thisplace.com.au - Two Paint or Not Two Paint?

Applying paint to plasterboard walls and ceilings is one of the most commonly performed building activities, yet it gives rise to many complaints of poor surface finish.

Why?

One of the problems is the 'two coat finish'. In other words, two coats of PVA, flat plastic or low sheen paint applied to the raw plasterboard surface. This is now an almost universal specification in project housing, and it's wrong! Quite wrong! The finished wall or ceiling is made up of two different materials - paper faced board and plaster jointing compound. Each has a totally different surface texture and porosity. (Porosity is the term used to describe the material's ability to draw water into it)

Before any paint film can be expected to provide a smooth, even, consistent surface of colour, texture and gloss, the porosity of the two different surfaces must be evened out. This is achieved with a sealer. The correct specification is therefore one seal coat followed by two finishing coats. The two finishing coats are there to provide cover by a combination of film thickness and density of colour.
Leading authorities, such as Australian Standards (AS 2311), plasterboard manufacturers and the Master Painters' Association, recommend three coat systems . Despite this, builders continue to search for two coat systems to cut costs. Paint manufacturers are under continuous pressure to develop such systems.

Source : Building Service Authority factsheet