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SURFACE PREPARATION:

Masonry exteriors can all be successfully painted, as long as you take certain precautions when preparing the surfaces. Before painting, it is important to ensure that the surface is sound, free of dirt, powdery dust and loose sand, yet rough enough to allow good adhesion of the coating. Efflorescence, a white, sometimes crusty or powdery material may also be present. If allowed to remain, this salty deposit can interfere with paint adhesion and ruin the appearance of the job.

UNPAINTED MASONRY:

If the masonry has not been painted before, it may be extremely porous. Rather than use large amounts of paint filling in surface porous. Start with an exterior latex primer recommended, this will provide a smoother, less porous surface on which to paint.

New masonry should cure for at least 30 days before painting. However, if unable to wait for this to happen, take these two points into account:

1. Wait at least 2 weeks then first apply an alkaline-resistant primer or sealer. Otherwise the degree of alkalinity may attack the paint, prematurely ruining film inte grity and fading the color.

2. Use 100% acrylic latex paint is far more resistant to alkaline attack than alkyd and vinyl acrylic latex paints.

PREVIOUSLY PAINTED MASONRY:

Use wire brushing to remove all powdery dust, dirt, peeling paint and other loose material, and then rinse it with clean water. Remove any mildew or efflorescent. Always use primer for the entire job, it will improve the overall adhesion and uniformity of appearance of the finish coat.

WHY IT’S IMPORTANT TO USE TOP QUALITY CAULK?

The great majority of exterior and interior paint jobs involve some use of caulk. And, according to the professional painters, the quality of caulk that is used can make a big difference in the appearance and long-term performance of any paint job. Top quality water-based all-acrylic caulks and siliconized acrylic caulks are the best choices for most applications. Benefits of top quality:

• Excellent adhesion

• Superior flexibility

• Greater long-term durability

• Paintable

• Less odor

PAINT SELECTION:

When it comes to repaint selection, a top quality 100% acrylic latex paint is an excellent choice for masonry surfaces. It is permeable, allows moisture within the masonry to escape through the paint film rather than trapping it behind the film, potentially causing blistering and adhesion loss, as can occur with oil based coatings.

OIL BASED BINDERS:

Binders in oil-based paints are either natural or synthetic. The natural binder in an oil-based paint is made from a vegetable oil that “dries” when it is exposed to the air. Drying oils traditionally used in paints include linseed oil, tung oil and soya oil. Today, few paint are made with oil alone. Rather, they are based on modified oils called alkyds. Made from vegetable oils and synthetic resins, alkyds are chemical compounds that dry harder and faster than oils, Exterior oil-based wood primers often are made with a combination of oil and alkyds.

FILM FORMATION: OIL-BASED PAINTS:

Film formation of oil and alkyd-based paint is a two-step process. When an oil-based paint is applied to a surface, the liquid evaporates and leaves the binder and pigment on the surface. The oil or alkyd binder then dries, or oxidizes, as it reacts chemically with oxygen in the air. It is this oxidation that develops the hard, tough properties of an oil paint. Unfortunately, this reaction continues indefinitely, and over time can produce some unwanted results. For example, oxidation can cause yellowing that typically is bleached out by sunshine, but may be quite noticeable in areas not exposed to sunlight.

Other problems can occur later. The continuing oxidation process in oil-based paints can ultimately render the film not only hare, but also brittle. Then, when an exterior substrate expands and contracts, the paint film may crack and flake because it remains rigid. In interior situations, the paint may chip if struck by items such as furniture.

FILM FORMATION: LATEX PAINTS:

Film formation of latex paints occurs in a much different manner. As the liquid in the paint evaporates, the microscopic particles of latex binder and pigment that remain on the painted surface come closer together. As the last vestiges of liquid evaporate, capillary action draws the binder particles together, causing them to fuse and bind the pigment into a continuous, flexible film that will be water resistant when dry. This process is called coalescence. Since no oxidation takes place – either initially or over time – the film tends to maintain its flexibility over the life of the paint job.

The film formation process also allow latex paint to retain microscopic opening that allow it to “breathe,” that is, allow moisture vapor to pass through. Latex paint is thus more tolerant of moisture coming from inside the building than are oil or alkyd paints. Oil or alkyd paints from tighter film, and are prone to blister or lift if moisture is behind the paint. (Latex binder particles are extremely small and, in some cases, highly uniform. The particles in this magnified view are only .000008 inches in diameter.)

DRYING TIME:

Film formation and durability can also be affected if latex paint dries too quickly. That because fusion or coalescence of the latex binder takes some time to occur properly. Very quick drying can reduce the mobility of the particles before the film is adequately formed. It is best to avoid painting in direct sunshine because surface temperatures can be 10 to 20 degrees higher than the air temperature, especially if it is a dark color. To avoid this, work your way around the house or building so that you are always painting in the shade, especially in the warmer afternoon hours. Where this can be done, try to paint these areas in the early hour of the day.

Temperature

Relative Humidity

Wind

Sky

Between 65⁰F – 85⁰F

Between 20% - 80%

Little or no wind

Slightly overcast

(no direct sun)

PAINTING METAL:

Proper surface preparation plus the right choice of primer and paint, is key to a long lasting paint job.

