Preparation is very important when painting high abuse areas such as porches, decks and patios. Not only do they incur foot traffic but as a horizontal surface they collect pollution, leaves, pollen and other contaminants as well as being subjected to standing water and a high incidence of sunlight.
A thorough cleaning, either with a pressure washer or a scrub brush, is the first step. Mildew needs to be treated with a bleach and water solution (3 parts water to 1 part household bleach) or a commercial mildewcide. Protect yourself with goggles and gloves and other surfaces with drop cloths when using this type of solution. Be sure to thoroughly rinse any detergent and mildewcide after application. All loose, failing paint needs to be removed prior to recoating. Sand broken edges and any glossy surfaces. Pay close attention to the weather forecast as rain will collect more readily on horizontal surfaces. Also, try to avoid painting in direct overhead sun as this can cause heat blisters.
The following steps depend on whether the surface is masonry (concrete, brick, etc.), wood or composite material (i.e. Trex) and on the condition of the surface.
Masonry surfaces may need to be acid etched if the surface is smooth and dense, such as you would see on a garage floor. Follow the directions on the container carefully. Rough concrete or brick primarily needs to be cleaned as noted above. New concrete should be allowed to cure for at least 30 days before painting.
Be aware that masonry surfaces in contact with the earth may experience hydrostatic pressure. Moisture wicking up from the earth can cause blistering of almost any paint. You can test for this condition by taping a piece of 2 mil or thicker plastic, approximately 2 sq. ft. in area, to the surface for 24 – 48 hours. If moisture is condensed on the floor or plastic when removed it would be advisable not to paint this area. A concrete stain which allows evaporation would be preferable.
Wood surfaces usually need to be sanded to remove loose wood fibers. Be sure to thoroughly remove sanding dust when done. Any severely cracked or rotted wood should be replaced as these areas will be prone to paint failure, as well as for safety concerns.
Wood surfaces, if free of paint and uniform in appearance, can also be stained. A semi-transparent stain, while less protective than paint, avoids the maintenance associated with blistering and peeling common to wood deck surfaces.
Composite deck surfaces need to be clean and dry. Most composite surfaces hold paint well as they do not absorb moisture or shrink and expand like wood. Check with the manufacturer for recommendations before painting.
When painting new surfaces, thin the first coat 20-25% with fresh tap water as a primer. Once this is dry, apply one or two un-thinned coats as a finish.
If you desire a textured surface for non-slip properties, add the non-slip aggregate to the first un-thinned coat or broadcast it into the freshly applied wet film and sweep the excess aggregate away when dry. Then apply a regular coat over the aggregated finish.
You can walk on the painted surface the next day but wait a few days before moving patio furniture, bbq’s and other heavy objects onto the surface.
Keep in mind that painted or stained horizontal surfaces will require more frequent maintenance than vertical surfaces. A yearly inspection in the spring is advisable.