POWDER COATING OR ANODISING
Wet painting aluminium relies on etching primers to break down the refractory oxide and is generally unsatisfactory unless done by an expert professional. Powder Coating is the most common and best method of painting aluminium surfaces. The process relies first chromating the surface and then electrostatically charging a fine powder made up of resin and pigment that is sprayed on to the extrusion and then baked in an oven where the resin and pigment melts and cures.
Why powder coat?
Items that are powder coated last longer because the finish is far more resistant to scratching, chipping, fading and abrasion than other finishes. Powder coating doesn’t last forever, but usually lasts many times longer than any other form of painting. It is also a much thicker coating than can be obtained with paint. This thicker coating can provide a pleasant “feel” to an item. This is especially noticeable on hand railings and balustrades.
Colour choices are virtually unlimited, with high and low gloss, matt and metallic finishes. However, to generalise, gloss finishes deteriorate ahead of matt finishes and dark colours are more prone to fading than light colours. The “industry” is now moving toward “matt finishes” and “cooler colours”, especially in full sun, (as in balustrades, fences and gates). Also some resins last longer than others, but are naturally more expensive. We can advise on “commercial powders” and lasting qualities in extreme or salt environments.
The powder coat plant we use belongs to our “supplier” (McKechnie Aluminium Solutions Ltd) and is the most modern in NZ. McKechnie Aluminium Solutions is certified for both ISO9001 (quality management) and ISO14001 (environmental management) and complies with the Endurocolour Powder Coating Standard.
Basically anodising is harder than powder coating and the bond with the alloy is very secure. It can last longer in salt environments and be less prone to fading. But in saying that we have not known a powder coat bond to fail.
We use a lot of “silver” or “natural anodising” and silver anodised aluminium rails are an alternative to Stainless Steel rails which are prone to “tea staining”. Natural anodising may appear “softer” than stainless steel and a range of colours is available.
As anodic film is what occurs naturally on aluminium – (AlO2). The anodising process causes a more rapid growth of the film thickness through electrolytic action and then metal salts are added in the bath to induce colours. Finally the metal is sealed.
Electrolytic colours are limited to a range of bronzes and extending to ebony, (black). Electrolytic colouring involves electro-depositing stable metal compounds from a solution of metal salts deep into the pores of the anodic film, away from the effects of sunlight and corrosive elements. Anodising itself is an electro-chemical process that allows anodic film to grow on metal. The anodic film is porous, so the oxidisation mechanism continues reaching the parent metal and the film grows in a controlled manner. The anodic film is therefore integral with the parent metal from which it grows. There is no bond, (as for example), in the powder coat process and electrolytic colours are virtually impervious to fading.
Balustrade Exposure to Sunlight.
Balustrades are often subjected to extreme sunlight conditions because they are often built with a northerly aspect and do not get partial shading that windows get from the house eaves. Your balustrade railings are consequently more prone to fading than your window joinery. While anodising offers a lesser range of colours – in our view anodised railing will retain their colour and durability longer than powder coated railings.
How to care for coatings.
It is essential that aluminium extrusion is not set in concrete where salts attack the alloy and the coating. We normally separate the extrusion from contacting concrete, (at the attachment point) by using butyl rubber gaskets.
Both painted surfaces and anodised surfaces benefit from washing in mild soap and water. On no account use chemical washes or bleaches. Salt deposits and bird droppings are often corrosive to both glass and aluminium extrusion and many chemicals can cause staining. All powder suppliers recommend regular cleaning and with reasonable care your balustrades and handrails will give an excellent service life.
Glass can be treated with silicon and proprietary products such as RAINEX often prevent bird droppings from adhering and make cleaning easier. We can treat your glass balustrade upon installation. Anodised surfaces also benefit from treatment with RAINEX as they are porous and can take in the silicon and are less prone to bird droppings adhering to the coating.