Spray foam is insulation that is injected or "sprayed" onto the surface of the walls between the wall frame boards. It expands up to 100 times its size to fill in the wall cavity and then adheres to the inside of the wall boards. This spray foam is very difficult to remove and the process requires an extensive amount of work. It must be manually ripped from the walls in pieces. The job will require several hours of labour to clear just a few hundred square feet of insulation.
Cutting the Foam
To remove spray foam you must first cut the foam. It is a solid material, so cutting it into chunks allows the foam to be pulled off the wall in pieces. Since it sticks to the side of the wall frame boards, start your cut along the inside of the wall frame board. Use either a reciprocating saw or a spray foam knife, which is similar to a tree saw in shape and design. Slice down the inside of the wall frame board, then cut across the foam to the other frame board. Cut up along the second frame board for a foot, and then across to the beginning of your first cut.
Removing the Foam
Once you cut a square of the foam, pull it from the wall by inserting a crow bar into the foam and pulling it out. A sharp knife will also work. Any type of digging tool will be effective. This may take several tries before the foam comes free. Once you remove the first section, continue on to the next section. Continue to cut and remove blocks of the foam in this way. Be careful not to damage the wall board beyond the foam with your tools. Remain aware of how deep the foam is as you work.
Cleaning Up the Foam
Have a plastic bag handy to dispose of the blocks of foam as you pull them free. Use a wet-dry vac to vacuum up loose pieces of foam as you work. After removal, parts of the foam may still be stuck to the walls. Either leave the foam as is (no one will see this remaining foam and it will only add insulation to the wall) or use a metal scraper to remove it. Do not apply acetone or chemicals as they are harmful to use and pose a fire hazard.