Architects memo no. 18: May 1982
Coloured undercoats - they do make a difference
Enamel work in New Zealand is well established, both interior and exterior, as a three-coat system comprising primer, undercoat and topcoat. Each of these coats has a specific function, which probably bears restating.

The primer's job is to be able to get into an intimate contact with the substrate, adhere tenaciously to it, and prevent degradation to that substrate. The job of the undercoat is to stick to the primer, fill minor surface defects, provide film build and hiding, and leave a smooth, non-porous surface for the topcoat. The topcoat provides the gloss, the colour, and the durability.

If the topcoat is based on high-riding pigments such as iron oxides, or shaded whites they will generally have sufficient hiding power to completely obliterate the undercoat if evenly applied. Even with high-hiding topcoats however imperfect application can allow undercoats to grin through in brush marks, and sharp edges. This problem is greatly enhanced if the topcoat pigmentation is not of the high-hiding type. Many of the bright, accent colours in vogue today have in fact got relatively poor hiding power and total obliteration of the undercoat may require two or more coats.

The obvious answer to this problem is to supply undercoats to the same colour as the topcoat so that it plays its full part in the hiding of the system. Resene has provided such a service for the past ten years. These years of experience have shown that the use of coloured undercoats gives a depth of colour to the surface unable to be equaled by the painter's traditional method of tinting standard white undercoats. Depth of colour can simply not be achieved in that way.

Although the coloured undercoat system was primarily designed for the lower-hiding topcoats it has also proved valuable across the board due to the fact that tin areas of topcoat, as described earlier will not show undercoat grinning through.