Riddle me this about mixing polyester resin with catalyst using weight or volume.

[Alguy]

I'm looking at the instructions for TotalBoat Laminating resin and it says mix 7/8 drops of catalyst per ounce (or 1 teaspoon) of resin. I set out to find the answer and found some websites seem to use volume and others use weight. Totalboat says its based on weight. I just don't get the correlation. How does 1 tea= 1ounce. Am I just reading it wrong? Iv'e always gone by volume with the resin then add the number of drops. I measured it and as it turns out 1 ounce in volume almost equls 1 ounce in weight.

 

[racerone]

I use WEST SYSTEM Epoxy.--------Just 1 pump of resin and 1 pump of hardener.----Perfect every time.-----More money I know.-----But no smell and great results.

 

[froggy1150]

Unlike epoxy where you need to be accurately 50/50 poly has a "range". 2%.... if its hot and it sets off too fast you drop down and in the cold you add more. I dont think i have ever needed to go above 2% but i have dropped down to 1% when i was doing the big floor sections so i had good working time. Never had an issue with weak or incomplete cure at 1% but should stay 1 1/4 - 2 1/4%. Too hot a mix (3%) and you get brittle. Below 1% and it might feel hardish but wont be really cured.

 

[froggy1150]

I use a baby medicine dropper that has stops at 2.5 cc 5 cc 7.5 cc and 10 cc. Set it for the size batches you will be doing and all you have to do is dip and pull.i also use the 59 cent quart measuring cups from walmart. They have a handle and i get several uses out of them before they become hard to clean out with compressed air.

 

[Emerger]

I'm looking at the instructions for TotalBoat Laminating resin and it says mix 7/8 drops of catalyst per ounce (or 1 teaspoon) of resin. I set out to find the answer and found some websites seem to use volume and others use weight. Totalboat says its based on weight. I just don't get the correlation. How does 1 tea= 1ounce. Am I just reading it wrong? Iv'e always gone by volume with the resin then add the number of drops. I measured it and as it turns out 1 ounce in volume almost equls 1 ounce in weight.

It's easiest to go by volume. Metric makes it even easier. Look for a squeeze bottle type container with a graduated cap. I'm in Florida where it's hot and I use 8-10 cc (or ml) per quart (or liter) of resin so it's slow enough to wrangle with. You can also go on Amazon and buy graduated medicine cups for cheap. I've mixed hotter stuff when I'm in a hurry but I don't recommend it. Going by drops will get you close but the temperature will make it vary a bit. On a hot day you want 1% catalyst to resin but if it's cool go with 2%. One liter is 1000 ml so the math is easy.

 

[76SeaRay]

This is something I have been struggling with as well. The US Composites says 10 drops per ounce of resin. Since I am making larger batches (8 to 16 ounces of resin) counting drops just doesn't work (16 ounces requires 160 drops). I have been looking for a conversion table (convert drops to ounces for 1% and 2% on larger quantities for example) but haven't found one.

 

[todhunter]

This is something I have been struggling with as well. The US Composites says 10 drops per ounce of resin. Since I am making larger batches (8 to 16 ounces of resin) counting drops just doesn't work (16 ounces requires 160 drops). I have been looking for a conversion table (convert drops to ounces for 1% and 2% on larger quantities for example) but haven't found one.

Don't over-think it. The more you work with it, you'll figure out what works for you, and it doesn't have to be super exact. Here's the chart I made which I have hanging up over my mixing station. I use the little clear medicine cups that come with the catalyst from US Composites. In the table below, the numbers in the white cells are oz of resin. The rows correspond to what % you want to mix to, and the columns correspond to how much catalyst to add - easy to figure out on the medicine cups.

Most of my batches are 17 oz resin and 5 cc of catalyst. Any bigger and I risk spilling when mixing, because I am using quart cups. This table also works for making PB - just add cabosil and milled fibers to get the consistency you want.

 

[76SeaRay]

Thanks for the chart. I think that will help a lot of people getting started.