Epoxy 103

Why bother testing the epoxy pump?

Something happened today that prompted me to want to discuss epoxy ratio checking.

In the past I have mentioned that testing the “hardener to resin” ratio, as delivered by the pump, is very important, but I thought that there was no way anything could change this ratio, once the pump lever was bolted down tight.

I was wrong!

Today, as I nearly always do before a job, I checked the pump ratio again expecting it to be pretty close to the usual 44 parts of hardener to 100 parts of resin. Four attempts later, I was still getting fluctuating results from 27 to 100, to 35 to 100.

The pump lever, it seemed solidly attached in the usual position (I had marked it). So, what could cause this issue?

Opening the hardener lid, I could not see any problem. Until I drained the canister to clean the valve, that is, and what I found near the bottom was a bit shocking.

Hardener reservoir bottom after draining

Material collected from epoxy pump

I am not quite sure what the stuff is, and how long it has been building up in there. This material has the consistency of warm toffee.

Looks like a pecan, but it's not!

"Pecan" smushed with my thumb. It felt pretty firm, but not hard.

I have always done the “scratch test” on the cup I used to mix the epoxy, the day after construction, to test for hardness of the cured material. I did in this case as well, with satisfactory results, so this has obviously had no ill effects so far, except from clogging up the valve today.

Scratching last week hardened epoxy with scissor. "Ops check OK!"

I cleaned up both the canister and the valve with Acetone, and put everything back in as it was. 

I sure hope this is the last time I have to clean that mess!

Valve in place, and reservoir mounted back on the pump.

Doing another ratio test I finally got good numbers, 43.5 to 100.

Good test (bottom right) after cleaning

This time around, I decided to strain the hardener while pouring it in the pump reservoir, and I trapped more gunk straight from the can.

Kitchen strainer sacrificed for a worthy cause.

I will resolve to be even more religious about ratio testing from now on.

UPDATE:

While rereading the whole CP set (1398 pages), I ran into 2 vital entries I must have missed before...

CP 32 page 6

CP 29 page 5

So, I now have more guidance on what is going on with my epoxy, and what not to do.

Luckily for me, the situation above happened with the last few ounces of hardener left in the can, and because I always do the scratch test to make sure the epoxy hardened as intended, I know my last few layups have not been affected.

It is worth repeating that the presence of lumps, nuggets, crystals, or just a cloudy appearance in the hardener, is ground for work stoppage, and performing the reheating procedure highlighted above. 

This procedure reaches a much higher temperature (160℉ to 190℉ or 71℃ to 88℃) than suggested to me by Aircraft Spruce's customer service (120℉ - 49℃).