I wish I did this sooner

Measuring epoxy resin and hardener by weight instead of volume.


I know measuring by volume is usually good enough for most, But I make lots of small batches of epoxy for both HWS and non surfboard related applications, and sometimes they seem to take longer than they should to get as hard as they should, and sometimes not get as hard as they should.


I found that making 15ML batches by volume, compared to the weight, the ratio could be off by 15% even if poured with exacting precision accounting for menscus.  The smaller the batch the more the margin for error.  I would try and make larger batches and have another area which could use the extra epoxy, but this would slow down the original project and take extra time to apply within the pot life window, reducing overall outcome of both areas as I would really hate to waste epoxy, or anything for that matter.


With my 300 gram digital scale, well each drop of hardener weighs 0.08 grams at 70F ambients, and I have been able to get 100% precise mix ratios to the 0.0x gram.  300 gram max is a limiting factor however with my particular scale, but I will be acquiring a larger capacity scale when laminating my HWS as measuring by volume, compared to weight, allows too much room for error.


My 300 gram scale was only 11$.  Might be the best 11$ surf related tool I have ever bought.


One other bonus, is that sometimes when pouring the resin or hardener into the mixing cup, bubbles would be trapped in the resin making precise volume measurements practically impossible, and attempting to pop those bubbles would likely hide the graduations and not be effective anyway and there were times where I simply did not trust the mix and did not use it, but intentionally wasted it instead.


My scale turns itself off sooner than desired, so I make sure to measure the weight of the mixing cup and write things down so that I can multiply the resin weight by 0.43 or 0.44 depending on the epoxy System I am using. I find that cycling through the different scales, grams, oz, ect, allows it to stay on for longer while I clean the resin jug’s threads, and pick up the hardener jug and the self shut off feature has not been an issue since.


My favorite small medical mixing cups reveal a 30ML batch is quite close when measuring by volume, but 15ML and 7.5Ml batches were Not.  My larger  mixing cups are also vary in accuracy depending on graduations chosen.


The graduations mostly lie, the scale does not and makes the perfect ratio relatively easy to achieve.   Perfect epoxy resin / hardener ratio + complete mixing ensures the best possible result.  Anythng less is just that, but can certainly be ‘good enough’

I like removing that possible margin for error. 

I regret not getting a digital scale sooner, much sooner.




Me too. I used to guess visually as to what an ounce was, etc. But then I got a digital scale and that works great.

is your scale calibrated? How often do you test it?

I like syringes for measuring small batches.

I bought calibration weights but have not had to calibrate it as it reads dead on or only off by 0.01g.  I’ve put the 20 and 50gram calibration weights on it before each mix.  I once dropped the scale from a few feet up onto concrete and it still read correctly afterwards, to my surprise.




It really is pocket size, being about the size of my Samsung s4 mini smartphone in its case, but slightly thicker.


The Digital  scale reveals I was always going a smidge too light on the hardener no matter how precise I was with the volume in the medecine  or larger mixing cups.  Whether visual/ meniscus estimation error or cup graduation error or what combination thereof, I know not.


Not sure how much the ratio can be off and still be ‘good enough’ but I am anal retentive enough I really regret not seeking this level of precision sooner, much sooner, even after reading about the much improved precision  via digital scale here on Sways years ago by those with more experience.


I think part of my hesitance was the math, but multiplying resin weight by 0.44  then adding that number to the resin weight is hardly worthy of anxiety.  Just make sure to weigh the mixing cup itself in case there is a delay and the scale shuts itself off after resin is poured.  Also do not exceed the scale’s maximum ability such as i did when intending to mix a 300Ml batch.  Good thing I poured resin  precisely to the 200Ml line though and this volume measure batch was still ‘good enough’, but larger batches like these were rarely an issue when volume mixing.


Also wonder how different the epoxy offeringss are in regards to mixing precision.  My experiences are mostly with System3 GP, ClearCoat and SB112 resins, though last week I bought my third 1.5 gallon kit of Apex epoxy from Fiberglasssource.  They now have a whiter/ less amber hardener, and it does not fisheye as much as the previous 2 1.5 gallon kits and the cure time appears to be the same, which is pretty fast in my opinion.