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Would someone please care to explain the pros and cons of galvanized (hot & electro), stainless, zinc plated, spray (cold) galvanized, and (paint?) coated fasteners?

There seem to be different preferences and prohibitions for the type of wood (PT, ACQ) and the environment. For instance, carriage bolts come hot dip galvanized, but play structures come with coated bolts. Roofing nails come both hot dip and electro. Even indoor framing is done with galvanized nails.

Some last longer, others have better threads, some loose their protection upon driving/striking etc... and I am not sure what is hype, what is real, what I can get away with, and what is required.

For those willing to put in the effort of a good write-up, I appreciate a thorough and balanced answer. This forum still beats all sorts of blogs and other writings because readers here can follow-up with questions, rebuttals, and clarifications.

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Stainless Steel

If you want the best in corrosion protection, pick a metal that is difficult to corrode. Stainless steel is not impossible to corrode (there are various grades of stainless), but it survives in any outdoor environment and usually stays as shiny as the day you bought it. It even survives the highly corrosive environment inside pressure-treat wood.

The cons? It's a much softer metal than its regular steel cousin. If you need serious structural support, stainless is not the way to go (this is why stainless nails really aren't much of a thing). You also want to pre-drill holes (unless you buy the nice non-drill variety) because you can strip regular stainless screws far more easily.

Galvanized

There's two kinds

  • Electro galvanized is meant for indirect moisture contact like roofing (where the nail isn't directly exposed, but it could get some moisture). This is the weaker of the galvanized because the process doesn't get much zinc on the fastener
  • Hot-dipped is the far more common. It comes in all sorts of fasteners and can even be used for water pipe (not as good as plastic, but it'll work)

Because they're steel, you can find these in pretty much any type of fastener. Galvanized slows the process down by coating the fastener (usually steel) in zinc. As such, the zinc coating needs to corrode first before the underlying steel corrodes. But these still corrode, and they corrode fairly quickly in any place they are exposed to moisture. Don't use these anywhere you want to avoid visible rust.

Painted

Depends a lot on the paint. What you want are screws that have a semi-gloss finish (the gloss resists moisture better). These will still corrode (the threads will have their coating stripped when you screw them in), but they are generally designed to last a very long time (they are most commonly sold as deck screws). Beyond that, painted is usually slightly above galvanized in price and tends to be less prone to displaying rust (because the head is coated).

Also look for powder coating. This provides a superior paint grade as well, but it's a less-touted feature.

Other

There are some other types of coatings as well. I'm not sure what GRK/Tapcon uses in their screws but they don't tout any of the above. I doubt they're the only ones with a premium coating (GRK and Tapcon can be more expensive than stainless in some instances).

What to use?

If you're building a fence, galvanized is the cheapest (largely due to you have the option of nails). Galvanized will also offer you steel bolts, for which there isn't much substitute if you need structural support.

Screws offer more types of fastener (including the coveted stainless) and a wider variety of costs as well. I prefer screws because they often drive in easily with a power driver and you can always re-torque them if they work out of the material. I find painted work fairly well for a decent price (in fact I only keep painted ones around in longer sizes for small projects because they're only slightly more expensive than their un-coated brethren).

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  • Nice overview! "Galvanized ... Don't use anywhere you want to avoid visible rust." Carriage bolts for deck posts etc... are visible, exposed, yet hot dip. Why? Cost? – P2000 May 11 at 14:58
  • @P2000 Cost and structural. If you need it to hold structure, the rust is a secondary concern – Machavity May 11 at 14:59
  • Aha, I noticed coated bolts on a play structure (my hardware store doesn't have them). I suppose that's for strength + esthetics, which galv cannot accomplish. Also, would you use non-galv nails for indoor framing? I buy rolls of galv because I mix indoor & outdoor, but I was wondering whether indoor framing requires galv for other reasons – P2000 May 11 at 15:01
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    The only need for galvanized indoors might be in securing a bottom plate board for a wall to a poured concrete slab (where the concrete is a potentially wet zone). Beyond that, there's no real benefit to galvanized indoors. I too buy exterior to keep on hand so I can use for any project. There's not a huge cost difference between indoor and outdoor unless you're doing things at scale. – Machavity May 11 at 15:12

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