JCP Roofing Blog How To Paint A Galvanised Roof

Firstly, let us look at what galvanised iron is; According to Fired Earth, galvanised iron is steel that has been dipped into
molten zinc metal; this surges the corrosion resistance of the steel. The resulting material has a bright silver colour and is highly resilient to red rusting. Old galvanised iron may lose the protective zinc the surface coating and red rusting may then occur.

The surface of zinc metal oxidises quickly to form a protective carbonate/oxide layer, which protects the zinc from further damage. This layer causes most paint let-down’s because it can be relatively weak. Waterborne acrylic paints such as Homestead Roof Paint adhere well to clean galvanised iron and have superior exterior durability compared to enamels. However, galvanised iron is prone to “ white rusting” in moist or harsh environments and a property designed anti-corrosive primer Metal Prier (Water based) is necessary for long-term durability.

Surface preparation

The process of surface preparation is probably the most important part of the painting process; poor preparation is the principal cause of coating failure. It is extremely important that you remove the surface dirt, grease and any other impurities as well as loose paint coatings and surface oxidation (e.g. dull mat grey surfaces) to ensure optimal adhesion and durability of the paint system. The required steps are as follows:

  • Wash the surface thoroughly using water and a strong brush. This should be able to remove all loosely bound contaminants and poorly adhering paint coatings. Preferably use a spatula or a flat blade to check adhesion of any existing paint coatings. A high-pressure water jet is recommended.
  • Apply a quality Etch Cleaner to all exposed metal. This helps dissolve any surface oxidation and helps to remove any oily contamination. Leave in for 5-10 minutes maximum, and then proceed to rinse the roof with clean water. Leave the roof to dry out. Apply the primer within hours of cleaning to avoid possible recontamination of the surface.
  • Check the adhesion of any existing paint coatings by pressing adhesive tape.
  • Pull the tape off the surface and inspect underneath the tape.
  • No coating removed; no dirt or chalky material on the tape: Surface is suitable for painting.
  • Powdery layer removed (painted surfaces only) Paint surface is chalky: apply Fired Earth bonding Liquid.
  • Sandy particles removed.
  • Surface is dirty: rewash the surface
  • Paint coating removed
  • The surface of the coating is weak: strip the paint and repeat the cleaning process.
  • Prime exposed meta using anti- corrosive primer Metal Primer ( Water Based) for galvanised and leave t cure for 2-4 hours before continuing. If red-rusting is present, then use an appropriate anti corrosive primer Metal Etch Primer ( Solvent Based).

Paint Application

  • IBR or corrugated roofing: Apply a primer or Fired Earth Extreme Roof to the prepared surface using a roller (wool or Synthetic type); brush or by airless spraying. Two coats are recommended for optimum durability and quality of finish. Allow the first coat to cure for at least 2 hours before applying the final coat.
  • Gutters or downpipes: Apply a primer or Fired Earth Extreme Roof to the prepared surface by brushing. A small fine foam roller may also be used.

Calculating the amount of paint required

  • Estimate the plan area of the roof by measuring the length and breadth of the walls.
  • Multiply this area by 1.25, multiplied by 2 for two coats.
  • Estimate the paint quantity needed by dividing the above area by coverage rate of the product type.
  • One litre of paint will cover approximately 30m of 30mm radius down pipe or gutter. This should produce a slight excess of paint, which is useful for touch-up work as required.

Other important information

  • Never apply paint if rain is forecast, or expected, during the day of application
  • Apply paint after 8h00 (summer) or 10h00 (winter) to ensure the roof is not too cold or damp.
  • It is recommended that the paint is applied before 12h00 to avoid excessive roof temperatures and to allow the paint to harden sufficiently before any afternoon rain may occur.
  • Always use the SAME batch number for touch-up work. This reduces colour/sheen variations, which otherwise may be visible on the painted roof.

Description of products described above

  1. Metal Etch Primer (Galvanised): A specially formulated corrosion-inhibiting acrylic primer for galvanised iron in good condition. (Anti-Corrosive type).
  2. Metal Etch Primer: A primer for red rusted galvanised iron surfaces. (Anti-Corrosive type).
  3. Fired Earth Extreme Roof acrylic is a high-quality acrylic; medium sheen finish paint with outstanding weathering and alkali resistance properties. It can be applied onto suitably prepared fibre cement tiles, roof sheet, clay or cement roof tiles and pre-primed galvanised iron roofs. Available in the following colours: Black, Grey, Charcoal, Red, Brown, Terracotta and Green.

Other important information

  • Never apply paint if rain is forecast, or expected, during the day of application
  • Apply paint after 8h00 (summer) or 10h00 (winter) to ensure the surface is not too cold or damp.
  • It is recommended that the paint is applied before 12h00 to avoid excessive temperatures and to allow the paint to harden sufficiently before any afternoon rain may occur.
  • Always use the same batch number for touch-up work. This reduces colour/sheen variations, which otherwise may be visible on the surface being painted.

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