The coating on a roof sheet gets plenty of attention. The finish on the fixings holding it in place deserves consideration too.
Rain, condensation and the atmosphere around a building all influence the protection a fixing needs. That applies whether you are supplying a new industrial roof, replacing sheets on an agricultural building or completing a cladding repair.
Bright zinc, zinc and yellow, DACROMET and RUSPERT are familiar names, but what sits behind them? Here is a short guide to how these finishes developed and what they mean for roofing and cladding fixings today.
Zinc Plating: The Familiar Bright and Yellow Finishes
Zinc plating applies a thin layer of zinc to the steel. It provides what is known as sacrificial protection: the zinc corrodes in preference to the steel underneath.
BZP stands for bright zinc plated. Its familiar silver or slightly blue appearance is commonly associated with clear or blue passivation, a treatment applied after plating. Zinc and yellow uses zinc plating with a yellow passivated finish.
Both belong to the same broad coating family. The colour gives an indication of the finish, but the zinc thickness and passivation have a greater bearing on its corrosion resistance. Two similarly coloured fixings can have different levels of protection.
DACROMET and the Development of Zinc Flake Coatings
The late 1970s saw the introduction of DACROMET, which used zinc and aluminium flakes in a protective coating applied without electroplating.
It gave manufacturers another way to protect fasteners while keeping the coating relatively thin. Later developments included GEOMET, a chromium-free zinc flake system.
These developments broadened the choice of protective finishes. Zinc plating and zinc flake coatings both remain in use, with the particular treatment selected to suit the component and its application.
RUSPERT: Protection in Layers
Developed in Japan during the 1980s, RUSPERT combines metallic protection with a baked protective surface coating.
The conventional zinc-based system has three main layers. Metallic zinc sits over the steel and provides sacrificial protection. A chemical conversion film helps the layers bond and contributes to corrosion resistance. A baked ceramic surface coating forms the outer protective barrier.
The layers work together to protect the fixing. The zinc protects the underlying steel, while the outer coating helps shield it from the surrounding environment.
RUSPERT has continued to develop, with different formulations and performance requirements. This is where descriptions such as 500-hour and 1000-hour RUSPERT come into the conversation.
What Do 500 and 1000 Hours Actually Mean?
The hours refer to a controlled laboratory test, rather than time spent outdoors.
During neutral salt spray testing, coated samples are exposed to a salt mist and checked for signs of corrosion. The condition of the samples matters just as much as the time in the chamber. A report should identify what was tested, what was assessed and what counted as a pass, such as completing the stated period without red rust on the steel.
Where the specimens, test conditions and pass requirements are comparable, a 1000-hour requirement calls for a longer successful exposure than a 500-hour requirement.
It does not mean twice the lifespan on a roof. Salt spray hours cannot be converted into a reliable number of years on a building.
Higher-hour coating options are also available. The figure forms part of the specification, alongside the coating system, intended application and conditions in which the fixing will be used.
Choosing for the Building
For UK roofing and cladding, the surroundings matter as much as the product description.
A coastal site, an industrial building and an agricultural building can expose fixings to different conditions. Moisture and the atmosphere inside the building also need consideration, alongside the external weather.
The material and coating should suit that exposure and be compatible with the sheet or panel system. Any stated project specification or warranty requirements need to be checked when selecting the fixing.
Coating is also only one part of the selection. The point, thread, washer and length must suit the connection. Our guide to choosing the right roofing and cladding fixing explains those details.
Premium 1000-Hour RUSPERT as Standard
At Leoclad Supplies, premium RUSPERT coating with a 1000-hour neutral salt spray requirement comes as standard across the carbon steel roofing and cladding fixings in our Specialist Imported Range.
That includes our stitching, single skin and composite panel fixings. We chose this specification because we wanted it to be part of the products our customers order every day, and we are proud to include it as standard.
The fixing must still suit the application and building environment. Our Resource Centre brings together product data sheets and selection guidance to help you check the relevant details.
For help choosing a fixing, tell us the application, supporting material and thickness, sheet or panel build-up, and any relevant exposure or project requirements. We can help narrow down the appropriate options and provide the available technical information before you order.
Contact the Leoclad team to discuss your fixing requirements.