Zinc vs galvanised vs stainless steel screws: what’s the difference?

Don’t you hate it when you’ve got the wood sorted for your deck, wall or shelves, your wallet has taken a hit, and then you find it’ll cost another $100 for the right fasteners?

Yes, these little suckers, which we hope will always be lying around the garage, can be a bit of an investment, occasionally costing over a dollar per screw, depending on whether you need a bugle baten, carriage bolt, or self-drilling socket screw.

Many of the fasteners put into wood and metal in decades gone by weren’t up to the task or came with heads and shafts which can be difficult to remove. This is why, when you’re ready to fasten your building project, it’s essential to put in fasteners and/or nuts with the right drive screw drive type, the right coating and the right tip.

Firstly, let’s talk about what causes corrosion on your fasteners, to help you work out whether what you’re building comes with a risk that its fasteners will result in unanticipated damage.

The main types of screw coating and treatment

When talking screws, specifically, hot-dip galvanised, stainless steel, polymer coated and brass are four of the main types you’re going to encounter. Renovation Warehouse always stocks a few of these and will point you in the right direction if we don’t have the right length or type in store. Those coatings are because preservatives found in the H3-H5 standard of wood used for decks, piles and other outside structures can occasionally mean a risk of corrosion causing your joist hangers, bolts etc to rust, fail or snap.

Copper isn’t corrosive in a dry, inert environment, but copper ions can by lifted by water on wet wood into the metal hardware. The galvanic reaction then will cause steel to suffer from corrosion. Different species of tree will create different effects, as will the amount of time the wood is left wet.

Wet wood is often the problem

If wood has less than twenty per cent moisture content, the risk of copper leaking out and reacting is low. Generally, hot dipped galvanising (meaning a thick layer of zinc is applied to the screw or bolt) is the best defence against copper corrosion, especially in coastal regions where the salty air and water can act as an electrolyte, speeding up the corrosion. Slightly cheaper than hot dipped screws are those in which the zinc is applied by electroplating – but these fasteners are cheaper because they don’t have quite as long a life.

Stainless steel fittings/fasteners are what you really want as a defence against salty air, sea spray and salt water. Just check the rating – 304 is usual, but 316 grade is better.

How can I find the right fasteners on the shelf at Renovation Warehouse without reading 1000 packets?

Hot dip galvanised metal is known for its distinctive mottled look – so, easy to spot on the shelf. Fasteners that have been zinc plated are known for looking silver/gold/shiny.

There is also the chrome option. Chrome plating is as effective as zinc plating and looks terrific – but costs a bit more than your quick, ready, reliable hot dip galvanised fasteners. There are also several colour options in screws, caused by the variations in their coatings, from polymer and resin to silicon bronze, chromate and yellow zinc versus clear zinc.

Lastly, that beautiful woodwork project you have ready will be ruined if the wrong screw makes the wood split. Be sure to ask the Renovation Warehouse team if you don’t understand the difference between auger, fluted and serrated tips and the pros and cons of each.

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