I would like to make an L-shaped concrete bar top (single piece). However, I want to make the corner have a large curve (12-15" radius?). How can I create a mold to accomplish this? What materials should I be using? Will concrete stick to foam?
NOTE: I have woodworking tools at my disposal. No metal fabrication please.
Laminated MDF is the typical form material (aka, prefab shelf boards). You can usually get the laminate in strips (for backsplashes and edge-banding counter tops). I'd make the square parts of the form, then use several layers of the edge banding laminate to create your curve. Create a curve template out of plywood, then glue the laminate around the curve.
1/4" birch underlayment plywood (Tecply) should take that bend even without kerfs, moisture or heat. I'd probably double or triple it (without fastening together) for stiffness.
Build your form out of lumber, then either rabbet the lumber for the plywood to achieve a flush joint, or lay plywood all the way down the 2 sides adjacent to the bend.
Any type of thin plywood will do. Cut it into 6 inch strips and it bends easier. You might need two layers. Intalls the strips inside your frame, don't use the strips as your frame.
