Corrosion Protection for Screws and Nails

When looking to purchase fixings, whether for roofing purposes or otherwise, it’s easy to get lost in the huge variety. This article will break down the advantages and disadvantages of each type of coating available on the fixings stocked here at ERoofing. 

Black Phosphate 

• Cost-Effectiveness: *****
• Corrosion Resistance: ****
• Longevity: *

Black Phosphate is created by exposing metal to a combination of phosphoric acid and phosphate salts. The resulting black coating helps prevent corrosion from occurring. In the short term it produces very strong corrosion resistance while being cheap. However, black phosphate by itself doesn’t stack up to other methods in terms of full-bore corrosion resistance.  For this reason, it is often oiled or painted in order to extend its life if it is installed externally. Fortunately, black phosphate is an easily painted surface.

Fixings with Black Phosphate Coatings are primarily best for interior use such as drywall.

Zinc Coatings

• Cost-Effectiveness: ***
• Corrosion Resistance: ***
• Longevity: ***

Zinc Coatings can be applied in several different ways. The most common method for fixings is hot-dip galvanisation, where parts are immersed in molten zinc to provide a thick layer. Zinc has a long lifespan for a coating because it is more reactive. Essentially, even if the zinc layer itself is compromised, it is still a priority target for corrosive chemicals above the steel itself. This means that only when the zinc layer is completely destroyed will the steel in contact with it start to rust. 

However this property also means that zinc fixings should not be used in direct contact with metal that is neither zinc nor galvanic steel. This is because of galvanic corrosion, where one metal will react with another of a different kind. 

Fixings with zinc coatings are best for woodscrew purposes or when fixing in non-metallic materials like most corrugated sheeting. 

Silver Organic Coating

• Cost Effectiveness **
• Corrosion Resistance ****
• Longevity ***

A unique variation on zinc coatings. Silver organic coatings use a three-layer approach with an inner layer of zinc, a second layer of chemicals and a third, ceramic layer. The ceramic layer is baked in to make sure it’s totally durable. 

This inert surface makes it excellent for fixings that are metal-to-metal because the ceramic will prevent the materials from making direct contact. 

Stainless Steel

• Cost-Effectiveness: *
• Corrosion Resistance: *****
• Longevity: *****

Stainless steel is unmatched in terms of its corrosion resistance. This is because it is not merely a coating, rather the steel itself is different to normal steel. The alloy is partially composed of chromium which helps protect against rust. While there are still some metals that stainless steel screws shouldn’t be used with they will react badly, it is much less reactive than zinc so it is easier to use with more metals. Only zinc, aluminium, galvanised steel and cadmium should never be used with stainless steel. 

However, the high cost of stainless steel makes it unsuitable for most fixings. Only fixings which require a top level of both strength and water protection will need to be made of stainless steel. 

Choosing a fixing isn’t about choosing for your entire house. It’s about choosing the correct specific fixing for the correct specific task. At ERoofing we offer a huge range of both specialist and general screws and nails with many different coatings and purposes.