Fastener Durability

All cladding fasteners must be compatible with the material being fastened, suitable for the environment, and have a durability commensurate to that of the cladding material. All exposed fasteners must have a minimum durability of Class 4. (See Testing)

Only aluminium or stainless steel screws and washers should be used on pre-painted aluminium roof and wall cladding. Stainless steel fasteners must not be allowed to come into contact with the cladding and should be installed through oversize holes.

Sealing washers must be non-conductive to prevent electrical contact between the screw, the metal washer and the cladding surface.

Steel cladding screws can be subject to hydrogen embrittlement when they are hot-dipped galvanised. Alternative methods of galvanising, such as peen plating and other metallic coatings, in combination with an organic coating, are generally used for self-drilling screws.

Care should be taken to minimise damage to the head of the screw when using pre-painted, hot-dipped galvanised fasteners.

Sandblasting in exposed conditions can significantly reduce the coating thickness and the longevity of the fastener.

Premature failure can result when the shanks of the screws and the eaves purlin are exposed to sea spray, and a high-fronted gutter is recommended to help prevent this.

The performance of the shank of the fastener is also affected by internal environments when the contaminant is inside the building, e.g, animal shelters, fertiliser works.

 All fasteners should be easily identified by a code stamped on the head to identify the manufacturer and the coating class.