Lesson 2-2 MIXING AND PREPARING PROTECTIVE COATINGS
Now that you have a basic knowledge of the types of protective coatings, you are about to undertake the most important task of the trade--mixing and preparing the protective coatings.
2-8. Mixing, Coloring, and Tinting Paints
Coloring and tinting paint is not difficult when a new mixture of paint is first made; however, when you attempt to match paint already applied on a surface, it is difficult because paint changes shades after drying and aging. Coloring and tinting paint is a matter of trial and error. To be a professional protective-coating specialist, it is necessary that you understand the color combinations, color mixing, tinting, and color harmony. You must also understand how to mix paint by boxing (hand mixing) and by using power equipment, how to thin paint, and the special procedures required for mixing aluminum paint.
a. Color Combinations. Skillful mixing of colors is one of the most important aspects of painting and decorating, especially in interior decorating. The 12 colors found on a color wheel are grouped as primary, secondary, and tertiary.
(1) Primary colors. There are three primary colors (Figure 2-1). They are blue, red, and yellow.
Figure 2-1. Primary colors
(2) Secondary colors. Secondary colors (Figure 2-2) are made by mixing any two of the primary colors together. For instance, yellow and red form orange; red and blue form purple; and blue and yellow form green.
Figure 2-2. Secondary colors
(3) Tertiary colors. The remaining six places on the color wheel are filled by combining adjacent primary colors and secondary colors. These are called tertiary colors (Figure 2-3). This fills the color wheel with 12 colors, all full strength, which are known as hues.
Figure 2-3. Tertiary colors
b. Tints, Tones, and Shades. From the 12 hues, you can attain tints, tones, and shades:
c. Color Mixing.
(1) Oil-based paint. When you are mixing oil-based paint on the job, colors in oil are easier than powders to mix into the paint vehicle. Colors in oil consist of dry pigments (powders) ground in a vehicle of approximately 80 percent linseed oil and 20 percent volatile solvent. The solvent will make a paste that will satisfactorily flow from containers. The major colors in oil are black, blue, brown, green, orange, red, and yellow:
(a) Black. The blacks are bone black, high-colored carbon black, lampblack, and synthetic black iron oxide. Carbon black and lampblack are the strongest in shading strength. Carbon black and bone black are blacker in color. Lampblack, however, is the one you will most frequently use. Black iron oxide is used as a pigment in black metal-protective paints and is also used for shading purposes. You can thin pastes to brushing consistency by adding three parts linseed oil, one part spar varnish, and one-half part drier to one part of the pigment paste.
(b) Blue. The blues are iron blue (Prussian blue), ultramarine blue, and copper phthalocyanine blue. The permanency of iron blue is affected by alkalies, while ultramarine blue is susceptible to acids. Copper phthalocyanine blue is more durable in the light-blue tints. When exposed to the weather, these pigments have a fair permanency in tints or solid colors.
(c) Brown. The browns include metallic brown, burnt sienna, burnt umber, raw umber, and synthetic brown iron oxide. The browns are among the most durable pigments in paints that are exposed to the weather. Although adaptable as a trim color, metallic brown is more often used as a solid color. It is used to a great extent in paint for barns, metal roofs, and freight cars. The other browns are used more frequently for tinting paints and making stains. Brown iron oxide is also used as a pigment in some paints and enamels.
(d) Green. The greens are chrome green and chromium-oxide green. Use chrome green, composed of chrome yellow and iron blue, to make tints or solid-color paints. Chrome green is sensitive to alkalies. Chromium-oxide green, the more permanent of the greens, is used with white for tinting purposes. It does not have the tinting strength of chrome green but withstands high temperatures and is not effected by alkalies or acids.
(e) Orange. The oranges consist of two shades of chrome orange that are used for tinting and making solid-color paints. The pigments are basic lead chromate that is processed as light and dark. The dark pigment is used for making international orange paint. Both light and dark pigments are relatively permanent when exposed to the weather. Even though lead chromate is considered hazardous, the pigments in these paints will be difficult to replace because no other pigments have a similar light fastness and brightness.
(f) Red. The reds include Venetian red, bright-red iron oxide, Indian red, toluidine red, and mineral red. All of these pigments may be used for tinting purposes, except toluidine red. Indian red and bright-red iron oxide are very permanent and are used extensively in all types of paints, enamels, and stains. Venetian red and mineral red are often used in barn and roof paints. Toluidine red, which is a bright red, is permanent even when exposed to the weather.
(g) Yellow. The yellows include lemon chrome yellow, medium chrome yellow, yellow ocher, primrose chrome yellow, yellow iron oxide, raw sienna, and zinc yellow. The chrome yellows are satisfactory for tinting exterior paints. Raw sienna is more often used for tints and stains than as a solid-color trim paint. When mixed with white titanium dioxide in different amounts, it makes durable ivory and buff tints. Use yellow oxides particularly in solid-color paints and for tinting floor enamels. Use zinc yellow as a rust-inhibitive pigment in metal primers.
(2) Water-based paint. When you are mixing water-based paint on the job, mix water-soluble color pigments into the paint vehicle.
