Exterior House Painting Preparation

This page covers scraping, priming and caulking exterior siding and trim in preparation for painting. See the following pages of this article for help with painting exterior siding and painting exterior trim molding.

Exterior painting is more complicated and labor intensive than interior painting. Exposure to sunlight, rain, cold and heat is very stressing on the paint coating. Because of the extreme conditions exterior surfaces require specific preparation procedure, priming and a durable paint coating to ensure a lasting finish.

In addition to proper preparation, exterior surface will have to be in good repair before they are painted. If there are any breaks in exterior surfaces such as peeling paint, cracks or rotting wood, water will certainly penetrate these and ruin the new paint finish. See the article on repairing rotted wood for help with rotting wood and for help with cracks, use these caulking techinques to fill them before painting. Treating peeling paint and other preparation procedures are covered below.

Peeling Paint and Water Damage

Peeling paint is the biggest problem with most exterior paint jobs. Paint will always peel if there are any contaminants between the painted surface and the paint film. Contaminantion on exterior surfaces comes from a number of sources. Probably the most common is water but dust, rust, algae, mildew, smoke and air polutants can also cause exterior paint to peel.

Moisture affecting exterior painted surfaces can come from within or it may be saturating the surface from the outside as with rain or an overflowing gutter. In either case the water source must be remedied before any prep and painting can begin. Water from within a wall usually will be coming from a leaky pipe or rain water may backup in the gutter and run down the inside of the house siding.

Gutters are usually easily restored by cleaning leaves and other debris from them and the downspouts running to the ground. The downspouts will usually be harder to clean than the gutter requiring some disassembly at the bottom to clear them. After you've done this once you will likely want to avoid it again by adding gutter covers that will block more debris from collecting. Some gutter covers work better than others so if you can afford it, you should go the extra mile and get a high quality system that works well and will do so for years to come.

Exterior Painting Preparation

Start your exterior painting preparation by scraping all loose and peeling paint, putty and caulk from the surface. Slip a putty knife under to lift off loose material and use a pull–type paint scraper to remove paint, etc. that looks loose but doesn't come free easily.

Lightly sand the edges of any bare spots created by the scraping with 120 grit sandpaper for latex paint and 80 grit for harder, oil and alkyd–based paints. To determine the type of paint you're working with try sanding it lightly with 120 paper. If you create dust by sanding the paint, it's oil or alkyd. If the paint balls up or flakes come away from the surface, it's latex paint. Because of this tearing away of the paint coat, don't sand too hard on latex paint, it will create a rough edge around bare spots, encouraging peeling.

In addition to sanding to remove debris, you should also rough up any shiny paint like semi or high–gloss with a quick pass of the sandpaper. This will help the new paint bond better than it otherwise would to the slick finish.

Wash the Surface

After all the scraping and sanding has been done, wash the surface to be painted. Use a garden hose to rinse all the dust off the siding and then scrub it with a nylon brush or broom dipped in a cleaning solution of laundry detergent and warm water. If you have a mildew problem add a cup of household bleach to the solution before scrubing. Rinse the siding and let it dry completely before proceeding.

Prime the Surface

With your clean, dry exterior surface you're ready to do any necessary priming, caulking and repairs. Prime before you caulk or patch to ensure a good bond. There's no need to prime existing paint that is still in good condition. Primer is only needed to bond to bare spots and block stains or water damage. Let the primer dry overnight before proceeding but don't let it stay exposed for more than two weeks before finishing. Use a top grade exterior primer. Choose a latex primer if your exterior is in a dry climate that doesn't suffer from prolonged rain or damp conditions. If you're in a damp climate use an alkyd–based primer to be sure your new paint won't peel.

Repair Cracks and Other Damage

Use an exterior grade latex caulk for cracks and let it cure overnight before applying your new paint coat. Be sure to caulk all cracks and wood joints and around all trim like door and window frames. While you're at it, caulk any cracks around decorative trim moldings and around the door and window jambs.

Use an exterior spackle for minor repairs to wood trim and siding, and an epoxy filler for severely damaged and rotted wood. Let the patch material set according to the label directions and then sand it smooth. A sanding block or power sander will be needed to sand most exterior patching compounds. Remove the sanding dust and spot prime the patches with and alkyd based exterior primer.