Basic Chemistry, the Properties of Metals and the possible effect on ColorCote®
pre-painted metal products, spouting, downpipes and gutters
Basic Chemistry and the Properties of Metals
When different types of metals come into contact with each other, and particularly when water is present, chemical reactions take place which result in the metal higher up the galvanic hierarchy of metals (i.e. metals more resistant to corrosion) eating away metals lower down the order. Brass, copper, lead and stainless steel are higher up the galvanic hierarchy than the aluminium/zinc-coated steel and aluminium used as ColorCote® pre-painted metal substrates. Direct contact between these dissimilar metals will cause the ColorCote® systems to quickly corrode.
Water coming from copper and brass pipes or spouting can cause corrosion to pre-painted metal roofing and cladding too.
The best solution is to make sure there is no direct contact between dissimilar metals.
If necessary, inert membranes can be used to isolate two different metals. This is the case when ColorCote® AR8™ and ARX™ are fixed using stainless steel fasteners. A special low carbon washer is used between the two metals.
Other materials that will cause problems:
- Cement will have a corrosive affect on the paint systems and must be wiped off immediately
- Tanalised timber and some other timbers such as cedar can cause galvanic corrosion. In mild atmospheres seal the timber surface with an inert membrane at the points of contact. In severe and very severe conditions the two surfaces must be fully isolated by a rubber or neoprene gasket.
- Concrete and plaster can cause discolouration to the paint coating which should be protected by an inert membrane where they come into contact.
Materials Compatibility Table
Click table below for larger image
Disclaimer:
This chart has been compiled by New Zealand Metal Roofing Manufacturers Inc (NZMRM). Neither NZMRM nor Pacific Coilcoaters makes any warranties or representations of any kind (express or implied) with regard to the accuracy, adequacy, currency or completeness of the information, or that it is suitable for the intended use. The final responsibility for correct design and specification rests with the designer and for its satisfactory execution with the contractor.The decision to use a particular material, and in what manner, is made at your own risk.
For further information, contact your local territorial authority, NZMRM or Pacific Coilcoaters.