Everyone has read it…the epoxy manuals always suggest you test pump dispensers for accuracy.
You know, just to make sure they are dispensing the proper ratio of resin to hardener. Well, In the past, when I built my stitch n glue kayak, I just assumed they were correct. Yesterday, however, I decided to test my new dispenser pumps (purchased from Pygmy boats). I was shocked at the results. Here’s what happened:
- I noticed the restrictor tube looked a little short for the hardener pump, ie. it was not 1/2 the distance of the resin pump (I am using System Three epoxy, a 2:1 ratio system). This got me concerned, so I decided to accurately measure the results. I’m glad I did.
- I pulled out my ultralight backpacking digital scale and first measured the weight of a disposable plastic cup at 15 grams. I then tested both dispensers and measured the results, after subtracting the weight of the cup.
- After completing the test twice, I got the exact same results.
- One depression of my hand dispensers gave me 29 grams of resin and 10 grams of hardener. That is a 3:1 ratio not a 2:1 ratio. Wow, I’m so glad I tested this before glueing up my mast staves.
- I shortened the restrictor tube for the hardener by 1/8″ and did the test again.
- After repeating the test twice, I now got 29 grams of resin and 15 grams of hardener. That’s more like it.
Lesson learned, I will never trust hand despisers again without completing a thorough test for accuracy.
Hold the press…Pygmy boats just called and reminded me that the 2:1 ratio is by volume not weight. Oops…my entire test was performed on weight not volume. This has now demonstrated what often happens to me. The harder I try, the more trouble I create for myself. Oh well, we’ll see if it sets up. I was off almost 20%. So, let me modify the lesson learned. Don’t out think yourself…otherwise you will create more problems than you solve. I’ve reinstalled the short tube I cut off and will move forward and sin no more.
(Wait a minute…even when recalculating for volume, the pumps are still off a fair shot. After weighing all this out in my head, I plan on using the suggestions offered by those commenting below. I will use the pumps mainly as a dispensing tool so I don’t spill, but measure using the ideas below, especially for small amounts). Now…that’s my story and I’m sticking to it.