For those of us doing vehicle maintenance, this will be the most common barrier. Again a stiff brush is essential even if you apply it with an aerosol. Rinse and dry to avoid any fires later in the process.

• Clear greasy fasteners for penetration lubricant.

• Buy enough to be generous.

• Buy non-toxic particularly if you own pets.

• Buy non-flammable if available.

• Always wear eye protection.

• Always wear dermal protection.