Distempers: Properties, Ingredients and Process | Engineering Materials

The main object of applying distemper to the plastered surfaces is to create a smooth surface. The distempers are available in the market under different trade names. They are cheaper than paints and varnishes and they present a neat appearance. They are available in a variety of colours.

Properties of Distempers:

Following are the Properties of distempers:

(i) On drying, the film of distemper shrink. Hence it leads to cracking and flaking, if the surface to receive distemper is weak.

(ii) The coatings of distemper are usually thick and they are more brittle than other types of water paints.

(iii) The film developed by distemper is porous in character and it allows water vapour to pass through it. Hence it permits new walls to dry out without damaging the distemper film.

(iv) They are generally light in colour and they provide a good reflective coating.

(v) They are less durable than oil paints.

(vi) They are treated as water paints and they are easy to apply.

(vii) They can be applied on brickwork, cement plastered surface, lime plastered surface, insulating boards, etc.

(viii) They exhibit poor workability.

(ix) They prove to be unsatisfactory in damp locations such as kitchen, bathroom, etc.

Ingredients of Distemper:

Distemper is composed of base, carrier, colouring pigments and size. For base, the whiting or chalk is used and for carrier, the water is used. Thus it is more or less a paint in which whiting or chalk is used as base instead of white lead and the water is used as carrier instead of linseed oil.

The distempers are available in powder form or paste form. They are to be mixed with hot water before use. The oil-bound distempers are a variety of an oil paint in which the drying oil is so treated that it mixes with water. The emulsifying agent which is commonly used is glue or casein. As the water dries, the oil makes a hard surface which is washable.

It should be remembered that most of the manufacturers of ready-made distempers supply complete directions for use of their products. These directions are to be strictly followed to achieve good results.

Process of Distempering:

The application of distemper is carried out in the following way:

(1) Preparation of Surface:

The surface to receive the distemper is thoroughly rubbed and cleaned.

The important facts to be kept in mind are:

(i) The new plastered surfaces should be kept exposed for a period of two months or so to dry out before distemper is applied on them. The presence of dampness on the surface results in failure of distemper coating.

(ii) The surface to receive distemper should be free from any efflorescence patches. These are to be wiped out by clean cloth.

(iii) The irregularities such as cracks, holes, etc. of the surface are to be filled by lime putty or gypsum and allowed to become hard before distemper is applied on the surface.

(iv) If distemper is to be applied on the existing distempered surfaces, the old distemper should be removed by profuse watering.

(2) Priming Coat:

After preparing the surface to receive the coats of distemper, a priming coat is applied and it is allowed to become dry. For ready-made distempers, the priming coat should be composed of materials as recommended by the makers of distempers. For local made distempers, the milk is used for priming coat. One litre of milk will cover about 10 m² of the surface.

(3) Coats of Distemper:

The first coat of distemper is then applied on the surface. It should be of a light tint and applied with great care. The second coat of distemper is applied after the first coat has dried and become hard.

Following facts are to be remembered:

(i) The distempering should be done in dry weather to achieve better results.

(ii) The oil-bound distemper or washable distemper adheres well to oil- painted walls, wood, corrugated iron, etc. But a priming coat of pure milk should be applied before distempering is done on such surfaces.

(iii) The application of distemper by a spraying pistol is superior to that by brushes. The spraying affords smooth and durable film of distemper.

Wall Paper:

The wall papers are now widely used for developing decorative finishing of interior walls and they are made exclusively from paper or combined with other materials. They may be unprimed, primed, embossed, metal-coated, etc. They are available in one colour or multi-colour patterns printed on the face surface.

The surface on which wall paper is to be fixed is dried, levelled and made free from chalk or lime solution. All the cracks and slits are filled up with lime- gypsum solution. The surface is then pasted with wrapping paper or newspapers by applying suitable paste. The wall paper which is available in rolls is then hanged very carefully on the surface and the continuity of the pattern or design on wall paper is maintained.

The wall paper is available in a great variety of patterns and colours. The varnished wall paper can be polished after hanging to develop the effect of veneer-panelled wall. The wall papers of certain type are washable and they may be painted with oil paints. The wall paper with sound-absorbing properties is also available. The metal-coated wall papers are prepared from wall papers coated with a primer of metallic powder and then the patterns are printed or embossed on the surface.

Whitewashing:

The fresh lime is slaked at site of work and mixed thoroughly with sufficient quantity of water in a tub. It is then screened through a clean cloth. The clean gum dissolved in hot water is then added at the rate of 20 N per m³ of lime. The rice may be used in place of gum.

The surface to be whitewashed should be cleaned before the work is started. For whitewashing walls which are whitewashed before, the old loose whitewash is to be first removed and repairing to the plaster is carried out, if necessary.

The whitewash is applied with jute brush and the brush is so worked that a surface with uniform colour is obtained. The three coats are generally applied, each after the previous coat has completely dried.

The lime is toxic for germs. It reflects light and thus it increases the brightness of the surface. The whitewashing therefore is extensively used for interior wall surfaces and ceilings of houses.

The process of whitewashing is sometimes used for exterior wall surfaces also. A satisfactory work gives an opaque smooth surface with uniform white colour and does not readily come off on the hand, when rubbed.

Colourwashing:

This is prepared by adding the colouring pigment to the screened whitewash. It should be seen that the colouring pigment is not affected by the presence of lime. Ordinarily, the yellow earth is popular for colourwashing. Generally, the walls are colourwashed and ceilings are whitewashed. The mixture is to be kept constantly stirred during use.

The colourwash is applied in the same fashion as the whitewash. A satisfactory work does not give out powder when the finished surface is rubbed with the fingers.

The process of colourwashing imparts cleanliness and pleasant appearance of the surfaces which are treated.