Exterior Painting and Preparation
Understanding the materials
One of the problems with the exterior painting process is to overlook the importance of the primer and paint specifications. For each substrate paint manufacturers expend millions of dollars every year in experiments trying to improve the properties of their products according to the diversity of substrates. This is science, and we as professional painters, must respect it and read the data sheets and specs for all new products to make sure we understand their purposes, limitations, and applications.
Preparation
Sanding and scraping
Priming
Woodwork Preparation
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We must ensure the surface is healthy, sound, clean, and free from grease, dust, moss, mold, and mildew. Fill in cracks, holes, and opened joins with the appropriate exterior fillers. Applying a compatible caulk and primer lays the ground for a great finish work.
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For exterior bare wood sufrace:
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Lightly sand the surface to improve the primer adhesion. In environments where rotting wood, and fungi are likely to occur, treat with exterior wood preservative before priming. Then, apply a full coat of oil/alkyd or a sealant acrylic-based primer. Applying the appropriate primer for each situation clearly shows the difference between a washed-out color with visible stains from a bright and durable finish. Wood, especially cedar, holds chemicals, some of which flow to the surface and right through several coats of exterior paint.
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A topcoat on bare wood siding can cause cedar bleed as tree tannins escape the wood. In addition, escaping moisture is liable to cause a finish paint to peel from most types of wood in a relatively short time if a primer is not applied first.
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The role of primer is to act as an intermediary between the wood substrate and the topcoat. It should seal, hide, and bind wood fibers to make the surface more uniform. This allows the paint to adhere more tightly to the substrates. All primers are made to penetrate and bond but some can do more, such as hide colors of previous coatings, and block emerging stains. The type of surface and the external environment dictate which primer to use.
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Calcking: Siliconized, urethane, and acrylic caulks give paint jobs a smooth, pleasant look. But the benefits aren’t purely aesthetic, they tighten the joints prevent air leaks, and block water penetration. For a better outcome, this step should not be overlooked as well.
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Painting
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Metals Preparation
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Knowing which type of metal you’re working with is vital since it will influence the performance characteristics of the coatings that you select for the job. There are two categories of metal—ferrous (containing iron) and non-ferrous (not containing iron). How to distinguish them? A ferrous metal is magnetic and a magnet would stick to it while on a non-ferrous metal, a magnet wouldn’t stick. Therefore, a contractor needs to identify ferrous metals because they are corrosive and will rust. Corrosion is the oxidation of a substance and steel is one of several metals susceptible to this process. Aluminum will also corrode, producing a white powder called aluminum oxide. Non-ferrous metals are generally less reactive than ferrous metals. Using a primer or painting in zinc provides protection where small areas of steel and galvanized metal are exposed by scratches, drill holes, or cut edges. Coating the metal substrate with a primer and paint will provide barrier protection by isolating the metal from the environment and the potential electrolytes. “Several good paint systems are available for covering metal substrates. If galvanized, the surface should be cleaned and primed and a good latex paint applied to the surface. One of the most common mistakes made is when there is a small amount of rust on ferrous metal, and a contractor does not use a rust inhibitor primer; However, before coating the surface, the rust should be removed by scraping the surface with a wir-brush, sanding, abrasive blasting or dissolving the rust away with acidic solutions. Traditionally the best way to handle rust is to remove it down to a clean metallic surface, however, if this is not possible then scrape or wire-brush the metal down to a sound-rusted surface and apply a rust-inhibiting primer which will soak into the rust retarding oxidation. Primers are designed to protect the metals and provide a base for the finish coat. The finish coat protects the metal from moisture migration as it also provides some aesthetic appeal. But no coating can completely protect against water vapor, so the function of a rust-inhibiting primer is to absorb and tie up the water vapor as it comes through the coating, thus preventing rust-forming reactions with the metal.
Masonry Preparation
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Remove dust and dirt from the surface of the stucco. A thorough brushing of the stucco with the stiff bristles of a push broom is good enough for most of the new stucco. If the stucco has a deep texture, however, you might have to use a power washer to get the dirt out of the deepest crevices. You should apply the power wash with a low pressure to avoid damaging the stucco.
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Caulk hairline cracks with urethane or masonry-caulking. For larger cracks, remove the debris and use the appropriate stucco repair product to fill in the cracks.
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Allow the stucco to dry for several days before applying any primer or direct coating. Drying time depends on the weather, porosity, and texture of the stucco.
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Use a brush to spot priming the areas where cracks were filled and caulking was applied.
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