Calculate the amount of insulation by dividing your attic's square footage by the coverage area of the insulation package you plan to purchase.
Remove as much spray foam as possible with a scraper or blade, then use a rag dampened with mineral spirits or acetone to clean any remaining residue from the surface.
Spray foam becomes tack-free in 5 to 60 minutes and fully cures in about 8 to 24 hours, depending on the product and conditions.