GUIDANCE ON HOW TO ASSESS WHETHER AN AGED METAL COATING IS SUITABLE FOR RECOATING.

Metal roofing and cladding sheets can be protected indefinitely if correctly maintained, but advanced coating failure often spells expensive replacement of roof sheets. This article is intended to help you determine whether a roof or wall sheet is suitable for application of a refurbishment coating to lengthen the life of the structure, rather than full roof replacement.

How do I know if the original coating is suitable for application of a new coating?

In many cases, when protective coatings are subject to long term exposure to UV light the polymer bonds begin to slowly break down, causing colour loss and chalking.

The coating progressively weakens so it no longer has its original strength and flexibility. Small cracks and splits then form in the coating, trapping moisture which causes freeze thaw weathering. The cycle continues until the coating completely weathers away.

However the deterioration can be halted if it is treated in the window of time between chalking and cracking!

If the original factory applied coating is only chalking and fading, but still strongly adhered to the metal substrate, with no cracks, flaking or peeling, it is very likely that it is still suitable for recoating. Isolated spots of corrosion can be treated using our rust inhibiting primer.

If the original coating has worn very thin, is cracked and has extensive delamination it is clear that the material has failed and will not be suitable for a successful refurbishment. This is because the original coating is no longer adequately bonded to the metal and will not provide a stable substrate for a refurbishment coating.

How do I tell if the coating is chalking or cracking?

Chalking is a simple descriptive term used within the coatings industry to describe the formation of the dusty surface that forms on a coating after extended exposure to UV light. Typically, the coating will not have lost too much strength or thickness and is still a well adhered substrate for an application of a refurbishment coating to extend its life.

A coating will begin to crack after extensive chalking leaves the coating thin and brittle with very low resistance to thermal expansion. Small cracks quickly enlarge due to freeze thaw weathering, and at this point the coating is generally not adhered adequately to the substrate to provide a suitable base for a warranted refurbishment coating.

The only option then is to replace the sheets – far more expensive than maintaining the roof in the first place!