

03-25-2007, 02:40 AM
I used US composites. When in doubt,use the ratios. 4 parts resin to one part hardener by volume.I didn't weigh any of it. No miscures. If not,you are going to have to weigh each component by volume anyway because that is how it was designated.Seems like a setup for making something that is relatively straightforward into something complicated. Just like if you poured each component into seperate graduated measuring cups and poured them into a mixing cup. More of the resin would cling and stay behind than the hardener would but it would still set up properly if it wasn't too small an amount.Make sure the pumps are burped and you're good to go.

03-25-2007, 06:31 AM
Here are 2 links to measuring epoxy by weight at the Duckwworks site. http://duckworksmagazine.com/ Duckworks has a search function on the left side of the home page. There may be more information there.

Aticle 1) http://www.duckworksmagazine.com/05/articles/scale/index.cfm

Article 2) http://www.duckworksmagazine.com/05/articles/scale2/index.cfm

Dave Carnell
03-25-2007, 07:40 AM
I haven't mixed any epoxy in quite a while, but I always mixed by weight because I had a laboratory scale that weighed to about 0.05g. This scale let me mix accurately batches as small as 1 gram. As a parsimonious, depression-era Connecticut Yankee I wasted as little as possible.

Of course, the ratio depends on whether you are using 4:1. 2:1. or anything else. System Three gave the weight ratio in an old manual. I remember 0.44 parts hardener to 1.00 part resin for their 2:1 resin.

Bill Perkins
03-25-2007, 07:56 AM
Interesting website .It mentions a worldwide shortage of carbon cloths .Is this going into our military gear ,or what ?

03-25-2007, 08:10 AM
Raka 2:1 by volume is 100:43 by weight.

03-25-2007, 11:47 AM
Thanks for the ratio. I've been using a digital kitchen scale that can measure in grams. You don't have to mess with the pumps and can easily measure out any amount from ridiculously smalll up to five pounds.

P.I. Stazzer-Newt
03-25-2007, 12:20 PM
When I hit this problem, I contacted the manufacturer, who was polite and in a matter of minutes, gave the correct answer.

What you cannot do is; use the weight ratio from another maker, or for a different product.

03-25-2007, 06:05 PM
If you have accurate scales it would be possible to measure one mix by volume and weigh each part and then take the relevant ratios from each component. The test of the original volume measurement would be whether the mix goes off satisfactorily.

Weighing seems like a lot of buggering about though,given that each component still has to be poured into separate containers.
I mix by volume using pumps, small amounts by using separate plastic teaspoons, and havent had failures.
I use Altex 4:1

03-25-2007, 06:19 PM
If you would use system three T-88 you could mix equal parts of each.....

03-26-2007, 08:39 PM
Measuring out epoxy by mass won;t work unless you know the density of each component. One gram of hardener to 4 grams of resin won;t work unless the resin and hardener have the sae density. Get a ration from the manufacturer or just measure by volume.

03-27-2007, 11:18 AM
I used to build and restore/repair alot of fishing rods. I used syringes for the smaller amounts. Most of that epoxy is 1/1(flex coat or envirotex) ratio. When I was doing the glass on the Simmons in 88 deg temps,I can't imagine having the time to weigh it and keep the transition wetouts between batches wet. As it was,I was having to nearly run with it. My limit in that heat was 14 pumps of resin to 7 hardener of the 2/1 slow cure if you didn't want to see any of the weave of the cloth. I can't imagine the smaller amounts being any easier than syringes.
Not being argumentative here or disagreeing with others methods if that's what works for you but there is other ways for those who don't own scales. The amounts of resin left that the pumps don't pick up is what I poured and stored in the syringes.

John Meachen
03-27-2007, 06:01 PM
I have always found that the epoxy kit as supplied contains the correct amount of hardener for the resin.If the weight of each is given you can soon arrive at the mix ratio.No doubt there will be somebody along shortly to raise an objection to the principle.I have used scales for epoxies with mix ratios varying from 100:15 to 100:40 and including one at 100:37 you would need quite an array of pumps or syringes to do the same.An inexpensive set of digital scales with 0.1 gram resolution makes it easy to cope with the range of possibilities.

03-27-2007, 08:33 PM
I am just curious.What is the significant differences to need so many different ratios? I built a whole boat with two. A 2/1 thin, slow cure and a 1/1 thick ,medium cure for fairing mixes. I know some want faster cures etc, but do folks other than maybe in production work, really keep such a variety? At any rate,as suggested by the manufacurer,the pumps were the same just the pump count was different according to the ratio. I always ended up roughly with the correct amounts left in the containers once they were out of pumping range.Seems that if it was that critical,the manufacturer could not responsibly suggest such a method.It seems they would market the more user friendly version if they wanted folks to keep using their mix.