PAINTING OF DIFFERENT SURFACES

22.3.1 New woodwork

Normally, four coats of paint are required for new woodwork. The process of painting is as follows:

1. The surface of the woodwork is prepared to receive the paint for satisfactory working. It is necessary that the woodwork is sufficiently seasoned and it does not contain more than 15 per cent moisture at the time of painting. The surface of the woodwork is thoroughly cleaned and the heads of nails are punched to a depth of 3 mm below the surface.
2. The surface of the woodwork is then knotted.
3. The process of cleaning the surface using sand paper is then carried out.
4. The subsequent coats of paint, namely undercoat and finishing coats, are then applied on the surface. Extreme care should be taken to see that the finishing coat presents a smooth and even surface and that no brush marks are seen on the finished surface.

22.3.2 Repainting old woodwork

If the paint on the old woodwork has cracked or has developed blisters, it is to be removed. If the surface has become greasy, it should be cleaned by rubbing down with sandpaper or fine pumice stone. The old paint can also be removed by applying any one of the following three paint solvents.

1. A solution containing 200 g of caustic soda in a litre of water is prepared and used to wash the surface. The paint dissolves and the surface becomes clean.
2. A mixture consisting of one part of soft soda and two parts of potash is prepared and one part of quick lime is added afterwards. This mixture is applied on the surface in a hot state and allowed to stay for about 24 hours. The surface is then washed with hot water.
3. A mixture consisting of equal parts of washing soda and quicklime is brought to a paste form by adding required quantity of water. It is applied on the surface and kept for about an hour. The surface is then washed with water.

After removing the old paint from the surface, painting is carried out in 2 or 3 coats of an oil paint.

22.3.3 Painting new iron work and steel work

The surface of iron or steel to receive the paint should be free from rust, grease, dirt, etc. Suitable equipments such as wire brushes and scrapers are used to remove all loose scales, marks, etc. from the surface. Water with caustic soda or lime is used to remove grease. The cleaned surface is provided with a film of phosphoric acid. This film protects the surface from rust and it also facilitates the adhesion of paint. The coats of paint are then applied. The paint suitable to iron and steel surfaces should be selected for each coat. The priming coat or first coat is made by dissolving fine red lead powder in boiled linseed oil. After this coat has dried, two or more coats of the desired paint are applied over the priming coat, with the help of a brush or spray gun The finishing coat should present a smooth finish and precaution should be taken to avoid the presence of brush marks on the final painted surface.