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Drive screws that don't corrode

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Fasteners for pressure-treated wood
Hand holding screw
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Composite decking requires
a different thread pattern, as
shown above. Traditional-threaded
deck screws don't hold well and the
boards "mushroom" (form a convex
surface).

Fasteners for pressure-treated wood

If you purchase one of the new-generation pressure-treated woods (came to the market in 2004 or later), be sure to ask your retailer about recommended screws and fasneners. For example, your dealer may stock proprietary anti-corrrosion technologies matched for alkaline copper quat (ACQ) or copper azole (CA-B).

These multiple-coated screws have several advantages. First, some of the coated screws come in colors that help the fastener blend with natural and pressure-treated wood tones. Also, the additional coatings increase corrosion resistance. For example, the outer coatings resist tannic acids, making them suitable for use with cedar and redwood decking. These coatings also help prevent iron stain (if the coating remains intact). This type of stain should not be confused with extractive bleed. The latter can occur with any fastener.

Nevertheless, any coating has the potential to wear through and expose the underlying steel to corrosion. This wear typically happens when you drive the fastener. Some low-cost coated screws lose part of the coating covering their threads after one drive through dimensional pressure-treated lumber.

All of the fasteners we tried showed some wear in the coating covering the driving recess. If you are less than careful and leave the head of the screw slightly above the surface, foot traffic will abrade the coating, too.

Our advice: Buy a few sample screws and test-drive them in the material you intend to use. Also, ask the manufacturer about how well the screw holds up in a salt-spray test; disregard any fastener not test-rated for a minimum of 1,000 hours.

Yellow-zinc coated steel
Some fasteners with this electro-plated coating are labeled as being corrosion resistant, but they are not appropriate for exterior applications.


Continued on page 4:  Driving lessons

 

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