transparent coating when spread in a thin film over asurface, affording protection and decoration.Of the common types of varnishes, the mostimportant are the oils, including spar, flat, rubbing,and color types. These are extensively used to finishand refinish interior and exterior wood surfaces, suchas floors, furniture, and cabinets. Spar varnish isintended for exterior use in normal or marineenvironments, although its durability is limited. Toincrease durability, exterior varnishes are especiallyformulated to resist weathering.Varnishes produce a durable, elastic, and toughsurface that normally dries to a high-gloss finish anddoes not easily mar. Often, a lower gloss may beobtained by rubbing the surface with a very fine steelwool. However, it is simpler to use a flat varnish withthe gloss reduced by adding transparent-flattingpigments, such as certain synthetic silicas. Thesepigments are dispersed in the varnish to produce aclear finish that dries to a low gloss, but still does notobscure the surface underneath (that is, you can stillsee the grain of the wood).SHELLACShellac is purified lac formed into thin flakes andwidely used as a binder in varnishes, paints, and stains.(Lac is a resinous substance secreted by certaininsects.) The vehicle is wood alcohol. The naturalcolor of shellac is orange, although it can be obtainedin white. Shellac is used extensively as a finishingmaterial and a sealant. Applied over knots in wood, itprevents bleeding.LACQUERSLacquers may be clear or pigmented and can belusterless, semigloss, or glossy. Lacquers dry orharden quickly, producing a firm oil- and water-resistant film. But many coats are required to achieveadequate dry-film thickness. It generally costs more touse lacquers than most paints.STAINSStains are obtainable in four different kinds: oil,water, spirit, and chemical. Oil stains have an oilvehicle; mineral spirits can be added to increasepenetration. Water stains are solutions of aniline dyesand water. Spirit stains contain alcohol. Chemicalstains work by means of a chemical reaction whendissolved by water. The type of stain to use dependslargely on the purpose, the location, and the type ofwood being covered.SURFACE PREPARATIONLEARNING OBJECTIVE: Upon completingthis section, you should be able to describe theprocedures used in preparing surfaces forpainting.The most essential part of any painting job isproper surface preparation and repair. Each type ofsurface requires specific cleaning procedures. Paintwill not adhere well, provide the protection necessary,or have the desired appearance unless the surface is inproper condition for painting. Exterior surfacepreparation is especially important because hostileenvironments can accelerate deterioration.METALSAs a Builder, you are most likely to paint threetypes of metals: ferrous, nonferrous, and galvanized.Improper protection of metals is likely to cause fatiguein the metal itself and may result in costly repairs oreven replacement. Correct surface preparation, priorto painting, is essential.FerrousCleaning ferrous metals, such as iron and steel,involves the removal of oil, grease, previous coatings,and dirt. Keep in mind that once you prepare a metalsurface for painting, it will start to rust immediatelyunless you use a primer or pretreatment to protect thesurface.NonferrousThe nonferrous metals are brass, bronze, copper,tin, zinc, aluminum, nickel, and others not derivedfrom iron ore. Nonferrous metals are generallycleaned with a solvent type of cleaner. After cleaning,you should apply a primer coat or a pretreatment.GalvanizedGalvanized iron is one of the most difficult metalsto prime properly. The galvanizing process forms ahard, dense surface that paint cannot penetrate. Toooften, galvanized surfaces are not prepared properly,resulting in paint failure. Three steps must be taken todevelop a sound paint system.1. Wash the galvanized surface with a solvent toremove grease, waxes, or silicones. Manufac-turers sometimes apply these to resist “whiterust” that may form on galvanized sheets stored8-4
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