What is emulsion?

Emulsion -Everything you need to know about the versatile paint.

Emulsion paints are invariably the first choice for decorating walls and ceilings. Understanding more about them will help you to achieve a perfect finish every time. Read our tips and tricks to get 

Paint has come a very long way since man first used it to record scenes from everyday life on the walls of his caves 20,000 years ago. But the paints of today are not just decorative: they are highly sophisticated compounds, with an important protective function.

Emulsion paint – the type that is used more than any other – has seen the greatest advances. But as emulsions become more effective, they also become more specialized, with an increasingly bewildering choice of what to use where.

Emulsion paints come ready mixed or made up to the colour you want, with matt or silk finishes and in 5 litre, 21⁄2 litre and 1 litre cans. Good quality bristle brushes of the right size are still the most versatile means of painting walls and ceilings

What is emulsion paint?

Emulsion paint or PEP (plastic emulsion paint) is a water based paint. This means that particles of synthetic resin, acrylic or vinyl, are mixed with pigment (which gives the paint its colour) and are suspended in water. As the water evaporates, the particles join to form a film of resin on the surface. It also means that you can add water yourself to thin the paint and get it to the right consistency.

The resins in the paint mean that compared to old-fashioned finishes, emulsions are tougher, last longer, the paint retains its colour over a longer period and the surface can safely be washed down without the risk of paint dropping off in the process.

Emulsion paints are permeable (they allow moisture to pass through), non-toxic and alkali resistant. They are cheaper than oil based (gloss) paints, they dry quickly, and they are relatively easy to apply. The water content reduces the characteristic smell of paint to a faint odour which rapidly disappears. Because emulsion paints are thinned with water, any splashes can be wiped up with a damp cloth.

Where can I use it?

Emulsion paint can be used on walls and ceilings in all rooms. It can safely be applied to plaster, plasterboard, wood and hardboard and, since it is alkali resistant, it can also be used on surfaces such as brick and cement rendering, all of which have a high alkali content.

It will cover surfaces already painted with emulsion or gloss paint, although the latter must be rubbed down to a matt or flat finish first. Lining paper and wallpaper are also suitable, indeed if your surface is slightly uneven you may be able to avoid extra work by applying a textured lining paper and painting directly onto that.

Emulsions with gloss finishes can be used on skirting boards, doors and window frames. Although they are not as hard wearing as conventional oil based glosses, they are easier to apply, quicker drying and cheaper. Also, because emulsion paint is permeable you can use it on relatively new plaster even before it has dried out completely.

How thoroughly do I need to prepare the surface?

When using emulsion paint or any paint for that matter — cleanliness really is next to godliness. Modern emulsions are very good but they are not miracle coatings and they will not give an adequate finish to surfaces that are badly prepared. So while preparation may count for as much as half the time required to do the job, if carefully done, your efforts will be well rewarded.

Because paint will stick to whatever is immediately beneath it, surfaces to be painted must be free of dust, grease and any loose or flaking paint. They should then be washed down with detergent and rinsed thoroughly with warm water. Some surfaces will need to be rubbed down first, using wet and dry paper to roughen the surface for the first coat. (Do not rub down plasterboard, however, as the surface will be damaged).

How do I decide how much emulsion to buy? 

First measure up the area 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 percent; on highly textured surfaces the drop could be even more.

Emulsion paint is sold in 1 litre, 2.5 litre 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 an 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 emulsion 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 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.

Overthinning tends to be less of a problem than underthinning 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.

Is emulsion paint best applied with a brush or roller?

One of the big advantages of emulsion is that it is easy to apply, with little drag on the brush or roller compared to oil based paints. So whether you use a brush or roller is really a matter of personal preference. Both give good finishes, although rollers have the edge in speed of application. However, if you do decide on a roller you will still need a brush for painting into angles.

