In the 39th of a series of practical construction tips, Engineer Jagvir Goyal discusses aspects of exterior wall painting.
1. Cement paints used for painting external surfaces of walls are not fully resistant to algae and fungus. Other paints available are semi-acrylic and 100 per cent acrylic exterior emulsion paints. These paints perform well and provide protection against fungus and algae. However, these are much costlier than cement paints so work out your budget. The all-inclusive cost of semi-acrylic paints is around Rs 10 per sq ft. This includes the labour component too. Good semi-acrylic paint costs around Rs 100 to Rs 125 per litre. Just 1 litre should cover about 50 sq. ft. in two coats. Water curing of this paint is not required.
2. For really good results, choose 100 per cent acrylic exterior emulsion paint. It costs around Rs 180 to Rs 220 per litre and covers around 50 sq ft in two coats. The all-inclusive cost of application is about Rs 6.50 to Rs 7 per sq ft. Today, the labour component is almost equal to material cost if you engage skilled painters. This paint also requires no water curing.
3. Companies produce acrylic exterior emulsions with slight variations. Some paints are classified as shining, some with a metallic effect and others with elasticity to stretch themselves over hair s. These variations are because of additives while, basically, they are all acrylic emulsions. For example, Asian Paints produces Apex Ultima, Apex hi-stretch, Apex weatherproof exterior emulsion, Apex textured exterior emulsion and Ace exterior emulsion. The top paint companies today are Asian Paints, Goodlass Nerolac, Berger and ICI. Another company coming up is Nitco. Always choose an exterior paint that is dirt-resistant. Apex Ultima is extremely popular these days because of large-scale advertisements by the company. Indeed, cement paints are fast losing their market to acrylic or textured paints. Weathershield (ICI Dulux), Supercote, Apex Ultima (Asian Paints) and Ace exterior (Asian Paints) are all good exterior paints.
4. All acrylic emulsions can be applied by brush as well as roller. These resist high rainfall, algae, fungus, heat and humidity very well. Acrylic emulsion is also a breathable paint that doesn't allow moisture to be trapped inside the wall. On horizontal surfaces like the top of window projections, apply an additional coat as these surfaces are more subjected to weathering and rain.
5. A middle-order choice for external surfaces is textured exterior acrylic paints. These are paints with a variety of textured finishes that look like granite, Dholpur stone, wood, stencils, glazing, etc. These too are waterproof, anti-fungus, fire resistant, withstand rain and allow escape of trapped moisture. Textured paints are, in fact, toughened acrylic emulsions and are produced for both interior and exterior surfaces. If you want to paint a wall and forget about it for years together, these are your best bet. Siliceous aggregated marble chips, quartz powder and pigments are added to emulsified acrylic polymers to produce these paints. Most of them can be applied by brush, spray pump or trowel. While the basic coat is applied with a steel trowel, a plastic trowel is used for the final coat. Some paints can be applied by a roller too. The thickness of these paints is 1-2 mm. They dry up completely in 24 hours; after eight hours of application, there is no effect of rain.
6. Ensure that any fungus or moss on exterior surfaces is thoroughly cleaned with water and a wire brush. A bio wash solution now available in the market can be used if the moss or algae don't come off. Fill all s or dents with the putty produced by the same company whose paint you have selected. Otherwise, a mixture of white cement and white sand in the ratio of 1:3 can be used. Always apply a coat of acrylic primer before applying exterior paint. Add water to the primer and paint as per the supplier's recommendation as there is a large variation in recommendations by different manufacturers. Some paint companies allow 20 per cent water while others allow equivalent quantity, i.e. 100 per cent water. Allow four to five hours to pass after application of acrylic primer. Don't leave the primer coat unpainted for days. Apply two coats of final paint and give a time gap of five to seven hours between the two coats. To prepare the final paint, about 400 ml of water can be added per litre of paint. Check the manufacturer's instructions instead of leaving it to the painter.
7. While choosing painting materials, always choose readymade shades rather than made-up shades. Made-up shades may show inconsistency and patches. Avoid mixing of shades to produce a colour of your choice even if your painter assures you of a uniform colour. There is every chance that you will end up with different shades on the walls of a room.
8. Never avoid primer coats. It is very important to apply them. These cause better adhesion of paints to the walls. They also reduce the absorption capacity of walls and make the surface to be painted smoother. For repair of any s in walls, use the putty supplied by the paint manufacturer or 1:3 white cement sand mix. Apply another primer coat if a major filling job has been done.
9. For exterior surfaces, heritage surface textures are the most attractive surface finish. Buy these if you can afford them—they stand the test of time. The thickness of these finishes is only 0.8 mm to 1.2 mm. So keep the plastered surface perfectly level if you choose a heritage finish. Apply only a single coat of heritage finish. Choose among granules, flakes and granite finishes. The granule finish is cheapest and the granite finish is costliest. The rates vary from Rs 15 per sq ft to Rs 40 per sq ft including application. The heritage finish comes in two parts. One part is the dry flakes or granules while the second part is the bonding agent. Add water to the mixture if necessary and apply on plastered surface with a trowel. An additional coat that looks like lamination can be applied Roller coat application of heritage finishes is very costly; it uses acrylic co-polymer as an ingredient and requires a special roller. So choose flakes or granules with colour mixing of your choice. A heritage finish is suitable both for inner and exterior surfaces. Make sure you get it done from an authorised dealer for a lifelong, maintenance free surface.
10. Another unique textured wall finish is the spectrum finish. Cheaper than a heritage finish but with unique designer characteristics, this finish comes in a range of single and double-coat application products. Check out the shade card of these finishes to make a decision. The rate varies from Rs 8 to Rs 30 per sq ft. Spray coat and granule finishes are the most preferred. Spectrum paint finishes are especially suitable for hot areas as they do not fade even when exposed to extreme heat.