Whether you’re painting exterior or interior surfaces, latex paints are probably the best bet. The next sections explain why.
Two essential definitions.
► Oil-based paints and stains may contain linseed oil, tung oil, or synthetic resins called alkyds. Because alkyds are the most common "oil" in oil-based paints, professionals often use the term alkyd instead of oil-based. However, oil-based is the broader, more inclusive term for products that must be thinned and cleaned up with solvents. Today only about 10 percent of house-paint sales are oil based.
► Latex paints and stains are water based and thus can be thinned with water and cleaned up with warm, soapy water. In recent
LANGUAGE: PRIMERS, PAINTS, AND STAINS
An important base coat, primer is applied to substrates such as raw wood, drywall, plaster, or previously painted surfaces. Above all, primers must stick to the substrate; they may also contain stain blockers, preservatives, pigments, or other additives to hide flaws and ensure more uniform top coats of paint.
► PAINT. If primer’s job is adhesion, paint’s is protection-protecting the primer and substrate from moisture, mild abuse, and (if it’s exterior paint) UV rays. Paint must also hold color, dry smoothly, and withstand weather, so its pigments, solvents, and additives must be carefully blended and held together by a binder, or resin.
► BINDER. Binders determine a paint’s penetration, adhesion, drying rate, flexibility, and durability. In relation to pigment, the more binder a paint has, the shinier and more durable its finish will be. Glossy paints tend to have high binder-to-pigment ratios.
► PIGMENT. Color is determined by pigment. The more pigment a paint has, the more intense its color and the better it hides what’s beneath.
► VEHICLE. A paint’s liquid component, the vehicle, is needed to suspend the pigments and binders. Oil-based vehicles (linseed oil, tung oil, or modified oils called alkyds) thin with mineral spirits, also known as paint thinner. Latex paints suspend polymer particles (plastic) in water.
► STAIN. Penetrating or semitransparent stains are most often pigmented oils that soak into wood and form a thin film on the wood’s surface; there are also water-based stains. You can see wood grain through stain. Although stains may contain water repellants, preservatives, and some UV blocking, they don’t protect wood as well as paint does and so must be reapplied periodically-say, every 2 years to 4 years.
► S0LID-C0l.0R STAIN. solid-color stain, a fast-growing group of exterior coatings, is more like thinned paint than stain. It’s popular because wood texture (but not wood grain) remains visible. However, solid-color stains have only about half the life span of painted surfaces. Acrylic latex solid-color stains are the most durable.
decades, latex paints have improved so dramatically that they now account for about 90 percent of house-paint sales.
Oil-based: Advantages and disadvantages.
Oil-based paints are durable and tenacious, adhering even to glossy or chalky surfaces. Thus many pros still insist on an oil-based exterior primer, even if they’ll be applying latex top coats. Many old-school painters also favor oil-based paints for interior trim, because they dry slowly and level well, thus minimizing brush marks.
Problem is, oil-based paints never completely cure. Rather, they oxidize and, over the years, erode and crack. Any siding, especially wood, expands and contracts as temperatures fluctuate, so the inflexibility of oil-based paints leads to cracking and more commonly chalking, a powdery residue of oxidized oil and pigment. In addition, mold feeds on the organic compounds in oil-based paints. But the biggest problem is their solvents: noxious, volatile, polluting, and tedious to clean off tools and equipment.
Latex: Advantages and disadvantages. Acrylic latex has almost everything a painter or a substrate could want: As the paint or stain dries, its water base evaporates with minimal odor, leaving a thin coat of polymer particles (plastic) that remains flexible and so rarely cracks, as oil-based paints often do. Latex is also semipermeable, so moisture generated inside the house can migrate, through the paint, to the outdoors. Because latex is synthetic, it’s inhospitable to mold. Finally, latex cleans up easily and dries quickly.
Inside, latex is the only paint to use on dry — wall, for it won’t raise the paper surface of panels.
Clear FINISHES
Clear finishes include polyurethane, varnish, lacquer, and shellac. Polyurethane, also called poly, is the most durable of the clear finishes and thus the most suitable for heavy-traffic surfaces, such as trim and stair parts. Although poly and varnish resist moisture, they may become cloudy with sustained exposure to wet conditions. Shellac also clouds up near water. Spar varnish—originally used on boats—has a hard finish that stands up well to water, if well maintained. For more about clear floor finishes, see Chapter 20.
Exterior latex is colorfast, durable, and easy to apply. However, its quick drying characteristic can be a problem if you’re painting an exterior in 90° heat, which causes the paint to dry on the brush. In that case, additives like Flood’s Floetrol® will slow drying time and so extend latex’s “brushability.”
