Aluminium windows and doors can be supplied in either an anodised or painted finish.
Anodising is an electro-chemical process where a natural oxide film is created by passing an electric current through a sulphuric acid solution with the aluminium extrusion acting as the anode. The anodised film created can be coloured using pigments, organic or inorganic dyes.
The thickness of the anodised coating can be varied by the processing time. The thickness of anodising for doors and windows is usually between 15 and 25 microns.
Paint is applied by either a liquid organic coating or by powder coating
Pre-treatments for powder coating on architectural aluminium
To ensure good adhesion of powder coating to an aluminium surface and protect against any subsequent corrosion, it is necessary to pre-treat the aluminium prior to the application of the powder coating.
This Pre-treatments for powder coating Position Paper summarises how the specification of powder coatings on architectural aluminium with respect to the pre-treatment may change, given the use of alternative pre-treatments to those based on hexavalent chromium compounds. In addition, BS 6496 which was used to specify pre-treatment was withdrawn in 2017 and its replacement, EN 12206-1, is being revised. Some questions to ask your powder coater in relation to the pre-treatment options are given in the paper.