Exterior Painting and Preparation

Sanding and scraping

Priming

Understanding the products

One of the problems with the exterior painting process is to overlook the importance of prime and paint specifications. For each substrate paint manufactures expend millions of dolares every year in experiments on their labs trying to improve the properties of their products acording to the diversity of substrates. This is science, and we as professional painters, must respect it and read the data sheets and spects for all new products to make sure we understand their purpposes, limitations and applications.

Preparation

Woodwork

  • Ensure the surface is sound, clean, dry and free from dirt, grease and any other contamination. Fill any cracks, holes and open joins with appropriate exterior filler. ​

  • For exterior bare wood sufrace: 

    • Lightly sand the surface to improve the paint’s adhesion. In environments where wood rotting fungi is likely to occur, treat with exterior wood preservative prior to priming. Then apply a full coat of oil/alkyd or acrylic based pimer. Using the right primer in the right situation can make the difference between washed-out color with visible stains or a bright and durable finish.Wood, especially cedar, holds a lot of chemicals, some which flow to the surface and right through several coats of exterior paint. A topcoat on bare siding would in short cause "cedar bleed" as tree tannins escaped 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 primer is not used first.The job of the 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 surface. In other words, when you apply an enamel topcoat to a primed door, you are applying the paint to the primer, not to the wood. All primers are made to penetrate and bond. But some can do more, such as hide colors of previous coatings, while others might hide less but do better at blocking emerging stains. The type of surface and the external environment dictate which type of primer to use. 

    • Calcking: Siliconized or top-of-the line polyurethane acrylic caulks give paint jobs a smooth, pleasing look. But the benefits aren’t purely aesthetic. Tight joints also prevent air leaks and block water penetration. For a better outcome this step shold be on top of the surface already primed to better adhere.

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Metals

  • 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, it is important for a contractor 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 react ive than ferrous metals.Using a primer or painthigh 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 ungalvanized, the surface should be cleaned primed and a good latex paint topcoa 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, prior to coating the surface, the rust should be removed by scraping the surface with a 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. Pri-mers 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

  • 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 washer with a low pressure to avoid damaging to the stucco. 

  • Caulk hairline cracks with urethane or masonry-caulking. For larger cracks, remove the debris and use appropriate stucco repair product to fell in the cracks. 

  • 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.

  • Use a brush to spot priming the areas where cracks were filled and caulking was applied.

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