Double Boiled Linseed Oil is commonly used as a waterproofing and sealing agent, protecting unfinished wood surfaces against minor surface damage, grazes, and watermarks. The level of waterproofing provided by linseed oil doesn’t withstand outdoor use and should be taken into consideration. In the steel industry, linseed oil protects against corrosion and repels water to avert rusting. As a carrier oil, linseed is formulated into oil paints and blended with stains to increase drying efficiency. Linseed oil is not food grade.