Bases

The bases is the principal constituent of the paint. It forms the bulk of the paint and forms an opaque layer to obscure the surface of the material painted. It possesses binding properties which reduce the shrinkage cracks formed in the film on drying. Some the examples of base are:

(i) White lead:

• It is a carbonate of lead and forms the base of lead paints.
• It possess good bulk and is the most widely adopted base.
• It is dense, permanent and waterproof.
• It is not suitable for delicate work owing to discoloration of lead due to exposure to sulphur vapours.
• It is most suitable for wooden surface and not used for iron surfaces due to its inability to protect it against rusting.

(ii) Red lead:

• It is an oxide of lead and forms the base of lead paints.
• It is suitable for painting iron surfaces & for providing a prime coat to wooden surfaces.
• It solidifies in a short time with linseed oil and hence it is used as a drier also.

(iii) Zinc lead:

• It is an oxide of zinc and forms the base of zinc paints.
• It does not gets discolored on exposure to sulphur vapours.
• It forms less bulk and hence it is costlier.

(iv) Oxide of Iron:

• It forms the base of iron paints.
• It’s tint varies from yellowish brown to black.
• It is effective against preventing rusting and generally used as a prime coat for iron surfaces.

(v) Aluminium Powder:

• It forms the bulk of aluminium paints.
• It prevents cracking and warping of wood and is generally used as a prime coat for wooden surfaces.

DEFECTS IN PAINTING

Following are the defects commonly found in the painting work:

(i) Blistering : In this, bubbles are formed under the film of paint as a result of water vapours trapped behind the painted surface. It is caused due to factors such as improper seasoning of timber, execs oil in final coat etc.

(ii) Bloom : In this defect, dull patches are formed on the finished polished surface. It is caused due to bad ventilation or some inherent defect in paint.

(iii) Fading : It is characterized by the gradual loss of color of painted surface & is mainly caused as a result of sunlight.

(iv) Flaking : Appearance of loose portions on painted surface is known as Flaking. It is caused due to poor adhesion.

(v) Flashing: Appearance of glossy patches on the painted surface is known as Flashing. It is mainly caused due to poor workmanship, cheap paints, weather action etc.

(vi) Grinning : If the final coat of paint doesn’t possess sufficient opacity, then background is visible. This is known as Grinning.

(vii) Running : In this defect paint runs back leaving behind some small uncovered areas. It is caused when the painted surface is too smooth.

(viii)Sagging : It occurs when a vertical or inclined surface is too thickly painted.

(ix) Saponification : Formation of soap patches on painted surface is called saponification. It is caused due to action of alkalies.

(x) Wrinkling : It occurs when a horizontal surface is too thickly painted.

TYPES OF VARNISHES

Depending upon the solvents used, Varnishes are classified as follows:

(i) Oil Varnishes

• It uses linseed oil as a solvent.
• It uses hard resins such as amber and copal.
• A small quantity of turpentine is also added if required workability is not achieved.
• It dries slowly but forms a hard and durable surface.
• It is specially adopted for exposed work which require frequent cleaning such as coaches, house fittings etc.

(ii) Spirit Varnishes

• It uses methylated spirits of wine as a solvent.
• It uses soft resins such as lac or shellac.
• It dries quickly but doesn’t form a hard and durable surface.
• It is generally used for furniture.
• French polish belongs to this category of Varnishes and is one of the finest finish for ornamental furniture.

(iii) Turpentine Varnishes

• It uses turpentine as a solvent.
• Resins adopted are of soft variety such as gum dammar, mastic and rosin.
• It dries quickly but is not tough and durable as oil varnishes.
• It possesses light color.

(iv) Water Varnishes

• It uses water as a solvent.
• It uses shellac as resin which is dissolved in hot water along with sufficient quantity of either ammoniaor boric or potash etc so that it is completely dissolved.
• It is used for varnishing maps, pictures, delicate interval work etc.

PROPERTIES OF DISTEMPERS

• They shrink on drying. Hence, if the receiving surface is weak, cracking and flaking may occur.
• Their coating is usually thick and more brittle than other type of water paints.
• Its film is pervious in nature and hence it permits new walls to dry out without any damage to the film.
• They are generally light in color and provides a good reflective coating to the surface.
• They are less durable than oil paints.
• They exhibit poor workability.
• They can be applied on brickwork, plastered surfaces, insulating boards etc. but prove to be unsatisfactory in damp locations like kitchen, bathroom etc.

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