Restoration Guide: Paint and Finishes for Exterior Walls
Editor's Note: This is article 18 of 18 in Chapter 2:Exterior Walls of the Old House Web's Home Restoration Guide. This guide was developed and edited for old homes from original material in the U.S. Housing and Urban Development (HUD) Rehab Guide.
18. PAINT AND OTHER EXTERIOR FINISHES
Paints and stains keep wood from deteriorating under moist conditions, and they also help repel damaging ultraviolet rays from the sun. Wood that is directly exposed to excessive sunlight, wind, or rain deteriorates more quickly than protected areas of a home. Typically, deterioration happens faster in south and west-facing walls, as well as the highest sections of buildings.
How long paints and stains last is directly related to the wood type and grain patterns. Knowledge of wood characteristics can help you choose the best paint or stain for your next home remodeling project.
1.1: Wood Characteristics
- Grains: Vertical-grain wood such as Western cedar and redwood hold paint well because of their narrow grain bands. Woods such as Douglas fir and pine have dense, wide, flat grains that don't hold paint as well--especially if they aren't rough sawn.
- Density: Woods such as Douglas fir, pine, and oak often swell, cup, and twist more than lighter-density woods such as redwood, cypress, and cedar. As a result, protective coatings are stressed and often crack or flake.
- Knots: Knots are caused by branches in the tree trunk. They are harder than the surrounding wood and don't take paint or stain well.
- Texture: Hardwoods such as oak or ash often have small pinholes in their finish due to large pores in the wood. Poplar, magnolia, and cottonwood take paint or stain better.
1.2: Types of Paint and Stain
Most paints used in residential construction are oil based or latex based. Oil-based paints cure when they react with oxygen to form a polymeric film. Latex paints usually outperform oil-based paints, and oil-based paints provide a more permeable barrier to moisture. When it comes to painting during a home renovation, don't skimp on the paint. Expensive paints contain more pigments, so they cover better, last longer, and in the long run are more cost effective.
Section 2--Maintaining Painted or Stained Surfaces
Dirt, grime, and chalk from weathered paint can be removed with a non-metallic brush and water. Mold and mildew can be removed from finished surfaces by scrubbing with a solution of bleach and water. Rinse all surfaces before re-applying paint or stain.
Regular refinishing extends the life of the wood and the paint or stain.
2.1: How to Properly Prepare Coated Surfaces
When remodeling, careful examination of painted surfaces is likely to turn up areas where the paint has flaked or peeled. Deteriorated coatings can be removed in many ways:
- Chemical stripping
- Power washing
Orbital disk sanders work best to remove old paint. If using chemical strippers, such as TSP, it's important to sand the wood after stripping. Most paint fails from excessive moisture, or from being applied over deteriorated paint. Don't skip this important step when remodeling.
2.2: Applying Paint to New Wood and Previously Painted Surfaces
The best way to make paint last the longest on new wood is to use a paintable, water-repellent preservative, the U.S. Forest Products Laboratory recommends. When painting over an existing coating, it's important to sand the old paint to provide a uniform surface for better coverage.
Wood should be painted within a few weeks of installation, since dirt and grime can clog the wood's pores and prevent adhesion. Two coats of high-quality house paint are recommended over a primer coat--especially on walls that face the sun or get the most weather.
A single coat of paint can last four to five years, while two coats can last a decade.
Section 3--Choosing Stain for New or Previously Stained Surfaces
Stains usually contain linseed oil to seal the wood, as well as fungicides, water repellents, and UV blockers. Stains have different shades (pigments) that either darken wood grain or enhance it. Solid-colored stains often are applied over primers, but clear stains aren't.
Stain has a long track record of outperforming paint, but clearer stains need to be maintained more often.
Section 4--Using Acrylic Stains
A number of stain manufacturers have developed all-acrylic stains specifically for siding. These stains form a protective film that is thinner than acrylic paint but also resists cracking, blistering, and peeling. When they are combined with a primer coat, acrylic stains retain color better than oil-based stains. They can be used on top of previously stained materials such as siding, trim, and rough-faced plywood soffit sheeting.
Section 5--Specialty Coatings
There are many specialty coatings available, such as:
- Masonry-specific paint
- Clear, oil-based finishes that help prevent wood from graying
- Chemical cleaners that remove mildew, mold, and dirt
- Brighteners that remove tannic acid stains from redwood and cedar
Inquire with a paint or stain professional about the proper use and application of specialty coatings.