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General Tips for Painting and Coating

Paintings and coatings are the two generic terminologies used in construction industry very commonly. Though technically speaking these are two different processes, Coatings in a larger perspective encompass paintings also. A coating actually is a layer of material deposited onto a substrate to enhance the surface properties resistant to adverse environmental exposures and also providing aesthetic properties. Some of the specialty coatings available in the market may not involve the deposition process. Factors affecting the choice of a coating include service environment, life expectancy, substrate material compatibility, component shape and size, and cost. While painting forms a film, coating forms a layer thickness varying from microns to several mm. In the following tips, coating is used in general sense.

Step by Step

• Understand the specification stipulated.
• Understand the surface of application and the product type.
• Check the surface condition and repair if required.
• Clean the surface thoroughly using air compressor if required.
• Keep all tools and tackles ready. These will include brushes, ladders, rollers, safety and protection items like masks, cap and goggles, appropriate clothing to protect the skin.
• Use standard thinners, primers, paints and other additives maintaining the mixing ratio constant.
• Keep the painting area well ventilated and free from dust and foreign particles. It not only helps to dry faster but also protects you from fumes and other hazards.
• Patch cracks, holes and other imperfections before applying the first primer coat.
• Apply First Coat of Primer: Primer coat is essential as they help in providing a smooth surface, making the surface less absorbent, thus increasing the spreading capacity of the paint. Primer also gives uniform colour and texture to the finished paint, and provides better adhesion to the top coats. The type of primer to be used depends on the kind of surface to be painted, i.e. different primers exist for interior, exterior, wood, metal surfaces.
• Allow the primer coat to dry. Apply new coat only when the previous coat has satisfactorily dried up.
• Apply leveling or Putty Coat- Putties are generally used in the case of fresh painting or walls that require total overhauling just like fresh walls, they may not be used for repainting or touch up exercises. Wall putty should be applied to walls after first primer coat has dried. It will fill in minor cracks and surface imperfections, and provide a protective sub-layer for the expensive paint. As per the requirement 1-2 coats of putty can be applied, but do allow the previous coat to dry before applying subsequent coat.
• Clean the surface before applying the second primer coat.
• Second Primer Coat- Generally repainting services require a single coat of primer, but for fresh surfaces or the surfaces that need considerable levelling and removal of undulations, two primer coats are required. Care must be taken that the second primer coat be applied only after the putty coat(s) has dried completely.
• Clean the surface thoroughly.
• Apply the finishing coat in two or three layers. Generally two coats of finish coat are required to get the desired finish and colour. It is important that each coat must be completely dry before the application of next one. Please refer to the instructions with the paint purchased for finding out drying time and special instructions if any.
• Allow the surface to dry and ensure dust free zone while the paint is wet.

General Care¹

• Keep brushes from drying by putting them in respective solvent until you are ready to clean them.
• If possible mix different containers of the same paint type and shade into a larger box to provide a uniform colour and touch-ups for all areas painted with the shade of paint.
• Follow manufacturer’s label directions.
• Always remember to box your paints otherwise they may dry if left open.
• Store paint properly and keep from excessive heat or cold exposure.
• Always use good quality paints for superior long lasting finish.
• Stir paint thoroughly before any applications. Paint is made up of a base and pigment, and it may separate. So use a stir stick to ensure you mix the paint well.
• Always clean the surface to be painted, scrape off loose paint/lime wash and sand the surface for a smooth finish.
• Do calculate how much paint you will need.
• Prime the walls if going from one extreme colour to another. For instance, if the walls are tan and you want deep green, paint first with a primer tinted to match your intended top coat to ensure you'll end up with the true colour.
• When working with latex paint use brushes with synthetic bristles. For oil or alkyd based paints natural bristles is a better choice.
• Never apply latex on an oil finish and vice versa without first sanding the walls. If using a primer, choose primer of the same composition (oil or latex) as that of the intended topcoat.
• Do not smoke or bring insidious items that can cause fire in the painting area.
• Never apply paint on poorly prepared surfaces because it may lead to undue problems and imperfect finish.
• Don't paint over a damp surface with oil-based paints.
• Don't sand woodwork across the grain.
• Don't rush your painting exercise. Best results can be achieved with a little patience. Plan on making it a full-day affair and you won't get tired or frustrated.
• Don't' change cans of paint in the middle of a wall area. This may bring a change in tone and shade.
• Don't' use gasoline to clean up brushes.
• Don't add thinner to the product unless directions call for it: If it is too thick, find out what can be done, or what the best solution is because paint thinner is not always the best solution, and could cause your paint to not work as well.
• Never dispose of paint irresponsibly. Check your area for local hazardous waste recycling centres.

Surface Preparation²

Surface preparation is one of the most important activities in the whole process because it directly affects the surface finish of the paint. It is not only critical in getting good results; it actually helps save time and makes the painting exercise economical.  It is said that the most expensive paint, the finest brush and best painting technique cannot compensate for a poor surface preparation. During the surface preparation exercise it is recommended to wear safety goggles and a mask to avoid being exposed to unnecessary dust. Some of the tips to get effective surface are listed below: 

• Use a paint scrapper, a putty knife or a sand paper to remove loose particles or flakes and ensure that the surface is free from dust, dirt, grease etc. For lime wash coated walls it is suggested that you scrape it off using a Paint Scrapper or even sand paper. For oil-base painted walls you can remove the gloss by sanding as well. Ensure that all flaking paint is also removed and what paint is left adheres tightly to the wall.
• Be careful on wood siding to avoid gouging the wood with a scrapper.
• Patching cracks - Dig out the cracks with the help of a screw driver to remove all loose material and fill them with plaster or putty mixture. When dry, smooth the surface with the help of a 220 grade sanding paper.
• Patching Holes – Dig out the holes a little to remove loose material and patch up all the holes using plaster, putty or lightweight spackle.
• Remove patches, mildews - If painting over a previous coat of paint, one must remove any mildew with a mild solution of bleach and water in a one-to-four ratio or with the help of a mildew cleaner.
• After all scrapping and patching it is advisable to sand the entire surface. An 80 grit sandpaper would be ideal. Take care to start sanding only when all the patching has dried.
• To remove dirt or grease wash walls with water. Start the painting procedure only when the walls are dry.

