Varnishes

Varnishes

1. Varnishes Building Construction Material

2. Definition A Varnish may be defined as a “homogeneous liquid Containing essentially a resinous substance dissolved in a suitable oil or a volatile liquid”. A Varnish does not contain any pigment. However it is always used as a finishing coat.

3. Varnish

4. Function of Varnish More Commonly a Varnish is used over a wooden object as a decorative & Protective Covering . The Varnish brings out the grains of wood in a brilliant manner when given without a paint. On the painted surface, varnish imparts a delicate brilliance. Moreover, the resinous material dissolved in the varnish forms a thin film on the drying which protects the surface below from deterioration to moisture.

5. Function of Varnish

6. Ingredients of Varnish The two essential component of varnish are a base or resinous substance and a solvent. The resin of varnish may be natural or artificial . Natural resin used in varnish are rosin, copal, shellac, amber, and dammar. Synthetic resin include phenyl, and vinyl resins . The main solvent used in varnish are boiled linseed oil , turpentine, and methylated spirits. Water has also be used in some special varnishes.

7. Natural Resins

8. Artificial Resins

9. Rosin

10. Copal

11. Shellac

12. Amber

13. Dammar

14. Solvent Used In Varnish

15. Type of Varnishes Some common types of varnishes distinguished on the basis of the solvent of constituents are as follows: Oil Varnish Those Varnish in which linseed oil has been used as a solvent form this group. The base material may be amber or copal. Although they dry slowly, they form a hard and durable film. Hence they are popular for use in external finish. They are quite resistant to weather changes.

16. Oil Varnish

17. Type of Varnishes Turpentine Varnish These are made by dissolving gum, mastic or rosin in turpentine. They have the advantage that they dry quickly. At the same time, the film formed is neither much durable nor resistant to moisture. Hence they are used only in interior work.

18. Turpentine Varnish

19. Type of Varnishes Spirit Varnishes They are commonly used varnish for furnitures. They consist of Shellac dissolved in methylated spirits. French Polish is a varnish belonging to this group. Sometimes a small quantity of a pigment is also added to give a desired shade to the finish. The spirit varnish are also not much durable. They are also not resistant to weather changes. Hence these can be given only on wooden articles protected from rain, gases and light.

20. Spirit Varnishes

21. Type of Varnishes Japans These are a class of varnishes that have asphalt as an Important ingredients . Asphalt is dissolved in a linseed oil in the presence of a volatile thinner. JAPANS are applied mostly to metal surfaces. The surface is first- given a coat of JAPANS and then heated to baking temperature at 210 C for few hours. On Cooling, the paint forms a coating that is highly resistant to chemical corrosion.

22. Japans

23. References Building Construction : Dr B.C. Punmia Civil Engineering Material : Prof. Singh Internet Web Sites

24. Thanks…