Experiment & discovery for mixing epoxy

[Steve Sawyer]

I read some of System Three's book on epoxy a while back, and one thing that stuck with me is the importance of thorough mixing. I like to use 3-oz plastic bathroom cups in the shop, but they have nooks and crannies that can make it hard to dig out all of the resin and/or hardener so I'm never sure that I've gotten everything thoroughly blended, so I don't usually use them for mixing epoxy.

For some reason I resisted trying those silicone-rubber based gluing tools, but finally gave 'em a try last year when I bought a kit with several brushes/applicators, a "comb" for applying glue to larger areas, and a tray for holding a pool of glue from which you can dip the brushes, and immediately discovered that they work extremely well. The control in the application of glue is excellent, and any PVA glue that dries onto them peels right off.

So yesterday I needed to mix up a small batch of epoxy for a job I was doing, and was wondering if those silicone applicators (the brushes have a paddle on the opposite end) would work as well with epoxy. As a test, I dipped one of the brushes into the epoxy and set it on a shelf to let it cure.

This morning, the epoxy had cured, and sure enough, it just popped right off of the silicone brush! These will work really well for mixing in those bathroom cups because they're flexible enough to scoop up all of the resin & hardener ensuring that nothing gets left behind, and the brush end will work much better than the popsicle sticks and the like that I usually use to spread epoxy.

[Gordon Bellerose]

I have heard, and read that silicone is a bad thing to get in some finishes. It causes fisheye.
I do not use solvent based finishes, only water base, so I cannot speak from personal experience.

I may do a bit of research around this topic to find out for sure.

[Eric Baack]

I like to mix my epoxy on a large enough flat surface using a popsicle stick so that I'm sure to be able to scrape it all up off of the surface.

[Steve Sawyer]

You're right, Gordon - however silicone rubber doesn't cause a problem because it's not a liquid that will contaminate a surface. I know some had expressed this concern when these products first came out a few years ago, but experience has shown that there is no mold release or anything else that will leach out of this material to cause any contamination. I've used them on furniture projects with both oil-based and polyurethane finishes. I also have a small silicone baking sheet that I use as a tote for finishing materials and when doing glue-ups where I can safely set a wiping rag or glue brush without getting anything on the surface of the project or on the workbench, and I've never had a bit of trouble.

[Steve Sawyer]

I like to mix my epoxy on a large enough flat surface using a popsicle stick so that I'm sure to be able to scrape it all up off of the surface.

I've done that too - the silicone rubber gluing kit I bought has this nice tray that would be perfect for mixing that way.

I will also squirt the two parts into the corner of a snack-sized ziploc bag, then smear it around and squeeze it back & forth to mix. I then snip a tiny hole in the corner and use it like a pastry tube to apply exactly where you want it. The downside of that technique is it's hard to ensure you have a 50/50 mix unless you're using one of those hardware-store dual-plunger syringes. I got a gram scale recently and will use that to mix by weight for this technique when using the stuff I normally have on-hand in the 8-oz squeeze bottles.

[David King]

You really need to use two mixing cups and stirrers to get a sure mix. Mix for two minutes in cup one with with stirrer one, dump into cup two and mix again with new stirrer. That eliminates any unmixed areas getting included in a joint or finish.

[Steve Sawyer]

You really need to use two mixing cups and stirrers to get a sure mix. Mix for two minutes in cup one with with stirrer one, dump into cup two and mix again with new stirrer. That eliminates any unmixed areas getting included in a joint or finish.

So, if I'm mixing up a total of 4 grams of epoxy, I put 1 gram each of resin/hardener in one cup, then 1 gram each of resin/hardener in a second cup, then mix as you describe above?

[Brian Evans]

I use West with the pumps, and I use paper chinese food containers, like a two cup sized short bowl. I asked my wife to buy some for meat least 15 years ago, she looked for them and found some at a commercial paper product distributor in town. They came in a box of 1,000... I still have way over half left.

[Barry Daniels]

West system pumps work well for large quantities but not so much for small batches. I got a tiny electronic scale from Ebay that goes down to a hundredth of a gram. Small batches are no problem for me now.

[Steve Sawyer]

West system pumps work well for large quantities but not so much for small batches. I got a tiny electronic scale from Ebay that goes down to a hundredth of a gram. Small batches are no problem for me now.

That's why I invested in a similar scale. I very seldom mix up more than a few grams at a time.

[Randy Roberts]

I have always used syringes to measure out epoxy.
Stick and plastic cup, or for small amounts, a postem pad works well. Mix on the pad, peal off and the remaining unused on the sheet of paper is a good monitor for "is it hard yet".

[Clay Schaeffer]

For small quantities I use a triple beam balance and a small plastic cup. I squirt the hardener in first (using the pump), calculate the weight , and then add the appropriate amount of resin. I mix it with a compound tool (small metal spatula) and usually spread it with the plastic inner portion of a cheap foam brush (sans foam).
I like adding both components in the same vessel and adding the smaller quantity first. I think there is less chance of mixing an improper ratio this way.

[Randolph Rhett]

Post-it pads! Brilliant!

[David King]

You really need to use two mixing cups and stirrers to get a sure mix. Mix for two minutes in cup one with with stirrer one, dump into cup two and mix again with new stirrer. That eliminates any unmixed areas getting included in a joint or finish.

So, if I'm mixing up a total of 4 grams of epoxy, I put 1 gram each of resin/hardener in one cup, then 1 gram each of resin/hardener in a second cup, then mix as you describe above?

Steve sorry for the lousy explanation. Start by mixing the total amount as you normally would in one cup. Once you have that cup mixed up you dump the contents of that cup into a new cup (presumably leaving behind most of the unmixed areas around the sides and bottom corners). You continue mixing in the second cup with a fresh stirring stick just to be sure no unmixed epoxy is left on the stick. I use the unwaxed 2 oz paper pill dispenser cups for small batches. I generally have a shop full of good stirring sticks in many different woods.

[Steve Sawyer]

David - got it - thanks for the clarification!