Exterior paint fades because ultraviolet radiation breaks down both the pigment and the binder holding it. Deep reds, bright blues and organic-pigment colours fade fastest. Inorganic pigments and acrylic or silicone binders resist far better. South and west-facing walls fade two to three times quicker.
The best time to paint a house exterior in India is October to March, after the monsoon ends and before peak summer. Ideal conditions are surface temperature below 40 degrees Celsius, relative humidity under 85 percent, and no rain forecast for 24 hours after application.
Exterior wall seepage usually comes from four sources: cracked plaster, failed parapet or chajja joints, leaking pipe penetrations, or rising damp from the plinth. Paint cannot stop active seepage. The crack or joint must be sealed and the wall dried before any coating is applied.
Algae and fungus grow on exterior walls where moisture, shade and organic dust meet. North-facing and tree-shaded walls are affected first. Treatment requires killing the growth with a biocidal wash, letting the wall dry fully, then applying a paint containing fungicidal and algaecidal additives.
Exterior wall cracks are classified by width. Hairline cracks under 0.3 mm are cosmetic and can be sealed with a crack-bridging exterior paint. Cracks between 0.3 and 3 mm need filler and mesh. Anything wider than 3 mm, diagonal, or growing needs a structural engineer before painting.
Efflorescence is a white crystalline deposit left when water carries soluble salts from inside masonry to the surface and evaporates. It is common on new construction and damp walls. Painting over it causes rapid peeling. It must be brushed off dry, the moisture source fixed, and an alkali-resistant primer applied.
Chalking is the powdery residue left when a paint’s binder degrades under UV exposure and releases loose pigment. It signals a high pigment-to-binder ratio, typically in low-cost emulsions. New paint applied over a chalked surface will not bond and must be preceded by thorough washing and a sealer coat.
Painting an exterior wall follows six steps: clean the surface, repair cracks, apply exterior putty where needed, prime, then apply two finish coats. Allow 4-6 hours between coats and avoid painting when rain is expected within 24 hours or when the surface is above 40 degrees Celsius.
Exterior primer is essential on new plaster, chalking surfaces and alkaline walls because fresh cement has a pH high enough to break down paint binders. On sound, previously painted walls in good condition, a primer coat is often optional and an extra finish coat may serve better.
On exterior walls, putty goes first to level the surface, followed by primer to bond and seal, then finish coats. Putty fills undulations while primer creates adhesion and blocks alkalinity. Only exterior-grade acrylic or water-resistant putty should be used outdoors.
