Paint and Varnishes

Paint is a mixture of pigment, base, vehicle (oil), drier and thinner, applied as a coloured opaque coating. Varnish is a solution of resin in oil, turpentine or spirit, applied as a transparent coating.

Paint is a mixture of a base, vehicle, pigment, drier, thinner and sometimes extenders, in liquid form. When applied, the thinner evaporates, the vehicle dries and a hard coloured film remains.

1. Base: The main solid that forms the body of the paint and gives opacity. It fills pores and gives a uniform surface. Examples: white lead, zinc white, titanium white, red lead, iron oxide, aluminium powder.
2. Vehicle (carrier): A liquid, usually a drying oil (linseed, tung, poppy oil) that holds the base and pigment, spreads them and binds them to the surface on drying. It forms the tough film and gives durability and gloss.
3. Pigment: A fine colouring powder that gives the colour and also helps resist weathering (e.g. lamp black, chrome yellow, Prussian blue, red oxide, ultramarine). It also gives some opacity.
4. Drier: Added (about 8% by weight of oil) to speed up oxidation and hardening of the oil. Examples: litharge, red lead, manganese dioxide, cobalt compounds.
5. Thinner (solvent): Added to make the paint thin enough to spread and to dissolve the vehicle; it evaporates after application. Examples: turpentine, mineral spirit, naphtha.
6. Extender/adulterant (optional): Cheap inert filler such as barytes, gypsum, china clay, which adds bulk and reduces cost.

Ready mixed paint contains all of these in a can and needs only stirring and thinning before use.

Termites are small wood-eating insects that live in colonies in the soil and enter buildings through cracks, joints and wood. Anti-termite treatment poisons the soil and protects the building so the colony cannot reach it.

Importance

• Protects wood and timber: Termites eat doors, windows, frames, flooring, furniture and roof timber, weakening them.
• Prevents structural damage: Damaged roof members, floors and trusses can fail, endangering life and property.
• Protects other materials: Termites also damage paper, books, cloth, wiring insulation, cardboard and plastic.
• Saves repair cost: Treatment during construction costs little (about 1–2% of the building cost) compared with expensive repair or replacement later.
• Lengthens building life: Timber components and finishes last longer.
• Keeps hygiene and appearance: Mud tubes and damaged walls spoil the look and finishes.
• Hard to treat later: Once termites are inside, treatment is difficult, disruptive and not always fully effective; pre-construction treatment gives a continuous chemical barrier below the building.
• Relevant in Nepal: Terai and warm, humid regions have heavy termite activity, so treatment is recommended in foundations.

Paint is a coloured protective coating applied in liquid form on a surface that dries to a hard film. Functions in construction:

1. Protection: Shields wood, steel and plaster from moisture, rain, sun, and chemical attack.
2. Prevents corrosion and decay: Forms a barrier against air and water, stopping rusting of steel and rotting of timber.
3. Decoration: Gives colours, smoothness and attractive finish to interiors and exteriors.
4. Hides defects: Covers minor surface irregularities and stains.
5. Hygiene and cleaning: A smooth film is easy to wash and does not harbour dirt or germs.
6. Light reflection: Light shades improve lighting inside rooms; special paints reflect heat.
7. Special uses: Marking and signs (road marking), fire-retardant, waterproof and anti-fungal coatings.
8. Durability: Increases the life of the structure and lowers maintenance cost.

Anti-termite treatment (IS 6313, Part 2) creates a chemical barrier of poisoned soil between the ground and the building. Common chemicals are chlorpyrifos 20% EC, imidacloprid and similar emulsions diluted in water.

Pre-construction treatment

1. Excavation of foundation: Treat the bottom and sides of the trench after excavation. Apply 5 litres of emulsion per $m^2$ of the bottom surface, and 7.5 litres per $m^2$ of the vertical sides (up to about 300 mm height).
2. Backfilling: Treat the backfill earth in layers of 150 mm at 7.5 litres per $m^2$ of surface (about 15 litres per $m^3$ of earth in some practice).
3. Plinth filling: Treat the top surface of the filled earth before the soil-bearing floor is laid, at 5 litres per $m^2$.
4. Junctions: Treat the junction of wall and floor with 7.5 litres per running metre; make pockets in the walls with a rod and pour the emulsion.
5. Surroundings: Treat the soil along the external wall perimeter, usually up to 300 mm wide and 300 mm deep, at 2.25 litres per running metre.

During construction

• Use treated timber for frames, remove stumps and roots from the site, and avoid wood scraps in the filling.
• Do not disturb the treated soil; if disturbed, re-treat it.
• Give a damp-proof course and keep wood from direct contact with the ground.

Post-construction

Drill holes in floors and walls along the plinth and inject the emulsion into them; treat the outside soil by trenches.

Emulsion paint is a water-based paint in which resin (acrylic or vinyl) particles are suspended in water. It is used on interior and exterior walls, is odourless, quick drying and washable.