Whichever you use, make sure you get the best you can afford and the right size. If you stick to brushes, buy a 100mm-150mm flat wall brush and a smaller brush for edges and detail work. Try to get brushes with bristles made of hogshair. They are more expensive, but cheaper brushes with synthetic bristles do not hold the paint as well and may spoil your work. When buying a brush, test the quality of the bristles in your hand – they should feel soft to the touch.

For roller work on walls and ceilings a good quality short-pile mohair or synthetic pile fabric is best. Cheaper disposable foam plastic rollers are available, but unless you are after a textured effect they are not really worth any saving you might make. The best size is 150mm-200mm.

Both brushes and rollers should be cleaned in luke-warm water immediately after use otherwise the paint will dry and become extremely difficult to shift.

Are there any alternatives to brushes and rollers?

Yes. Paint pads are worth considering. They consist of short pile face – usually mohair attached to a foam pad or cushion fitted to a handle, and are quite easy to use. A paint mitten is useful for applying emulsion behind radiators and pipes which can be difficult to coat by normal methods.

There are a number of sprays you can either buy or hire. They give a very even finish but, unless you are painting the whole house, the extra cost and preparation – all surfaces not to be painted must be securely masked – will offset the advantages of quick and easy applications.

You can also buy a portable system which pumps the paint from a paint tub to a brush, pad or roller. The tub is inserted directly into the machine, which is worn around the waist. The finish is comparable to that of a brush or roller but it does require its own special one litre tubs of paint.

Should I use drip or non-drip emulsion?

The advantages of non-drip thixotropic emulsion are that they are clean to use and their spreading rate is usually very good.

However, if thinned they lose their gel or non- drip qualities and become more like liquid paints. Also the fact that they go on in thicker coats tends to make them less economical than ordinary liquid emulsions.

Liquid paints are certainly better on surfaces where thinning is required and it is worth bearing in mind that this is the type that most professional decorators prefer.

How long does emulsion paint take to dry?

It tends to dry more quickly than other paints. The surface should be touch-dry after 1-2 hours and can be recoated after 2-4 hours.

Also, because emulsion dries by evaporation of its water content (see above) it is a good idea to keep windows closed while painting to prevent the paint from drying too quickly. When the work is finished it is a good idea to open the windows to remove the moisture from the atmosphere.

What sort of finish will I get? When paints dry they produce varying grades of sheen. These range from matt or flat finishes through increasing degrees of lustre to high gloss finishes. So silk finishes give a silken sheen to the finish, an eggshell finish closely resembles the lustre of an eggshell and A colour tinting machine can be used to mix over 800 colours by adding measured amounts of colour tint to a base paint

It’s worth bearing in mind that different manufacturers sometimes use varying names for their finishes one may say ‘silk finish’. another, ‘semi matt’. So check the sample cards to make sure of what you are getting.

What choice of colour have I got? 

Very wide. Most paint manufacturers produce a colour chart showing the colours. that are available. These charts vary in quality but most of them are laid out linking colours and shades together to help you choose the one you want. The colours available are updated from season to season new ones are introduced and the less popular ones may be discontinued.

If the colour you want is not available in the basic colour range most specialist paint shops and some general DIY shops can mix the colour you want for a slightly higher price. The stockist has a series of basic colours and a machine with different colour- ants. Using a mixing guide and a shaker it’s possible to make upwards of 800 other colours for you. However, it’s important to make sure you buy as much as you need. If you have to buy extra, it is by no means guaranteed that it will be exactly the same shade. If you do run out, try to finish on a complete wall. In this case, any variation will only show at the join in the corner.

There seems to be so many colours in the shops. Are they standardized in any way?

In the UK. some are. At the beginning of 1982 the major paint manufacturers agreed to standardize 66 emulsion colours to a British standard. This is called British Standard (BS) 4800 and it can be useful if you want to match up a colour at a later stage

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providing you make a note of the BS 4800 number. And since all paint manufacturers make a BS range. it doesn’t matter whose paint you use.