First measure up the area that is to be painted. On most tins of emulsion a spreading rate will be quoted ? usually somewhere between 12 and 16 square metres per litre. However, it is worth noting that the spreading rate applies to smooth surfaces: if you are painting rougher surfaces allow for a decrease in coverage of around 10 to 15 per cent; on highly textured surfaces the drop could be even more.

Emulsion paint is sold in 1 litre, 2.5 litres and 5 litre cans. They vary in price but generally the cheaper paints have more thinner in them and you may find that you need an extra coat.

On most surfaces you can budget for two coats of emulsion ? although if you are re?painting with the same colour you may be able to get away with one. Generally more coats will be needed going from a dark to a light colour than the other way round.

When do I need to use a primer?

Generally you should not need one, although it depends on the surface you are tackling. For instance plaster, plasterboard and paper can be painted over as soon as they are clean, although oil based primer/sealer may be needed to prime dry lightweight plaster. (Although water based primers are available, oil based types are preferable because they seal the surface before the first coat of emul?sion is applied).

An oil based primer should be used to stabilize old powdery paint and distempered walls. If applied to bare, painted or papered surfaces, it will seal unsightly water-soluble stains which would otherwise show through, however many coats of emulsion you used. In much the same way, if you are applying emulsion over paper with gold on it, apply a primer coat first or you will find that the gold starts to come through.

Above all, remember that applying a coat of primer is no substitute for adequate surface preparation.

How much thinner should I use?

It depends on the surface. On absorbent surfaces - wallpaper and lining paper - you should thin more on the first coat than the second; sometimes as much as one part water to two parts paint. The second coat should be one part water to three or even four parts paint. On smooth surfaces thin less on the first coat. And if an oil based sealer has been used it may not be necessary to thin at all. On the second coat thin as above.

When thinning emulsion, it is important to remember to mix the paint thoroughly. You are more likely to achieve a thorough mix if you whip the paint rather than stir it slowly.

Over thinning tends to be less of a problem than under thinning as it is much easier to apply an extra coat of emulsion than to correct an undercoat which has dried too thickly and is unevenly spread.

As a rule of thumb, if the paint is dragging slightly on the brush you can assume that it has been thinned sufficiently.