Expanding foam can mend even large holes in an interior or exterior wall. There are two kinds of foam: polyurethane and latex. Polyurethane foam is rigid and porous when cured and can be sculpted when dry. Latex foam is spongy and cannot be sculpted when cured, but can be shaped while wet. Both types of foam stick to most surfaces such as wood, metal, drywall or masonry.
Practice with expanding foam first if you are unfamiliar with the product. Spray a little on a piece of newspaper to see how it expands.
Spray polyurethane expanding foam sealant into the hole. If the hole is really large, mist with water between layers to speed up the curing process. Fill the hole about halfway -- it will continue to expand while drying. Allow to cure for eight hours or overnight.
Trim off extra cured foam with knife and sand the foam until it is level with the rest of the wall.
Clean the patch with a rag and paint.
Always use gloves when handing expanding foam it will stick to skin and is difficult to wash off. A can of expanding foam will seal itself after two hours and cannot be capped. Plan using the can in one session.