Procedure on a wall surface

1. Curing: Let new plaster cure and dry for at least 4 weeks (moisture below about 12%).
2. Surface preparation: Remove dust, loose particles, oil, grease and old flaking paint with a wire brush or sand paper. Fill cracks and holes with putty and sand smooth.
3. Primer coat: Apply one coat of water-based wall primer (cement primer for new surfaces) with a brush or roller. Allow it to dry for 4–6 hours.
4. Putty (wall putty): Apply two thin coats of putty with a putty blade for a smooth base; sand lightly after each coat and dust off.
5. Paint mixing: Stir the paint well and thin with clean water (about 20–30% for the first coat).
6. First coat: Apply evenly with a brush, roller or spray, working from top to bottom and in the same direction, and allow 4 hours (or as per manufacturer) to dry.
7. Second and third coats: Sand lightly between coats, then apply the final coat, less thinned, to get a uniform finish.
8. Finishing: Clean splashes from floor, windows and fittings; protect the film from rain and water until fully dry.

Distemper is a water-bound paint made of chalk (whiting) or lime as a base, with glue or casein as a binder, pigment for colour and water as the thinner. It is applied on plastered walls and ceilings of interiors to give a decorative, matt finish at low cost.

• Oil-bound distemper is another type, in which the binder is a drying oil, making it washable.
• Dry distemper is supplied as powder; it is mixed with water, and the coat is not washable and may be rubbed off.

Distemper is cheap, easy to apply, dries quickly and gives a soft matt effect, but it is not suitable for exteriors or damp places because it is not durable, cannot be washed (dry type), and must be recoated every few years.

A good paint should:

• Spread easily and uniformly, and have good covering power.
• Dry within a reasonable time to a hard, smooth, glossy film.
• Stick firmly to the surface without cracking, blistering or peeling.
• Resist weather, sunlight, moisture and chemicals.
• Keep its colour without fading.
• Be cheap, durable and easy to clean.
• Not contain harmful substances and be free from bad odour.
• Not settle or form a skin in the container during storage.

Paint is a liquid mixture of a base, pigment, vehicle, drier and thinner that forms a hard, opaque coloured film when dried on a surface. Varnish is a solution of resin (natural or synthetic) in oil, turpentine or spirit that dries to a hard, glossy, transparent film.

Purpose of paints

• Protect surfaces (wood, steel, plaster) from weather, moisture, decay and corrosion.
• Decorate with colour and a smooth finish, and hide defects.
• Make surfaces hygienic and easy to clean.
• Improve life of the structure and reduce maintenance.

Purpose of varnishes

• Protect the surface (mostly wood) from moisture, dust and insects, while keeping the natural grain and colour visible.
• Give a glossy, attractive finish to furniture, doors, windows and floors.
• Provide a hard, water-resistant layer over painted surfaces and paintings.
• Make the surface easy to clean.

Varnish is a transparent protective coating of resin dissolved in a solvent. Its functions are to:

• Protect timber and other surfaces from moisture, dust and wear.
• Show and improve the natural grain, colour and beauty of the surface.
• Give a hard, smooth, glossy and washable finish.
• Preserve painted surfaces and make them last longer.

A good varnish should:

• Be clear, transparent and give a glossy, smooth film.
• Dry quickly and form a hard, tough film that does not crack.
• Spread easily and stick well to the surface.
• Show the natural grain and colour of the wood without clouding.
• Resist water, heat, scratches, sunlight and normal chemicals.
• Not turn dull, white or sticky with time.
• Be durable and free of bad odour.

Varnish is a solution of resin in a solvent, and its main ingredients are:

1. Resin (gum): Natural (lac, copal, rosin, amber) or synthetic resin. It forms the hard, shiny film on drying.
2. Solvent (thinner): Dissolves the resin and makes the varnish spreadable, and evaporates on drying. Examples: turpentine (oil varnish), methylated or wood spirit (spirit varnish), water (water varnish).
3. Drying oil (in oil varnish): Linseed or tung oil, which gives toughness, elasticity and durability.
4. Drier: Compounds such as litharge or manganese salts that speed up drying.
5. Colouring matter (optional): Dyes or pigments added to make coloured varnish.

Steps for painting a new wood surface:

1. Seasoning and cleaning: Use well-seasoned timber; rub the surface with sand paper to remove dust, loose fibres and roughness.
2. Knotting: Cover knots and resinous spots with a coat of shellac knotting (or aluminium paint) so resin does not bleed through.
3. Priming: Apply one coat of wood primer (e.g. red lead or pink primer) and let it dry.
4. Stopping: Fill holes, cracks and dents with putty and sand smooth.
5. Undercoat: Apply one or two undercoats, rubbing lightly with fine sand paper after each.
6. Finishing coat: Apply the final coat of paint evenly with a brush, in the direction of the grain, after the undercoat is dry.

