Got things ready late this morning, after putting the buck and form out in the sun for a while to warm up. About 55F overnight in the garage. I've been keeping the paints, varnish and silicone materials inside the laundryroom at 72F to make things easier in this process.
I made the form pretty tight. The silicone just has to be thick enough at its thinnest areas to prevent tearing during handling / demolding cycles. The form itself supports the casting process, the silicone is just there for details and shapes.
I got the first 1/2gal of silicone RTV mixed up and litterly the moment before pouring, looking for the spot to stream it into the mold, I realized I'd forgot to lube things up. Good thing the mix has a long pot time (50mins). Got things sprayed down with cooking spray (canola oil) and wiped around, a nice wet coating of mold form and buck. And nice part about casting a concrete buck is you don't have to glue or hold it down. It isn't gonna float up out of the pour.
So I poured in the corner and watched it all flow around the bottom sides and up. And a long way left to go. Would the gallon kit be enough? I hoped so. Mixed another half gallon and in it went - another advantage of long pot time, same pot, good intermixing. No need to let one layer set up first. And still came up well short of the top of the form. Which I made about 1/2" above the top of the buck.
Then I mixed what was left of the kit, about another pint. STILL short. So I broke out the 1st kit I bought for the pencil liner gang mold and mixed another pint and came close enough to filling the form to call it good.
So I still have enough left in this first kit and will have to buy another 'gallon' kit to make the 2nd mold in the other half of the gang form. It's a 5qt pour.
When it is all ready to go I should be able to mix and dye a 60# bag of mortar and cast 2 capstones and the 6 pencil liner pcs. with very little left over, if any. The capstone molds need to survive 15 cycles.