Powder coat galvanised steel
Powder coat galvanising ensures a professional look, free from amateurish runs and brush marks. With the Tri-Resin System™ the galvanised steel will be better protected.
Left: Steels with varying silicone contents can produce different gloss galvanising, this can sometimes help predict whether the galvanise will produce pin holing during powder coating.
Disadvantages of galvanising
- More difficult to achieve smooth, blemish free paint finish.
- Can produce gas holes (pin holes) in paint finish.
- Galvanise can be a rough finish, requires a lot of fettling.
- Galvanising is an extra expense to the finishing.
- Possible distortion of light material.
Advantages of galvanising
- Well proven method of protecting steelwork.
- Component should not produce brown rust marks.
- Component should remain structurally sound, for longer compared to non galvanised.
- Seals inaccessible areas that paint cannot reach.
Galvanise gets where paint cannot
This design is a good example of what should be galvanised. The use of circles has produced areas where it would be very difficult to seal with just paint. For this and other designs, which would cause similar areas of no panting, get it galvanised first. The Tri-Resin System where applied, makes a very good paint barrier for corrosion resistance, but the metal design has to be appropriate for good cover.
Left: A good example of what should be galvanized
Not enough paint protection
Zinc is a very is reactive metal that will readily oxidise under the paint if it has access to air and moisture. This is why the Tri-Resin System is used. Three coats of paint are applied to seal the zinc.
Right: Coating has not produced a waterproof barrier (images shown to the right and below not painted by Windridge Coatings).
Why powder coating needs to be washed
One of the worst environments for any paint system is marine. This can be even more difficult when rain is not given access to wash off the salt. In an open environment where the component is exposed to salt and moisture e.g. damp mornings but never washed, the corrosive salt water solution can attack the paintwork unabated. Here we see the upright exposed to the rain is in good condition but the cross section under the shelter is badly corroded.
Tri-Resin System (Galvanise)
As can be seen, galvanising and powder coating is not the whole story. With out the correct pre-treatment any paint will flake off galvanise. We have seen that zinc is a reactive metal and unless it is sealed from the elements it will corrode under the paint. The Tri-Resin System™ is a three coat paint system originally designed to protect the zinc from corrosive compounds. So effective has it been it is now applied directly onto steel.
Warranties and guarantees
The above bus stop picture is a good example why all warranties insist on the paintwork being washed at regular intervals. The more corrosive the environment the more it needs to have the corrosive elements washed off. If this is not done the warranty will be void.
- Zinc coated steel: this includes zintec sheets, zinc plated, galvanised steel, hot dip galvanising, zinc galvanising, and zinc galvanising, this is sometimes referred to as Duplex coating.