THE FUNCTION OF PAINTS AND STAINS
Almost every kind of surface, from drywall to concrete, needs protection from the elements. These damaging elements can range between raging blizzards to innocent looking sunlight on a bed room wall. The total thickness of the paint that ends up on the exterior of your residence is usually about one tenth the thickness of your skin, and interior paint is even thinner. We ask a lot of that coating of skin. What it can do depends upon a number of factors, like the quality and kind of paint or stain, and how well the walls prepped and painted.
Paint and stain should be durable, resisting fading and abrasion and allowing repeated washings. Interior paint should go on with minimal spattering. An excellent interior stain or clear finish should resist fading, peeling, or yellowing, and also be easy to maintain, free of impurities or waxes that could collect dirty residue and make cleaning or recoating difficult. External paints should dry with a toughness that resists deterioration from all types of exposure, and an elasticity which allows for constantly expanding and contracting areas. With their deep penetration and resistance to ultraviolet (UV) light, the stains and finishes on your home's exterior should provide a similar high performance.
Historical Development of Stain and Paint
The oldest known paint was utilized by the painters of Lascaux, who ground natural pigments with water and a binder that may have been honey, starch, or gum. You might be wondering why these cave paintings have lasted a large number of years as the paint on the south side of your property is peeling after only three winters. Here's why: The regular mild temperature, humidity, and dark interiors of caves are ideal chemical preservatives. Your home, on the other hand, is subjected to a myriad of weather and conditions.
The Egyptians knew as soon as 1000 B.C. that paint could protect as well as decorate. Beeswax, vegetable oils, and gum arabic were heated and mixed with Earth and vegetable dyes to paint images which have lasted a large number of years. The Egyptians used asphalt and pitch to preserve their paintings. The Romans later used white lead pigment, creating a formula that would exist almost unchanged until 1950.
The Chinese used oil from the Tung tree to cement the Great Wall, and to preserve wood. The Chinese used gums and resins to make sophisticated varnishes such as, shellac, turpentine, copal, and mastic. The formulas and applications for those varnishes also evolved little during the centuries.
Milk paint dates back to Egyptian times, was widely used up until the late 1800’s when oil-based paints were introduced. Odorless and non-toxic, milk paint today has been revived as an alternative interior paint. Cassein, the protein in milk, dries very smooth and hard, and can be tinted with other pigments. Like stains, milk paint must be sealed with a wax or varnish, which is very durable.
Fashioned from hogs' bristles, badger and goat hair, brushes also changed little for many centuries. Bristles were hand bound, rosined, and greased, then hand laced into the stock of the brush. Hog's hair brushes, called China bristle brushes, remain a preferred brush for oil-based paints.
Pigments originally originated from anything that bore a color, from ground up Egyptian mummies to road dirt and grime. Most mineral or inorganic pigments originated from rust, potassium, sea salt, sulphur, alum (aluminum), and gypsum, among others. Some extravagant projects incorporated treasured stones such as lapis lazuli. A huge selection of organic pigments from plants, insects, and animals made up the rest of the painter's palette.
Paints and stains changed little from the time of the Pharaohs to the Industrial Revolution. A book on varnishes shared in 1773 was reprinted 14 times until 1900, with only slight revisions. However, the colder climates of northern Europe did bring about the need for more durable paint, and in the 1500s the Dutch artist Jan van Eyck developed oil-based paint.
Starting during the Middle Ages lead, arsenic, mercury, and various acids were used as binders and color enhancers. These and other metals made the mixing and painting process unsafe. Paints and varnishes were usually blended on site, in which a ground pigment was mixed with lead, oil, and solvents over sustained high heat. The maladies that arose from poisonous exposure were common among painters at least before late 1800s, when paint companies started out to batch ready mix coatings. While exposure to poisons given off during the mixing process subsided, contact with the harmful materials inherent in paints and stains didn't change much until the 1960s, when companies ceased making lead based paints.
World War I forced the U.S. painting industry to modernize. Manufacturers had to discover a replacement for the natural pigments and dyes that came from Germany. They started to synthesize dyes. Today many pigments and dyes are chemically synthesized.
Improvements in the painting industry have extended well beyond pigments. Water-based latexes have gained in level of popularity as a safe, quality option to oil-based paints. Latexes have improved from simple "whitewashes" to highly advanced coatings that can outlast oil-based products. Both oil-based and latex coatings are emerging every year with noteworthy improvements, like the ground metal or glass that's now added to reflect destroying UV light.
