Decorating: Interior Paint Finishes

Painting walls, ceilings, woodwork and metal is something everyone seems to have tackled at some time. Every year the paint makers sell us millions of tins of paint, in hundreds of colours. Here’s what you need to know to pick the right one.

To understand how paint works, you need a little technical background information. All paints consist of three main ingredients — binder, thinner and pigment.

The binder makes the paint stick to the surface. As it dries it forms a solid but elastic film that’s resistant to water and chemicals and wears well if rubbed or knocked. Binders used to be natural oils or resins such as linseed oil or copal, but now man-made chemicals are usually used. You’ll recognise their names from paint tins — words like alkyd, polyvinyl acetate (PVA), acrylic, polyurethane and Silthane.

The binder is mixed with the pigment — usually titanium white, along with other coloured dyes.

The thinner makes the binder liquid enough to be applied easily and evenly, and evaporates as the paint dries. Paints are thinned either with water or with a petroleum-derived solvent, usually mineral turpentine (turps or white spirit). Water-based paints are usually called emulsions. Most people think of the second category as ‘gloss paint’ — paint that dries to a shiny finish. But because it’s actually the binder that dictates what finish the paint will have, it makes more sense to call these paints solvent-based.

Jelly (gel) paints

Traditionally, paints are runny liquids. But nowadays many paints — both emulsions and solvent-based paints — have special additives to give them a jelly-like consistency. They’re called ‘thixotropic’, or non-drip paints, and can be applied in thicker films (and with fewer drips) than runny paints. They should not be stirred in the tin (they go runny, and drip) but, if it is necessary to mix in any clear liquid that may have separated out, the paint will revert to a jelly if left to stand for a couple of hours.

How paint dries

Once the paint is applied it begins to dry. In modern paints with resin binders, the thinner (water or solvent) evaporates and the resin molecules start combining chemically to form a continuous film. Good ventilation, warmth and light help to speed up the drying process; cold and damp slow it down, and can stop the film forming properly.

Different finishes

The finish you get when the paint has dried can be high gloss, a silky sheen or matt (non-reflective). Paints giving a matt finish contain more pigment than ones drying to a high gloss, and the particles are actually larger. As a result, the surface is slightly rough and scatters light falling on it instead of reflecting it like a mirror.

Gloss, satin (or silk) and matt finishes are available in both emulsion and solvent-based paint types. Water-based gloss paints are not as durable as solvent-based ones, lose their gloss more quickly and come in a smaller range of colours. However, they are widely used in countries where high temperatures would make solvent-based paints dry too quickly.

Gloss finishes are commonly used on wood and metal; matt finishes on walls and ceilings. However, there’s nothing to stop you using them the other way round (but remember that a gloss finish highlights the imperfections of a rough surface).

Satin-finish paints are widely used on all surfaces nowadays, although solvent-based types perform best on wood and metal. Gloss finishes are generally more durable and easy to clean than satin or matt ones.

Pros and cons

The different properties of emulsions and solvent-based paints will affect your choice of type for a particular job. Here are the advantages and disadvantages of each type.

Ease of application: most people find emulsion paints quicker to apply than solvent- based ones, and also find it easier to get even coverage free from brush marks. Brushes, rollers and paint pads (and even spraying equipment) can be used with either type, but rollers are seldom used with gloss finishes.

Coverage: solvent-based paints usually cover a bigger area per litre than water-based paints. Runny paints cover 25 to 30 per cent more than the same volume of non-drip paints.

Drying: emulsions dry much more quickly than solvent-based paints, so there’s less disruption in the house after you’ve finished decorating and second coats can be put on more quickly (read the instructions on the tin for precise details about re-coating times). Solvent-based paints have a distinctive (and some say, an unpleasant) smell, while emulsions have little smell.

Durability: solvent-based paints are generally harder-wearing than emulsion paints. Repeated washing of matt emulsions can give the surface a noticeable sheen.

Priming: emulsions can be used on bare walls and ceilings, acting as their own primer and undercoat. Solvent-based paints need separate primers and undercoats. Adding to the time involved in using them — see Paint Primer – For Successful Painting Results.

Cleaning equipment: emulsions can be cleaned from painting equipment with water, while solvent-based paints generally need a special cleaner — white spirit, paraffin or else a proprietary brush cleaner; even paint stripper if the paint has hardened. Some solvent-based paints now have special additives that allow you to wash them out with hot soapy water.

Price: when gloss paints for woodwork were oil-based, and walls were painted with distemper, the price of the former was much higher than the latter. Nowadays, with man-made resins and pigments being used in both types, the price gap has virtually disappeared and cost is unlikely to be a big factor in your choice of paint type.

Paint sizes

Paint is now sold only in metric-sized tins. Common sizes include 500m1 (7/8 pint), 1 litre (1-3/4 pints), 2-1/2 litres (4-1/2 pints) and 5 litres (9 pints). Emulsions are seldom available in tins smaller than 1 litre, while solvent-based gloss may be available in tins as small as 125 ml (about ¼ pint) — ideal for touch-up jobs or for picking out contrasting colours on small areas.

08. August 2011 by admin
Categories: Equipment, Painting, Preparation | Tags: , , , , | Comments Off on Decorating: Interior Paint Finishes

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