Painting On Different Surfaces
The process of painting depends on the nature of the surface to be painted. A brief description of painting on each of the various surfaces is given below:
(1) New wood work: Normally four coats of paint are required for new woodwork. The process of painting is carried out as follows:
(i) The surface of wood work is prepared to receive the paint. For satisfactory working, it is necessary that the woodwork is sufficiently seasoned an it does not contain more than 15 per cent moisture at the time of painting. The surface of woodwork is thoroughly cleaned and the heads of nails are punched to a depth of 3 mm below the surface.
(ii) The surface of the woodwork is then knotted.
(iii) The priming coat is then applied on the surface of new woodwork. Generally, the priming coat is applied before the woodwork is placed in position.
(iv) The process of stopping is then carried out.
(v) The subsequent coats of paint, namely, under costs and finishing coats, are the applied on the surface. The extreme care should be taken to see that the finishing coat presents smooth and even surface and that no brush marks are seen on the finished work.
(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 sand-paper or fine pumice stone. The old paint can also be removed by applying any one of the following three paint solvents:
(i) A solution containing 2 N of caustic soda to a litre of water is prepared and used to wash the surface. The paint dissolves and the surface becomes clean.
(ii) A mixture consisting of one part of soft soap and two parts of potash is prepared and one part of quicklime is then added after wards. The mixture is applied on the su
(5) Galvanized ironwork: As the paint will not adhere to their surface of galvanized ironwork, some treatment is to be given to the surface before a priming coat is applied. It is a general rule not to paint to galvanized iron work until it has been exposed to weather for a period of one year or so. However, if it is necessary to paint new galvanized ironwork, any one of the following tow solutions is applied on the surface:
(i) A solution containing 0.04 N of copper aceteate to a liter of water.
(ii) A solution containing 0.13 N each of muriatic acid, copper chloride, copper nitrate and sal-ammoniac to a litre of soft water. This much quantity of solution will cover an area of about 250 to 300 m2.
The solution is taken in a glass vessel or earthenware vessel. This will prevent the precipitation of copper salts. When the solution is applied on the galvanized iron work, the surface is turned black and after a period of about 12 hours, the coat of paint may be applied on the surface.
Alternately, a wash of washing soda or zinc sulphate may be given on the surface and when it dries, a priming coat of red lead mixed with linseed oil and turpentine may be applied on the surface. When priming coat dries, a suitable paint may be applied on the surface.
(6) Metals: The surface of the metal to be painted should be clean and free from dirt, grease, etc. It should be such as to provide key for the paint. Depending upon the nature of metal, suitable paint is selected. Depending upon the nature of metal, suitable paint is selected. For instance, the priming coat for aluminium surface should be of zinc chromate and that for zinc surface, it should be of zinc oxide.
(7) Plastered surfaces: For successful application of paint on cement plastered surfaces, the following factors should be carefully considered:
