Drive screws that don't corrode
Coated steel fasteners
Because of the many available coatings and different processes for applying them, this category can confuse many DIYers. Most local hardware outlets still sell the galvanized fastener as their basic exterior-grade fastener. Generally speaking, the thicker the galvanized coating (consisting mostly of zinc) the more durable it will be. You'll find the thickest zinc coatings on hot-dipped nails, but you may have a hard time finding hot-dipped galvanized screws. That's because the thick, globby coating tends to clog the threads and driving recess of the screw, making it hard to drive.
Commonly available galvanized screws are either mechanically galvanized or electro-galvanized. At the lumberyard, you can quickly tell these two types apart because mechanically galvanized screws have a dull gray surface and electro-galvanized screws have a shiny silver-color surface. We do not recommend electro-galvanized screws (also called clear-zinc coated) for exterior applications. They will corrode quickly in contact with the elements.
Mechanically galvanized screws are generally suitable for decks and other outdoor projects made of pressure-treated lumber. Nevertheless, you should not use them with PT lumber in contact with the soil, in high-moisture areas, or in areas with salt content in the air. Also, keep in mind that mechanically applied zinc contains some iron that is susceptible to attack from the tannic acids that occur in redwood and cedar. The acids combine with the iron to form a dark stain around the fastener head.
As you can see in the photo shown, manufacturers have improved the basic electro-galvanized fastener by adding a polymer coating (often pigmented) on top of the galvanized coating.
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