According to their site, Coroplast is difficult to glue to itself and other materials, but that "corona treatment on the surface is necessary for most of the methods that are successful."

Materials like this have a high surface energy which makes them difficult for adhesives to stick to. Corona treatment is usually done with high-voltage arcing -- wires passing over the plastic cause electric arcing that essentially 'zaps' the surface and lowers the material's surface energy. O.K., so you may not want to try this at home, but the same effect can be achieved by simply flaming the surface. Just touch the surfaces to be glued with a flame. I wouldn't use a propane torch because it's too hot, but use a cooler flame like a ligher, candle, or maybe one of those barbecue grill lighters. Ideally you'd want something that throws a little bit bigger flame, like my camp stove does before the fuel is vaporized in the line. Hmmm -- maybe an alcohol lamp? All you need to do is barely touch the flame to the surface, and then don't touch those flamed surfaces with your fingers before you glue them together. It'd be worth doing a little test on...

I like the idea of ultrasonic welding (essentially rubbing 2 pieces of Coroplast together really fast so they melt together)...I'd like to see someone attempt this in their garage...

Dean