Prep For Exterior Painting
By Owen Whetzel
When planning your painting project, one of the most important steps—in fact, thought by many professionals to be the most important—is the prep work you do. Prep, the common term for preparation, usually involves removing all organic growth, cleaning, sanding, filling, caulking, and masking surfaces, to be painted. Prep may take more than half of the total time of the painting project, but spending that time will help you achieve the best results.
Before you begin:
- Do a thorough inspection of all surfaces, to be painted. Problems that cause peeling, cracking and flaking, or blistering must be corrected or you will eventually end up with the same problems.
- If your building was built prior to 1980, also take time to read "Lead in Paint, Dust, and Soil," on the U.S. Environmental Protection Agency (EPA) website.
- It is important that primer or paint not be applied, when the temperature drops below the minimum application temperature given on the container, just as it is important the paint not be applied, when the temperature rises above the maximum application temperature given on the paint container. Use these temperature ranges as a guideline, when doing preparation as well.
- Place deck chairs, patio umbrellas and furniture, barbecue, etc. away from what you will prep and paint. Also, have plenty of heavy-duty cloths, plastic or paper drop cloths, to wrap and cover plants, and to cover other areas, you don't want possibly spattered.
Is latex or oil currently on walls and trim?
If you want to test to see if a water-based or oil-based paint has been applied to an exterior surface, try the following:
- Dampen a small section of a cloth with denatured alcohol (shellac thinner).
- The cloth should be a different color than the paint, so you can see, if some of the paint is being removed.
- Choose an inconspicuous location on a painted surface.
- Using the area of the cloth dampened with denatured alcohol, scrub the surface in a circular motion about the size of a quarter.
- If paint appears on the cloth, often somewhat thick or gummy, the paint is water-based.
- The alcohol will not remove oil-based paint.
I have paint, but is it oil- or water-based?
If you have an unlabeled container of paint and want to see, if it is latex (water-based) or oil-based, try the following:
- Put about two tablespoons of paint into a clear glass jar.
- Add water.
- Put the lid on the container and shake well.
- If the water mixes in and thins the paint, it is water-based.
- If the paint separates from the water, it is oil-based.
Remove organic growth
Ivy and other plants have tendrils, that hold the plant to a wall, and they must be removed before painting. Tendrils can sometimes be scrubbed away, using a non-metallic stiff-bristle brush and a detergent solution. Mix a solution of one-third cup Tide powder laundry detergent (without additives, such as bleach) and one-gallon of warm water. Wet the wall or trim using a garden hose. Vigorously scrub the tendrils. Rinse thoroughly.
One word of caution: If plant growth has been on a surface for a number of years, you may find hardened debris on the surface. Removing it by scraping and wire brushing may work on wood and some masonry, but doing so can damage stucco and concrete. If plant material cannot be removed from stucco or concrete by using detergent and brush scrubbing, then you may need to have the wall sandblasted clean by a contractor, who is experienced in sand- or bead-blasting stucco finishes and concrete, before repainting.
Another organic growth is fungus (mold and mildew), which is not uncommon to find on exterior surfaces. (Moss, also common in some areas, is killed by using a commercial moss killer, that will not harm the surface on which the moss is growing.)
To kill most mold and mildew, use liquid household chlorine bleach. When a surface is shaded and it's cool outside, wet the wall using a garden hose. Add 1-quart of liquid household chlorine bleach to 3-quarts of warm water. Scrub the walls or trim using a non-metallic stiff-bristle brush. For this solution to be effective, it must remain on surfaces long enough to kill any fungus. Rinse thoroughly.
If you want to wash and kill organic growth in one process, use the following recipe: To 3 quarts of warm water add: 2/3 cup TSP substitute, 1/3 cup Tide powder laundry detergent (without any additives such as bleach), and 1 quart household liquid chlorine bleach. The ingredients should be proportionally increased (e.g., doubling each ingredient will produce approximately 2-gallons, tripling 3-gallons, etc.). If you use Jasco TSP No-Rinse Substitute, it contains a deglosser and will dull painted surfaces, which is desirable prior to painting.
You should scrub all surfaces, not simply spot scrub. Splattering the solution onto walls or surfaces, that you are not going to paint, could leave them dull in spots and they will need to be repainted. Since detergent is mixed into this solution, you must rinse thoroughly. Therefore, ignore Jasco's "no-rinse" instructions, if you use that product.