Steps for painting a new plastered surface:

1. Drying: Let the plaster cure and dry fully (at least 2–3 weeks) so alkali and moisture escape.
2. Cleaning: Remove dust, loose particles, mortar splashes and efflorescence with a wire brush and dry cloth.
3. Repair: Fill cracks and holes with cement or putty, and level with sand paper.
4. Priming coat: Apply a coat of alkali-resistant (cement) primer to seal pores and make the paint stick.
5. Putty/filler: Apply wall putty if a very smooth surface is needed; sand after drying.
6. Undercoat: Apply one coat of undercoat and sand lightly.
7. Finishing coat: Apply two coats of the final paint, each after the earlier coat is dry.

Preparation of an old painted surface:

1. Inspect the old paint: if it is sound and firmly stuck, only cleaning and light rubbing are needed; if flaking, cracked or blistered, remove it fully.
2. Remove old paint: Scrape with a scraper or wire brush, or use a paint remover or blow lamp for thick coats.
3. Clean dust, dirt, oil, grease, mould and efflorescence with a brush, soap or detergent water, then rinse and let dry.
4. Rub down with sand paper (glass paper) to roughen glossy areas and give grip for the new coat.
5. Repair: Fill cracks and holes with putty or filler, and sand smooth.
6. Rust and knots: Remove rust from metal with a wire brush; treat bare patches and knots with primer or knotting.
7. Prime bare spots and then apply the new undercoat and finishing coats.

Knots in timber contain resin that oozes out through the paint and spoils the finish, so they must be treated (knotting) before painting.

1. Clean the knot with sand paper and remove loose fibres and dirt.
2. If resin is oozing out, scrape it off or burn it with a hot iron or blow lamp, and clean it again.
3. Apply two coats of knotting: a solution of shellac in methylated spirit (or a coat of red lead or aluminium paint) over the knot and slightly beyond it, allowing it to dry between coats.
4. Fill any hole with putty, sand smooth, then apply the primer and paint coats.

This seals the resin and prevents the knot from showing through the paint.

What is distemper

Distemper is a water-based paint with chalk (or lime) as the base, glue/casein as binder, pigment and water, used for interior plastered walls and ceilings.

Commercial forms

1. Dry distemper: Supplied as powder in packs.
2. Oil-bound distemper: Supplied as paste (thick liquid) in tins, with oil as binder.

Preparation in the field

• Dry distemper: Mix the powder in the quantity of clean water as stated by the maker (about 1 part powder to 1 part hot/cold water), stir to a thick smooth paste, then dilute and stir until it is of brushing consistency. Strain and use warm, within the day.
• Oil-bound distemper: Stir the paste thoroughly, add water slowly (1 : 1 or as per instructions) to get a creamy mixture, and strain through a cloth before use.

Distemper is applied on new or old plastered walls as follows:

1. Surface preparation: For new plaster, let it dry for at least 2–3 weeks; clean off dust and loose material. For an old surface, scrape the old distemper and wash it off.
2. Fill cracks with putty and rub smooth with sand paper.
3. Primer coat: Apply a coat of priming distemper (or a prepared wash) to seal the surface.
4. Mix the distemper with water to proper consistency and strain it.
5. First coat: Apply with a wide distemper brush in horizontal strokes, then cross strokes, working quickly to avoid joints; let it dry for 24 hours.
6. Second coat: Apply in the same way over the dry first coat.
7. Finish: Clean splashes. Complete a whole wall without a break to prevent visible patches.

Common defects in paint work:

1. Blistering: Bubbles in the film caused by moisture or gas trapped under the paint, or painting on a damp surface.
2. Flaking (peeling): Paint comes off in flakes because of poor surface preparation or dampness.
3. Cracking and crazing: Fine cracks forming from ageing, an unequal drying rate or painting a hard coat over a soft one.
4. Chalking: Powdery surface from decay of the binder by sun and weather.
5. Fading: Loss of colour by sunlight or chemical action.
6. Sagging (running): Paint flows down in curtains when applied too thick or too thin.
7. Wrinkling: Surface skins before the layer below dries.
8. Bloom and grinning: Dull cloudy film, or the earlier coat showing through because of poor covering power.

Post-construction treatment is done in an already built building to kill termites present and to build a chemical barrier outside and inside, as per IS 6313 (Part 3). It uses the same chemicals (chlorpyrifos or imidacloprid emulsion) as the pre-construction method.

1. Inspection: Find the entry points, mud tubes, damaged wood and nests.
2. Treatment of the plinth (inside): Drill holes of about 12 mm diameter at 300 mm centres along the junction of wall and floor, in the floor next to the wall; inject the emulsion by pressure (about 7.5 litres per running metre) and seal the holes with cement mortar.
3. Outside soil treatment: Dig a trench about 300 mm wide and deep along the external perimeter, treat the soil at about 7.5 litres per running metre of trench, and backfill in layers while sprinkling the emulsion.
4. Treatment of cracks and voids: Drill and inject the chemical into wall cracks, expansion joints, and behind skirting.
5. Treatment of wood: Spray or inject termiticide into wooden frames, and replace badly damaged members.
6. Nests: Destroy visible mounds by digging and pouring the chemical.
7. Follow-up: Re-inspect yearly; repair any breaks in the barrier.