A milestone in the evolution of coatings occurred in the very early 1990s with the introduction of a fresh category of paints and stains known as "water borne." Created by the need to adhere to stricter regulations, water borne coatings reduce the volatile organic chemical substances, or VOCs, found in standard paint and stains. Dangerous and flammable, VOCs evaporate as a coating's solvent dries. They can be inhaled or soaked up through your skin, and create ozone pollution when exposed to sunlight.
THE CHEMISTRY OF STAINS AND PAINTS Paints and stains contain four basic types of materials: solvents, binders, pigments, and additives.
Paint and Stain Binders and Solvents
Solvents are the vehicle or medium, for the substances in a paint or stain. They determine how fast a covering dries and exactly how it hardens. Water and alcohol are the primary solvents in latex. Oil-based solvents range between mineral spirits (thinner) to alcohols and xylene, to napthas. The solvent also includes binders, which form the "skin" when the paint dries. Binders give paint adhesion and durability. The cost of paint will depend in large part upon the grade of its binder.
Because water is the vehicle in latex paint, it dries quickly, enabling recoating the same day. The odor that you see when using a latex paint or stain is the "flashing," or evaporation, of the binder and solvents. The binders in latex are minute, suspended beads of acrylic or vinyl acrylic that "weld" as the paint dries. Latex enamels include a higher amount of acrylic resins for greater hardness and durability.
Alkyds and oil-based paints are basically the same thing. The word alkyd comes from "alcid," a combination of alcohol and acid that acts as the drying agent. Both have the same binders, which may include linseed, soy, or Tung oils. Oil based and alkyd enamels may contain polyurethanes and epoxies for extra hardness. Alkyd paints come in powerful combinations such as two part polyester-epoxy for commercial use and a urethane revised alkyd for home use. Urethane boosts toughness.
Water borne coatings use a two part drying system: water is the drying agent, and oils form a hard-drying resin. These new coatings match and sometimes out perform their oil-based cousins. They resist yellowing, are stronger, require only water clean-up, have little odor, and are non-flammable. One disadvantage: They swell hardwood grain and require sanding between coats.
Pigments; Paint and Stain
Pigments will be the costliest component in paint. Besides providing color, pigments also have an impact on paint's hiding power - its capability to hide an identical color with as few coats as is feasible. Titanium dioxide is the primary and most expensive ingredient in pigment. Top quality paints not only have significantly more titanium dioxide, but also more finely ground pigment. Inexpensive paints use coarsely ground pigment, which doesn't bind well and washes off more easily.
Paint and Stain Additives
Additives determine how well a paint contacts, or wets, the surface. In addition they help paint flow, level, dry, and resist mildew. Oil is the surfactant, or wetting agent, in oil-based paint. These paints have a natural thickness and capability to flow and level; they go on smoother than latex and dry more slowly, so brush streaks have more time to smooth out. That is why oil-based paints have a tendency to run on vertical surfaces more than latexes do.
Latex paint has been trying to catch up with oil-based paint over the years. Today many latexes outperform oil-based paints and primers, thanks to thickeners, wetting agents (soapy substances that are also known as surfactants), drying inhibitors, defoamers, fungicides, and coalescents. Defoamers keep latex paint from bubbling and leaving pinpricks (called "pin holing") in the paint as it dries. Bubbling is induced when the soap wetting agent rises to the top as it dries. The better the paint, the less pin holing you should have. It used to be that if latex paint was shaken at the paint store you had to allow it to settle for a couple of hours. This is certainly no longer the truth with better paints, which may be opened up and used right from the shaker with no threat of pin holing.
Coalescents help latex resins bond, especially in colder weather. Oil-based paint, because it dries slowly and resists freezing, can adhere and dry in temps from 50°F to 120°F. With added coalescents and, believe it or not, antifreeze, some latexes can be employed in the same heat range, and even lower. Some outdoor latexes can be safely applied at conditions as low as 35°F. Companies including Pratt & Lambert, Pittsburgh Paint, and Sherwin Williams have removed the surfactants to help their latex paints be applied in lower temperature ranges. As the wetting agents have been removed, the latex dries faster.
UV blocking additives have been put into paints and stains to help slow deterioration. Sunlight is accountable for much of the breakdown of any covering. It fades colors, dries paint, and increases the expansion and contraction process that makes paint crack and peel off. UV blockers in paint may consist of finely ground metals and ground glass which is currently being added for increased reflection of natural sunlight.
If you are in a region with plenty of humidity, rainfall, and insects, you may need to consider adding a biocide or fungicide to your paint. Biocide deters insects, and fungicide counters mildew. Many coatings already contain some fungicide, but only in small concentrations because of strict interstate regulations.
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Lake Stevens WA 98258
(425) 512-7400
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