Painting and colouring

Painting and colouring, by Prof. Sagar Raut

1. BUILDING CONSTRUCTION & MATERIALS Painting & Colouring BY :- PROF. SAGAR R. RAUT ASST. PROFESSOR JAGADAMBHA COLLEGE OF ENGINEERING AND TECHNOLOGY YAVATMAL.

2. Paints & Painting Paints :- Paints are liquid compositions of pigments and binders which when applied to the surface in thin coats dry to form a solid film to impart the surface a decorative finish, apart from giving protection to the base material (i.e., concrete, masonry and plaster surfaces) from weathering, corrosion and other chemical and biological attacks. Paints preserve timber structures against warping and decay. Most of the metals corrode if not painted at suitable interval. Painting on surfaces impart decoration, sanitation and improved illumination.

3. Paints & Painting Calcareous surfaces, like lime and cement plastered surfaces, are highly alkaline in the initial stages, they retain large quantities of water during construction and it takes long time for the greater part of the water to evaporate even when the atmospheric conditions are favorable. Therefore, in applying a paint system on these surfaces, it is essential to take cognizance of the stored up moisture and also the alkalinity of the surfaces. These surfaces are porous and present problems, such as variable suction, surface imperfections, growth of moulds, mosses, lichens and algae. As each of these have adverse effect on most of the surface coating materials, finishing of these surfaces need special care.

4. CHARACTERISTICS OF AN IDEAL PAINT An ideal paint should possess the following characteristics : (1) Paint should form hard and durable surface. (2) It should give attractive appearance. (3) It should be cheap and readily available. (4) It should be such that it can be applied easily to the surfaces. (5) It should have good spreading quitlity , so as to cover maximum area in minimum quantity. (6) It should dry in reasonable time. (7) It should not show hair cracks on drying. (8) It should form film of uniform colour , on drying. (9) It should he stable for a longer period. (10) It should not be affected by atmospheric agencies.

5. Points to be consider while painting:- For efficient planning and execution of painting work on plaster surfaces, the following information should collected : Type of concrete, masonry or plaster surfaces to be painted, the type and nature of previous treatment, if any. Situations of use, namely, external finish or an internal finish; and the extent to which the surface will be exposed to weather and rain ; and In the case of new plastered surfaces, the nature of backing, the type of plaster undercoat and finish, the approximate date of completion of the plaster work in individual rooms ; and any addition of lime to the plaster finishing coat should be noted.

6. Constituents of Paints. An oil paint is generally made up of six main constituents given below: Base Vehicle or Carrier Drier Coloring pigment Solvent or thinner

7. Constituents of Paints. a. Bases:- The pigments commonly used as the principal constituents for forming the body of various types of paints are given below: White lead Red lead Lead Zinc white or zinc oxide Iron oxide Titanium white or titanium dioxide L ithophone

8. Constituents of Paints. b.Vehicle or carrier or binder :- These are liquid substances which hold the different ingradients of a paint in liquid suspension. The carrier or vehicle makes it possible to spread the paint evenly on the surface. The vehicles generally in use are : ( i ) Various forms of linseed oils (such as raw linseed oil, boiled linseed oil, pale boiled linseed oils, double boiled linseed oil and stand oil, (ii) Tug oil (iii) Poppy oil (iv) Nut oil.

9. Constituents of Paints. b. Vehicle or carrier or binder :- Raw linseed oil is thin, but it takes a long time to dry. Boiled linseed oil is thicker. For delicate work, however, only raw linseed oil is used along with driers and poppy and nut oil. It is used for interior work. Double boilecl linseed oil dries very quickly and is suitable for external work. It requires thinning agent like turpentine. Tug oil is used for preparing paints of superior quality. Colours in poppy oil last longer.

10. Constituents of Paints. c. Drier Driers are used to accelerate the process of drying and hardening, by extracting oxygen from the atmosphere and transferring it to the vehicle. However, driers reduces the elasticity of the paint; they should not be used in the final coat. Driers may be in the form of soluble driers or paste driers. Liquid driers are finely ground compounds of metals such as cobalt, lead, manganese dissolved in a volatile liquid. Paste driers consist of compounds of the above metals mixed with large percentages of inert fillers such as barytes , whiting etc.. and then ground in linseed oil.

11. Constituents of Paints. c. Drier The inert fillers serve the following purposes : Reduce the cost of paint, Improve durability, Modify the weight, and Prevent shrinkage and cracking. However, these are termed as adultrants , and their weight should not exceed one-fourth the weight of the base. Litharge ( PbO ), red lead (Pb 3 4 ) and sulphates of zinc and manganese are also used as driers. Litharge is most common in use but in general lead drier should not be used with zinc paints.

12. Constituents of Paints . d . Colouring pigment Colouring pigments are added to the base to have different desired colours . Pigments can be divided into the following divisions 1 Natural colours Ochres , umbers, iron oxides. 2 Calcined colours Lamp black, Indian red, carbon black, red lead. 3 Precipitates Prussian blue, chrome green, chrome yellow. 4 Lakes Prepared by discolouring barytes or china clay with the help of suitable dyes. 5 Metal powders Powders of aluminium , bronze, copper, zinc, etc.

13. Constituents of Paints. d . Colouring pigment

14. Constituents of Paints. d . Colouring pigment

15. Constituents of Paints. d . Solvents or Thinner

16. Types of Paints . Aluminium paints Anti-corrosive paints Asbestos paints Bituminous paints Bronze paints Cellulose paints Casein paints Cement based paints Enamel paints Oil paints Rubber base paints