section, we’ll cover some of the most commonlyencountered types.OIL-BASED PAINTS.— Oil-based paintsconsist mainly of a drying oil (usually linseed) mixedwith one or more pigments. The pigments andquantities of oil in oil paints are usually selected onthe basis of cost and their ability to impart to the paintthe desired properties, such as durability, economy,and color. An oil-based paint is characterized by easyapplication and slow drying. It normally chalks in sucha manner as to permit recoating without costly surfacepreparation. Adding small amounts of varnish tends todecrease the time it takes an oil-based paint to dry andto increase the paint’s resistance to water. Oil-basedpaints are not recommended for surfaces submergedin water.ENAMEL.— Enamels are generally harder,tougher, and more resistant to abrasion and moisturepenetration than oil-based paints. Enamels areobtainable in flat, semigloss, and gloss. The extent ofpigmentation in the paint or enamel determines itsgloss. Generally, gloss is reduced by adding lower costpigments called extenders. Typical extenders arecalcium carbonate (whiting), magnesium silicate(talc), aluminum silicate (clay), and silica. The levelof gloss depends on the ratio of pigment to binder.EPOXY.— Epoxy paints area combined resin anda polyamide hardener that are mixed before use. Whenmixed, the two ingredients react to form the endproduct. Epoxy paints have a limited working, or pot,life, usually 1 working day. They are outstanding inhardness, adhesion, and flexibility-plus, they resistcorrosion, abrasion, alkali, and solvents. The majoruses of epoxy paints are as tile-like glaze coatings forconcrete or masonry, and for structural steel incorrosive environments. Epoxy paints tend to chalk onexterior exposure; low-gloss levels and fading can beanticipated. Otherwise, their durability is excellent.LATEX.— Latex paints contain a syntheticchemical, called latex, dispersed in water. The kindsof latex usually found in paints are styrene-butadiene(so-called synthetic rubber), polyvinyl acetate (PVAor vinyl), and acrylic. Latex paints differ from otherpaints in that the vehicle is an emulsion of binder andwater. Being water-based, latex paints have theadvantage of being easy to apply. They dry throughevaporation of the water. Many latex paints haveexcellent durability. This makes them particularlyuseful for coating plaster and masonry surfaces.Careful surface preparation is required for their use.RUBBER-BASED.— Rubber-based paints aresolvent thinned and should not be confused with latexbinders (often called rubber-based emulsions).Rubber-based paints are lacquer-type products anddry rapidly to form finishes highly resistant to waterand mild chemicals. They are used for coating exteriormasonry and areas that are wet, humid, or subject tofrequent washing, such as laundry rooms, showers,washrooms, and kitchens.PORTLAND CEMENT.— Portland cementmixed with several ingredients acts as a paint binderwhen it reacts with water. The paints are supplied as apowder to which the water is added before being used.Cement paints are used on rough surfaces, such asconcrete, masonry, and stucco. They dry to form hard,flat, porous films that permit water vapor to passthrough readily. When properly cured, cement paintsof good quality are quite durable. When improperlycured, they chalk excessively on exposure and maypresent problems in repainting.ALUMINUM.— Aluminum paints are availablein two forms: ready mixed and ready to mix.Ready-mixed aluminum paints are supplied in onepackage and are ready for use after normal mixing.They are made with vehicles that will retain metallicbrilliance after moderate periods of storage. They aremore convenient to use and allow for less error inmixing than the ready-to-mix form.Ready-to-mix aluminum paints are supplied intwo packages: one containing clear varnish and theother, the required amount of aluminum paste (usuallytwo-thirds aluminum flake and one-third solvent).You mix just before using by slowly adding thevarnish to the aluminum paste and stirring. Ready-to-mix aluminum paints allow a wider choice ofvehicles and present less of a problem with storagestability. A potential problem with aluminum paints ismoisture in the closed container. When present,moisture may react with the aluminum flake toform hydrogen gas that pressurizes the container.Pressure can cause the container to bulge or even popthe cover off the container. Check the containers ofready-mixed paints for bulging. If they do, puncturethe covers carefully before opening to relieve thepressure. Be sure to use dry containers when mixingaluminum paints.VARNISHESIn contrast to paints, varnishes contain little or nopigment and do not obscure the surface to whichapplied. Usually a liquid, varnish dries to a hard,8-3
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