IMPORTANT! When using liquid household chlorine bleach or any cleaning solution, always wear chemical-resistant, waterproof gloves; eye protection, preferably safety goggles; a respirator mask; and protective clothing; and make certain there is adequate ventilation -- fresh air entering the space and stale air being exhausted. Never mix chlorine bleach with ammonia or products containing ammonia! Always add chemicals, such as liquid household chlorine bleach, to water, never water to chemicals, to minimize the chances of chemicals splashing or reacting. Always test whatever method you use in a small, inconspicuous area, to be certain the product and/or method doesn't do more harm than good. Regardless of what product or products you use, be certain to follow the manufacturer's instructions and warnings carefully.
Pressure washing is not always effective at killing organic growth, but works well for general removal of dust, dirt, and some debris, when you use a cleaning product, that is made for the job.
Use caution, when pressure washing, that you do not get water and/or cleaning solution under siding or trim boards. Select your nozzle and pressure carefully. For example, 1,000 psi in a concentrated stream can break window glass and erode the soft portion of wood.
If pressure can be regulated, instructions for doing so may vary from pressure washer model to model. Therefore, you will need to refer to the instructions, which came with the pressure washer. If you do not have the original instructions or an owner's or user's manual, you may be able to obtain one from the manufacturer. If you don't have an address and telephone number for the manufacturer, it can usually be located through a Web search; the "Thomas Register," a comprehensive set of reference books or online at http://www.thomasnet.com/; or in a brand name directory, such as "Brands and Their Companies," published annually by Gale Research. The "Thomas Register" and "Brands and Their Companies" are usually found at most public libraries. If the pressure washer is a Sears Craftsman brand, the owner's manual may be available from Sears PartsDirect.
IMPORTANT! Once you have washed surfaces, you should allow from 12 to 48 hours—depending on weather conditions—for the surfaces to thoroughly dry. Painting a damp surface will usually lead to poor adhesion and paint blisters.
Paint blisters must be removed, but first determine why the paint blistered and correct the problem. According to the Rohm & Haas Paint Quality Institute, the possible causes of blistering are:
- "Painting a warm surface in direct sunlight.
- Application of oil-based or alkyd paint over a damp or wet surface.
- Moisture escaping through the exterior walls (less likely with latex paint than with oil-based or alkyd paint).
- Exposure of latex paint film to dew, high humidity or rain shortly after paint has dried, especially, if there was inadequate surface preparation.
- If blisters go down to the substrate: try to remove the source of moisture. Repair loose caulking; consider installing vents or exhaust fans. Remove blisters.
- If blisters do not go all the way down to the substrate: remove them by scraping, then sanding, prime bare wood and repaint with a quality latex exterior paint."
Peeling paint must be removed, but first determine why the paint peeled and correct the problem. The possible causes of peeling are:
- Seepage of moisture through uncaulked joints, worn caulk or leaks in roof or walls.
- Excess moisture escaping through the exterior walls (more likely if paint is oil-based).
- Inadequate surface preparation.
- Use of lower quality paint.
- Applying an oil-based paint over a wet surface.
- Earlier blistering of paint.
- Try to identify and eliminate source of moisture.
- Prepare surface by removing all loose paint with scraper or stiff wire brush, sand rough edges, and apply appropriate primer.
- Repaint with a top quality acrylic latex exterior paint for best adhesion and water resistance."
Voids in wood are filled using a patching compound formulated for exterior/outdoors or in stucco, they are filled using what is known as stucco patch. Wood surfaces should be sanded and uneven areas feathered (sanding the edges of the scraped areas, to provide a smooth surface).
One of the most often encountered problems in stucco patching is making invisible patches, that match the texture of the stucco. If the stucco is not smooth, matching the texture is usually accomplished by adding clean, salt-free sand (never use beach sand) to the stucco patch mix. Add a small amount of sand to the mix and then trowel that onto a piece of scrap cardboard or plywood. You can then make a comparison between the texture of your mix and the existing stucco. If needed, gradually add more sand until you have a match.
Remove old caulk
Exterior paintable caulking compound should be applied to all joints (wall to roof, windowsills, trim, etc.), before painting. If you want to use caulking compound that cannot be painted, it should be applied after the paint has dried.
