General:
A galvanised surface, especially when new, is particularly difficult to paint for the following reasons:
- It is so smooth and does not provide a good key for most paints.
- It is usually heavily pretreated by the steel manufacturer to prevent white rust on storage and this pre-treatment must be thoroughly removed before paint is applied.
Zinc as a metal can react with the ingredients in some paint to form salts between the paint and the surface, thus further reducing adhesion. It was the practice in years gone by, either to allow the galvanised iron to weather to obtain a surface receptive for paint, or to use mordants such as copper sulphate, vinegar, spirits of salts, etc. These methods are now obsolete having been proved technically unsound.
Preparation:
New:
Hose or rinse down with clean water to remove heavy dust, grit or organic matter. Clean down with Dekro Galv-O-Clean Degreaser or Galv-Etch by working over the surface using a mop, brush or hessian. Thoroughly rinse down with clean water to remove residues. Note whether the final rinsing water forms a continuous film over the surface. If it does, then cleaning is sufficient, if not, repeat the cleaning operation.
Previously painted:
If the existing paint is in poor condition, remove by scraping, burning or with Dekro Super Paint Stripper. Then proceed as for new work.
If the existing paint is in good condition wash down to remove dirt, grease, dust or other contaminants with a suitable concentrated detergent. Abrade glossy surfaces with a suitable abrasive and dust off.