PAINT MIXING AND CONDITIONING
Most paints used in the Navy are ready-mixed, meaning the ingredients are already combined in the proper proportions. When oil paint is left in storage for long periods of time, the pigments settle to the bottom. These must be remixed into the vehicle before the paint is used. The paint is then strained, if necessary. All paint should be placed in the paint shop at least 24 hours before use. This is to bring the paint to a temperature between 65°F and 85°F.
There are three main reasons to condition and mix paint. First, you need to redisperse, or reblend, settled pigment with the vehicle. Second, lumps, skins, or other impediments to proper application need to be eliminated. And, third, the paint must be brought to its proper application temperature.
Paints should be mixed, or blended, in the paint shop just before they are issued. Mixing procedures vary among different types of paints. Regardless of the procedure used, try not to overmix; this introduces too much air into the mixture. Table 8-3 outlines the types of equipment and remarks for various coatings. Mixing is done by either a manual or mechanical method. The latter is definitely preferred to ensure maximum uniformity. Manual mixing is less efficient than mechanical in terms of time, effort, and results. It should be done only when absolutely necessary and be limited to containers no larger than 1 gallon. Nevertheless, it is possible to mix 1-gallon and 5-gallon containers by hand. To do so, first pour half of the paint vehicle into a clean, empty container. Stir the paint pigment that has settled to the bottom of the container into the remaining paint vehicle. Continue to stir the paint as you return the other half slowly to its original container. Stir and pour the paint from can to can. This process of mixing is called boxing paint. The mixed paint must have a completely blended appearance with no evidence of varicolored swirls at the top. Neither should there be lumps of undispersed solids or foreign matter. Figure 8-1 illustrates the basic steps for boxing paint.
Table 8-3.Mixing Procedures
Figure 8-1.Manual mixing and boxing.
There are only three primary true-pigmented colors: red, blue, and yellow. Shades, tints, and hues are derived by mixing these colors in various proportions. Figure 8-2 shows a color triangle with one primary color at each of its points. The lettering in the triangle indicates the hues that result when colors are mixed.
When received, paints should be ready for application by brush or roller. Thinner can be added for either method of application, but the supervisor or inspector must give prior approval. Thinning is often required for spray application. Unnecessary or excessive thinning causes an inadequate thickness of the applied coating and adversely affects coating longevity and protective qualities. When necessary, thinning is done by competent personnel using only the thinning agents named by the specifications or label instructions. Thinning is not done to make it easier to brush or roll cold paint materials. They should be preconditioned (warmed) to bring them up to 65°F to 85°F.
Normally, paint in freshly opened containers does not require straining. But in cases where lumps, color flecks, or foreign matter are evident, paints should be strained after mixing. When paint is to be sprayed, it must be strained to avoid clogging the spray gun.
Skins should be removed from the paint before mixing. If necessary, the next step is thinning. Finally, the paint is strained through a fine sieve or commercial paint strainer.
Try not to tint paint. This will reduce waste and eliminate the problem of matching special colors at a later date. Tinting also affects the properties of the paint, often reducing performances to some extent. One exception is the tinting of an intermediate coat to differentiate between that coat and a topcoat; this helps assure you dont miss any areas. In this case, use only colorants of known compatibility. Try not to add more than 4 ounces of tint per gallon of paint. If more is added, the paint may not dry well or otherwise perform poorly.
When necessary, tinting should be done in the paint shop by experienced personnel. The paint must be at application viscosity before tinting. Colorants must be compatible, fresh, and fluid to mix readily. Mechanical agitation helps distribute the colorants uniformly throughout the paint.
The common methods of applying paint are brushing, rolling, and spraying. The choice of method is based on several factors, such as speed of application, environment, type and amount of surface, type of coating to be applied, desired appearance of finish, and training and experience of painters. Brushing is the slowest method, rolling is much faster, and spraying is usually the fastest by far. Brushing is ideal for small surfaces and odd shapes or for cutting in corners and edges. Rolling and spraying are efficient on large, flat surfaces. Spraying can also be used for round or irregular shapes.
Local surroundings may prohibit the spraying of paint because of fire hazards or potential damage from over-spraying (accidentally getting paint on adjacent surfaces). When necessary, adjacent areas not to be coated must be covered when spraying is performed. This results in loss of time and, if extensive, may offset the speed advantage of spraying.
Brushing may leave brush marks after the paint is dry. Rolling leaves a stippled effect. Spraying yields the smoothest finish, if done properly. Lacquer products, such as vinyls, dry rapidly and should be sprayed. Applying them by brush or roller may be difficult, especially in warm weather or outdoors on breezy days. The painting method requiring the most training is spraying. Rolling requires the least training.