Epoxy ratio by weight

[Hmerkle]

Many times I need a small amount of epoxy.

The West Epoxy system is a 5:1 mix. I have the pumps off the gallon containers...

Now when I want to mix say a "thimble full" I know I need to use a weight measure.

I found this after some research on line...

Epoxy Ratio Calculator

The problem comes that I have 12 units (say grams or ounces) so 10 units of resin and 2 units of hardener...
This raised a question in my head since this is EXACLTY 5:1 (10:2) but we know that the weight ratio SHOULD be different since the weight/ volume of hardener vs. resin is different... hence why you want to use a calculator...

So my question is this, am I thinking wrong or is calculator flawed?

 

[Henry W]

No direct experience with epoxy, but from a knowledge of chemistry point of view mixing volume/volume is what you do with pumps, and mass/mass is with scales. The difference between the two methods comes if the two components have different densities (weight per unit volume). There's likely no way to know the density accurately to be able to calculate the mass/mass ratio unless this info is given by the supplier. A Technical Data Sheet might have it.
The good news is that organic compounds don't really very in density that much (+/- 10%), so chances are your mixing a thimble full will work out.

AND, that epoxy weight ratio chart shown assumes vol/vol and mass/mass are the same.

 

[tghsmith]

when mixing small amounts I use a trick taught to me by a fishing rod maker years back,, small syringes will give you accurate measures,, 5 and 10 cc's work well, label them for resin and hardener they will be able to be reused for a while..

 

[Hmerkle]

when mixing small amounts I use a trick taught to me by a fishing rod maker years back,, small syringes will give you accurate measures,, 5 and 10 cc's work well, label them for resin and hardener they will be able to be reused for a while..

Do you store them in a ziploc bag or something?

 

[tghsmith]

I normally slide them back into the sleeves they came out of and rest them in a plastic cup, ziplocks would work,, if you get the syringes with end caps you can load them up to store A and B and cap them after use

 

[JNCarr]

Not sure what your question is, but if it's how to go from a 5:1 weight ratio to an x:1 volume ratio, here it is.

Looking at the MSDS for both the resin and hardener, the resin has SG of 1.15 and the hardener 1.05. So to maintain a ratio of 5:1 in weight you need a 4.56:1 in volume. You can use the same on-line calculator just enter 4.56 and 1 and the desired VOLUME. The calculator doesnt care as long as all the units are the same - it's just doing the math.

 

[Gofor]

When I worked with coatings, we used various two and three component types, including epoxies and polyurethanes. The mix was always by volume, unless otherwise stated.. The syringe method is a very accurate way to mix micro-quantities.

That said, for 1:1, I usually just put a couple strips of 2" wide packing tape on the workbench, and eyeball it putting down beads of the same width and length and then mixing it. This gives me a test sample after I apply it to test the cure. For cracks and knots, I outline the area with blue painters' tape, and trowel in the epoxy. When the residue on the mixing tape gets to a hard rubber consistency, I then know its time to remove the painters' tape and shave off the excess with a sharp chisel, bevel down. That reduces my sanding time to almost nil, and makes clean-up a breeze by just disposing of the mixing tape.

 

[woodlaker2]

Many times I need a small amount of epoxy.

The West Epoxy system is a 5:1 mix. I have the pumps off the gallon containers...

Now when I want to mix say a "thimble full" I know I need to use a weight measure.

I found this after some research on line...

Epoxy Ratio Calculator

View attachment 224230

The problem comes that I have 12 units (say grams or ounces) so 10 units of resin and 2 units of hardener...
This raised a question in my head since this is EXACLTY 5:1 (10:2) but we know that the weight ratio SHOULD be different since the weight/ volume of hardener vs. resin is different... hence why you want to use a calculator...

So my question is this, am I thinking wrong or is calculator flawed?

Thanks for starting this thread Hank. And thanks to others who have responded with clarifying info..

Many times I need a small amount of epoxy.

The West Epoxy system is a 5:1 mix. I have the pumps off the gallon containers...

Now when I want to mix say a "thimble full" I know I need to use a weight measure.

I found this after some research on line...

Epoxy Ratio Calculator

View attachment 224230

The problem comes that I have 12 units (say grams or ounces) so 10 units of resin and 2 units of hardener...
This raised a question in my head since this is EXACLTY 5:1 (10:2) but we know that the weight ratio SHOULD be different since the weight/ volume of hardener vs. resin is different... hence why you want to use a calculator...

So my question is this, am I thinking wrong or is calculator flawed?

Thanks for starting this post. And thanks to those who offered clarifying info.. Useful.

 

[Oka]

Typical I use 1 to 1 epoxy types, weigh each bottle and use that weight ÷ by 100 as the specific diviser. Then I can match the ratios perfectly.
That works as well. Thanks for finding this it will make it easier

 

[Hmerkle]

Not sure what your question is, but if it's how to go from a 5:1 weight ratio to an x:1 volume ratio, here it is.

Looking at the MSDS for both the resin and hardener, the resin has SG of 1.15 and the hardener 1.05. So to maintain a ratio of 5:1 in weight you need a 4.56:1 in volume. You can use the same on-line calculator just enter 4.56 and 1 and the desired VOLUME. The calculator doesnt care as long as all the units are the same - it's just doing the math.

Thanks Joe,
So that would suggest in your example if I have a 5:1 in volume with the example you suggest the weight ratio is 4.56:1 so at that point, the math is easy 5 grams of hardener that would be 22.8 grams of resin...

So for the West Systems resin 105 specific gravity is 1.15 the hardener is 1.05 (guessing this is where you took your example from...) so the 4.56:1 is a valid weight ratio...

 

[JNCarr]

Thanks Joe,
So that would suggest in your example if I have a 5:1 in volume with the example you suggest the weight ratio is 4.56:1 so at that point, the math is easy 5 grams of hardener that would be 22.8 grams of resin...

So for the West Systems resin 105 specific gravity is 1.15 the hardener is 1.05 (guessing this is where you took your example from...) so the 4.56:1 is a valid weight ratio...

No - it's the other way around. I read your original message to say the 5:1 ratio is the weight ratio so the 4.56:1 is converting weight ratio to volume ratio.
If what you want is to go from a 5:1 volume ratio to equivalent weight ratio, it would be 5.48:1. In this case you'll have a target weight.
Yes - this is specifically for the West Systems 105 and hardener. The resin SG is 1.15 and the hardener SG is 1.05.
Again - just enter in the calculator.

 

[Scott H]

If you find the TDS for the specific resin and hardener combination, it has the weight ratios directly stated.

E.g.
105 resin and 205 hardener: 5.19:1 (see TDS here)
105 resin and 206 hardener: 5.36:1 (see TDS here)

 

[Hmerkle]

Thank you Joe (@JNCarr) and Thank you Scott (@Scott H) that is exactly what I was looking for.

I used to use some store-brand 5-minute epoxy if I had a small job to do while looking at a gallon of "ready-mix" right to my left!

#WhatmakesthissiteSOGREAT