Before you can begin painting your historic house or building, you will have many preparations to make. Some of the key preparations you must make include:

• Choosing the right type of paint and primer for your project.
• Determining the amount of paint and primer you need.
• Selecting and purchasing the best painting supplies.

Choose the Right Type of Paint and Primer

When you purchase paint for your painting project, you must choose between oil-based and latex-based paint. Oil-based paints are durable, water repellent and help condition old, dry wood because they penetrate more than latex paints. However, the Environmental Protection Agency (EPA) is slowly working toward the complete elimination of oil-based paints. Modern oil paints use a variety of petroleum-based products and other volatile chemicals, called volatile organic compounds (VOCs), as the liquid vehicle for the solid content. These VOCs have a negative effect on the ozone layer and your health. The unpleasant odor you smell when you use oil paint includes both the paint chemicals and the evaporation of the VOCs in the chemicals.

Latex paint technology is steadily improving. Latex paints are often called water-based paints. They are very easy to apply and clean up, and they have better vapor permeability than oil paint. Latex paints cure more quickly and completely than oil paints. As soon as the water vaporizes, the paint is cured, leaving behind all the solids like resin, additives and pigments.

Latex paint is available in a variety of sheens, and paint manufacturers have minimized the problem of fading in latex paint due to ultraviolet light exposure. Latex-based paints use petroleum products and contain VOCs, but they have fewer chemicals than oil paint. Most latex paints meet the EPA's standards for VOCs and are healthier for you and the environment.

Some of the largest paint companies are now marketing elastomeric paints, sometimes called spray-on-vinyl. Elastomeric paints are thick and stick like glue, but they have virtually no vapor permeability. This means that water vapor cannot escape through the paint like it does with standard latex-based paints. Water vapor can build up underneath these paint coatings, and eventually the hydrostatic pressure will push the paint off — and the face of the wood siding with it. This ruins the wood permanently.

One critical point you should look for in any paint is the solids content. The higher the solids content, the better the paint quality is. Any paint with less than 58% solids by volume does not contain enough solids content to adhere properly to the surface and wear over many years. You can check the solids content of any paint by visiting the paint manufacturer's website to see the manufacturer’s data sheet.

The key difference between interior and exterior paints is the additives. Additives will enhance or alter the properties of the pigments, solvents and binders. Interior paints are formulated to be scrubbed and cleaned, and to resist staining. The best exterior paints generally have more solid content than most interior paints. The higher solid content provides better wear against the weather elements. Exterior paints also have ultraviolet light fading inhibitors and mildew resistance.

You must also choose a primer for your painting job. Alkyd oil-based primers are still superior to any latex-based primers. Alkyds (natural oils) have better penetration qualities than latex and help condition old, dry wood. Chemists at all the major paint manufacturing companies are getting close to producing a water-based, low-VOC primer with good penetration qualities.

Select the Best Painting Supplies

High-quality paint brushes and rollers are essential to a quality paint job. Spend as much as you can afford for the best brushes. The best brushes to use for oil paints are natural bristled (often made with hog hair) and are sometimes called “china bristled.” A variety of polyester and nylon brushes are available for water-or latex-based paints.

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A china bristle paint brush is recommended when using oil based paint. Source: Bob Yapp

When you are selecting brushes, choose brushes with thick bristles and no hollow area in the middle. They should have a split end on each bristle. These split ends are called flags in the painting industry. The end of the bristles should be tapered or chiseled to allow the paint to flow freely. Good brushes will rarely lose any bristles, but cheap brushes will leave bristles all over your paint job. Good brushes can be cleaned and used for decades.

Roller covers come in a variety of qualities and thicknesses. Avoid the packages of cheap rollers with cardboard center tubes. The best roller covers have plastic or phenolic resin center tubes that hold up to the moisture. You should also look for rollers that are labeled "shed resistant." These rollers won't shed fabric material all over the wall you are painting. To produce an extra smooth finish that mimics historic brush painted surfaces, use either a ¼-inch or 5/16-inch nap roller cover. Nap rollers that are between 3/8 and 3/4 inches produce a progressively thicker texture.

Determine How Much Primer and Paint You Need

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To calculate how much paint you'll need to paint a room, start with measuring the walls: height times width equals the square footage (area). You can also measure the windows and doors and subtract that area from the overall square footage. Source: WHS - State Historic Preservation Office

Before you can purchase primer and paint, you’ll need to figure out how many cans of each one to buy. If you are applying primer to bare wood, plaster, or drywall, you should be able to cover around 200 square feet of wall surface area per gallon of primer. A gallon of interior or exterior paint will cover between 250 and 350 square feet of wall surface area. If you thoroughly cover the surface you are painting with primer, you should be able to cover close to 350 square feet per gallon of paint.

To determine how much square footage you need to paint, you’ll have to take some measurements. For example, if the room you are painting has a 10-foot ceiling and four walls that are 12 feet wide, you figure the square footage this way:

10 feet (height) x 12 feet wide = 120 square feet x 4 walls = 480 square feet

To determine the amount of paint you need, take your total (480 square feet) divided by the average coverage of 300 square feet to arrive at 1.6 gallons.

If the doors and windows in the room you are painting occupy a significant amount of space, you can subtract the square footage of those from the total area.