Travis Jordan wrote:

DiezMon wrote:
I was thinking I'd build the mold with 3/4" ply, then line the inside
with Masonite so it's mucho smooth. waddya think?

Any other "cleaner" release agents I could use?

I don't use a release agent and have never had a problem. Plain old
sheathing plywood is plenty smooth enough, especially if you are going
to paint the planter. Just use a wet mix and after pouring tamp it down
to eliminate any bubbles as marks recommended. Pound a bit on the side
of the mold, too.

Possibly that white "tile board" Masonite stuff would leave a good
finish. Also consider rigid foam board insulation and the possibility of
routing decorative features in the foam to cast them into the planter.

Pete C.