Coroplast is a type of corrugated plastic most often used in signmaking. Crafters have had success using it to build models, such as model aircraft, because of its light weight and hollow inner structures. Like other plastics, Coroplast pieces can be difficult to glue together without resorting to heat welding, as the polyethylene in Coroplast makes it chemical-resistant. You can strip this property from the surface of the plastic to make it more easily bondable with glue.
Cover a work table with large ceramic tiles to create a fireproof surface.
Lay your Coroplast pieces flat on the fireproof surface, with the sides you would like to glue facing upward.
Heat a propane torch to a low flame. Pass the torch quickly over the Coroplast, heating only the areas you want to glue. Do not overheat the plastic, as you risk melting or weakening it.
Place a drop of water on part of the surface you heated. If the water beads up, you did not succeed at burning away the surface treatment and must repeat Step 3.
Place tiny drops of cyanoacrylate glue close together where you want to join Coroplast pieces. Press the pieces together.
Let the glue dry completely.