Emulsion paint is, in some cases, an adequate alternative to gloss paint. Apart from its tendency to induce condensation, a gloss paint finish is often unsuitable for walls because of its shiny appearance, which emphasises any slight irregularities in a wall surface. Most interior walls look better with a matt or slightly glossy eggshell finish. The development of emulsion paints, in which particles of the medium are dispersed in water, represented a great advance for the home decorator, since they combine the advantages of a flat finish oil paint with the convenience of a water paint for thinning and cleaning of brushes. Most modern emulsion paints are composed of a synthetic resin emulsified in water.
The finished surface of these paints is very durable and will withstand frequent cleaning. Even more resistant to dirt and moisture are co-polymer or plastic emulsion paints such as those which provide a vinyl finish. These form a continuous surface of plastic ‘skin’ and must be applied to walls that are smooth and free from grease, flaking paint and paper. Oil bound water paint, or distemper, is similar to conventional emulsion paints, but is cheaper and not nearly as durable. Acrylics represent the latest development in emulsion paints and can be used almost anywhere even on damp external walls.
Thixotropic paints are Jelly’ paints with a dense medium which thickens the consistency of the paint, largely eliminating the problem of paint drips. A further advantage to the handyman is that the increased thickness of the paint film results in a greater opacity, so that one coat is often sufficient to produce a uniform tint. The most professional looking results, however, will be obtained by building up several thin layers of paint. Thixotropic paints come in a wide range of colours in gloss, emulsion and vinyl finishes.
Cellulose paints must be applied with a spray gun for best results and are not very suitable for domestic use. They are best used on metal and other surfaces which will need a high gloss finish. Stone paints have small particles of stone mixed in an emulsified resin base. Their normal use is for external brick or rendered surfaces, but they can be used internally to improve the appearance of a brick or a cement rendered wall. Many other paints have been developed for special situations. These provide rust, damp, fungus, fire, or acid and alkali resisting finishes.
Varnishes and sealers are used where exposed natural surfaces, such as wood, stone or slate, need protection. They are transparent and usually based on linseed oil or polyurethane resins. When the natural surface is to be retained, but the colour needs improving, a varnish incorporating a stain can be used.
Primers
To obtain a smooth finish, the top coat of paint must adhere thoroughly to the wall surface. Some surfaces, such as old plaster, may vary in their porosity, and if a top coat paint is applied directly onto this surface, it will produce a patchy finish. Primers, therefore, are used as base coats to provide uniformly absorbent surfaces for later coats of paint, and to seal in alkalis or other chemicals which might affect the decorative finish. Primers are usually white or pink.
Undercoats
One or more coats of undercoat are usually necessary on new walls to build up the colour to a dense uniform level. Normally they are fairly thin, but have a high pigment content to give good opacity, and they dry to a matt finish. Existing paint, if it is in good condition, will need only one undercoat and one top coat in most cases. It is important, however, to ensure that existing coats are adhering properly and are being uniformly absorbed. Be certain that new paint is compatible with the old paint you are working over, as some paints react with chemicals in other paints.