I am planning on finally fixing up my old surfboards and need advice on measuring the proper amount of catalyst. My usual method is to squirt it in a cup until it looks right- obviously not very accurate. So can anyone tell me the proper resin/catalyst in ml. per ounce (or equivilent)? Thanks in advance.
The amount of catalyst or hardner used depends on the resin you are using. If it is polyester resin, you would use MEK-P at anywhere between 1/4% to 2% depending on the temperature of the resin.
If you are using epoxy, the amount of hardner depends on the manufacturer of the resin. The ranges on epoxy can run from as much as 2 to 1 ratio down to as little as 10%. Read the instructions if using epoxy!
Ken
Airframe- thanks for the info. I am using polyester resin. I knew I had left out some important details, doh!
The book Essential Surfing by George Orbelian recommends the following:
For One Quart Resin: @ 1/2 % use 5cc catalyst
@ 3/4 % use 7cc
@ 1 % use 9cc
@ 1 1/2 % use 14cc
@ 2 % use 18cc
LESS THAN ONE PINT-
“For resin quantities less than one pint use 7 drops (slow set), 10 drops (medium set), 13 drops (fast set) catalyst per fluid ounce of resin.”
Doug
I appreciate everyone posting the info. That tells me exactly what I needed to know. I will be doing repairs on a early 80’s twin/ tri-fin round pin. I will post photos when I am done.
…be careful, not all the polyester resins needs the same quantity of MEKP…for ex.: some catalized really soon in small quantities but not in larger ones
A “gel time test” would be a good idea with any of the resins…
Ken
“Different polyester resins catalyse different”. Pretty true. All polyester resins are formulated with something known as “cobalt based accelerator” (at least in French, anyone knows the exact translation?). The more there is, the less MEKP is necessary and the faster the resin will set. I remember using resin in the past (around 1970) that was not pre-accelerated and we had to add the cobalt agent first. I think 0,2% was the right percentage. Also that thing would burst out if put in contact with MEKP so you had to be very careful not to mix them, and we used to stock them very far away from each other. I am no chemist but I strongly suspect that the reaction between cobalt and MEKP is what provides the heat which in turn makes the resin polymerize. Manufacturers must act on percentages of cobalt to make a resin “fast” or “slow”. For instance, Silmar is fast as compared to Reichold, in my experience.
is that why silmar is blue?
No, I don’t think so. The blue color (I believe) comes from additives known as “azurants optiques” in French (“optical azuring agents”?) When adding catalyst, blue turns to greenish then becomes more or less clear as the resin sets.