Hey, Charles-

I use MAS, and until last year, only used slow hardener. My old shop temps were between 62-65F, and slow worked beautifully (for me, anyhow, being a bit stupid about epoxy).

In my new shop, I found myself glassing in 55-58F temps. The slow worked, but took over a day until I could do anything with it. I added one squirt of fast hardener for each nine of slow, and it worked well. It was striking how a little bit had such an effect. I just bought a quart of the fast; figure it will last a while. At the temps I'm talking about, I would not use more that 10% fast for glassing work, unless you are much better at it than I am. I am pretty slow myself . Mike