NOTE: Colors in oil cannot be mixed with water-based paints.
d. Tints or Shades. When you tint or shade paint with paste, mix the paste with a small amount of the paint vehicle to thoroughly break it up then strain it through a cheesecloth. When you mix paint to match a certain color, add the tint or shade in small amounts and test the paint by brushing it on a surface that is similar to the one to be painted. Allow the paint to dry before checking for the proper match. If you have not produced the desired match, add more color or more base paint. If you notice streaks of color when you brush out the paint it is a sign that you have not thoroughly mixed the color into the base paint. If you add too much color to the base paint, you will have to add considerably more base paint to lighten the color. As a result, you will have more paint than you need for the job.
e. Color Harmony. Table 2-3 contains a list of do's and don'ts to consider when you select colors.
Table 2-3. Color selection
|Do's||Use light colors in a small room to create an impression of larger size.|
|Have continuing color flow through the building, from room to room, using harmonious colors in adjoining areas.|
|Paint the ceiling a deeper color than the walls if you want it to appear lower; paint it a lighter shade for the opposite effect.|
|Study color swatches in daylight and under artificial light, because colors often change under artificial light.|
|Emphasize horizontal lines in a room that is too tall, and emphasize vertical lines in a room with a low ceiling.|
|Dont's||Use bright color in a large area, or the will will detract from otherwise decorative furnishing as accent piece.|
|Paint the woodwork and the trim of a small room a different color from the background color, or the room will appear cluttered and even smaller.|
|Paint unfortunate architectural features, such as radiators, pipes, and similar projections, a color that contrasts with the walls, or they will be emphasized.|
f. Paint Mixing. You must mix (stir) primers and paints thoroughly. This will ensure that the paint pigment, which usually settles to the bottom of the container, and the paint vehicle are thoroughly mixed together. Mix primers and paint by boxing or using power-operated equipment.
(1) Boxing Use boxing when you are mixing paint by hand. Boxing consists of pouring the paint back and forth from one container to another. To do this, follow the procedures listed in Figure 2-4.
Figure 2-4. Boxing paint
(2) Using power-operated equipment. Power equipment that is normally used for stirring paints is the shaker or propeller type.
(a) Shaker-type mixers. Use shaker-type mixers to stir any type of primer or paint, but preferably those containing highly volatile thinners. These mixers can handle from 12 pint to 5 gallons, depending on the size of the machine. A typical shaker-type mixer is shown in Figure 2-5. These machines, which are generally electrically operated, blend paint materials by shaking them. The electric motor must be explosion-proof.
Figure 2-5. Shaker-type mixer
(b) Propeller-type mixers. Use the propeller-type paint mixers (Figure 2-6) to stir large quantities of primer and paint in open containers. Paint is agitated by the propellers or paddles attached to an electrically rotated shaft. The electric motor of this mixer must be explosion-proof.
Figure 2-6. Propeller-type mixer
g. Thinning. Thinners and solvents have definite functions in coating materials; but for economic reasons, packaged products generally contain the smallest possible percentage of volatile material compared to solid. The resulting high consistency makes it necessary to thin packaged materials to varying degrees to suit the particular material, the application method, and the surface being coated. General rules for thinners and solvents are —
Determine the thinning required for a particular job by using good judgment and actual testing. Excessive thinning or insufficient thinning is detrimental to the normal flow characteristics of a coating. Excessive thinning leads to runs and sags, and insufficient thinning causes rough coatings. The amount of thinning used for spray application directly influences the evaporation rate of the volatiles passing from the paint gun to the surface; a major portion of the thinner can be lost en route. The cooling effect of this evaporation, plus the cooling due to expansion of the atomizing air, may lower the temperature of the coating material as much as 20°F below that of the surrounding air. The temperature of the deposited film may fall below the atmospheric dew point, and atmospheric water vapor will condense the film. For example, when air temperature is 70°F and the relative humidity is 70 percent, the dewpoint is 63°F or 7°F below the ambient temperature. At this point, the adhesion qualities of enamel may be reduced. The refrigerating effect will also affect the drying and the flow of quick-drying materials.
h. Aluminum-Pigment Mixing. To overcome the difficulties encountered when dispersing aluminum paste or powder pigments (lacquers and varnishes), follow these steps closely:
(1) Weigh and measure the amount recommended on the container.
(2) Place the weighed pigment in a clean container that is large enough to contain the entire mix and allow room for stirring. In a separate clean container, measure the volume of the vehicle to go with the pigment.
(3) Pour the vehicle into the pigment in small quantities; never add the pigment to the vehicle. Stir each quantity thoroughly before more vehicle is added. Use 10 percent in the first addition, 10 percent in the second, 20 percent in the third, and then add the remaining amount to the pigment. Stir thoroughly to ensure the complete wetting of the pigment.
(4) Box the material by pouring it from one container to the other several times.
(5) Strain the material through double- or triple-thickness cheesecloth to ensure that no lumps remain.
(6) Stir the material occasionally during application. Stirring should be moderate and only enough to keep the pigment in suspension. Too much agitation may cause darkening and the loss of leafing power. Prolonged storage of mixed aluminum-coating materials may also destroy leafing power, so carefully estimate the quantity to prepare.