My fellow PDB author and friend Kim Katwijk introduced me to Heatcon’s thermal blanket system (800.556.1990, heatcon.com/industrial/heat-forming-kits) a few years back, and I’ve been using it ever since to bend composite and PVC boards. If a design includes curves, I try to use TimberTech or (preferably) Azek products, which are the easiest to bend with heat.
One kit—consisting of two 10-foot-long silicone-rubber thermal blankets and one control box—is required to bend a 10-foot-long plank; use two kits for a 20-foot-long deck board. Temperatures and times vary widely, but it typically takes about 35 to 55 minutes to heat an Azek cellular PVC deck board to its bending temperature of between 225°F and 275°F (see Tool Kit, “Bending Composite Decking,” May/June 2007 for more on this system).
I recently built an oven to cook up railing and other components. It’s about 8 inches wide and 11 feet long to accommodate the Heatcon blankets—my heat source. I biscuit-jointed treated 3/4-inch plywood for the sides and insulated it with 2-inch-thick rigid foam.
I built the box in one piece, then split it into two unequal pieces to create a lid (be careful not to place any screws where you are going to rip the box). Afterward, I sealed the inside seams with 3M Fire Barrier Sealant to keep as much heat inside as possible. When the sealant was dry, I layered foil skrim kraft paper on the inside of the box for even more heat retention.
I installed a piano hinge all the way down one side of the box, and a couple of hasp closures and a handle on the other side for opening and closing the lid. After laying the blankets in place, I stuck a couple of pieces of mesh wire into the foam sides of the box to keep the blankets from moving around. A plywood box holds the control unit in place. In use, temperatures inside the box easily reach in excess of 275°F, while the outside of the box stays a cozy 95°F.