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Selection
Galvanic Series
2 different metals in contact with each other, in the presence of water will corrode. The less noble metal corrodes sacrificially to protect the more noble metal. The table is the Galvanic Series. The further the metals are apart in the series the faster and more aggressive the corrosion.
Comparability of Metals or Alloys
The selection of roof sheets and accessories must be in accordance with the Table.
The selection of lower roof drainage system (runoff) and accessories must be in accordance with the Table.
Corrosion can also be initiated by contact with any of the following and must be avoided. Where it cannot be avoided a non-galvanic coating must be considered.
- Carbon in pencils and some rubbers.
- Wet and dry concrete.
- Soils
- Vegetable matter.
- Cleaning agents e.g. brick cleaning.
- Any material which will inhibit normal exposure to the atmosphere.
- Green or some chemically treated timber like CCA or tanalith treatments.
- Materials subject to cycles of dryness and wetness or which have excessive moisture content such as improperly seasoned timber.
- Accumulated debris/airborne fallout due to lack of maintenance.
- Anything that will hold moisture in contact with the cladding.
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