Whether you're coating a new substrate or repainting an existing one, it pays to use the correct products and procedures. Here is a guide to coating four of today's most popular exterior surfaces.
Fiber-cement siding, a combination of Portland cement, ground sand, cellulose fiber and select additives, holds paint exceptionally well. The siding is available either un-primed or pre-primed.
If improperly treated, cement-based products can be mildew magnets. A high quality exterior acrylic masonry primer will fortify the siding's mildew and efflorescence resistance. Caulk at the butt joints and apply the finish coat.
Exterior latex coatings are the best topcoat choices for new fiber-cement siding. Because they have a substantially higher film build than conventional paints, only one coat is necessary over a primed surface – and duration is guaranteed not to peel or blister.
When repainting fiber-cement siding, pressure clean with a minimum of 2100 psi pressure to remove all dirt, dust, grease, oil, loose particles, foreign material and defective coatings. Rinse thoroughly and allow to dry. Scrape away any remaining peeled or checked paint, and sand those areas. Also sand any glossy surfaces to make them dull.
Unless the substrate is exposed, a primer is not required when repainting fiber cement. One coat of a good quality exterior latex paint is all that's needed.
Cedar Shake or Siding
Cedar shake or siding, as well as redwood, is best primed with an exterior oil-based wood primer (some regions must use a latex primer due to VOC regulations). A primer is essential – it will serve as a barrier coat to help prevent tannin bleed, a brownish or tan discoloration that can appear on a painted wooden surface. Before coating, make sure that new wood is dry enough to absorb sprinkled water before coating.
If you plan to stain the cedar, apply two coats of a solid color acrylic exterior house stain.
One note of caution: Be careful if you decide to go with a semi-transparent stain because the shade of the substrate contributes to the final color, and the finished job may not look quite like what you had planned. It's a good idea to test the stain in an inconspicuous place before applying to the entire surface to make sure it will produce the color you want.
Another bit of advice: An acrylic solid color stain will offer best results for heavily knotted wood, as semi-transparent stains will not hide the knots completely.
If the cedar has never been painted or stained but has been exposed to the elements for more than 60 days, evaluate the level of decay before proceeding. Any loose, fibery, gray-looking areas should be lightly abraded prior to coating.
Aluminum siding should be power washed with the correct detergent to rid the surface of chalk, oil and other foreign materials prior to painting.
Unless it has a super-slick surface, aluminum siding rarely needs to be primed. Simply apply one coat of a good quality exterior latex paint by either brushing, spraying or rolling. Unless the surface is bent or damaged, you can achieve a terrific, factory-finished look.
The trick with painting or repainting brick is to power-wash or clean the loose powdery surface well enough without destroying it. This will minimize efflorescence problems later on.
The condition of the substrate is critical when painting or repainting. Brick or mortar cracks will telegraph through the topcoat and should be repaired with patches and sealants prior to painting.
Note: Brick should be allowed to weather for at least a year and then wire brushed to remove efflorescence.
Prep Makes Perfect
Paint failure is generally a symptom of poor surface preparation. Thoroughly cleaning the surface assures proper bonding of the paint and helps you get the most from your topcoat. Other considerations:
Old paint: Make sure glossy surfaces of old paint films are clean and dull before repainting.
Wood rot: Fix the water or moisture problem before painting. You may want to call a carpenter.
Efflorescence: If you see white fluffy deposits of salt crystals on the surface, scrub them off before painting.
Mildew: If there is the appearance of dirt even after washing, chances are there is mildew on the surface. Scrub with a solution of one part bleach and three parts water. (Wear rubber gloves and eye protection.) Allow to stand on the surface for 10 minutes, then rinse thoroughly. Repeat as necessary. Allow the surface to dry for 48 hours before painting.
Weather: Never paint immediately after a rain, when rain is predicted or during foggy weather. As a general rule, humidity should be no more than 85 percent. Avoid painting when temperatures rise above 90° F or fall below 50° F, unless the products are designed to be used under those circumstances.
Need help determining the substrate, the right preparation techniques, the right product or even the right color? Call or email Moorhouse Coatings TODAY!