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Painting Problems and Solutions
What is it?
- Thin light white powdery deposit on galvanized sheets. Generally seen on unpainted galvanized sheets. Painting over white rust can result in paint peeling. Not to be confused with “Paint peeling from galvanized substrates - Part 2
Possible Causes
- Galvanized components which were tightly stacked together with the presence of moisture. Generally occurs during storage and or transportation. The exclusion of carbon dioxide and presence of moisture in tightly stacked bundles can result in the formation of unstable zinc hydroxide. Once the galvanized surface is exposed to the atmosphere with the presence of carbon dioxide no further formation of soluble zinc hydroxide will occur and a stable zinc carbonate film will develop.
- The moisture present can be from various sources i.e. rolling fluids during profiling, exposure to rain and dew, condensation in stacked sheets due to rapid changes in temperature and a lack of ventilation between individual sheets even under covered conditions. Drying buildings and wet floors could also contribute to elevated humidity levels
How Can I Fix This Problem
- Asses the degree of the galvanized coating’s depletion. Remove white rust at spot areas with a stiff bristle brush (not a wire brush). Check residual zinc coating thickness with magnetic thickness gauge. SANS 121 (SABS ISO 1461) makes allowance for galvanized coating repairs
- Superficial white rust that has not resulted in severe zinc coating loss needs to be removed prior to painting as any loose deposits will impair paint adhesion. Small areas can be removed by abrading with a stiff bristle brush (not a wire brush). Large areas can be treated with proprietary products or simple chemical solutions. i.e. 1% solution of Trisodium Phosphate or 1% solution of Potassium or Sodium Dichromate slightly acidified with Sulphuric acid pH6. The solutions may leave a stained surface. In all cases effected sheets should be thoroughly washed and dried after treatment. Follow the appropriate precautions when working with hazardous materials. Follow manufacturer’s instructions.
Products in this colour
Duracoat Roof Paint
DuraCoat Roof Paint is designed for use on iron ro
Easy & Smooth Application
Excellent Adhesion
Excellent Durability
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