How-to Guides

Metal (Ferrous)

Corrosion is the biggest problem facing the iron and steel industry.

Primers incorporating rust-inhibitive pigments must be used on iron and steel. Rust inhibitive pigments include zinc phosphate, metallic zinc and calcium plumbate and are used in various binders like linseed oil, Alkyd resins or epoxy resins.

Cheap and inferior primers contain less than the minimum quantities of anti-corrosive pigments to be effective. They often do more harm than good as they need to be removed before an effective painting operation can be carried out.

Steelwork must be primed as soon as possible after it has been prepared. Even a few hours exposure to a damp or contaminated atmosphere will nullify the value of thorough preparation.

Preparation

New Ferrous Metal Surface

• Clean thoroughly to remove dirt, grease and oil.
• Sand or grit blast to remove rust and mill scale.
• If sandblasting isn’t economically viable, chip, scrape or wire brush the surface to remove rust from pitted or rough surfaces.
• Apply a rust neutraliser such as Dekro Hydromet.
• The cleaned or treated surface must be primed immediately.

Previously Painted Surface

If the paint is in poor condition:

• remove by scraping or burning.

If the paint is in good condition:

• clean thoroughly with a suitable solvent to remove all traces of dirt and grime.

If the existing paint is glossy:

• sand with a suitable abrasive
• dust off

Metal (Galvanised)

A new galvanised surface is generally quite difficult to paint for the following reasons:

• The surface is so smooth that it doesn’t provide a good key for paint.
• The steel manufacturer treats the metal to prevent rust. This treatment needs to be removed totally before painting can begin.
• Zinc can react with the ingredients in some paints to form salts between the paint and the surface, thus reducing adhesion.

Preparation

New Galvanised Metal Surface

• Rinse down the surface with clean water to remove heavy dust, grit and other organic matter.
• Use Dekro Galv-O-Clean Degreaser to further clean the surface.
• Rinse thoroughly with clean water.

If the final rinsing water forms a continuous film over the surface then you have succeeded in cleaning the surface sufficiently.

Previously Painted Galvanised Metal

If the existing paint is in poor condition:

• use a suitable concentrated detergent to wash down and remove all traces of grease and other contaminants.

If the existing paint is glossy:

• abrade with a suitable abrasive
• dust off.