Check glazing on windows
Old, damaged putty should be removed and replaced. You will find the length of time you need to wait before painting glazing compound on the compound container.
Use a painter's masking tape rather than a regular (manila-or off-white colored) masking tape, as it has a low-tack adhesive on the back, that doesn't dry-out as fast as regular masking tape. If you will be applying a water-base paint, such as latex or acrylic latex, a good choice of masking tape, that will minimize edge bleeding is FrogTape. If you use FrogTape, be sure to read: "How To Use FrogTape," which on the ShurTech Brands, LLC website.
Any masking tape should be removed, while the paint is wet. Avoid a heavy coat of paint over the edge between masking tape and for example, molding; otherwise, you will need to break the paint bond, using a single edge razor blade, wallpaper or other sharp knife blade, before the tape can be removed. Tapes will not provide sharp lines on textured or rough surfaces.
Exterior paint tips to keep in mind
Applying a latex (water-based) paint over more than 3 coats of an oil-based or alkyd paint is not recommended. Applying a latex paint may cause the layers of alkyd or oil-based paint to lift away from the substrate (the surface to which the paint adheres). This is known as paint incompatibility.
If you identify this as a problem, you have two choices:
- You can completely strip the paint, prep the raw surfaces (which may involve more than sanding all surfaces), remove all sanding dust, prime using a high-quality exterior primer, and repaint using a high quality exterior latex paint (preferably an acrylic latex paint), or
- You can prep the surfaces by scrubbing off all dust, dirt, debris, etc.; scraping away all loose paint and feathering (sanding) the scraped edges; and sanding all surfaces for best adhesion of the new primer. Remove all sanding dust and then prime using a high-quality exterior oil-based primer and then repaint using a high-quality exterior oil-based paint.
How much paint should I buy
First, choose the specific paint you plan to apply. The instructions and information on the paint container will indicate the paint coverage.
Measure all exterior surfaces to be painted - length and height and multiple them together. For example, the total length of walls is 200-feet and the height is 10-feet. 200 times 10 equals 2,000 or 2,000 sq. ft. To be certain, you will have sufficient paint, including enough for touch-ups at a later date, add 10-percent to your total calculations, which, in our example, totals 2,200 sq. ft. Now deduct the square footage of windows and doors. In this example, let's use 160 sq. ft. That leaves us with 2,040 sq. ft. Then divide the total number of square feet by the coverage indicated on the paint can of the product you have chosen. If the coverage is 380 sq, ft. per gallon, divide 380 into 2,040. In this example, the job would require approximately 5 1/3 gallons of exterior paint.
Calculated results should be used as estimates only. Results are not guaranteed and depend upon measurement, performance and skill of the individual user, as well as conditions under which the work is performed.
These suggestions for exterior prep are but a few of the tasks you may encounter. If you are not experienced at house painting, you may want to read a couple of books on the subject before you begin. OSH stores have a selection of books on painting. You should also find titles at a library. As mentioned, paying attention to prep will help you achieve the best paint job.
Be sure to always wear eye protection, gloves, a respirator mask, and protective clothing, when doing prep work and painting.
If you are uncertain about your abilities or if you lack the needed skills or tools, consider having the painting done by a licensed, qualified painting contractor.
If you are a California resident and decide to have any work costing more than $500 (labor and materials) done by a contractor, before entering into a contract you should request a free copy of "What You Should Know Before You Hire A Contractor," from the State of California, Department of Consumer Affairs, Contractors State License Board (CSLB). For the booklet to be mailed to you, phone 800 321 2752 (24-hours a day) and record your request, along with your full name and address. You may also read the booklet or download it from the Board's Web site. Select "Guides and Pamphlets," and then "What You Should Know Before You Hire A Contractor." It is available in English, Spanish, Chinese, Korean, Tagalog, and Vietnamese. You can also download other Board publications.
You will find Jasco TSP No-Rinse Substitute, sandpaper, paint scrapers, exterior-formulated spackling compounds and wood fillers, stucco patch, FrogTape, and other supplies you will need for your project in the paint department. Liquid household chlorine bleach is found in the Housewares department. OSH does not sell powdered Tide detergent.