straight and true - the path to a perfect lining

Architect's memo 53: August 1998

Blemish-free walls and ceilings are often a desired part of that space. It is axiomatic that high gloss paints are highly reflective and, as such, will highlight any blemish over which they have been applied. Perfectly matt paints, conversely, by absorbing light minimise such surface defects. Unfortunately very few matt paints are tough enough for use in high wear areas such as hallways, kitchens, laundries and bathrooms, rumpus rooms and the like. Low sheen paints, although tough, have the idiosyncrasy of exhibiting different glosses at different viewing angles. A surface defect invariably alters the topography and hence the angle at which light will strike it, leading to the defect again being highlighted.

The answer to the problem is to try to produce perfectly flat walls. This requires stable framing (such as kiln dried timber or metal) erected to tight tolerances and the lining material fixed and stopped to a high standard.

Even achieving this utopian state, however, still will not guarantee the desired result due to the inherent differences in porosity between the lining materials and the stopping compound. These differences affect the penetration and the surface characteristics of applied coatings which subtly alter their appearance.

Sanding of the surface to remove any excess stopping compound can dramatically exacerbate these problems with paperfaced plasterboard for whilst the stopping will sand smoothly, any sanding of adjacent paper will cause a dramatic roughening of that surface. These problems have seen the development of a new class of surface coating. These materials (such as Resene Broadwall Surface Prep) are very highly filled products designed to be applied in a heavy coat all over the wall or ceiling surface. They sand very easily to produce a smooth, uniform, relatively weak surface. They are strong enough to form a foundation for the direct application of finishing coats where the system is to be used in a relatively unstressed area. They do, however, benefit from the use of a sealer when used in the sort of stressed areas described above - an acrylic sealer (such as Resene Broadwall Waterborne Wallboard Sealer) being satisfactory for dry areas and a penetrating solventborne sealer (such as Resene Sureseal) for wet areas.

These new coatings do constitute an additional step and therefore increase costs, but, together with good building practises do bring the dream of perfection closer to reality.

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