Digital scale for Epoxy

Posted by Mark Camp on Dec 1, 2004

Some find it more convenient to weigh their epoxy resin and hardener; others don't. This is buyer's advice for those who decide to buy a digital scale for small batches.

I wanted to experiment with that technique, for the case of very small batches. For example to glue a small piece of wood. Only a few ml. is needed in many cases.

Today I use medicine droppers, which are fine, but I am always looking for a faster neater better way. (Please stand and recite the Engineer's Pledge with me, eh?: 'I am an engineer. But I change. If I have to. I guess.' Sit down.)

I purchased a digital scale at a cook's supply shop for about 30 USD.

Although I am delighted with my purchase (it turns out to be perfect for weighing food for a crash diet--working to increase the max crew capacity of the Sharpie by at least one) it is useless for epoxy. Problem is the precision (ie, the smallest unit it can increment by reliably).

So the advice is: if you buy a digital scale, check that it can distinguish 0.1 g or better. My scale increments 2 gram. at a time. For English Walnuts (that's 13 calories, by the way, but they taste very good) it's great. But a ml. of hardener shows up as "0 g."

Even a precision of 0.1 g is pushing it a little. One expert on the web said that epoxies can tolerate mixing errors around 5%. Or maybe he said 10%. Anyway, you could miss that tolerance with a 3 ml. batch of MAS, since it would have only 1 ml. of hardener, which weighs less than a gram. So a 0.1 g error would be 10%.

If you're off by 20% does it matter? Who knows, maybe not. Some folks are cautious and technical, some are more carefree and trust in their intuition; choose your personality and go with it.

But one appeal of the digital scale to me was not so much the accuracy as the convenience. One of the builders said it is great to just drop a little pool of resin into the container till it looks like enough, then check the scale and add half that amount of hardener and stir. Quick, no muss, no fuss.