The sections for my sewer are largely ready for paint and I decided to try something new instead of the usual PVA, paint, and water.
This stuff is pretty good. Your mileage may vary but I got all the main pieces of my sewers triple coated with spray primer. I think with extruded styrofoam sheets it will work better. The expanded polystyrene just has too much exposed area to do any less...
This is my fault. I gave this piece two coats of primer and didn't give it time to dry properly before giving it a coat of black. You can see I ended up getting a cool looking texture for my efforts. Seeing this patterning was enough to make me slow down and give the other pieces time to dry properly.