PHYSFCO-CHEMICAL STUDES ON BUILDING PAINTS FOR TROPICS

Abstract

For many centuries paints were used largely for decoration and aesthetic appeal. However, owing to tremendous developments in building construction and housing schemes, greater attention came to be paid to the protective aspect of painting. Protection of buildings is often required in exposed situations where sunlight in association with rain, wind, atmospheric pollution, etc., exerts a deleterious effect on paint film. The greater intensity of sunlight in tropics also affects the substrate with consequent rapid breakdown of paint film. Long periods of high humidity cause mould growth in addition to other painting troubles. In the light of the foregoing it is clear that the requirements of paints for tropics deserve special attention. The investigations reported in this thesis cover various aspects of the physico-chemical characteristics of cement-sand plaster and wood substrates including the development, evaluation and weathering of protective paints for buildings. : ii : Cement-sand plaster as a substrate for painting is of special importance in the tropics. A study has been made of the effect of various mix proportions and curing conditions of cement-sand plaster on the rate of absorption of thinners and diluents of paints. Adhesion and accelerated weathering performance of paints have also been studied on these plasters. Cement paint is widely used in building protection and decoration in the tropics, often on cement plastered surfaces. The effect of various ingredients such as calciumchloride, aluminiumstearate, calciumhydroxide, algicides and wetting agents on the service life of the paint and colour fadation of a few pigments have also been investigated with a view to formulate a cement paint suitable for tropics. The extractives present in constructional timbers often influence paint behaviour. A study has been made of the extractives in knots in chir (Pinus roxburghii), kail (Pinus wallichiana) and deodar (Cedrus deodara) and in turn the effectiveness of some sealing compositions for the knots was determined. These studies have been further extended to hardwoods which inhibit the drying of oil based finishes. : iii : Fire protection is not a problem peculiar to the tropics, but the high humidities prevalent in most areas necessitate the use of moisture resistant protective treatments. Attempts to formulate a fire-retardant paint composition for wood based on polyvinyl acetate resin emulsion and indigenously available chemicals are also reported in the thesis.