Types of Finishes

Most paints can be classified based on the finishes they exhibit. They can be generally categorized as:

• Flat Finish
• Eggshell Finish
• Gloss or Satin Finish

Flat Finish

A latex-based, versatile paint type, flat is normally used for walls and ceilings. Many types of finish are available: dead-flat matt, matt, a water-based eggshell and silk. Some formulations contain vinyl to make them more hardwearing. Flat is also best used on siding materials. It can help the material cope with moisture. Exterior flat is available with a smooth or rough texture. Apply all flat using as many coats as are necessary for even coverage. For use in a sprayer, dilute flat with 10 percent water.

Eggshell Finish

More durable than flat, eggshell has a slight sheen. Always check the exact finish because the degree of sheen varies between manufacturers. It is most commonly used on interior wood surfaces as an alternative to semi-gloss, although some manufacturers will specify that the paint may be used on exterior surfaces. Eggshell can also be used on wall surfaces where a hardwearing finish is required as it is easier to clean. Two coats will usually give an even color; use primer and first coat as required.

Gloss and Satin Finish

A very hardwearing finishing paint, gloss is used mainly on wooden and metal surfaces. Satin is used in the same way as gloss but is slightly less shiny and is increasingly popular, especially for interior woodwork. Both solvent-based and latex-based versions of gloss and satin paints are available. Latex-based paints are easier to apply and less prone to “yellowing” with age, but do not provide as high a shine or hardwearing a finish as solvent-based paints. Almost all gloss and satin paints are suitable for interior or exterior use. Some glosses are formulated especially for exposed exterior surfaces. Gloss is generally applied as a single coat over one or two coats of primer.

Paint Components

Typically, there are four main components in paint:

• Pigment,
• Binder,
• Liquid, and
• Additives.

Application methods depend on the particular paint, but can include spray application, brush methods, and electrostatic spraying. Pigment plays a large role in determining color and appearance. Some pigments also provide added bulk, helping to thicken the paint when needed. In its unmixed form, a pigment is simply a powder. There are two general categories of pigments: prime and extender.

Pigments

Prime Pigments- Prime pigments are mainly responsible for color or whiteness in paint, as well as the paint’s ability to hide undesirable surface flaws. In paints that exhibit a white hue, titanium dioxide is the main ingredient. In paints the express other colors, the pigments are selected to absorb only certain kinds of light, thus yielding a given color. Organic pigments yield the brightest colors, while inorganic pigments yield less bright but more durable colors.

Extender Pigments- Extender pigments are designed to add bulk, but are not as well-suited to hiding surface flaws as prime pigments. They do, however, influence the paint’s overall sheen, color retention, and abrasion resistance. Silica and silicates, for example, are extender pigments that increase the paint’s durability. Zinc oxide helps prevent mildew and corrosion, and is especially useful in outdoor applications.

Binders

In a paint mixture, the binder is responsible for providing adhesion, binding the pigment, and also gives the paint resistance properties which make the final coating tough and durable. The binder itself is clear and glossy, but the presence of pigment interferes with this quality. Depending on the ratio of pigment to binder, or the PVC (pigment volume concentration) the paint can assume varying levels of glossy finish. Paints with the glossiest finish often have typical PVC of 15 percent, while the most matte paints have PVC anywhere from 40 to 80 percent. Paints with less gloss have more binder per unit of pigment, and tend to be more durable. There are two specific types of binder: oil-based and latex-based.

Oil-Based Binder- Oil-based paint requires a binder that has similar properties to the paint—in this case, the binder oxidizes or dries when exposed to air, hardening along with the rest of the paint. Once applied, the liquid factor of an oil-based paint evaporates, and the binder then reacts with the air to harden into place with the pigment. However, sometimes this process can result in over-dry, brittle paint, and chipping can occur. Additionally, the oxidation makes the paint prone to yellowing.

Latex-Based Binder- Latex-based paints actually do not possess latex—rather, the binder that is used (plastic-like in nature) creates a film in the paint that resembles natural latex rubber. Almost all water-based paints have a latex-based binder. When the coating is applied, water evaporates from the paint, leaving behind a film of pigment and latex-based binder, which bind together into one continuous coating. The process by which the binder and pigment are fused is called coalescence. However, because the binding agent is thermoplastic, it cannot be applied at too low a temperature or the binder will be too hard and difficulty will arise during fusing. Common types of latex-based binder include acrylic and vinyl acrylic.

Liquids

In the most basic sense, the liquid component of paint is simply responsible for transporting the binder and pigment to the substrate surface. The type of liquid depends upon the other components of the given paint. Oil-based paints, for example, can use a basic paint thinner as the primary liquid. Latex-based paints, on the other hand, tend to use water as their liquid.

Additives

When certain properties need to be manipulated or enhanced, additives are often the solution. Thickeners, for example, are additives that help thicken the paint to make application easier. Surfactants help disperse pigments within the paint, ensuring the coat is even and stay in place. Co-solvents help the binder film formation and help prevent paint damage from occurring if the pain is frozen. Co-solvents also make application easier by lengthening the amount of time the paint can be open before beginning to set.

Reference: 1, 2 Jenson and Nicholson tips