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For the protection of the exterior of your wood-clad home there are basically two options that homeowners and professional painters can uses: paint or stain (You can also put on a low-maintenance vinyl siding!). The first is a film-forming surface and the latter is a penetrating agent that gets into the grain. The film-forming protecting finishes include paint, solid stain and varnish while the penetrating ones are preservatives, water repelling agents and semi-transparent oil-based pigments.
Paint has been around for a long time an it is composed of three main ingredients which allow thye paint to be mixed into a homogeneous solution and allows it to be applied:
Also called the vehicle this is the liquid that allows the ingredients to be spread evenly on the surface. By adding or taking away the solvent the painter can adjust the viscosity of the liquid which means make it thicker or thinner. In fact, the solvent in oil-based paints is called thinner. Solvents include petroleum distillates, alcohols, ketones and other liquid, organic compounds. For latex paints water is the solvent.
The binder is the film-forming liquid part of the paint. The molecules act like an adhesive and bind together as a result of evaporation of the solvent. The binder also holds the pigments of the paint in place and is responsible for the look: glass, satin or flat. Some binders set by temperature while others react to an extra agent that causes it to bond much like the way a fiberglass epoxy works.
The granular solids that provide the color to most paints are called pigments. These can be natural clays or other minute silica or mica grains or synthetic silicas or calcium-based substances. Lead used to be a popular pigment but health regulations have banned it from being used in paint products.
Acrylic latex resins are widely popular flexible and wear extremely well durable. According to painting professionals a quality acrylic latex paint on the exterior of a home will last longer than a similar quality oil-base one. In addition, latex paints porous meaning that they breathe and so can shed water. So if water enters the painted wall from the interior it will get trapped beneath an oil-base finish causing bubbling and blistering. Oil-based paints tend to get brittle with age.
In essence stain is made up of the same three (3) ingredients as paint: solvent, binder, pigment. These are not meant to form a film but because the viscosity is low they penetrate the wood surface. (The binder makes up the least amount of the substance of stain but is evident in all types.) Many transparent stains use linseed oil or alkyd as a binder. Exterior stains are left as they are but interior stains usually require a finish of polyurethane or varnish for added protection and looks.
These penetrating finishes are absorbed into the wood soaking the fibers and filling the surface pores so that water can't get in. Most of these penetrating finishes contain moisture repellents and can be utilized as an end-use finish or as strong base before painting. As well, many of the clear finishes contain wood preservatives which make them great for outdoor use as they fight mildew and fungi and, in some case, insect infestation.
Semi-transparent stain penetrates the wood and let the grain show through. Water-based decking oils, or stain, form a thin film and are not great for long-lasting performance like latex paints do, oil-based semitransparent stains allow the wood to breathe. so the finish. In addition, the pigment in this stain fights ultra violet light degradation. These work best on weathered, rough or other coarse wood.
Penetrating stains are suitable for decking, wood roof shingles, siding, trim, exposed
decking and fences. Like paint stains are applied with a brush, spray gun or roller. Work in the shade and do the whole job in one session to avoid separation marks.
In both painting and staining the preparation of the surface is crucial to the longevity and looks of the job. Green lumber or treated lumber does not accept either very well and must be seasoned - dried - before painting. Power-washing your house or deck is a good way to clean the surface before either painting or staining. This will take off any mold, dirt or residues that could impeded the adhesion.
For an old home scraping may be necessary to remove paint which the power washing has not removed. After scraping the wood should be allowed to dry because there may be moisture trapped between the film and the wood.
Old wood will accept both primer and stain readily, and the condition of the wood — that it, if it's weathered or just dry — will determine how much of the material will be used. Penetrating stain will soak into old wood a lot quicker and will need an extra coat or coats for full protection.