Preparing the Surface. The first consideration when preparing a ferrous metal surface in a non corrosive atmosphere for painting is to remove any loose rust that is present, as well as any peeling paint. On smaller jobs, use a chisel-style scraper and hand-held wire brush. Use the scraper to take off heavy rust and loose paint, then follow up by wire brushing the surface to remove as much of the rust residue as possible. It is not necessary to remove every bit of rust and take the surface down to bare metal, but rather to remove as much rust as these methods will allow. Surface preparation should not be omitted just because an iron or steel surface is new. New ferrous metal often has mill oil on it or small amounts of rust that are not readily visible. Not removing these before applying a coating could result in premature failure of the paint job.

TIMING OF PRIMING IS CRITICAL:

Once a ferrous metal surface is free from rust and other impurities, priming should be done as quickly as possible. This timing is vital because rust can begin to re-form on iron or steel if the surface is exposed for as little as a day or two. If that happens, you’ll have to prepare the surface again. When painting ferrous metal, it is important to apply a top quality metal primer because it must perform two vital functions: provide the bond between the topcoat and the metal, and inhibit corrosion. This is a point you should not compromise. When priming ferrous metal:

DO: Use a quality exterior rust-inhibitive primer.

DO: Apply the primer at the recommended spread rate in order to achieve adequate film thickness, which directly impacts corrosion resistance.

DO NOT: Thin the primer before application, unless recommended by the manufacturer.

DO: Consider applying a second coat of primer for maximum corrosion resistance. Top quality acrylic latex corrosion inhibitive primers work well in applications where the metal is not exposed to heavily corrosive atmospheres, such as acidic or salt air. Unlike oil-based or solvent-based primers, they can be applied immediately after cleaning the surface, even if it is still slightly wet. Zinc-rich and zinc chromate epoxy and alkyd primers are more appropriate for more highly corrosive settings. Selecting the right topcoat is also important when painting ferrous metals. A high quality acrylic latex paint is generally a good choice because it can last as much as two to four times longer than conventional alkyd paints without serious cracking or fading, has a much quicker drying time, and is easier to handle and clean up. In addition, always apply primer and paint to metal in thick coats for optimum durability and rust resistance. That’s because the thicker the coat, the less chance of moisture penetrating the paint and reaching the substrate.

DIRECT-TO-METAL COATINGS:

Another option when painting metal is Direct-To-Metal (DTM) coatings. These coatings are designed for direct application to metals without the use of a primer. They function as both primer and topcoat in one product. DTM coatings can be used for a variety of applications, are available in semi gloss or gloss formulations, and are now offered in high performance latex products. To ensure proper protection of the metal, two thick coats are usually recommended. Regardless of whether you use a DTM coating or a primer-topcoat system, it is not difficult to get years of reliable service from a metal paint job. The keys are taking the time to properly prepare the surface, promptly priming the surface, and applying thick coats of the right type of coating.

Actually, all exterior paint exposed to the weather will eventually fail at some point, no matter how well it has been applied, usually by cracking and/or loss of adhesion, or by erosion to the substrate. How long a paint job will actually last depends on a number of factors, including the nature and condition of the substrate. “What causes exterior paint to fail prematurely?” With that question in mind, here are seven factors we have observed as frequent causes of early paint failure:

1) Failure to smooth rough edges

Paint will not adhere well to an “unstable” surface such as old paint that exhibits marginal adhesion. The preventive measure is to taper the edges of the old paint by “feather sanding” them, using medium grit (#120) garnet paper for general exterior use, and finishing with fine grit (#220) garnet paper where close-up appearance is important with semi-gloss and gloss paint.

2) Failure to use a primer

In general, prime any surface that has not been previously painted. Also prime any surface areas exposed by loss of paint, such as those that have peeled after years of exposure or have been exposed as part of surface preparation.

The benefits of using an appropriate primer are consistent with those gained from good surface preparation. They include maximizing all of the following:

• Adhesion of the finish coat

• Uniformity of sheen or gloss

• Hiding and hiding uniformity

• Gloss development of the finish coat

• Mildew resistance

• Lack of discoloration from the substrate

3) Failure to correct a source of water behind the substrate

Even though a surface has been properly prepared and painted, the presence of moisture behind the paint can result in blistering and peeling.

4) Failure to apply paint at the correct spread rate

All of these properties are directly impacted by dry film thickness. In short, the thicker the film, the better the coating will perform in each of these properties. So be sure to follow the manufacturer’s recommended spread rate. Thinning paint prior to application can also compromise these properties.

5) Failure to apply latex paint at the proper temperature

The microscopic particles of binder in latex paint are thermoplastic, meaning they harden as the temperature drops. In order for them to fuse or coalesce and bind the pigment into a tough, continuous paint film, they must not be applied at too low or too high a temperature

6) Failure to use correct type and quality of paint

And, of course, there is always the suitability – and quality – of the paint. A paint designed for the job is essential. For example, gloss paint designed for use on metal will probably crack if applied to wood. Similarly, paint designed for indoor use will perform unsatisfactorily if used outdoors.

The quality of the paint is just as important. The Rohm and Haas Paint Quality Institute recommends using a top-of-the-line product for most exterior applications. Choosing an exterior paint based mainly on low initial price can compromise both protective and decorative properties. Generally speaking, top-of-the-line 100% acrylic latex paints provide the best overall performance.

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