This project was completed during the 3 day Advanced Fiber Reinforced Concrete Training at CHENG Concrete in Berkeley, California with guest instructor Chris Franzen from Surecrete. The unique characteristics of a fiber-reinforced concrete mix make it possible to cast a flat piece, wait until it enters a "false-set," and then bend the piece. For this we need a flexible mold, and in this Instructable we'll outline the steps needed to create a polyurethane rubber mold that will work for this technique.
Even if you aren't using a fiber-reinforced concrete system and bending concrete, the rubber mold-making steps are general enough to apply to any casting project.
Be sure to enter the Concrete & Casting Contest for a chance to win some nice prizes!
General Materials and Supplies:
- Cardboard, Poster Board, or Paper to make a mock-up
- (4' x 8' Sheet) Melamine Coated Particle Board (or plywood with a water proof coating)
- Jig Saw
- Orbital Sander / Sanding Block / Sandpaper
- 100% Silicone Caulk
- CHENG Curved Wall Sections (bendable plywood or straight walls will work as well)
- (15 lbs.) Polytek Polyurethane Mold Rubber 75-60 (or similar)
- Pol-Ease 2300 Mold Release
- (50 lbs.) - CHENG D-FRC Casting Blend Light Base (or Xtreme Series Concrete mix or similar GFRC mix)
- (1 bag) - CHENG Smart Color Indigo Pigment