I know this has been answered in another thread but I can't find that thread so what is commonly used to seal the typical pink or white rigid foam insulation so that you can then use bondo and glass to finish the surface for molding or finishing?

I did a google search as well but I don't seem to have the right key words as I am not getting the results I was hoping for.

I have a couple items to carve that I am not 100% sure what the final shape will be as I am not 100% of just what I want to do just yet or how I will shape it so I want to use the cheaper stuff first as well as try out this side of the molding process. I don't feel like pouring two part uerathane foam and then carving again. I would rather use the cheap foam and get the basic shape first and then spend some time cleaning up the shape and pull a mold from there.

1 of the parts is a water/air dam for the section that is between the rear of the front hood and the windshield that would shape around and with the wiper baldes and seal up against the under of the front lid to keep water out of the front trunk area and still look proper as with factory cars. I was looking into using thin poster board to get the basic shape but that wasn't working out very well so I thought foam would be the best way to get a basic shape carved out to see if the concept works. Hence the reason for cheaper and more easily manipulated rigid foam for the larger piece. I also don't want to go through the work of getting this foam piece carved and then find out I can't get it sealed so that I can pull a mold and put in a fiberglass piece as a final item.

Any help on the sealer would be great.