Guide to Working with Plastics: A Wealth of Fillers and Paints--The Fine Points of Application

Plastic-base coatings vary widely in both consistency and composition. Some are watery-thin for fast spreading; others are soupy for a textured finish. Some are made with water for easy cleanup, others with volatile solvents for quick drying. The variety of forms in which plastic- base coatings are produced has spawned an equally broad range of techniques for applying them to surfaces.

Brushes, of course, are the standard tool, but some coatings require natural-bristled brushes, whereas synthetic bristles work better for others. For general- purpose coatings, such as alkyds and phenolics, use a natural-bristled brush of good quality. Latexes demand nylon or polyester brushes, which don’t get soggy in water. Fast-curing, high-gloss epoxies and polyurethanes—often applied to metal or very smooth wood—are spread best with disposable sponge brushes. And there is a special nylon-bristled rough-surface brush that simplifies the job of working both latex and alkyd coatings into the cracks and crevices of stucco and brickwork.

The correct way to use the paintbrush also varies with the type of coating you have chosen to apply. Alkyds and latexes should be brushed thoroughly—first back and forth, then crosswise. Synthetic-rubber coatings, in contrast, should be brushed on with two or three strokes— just enough brushwork to spread them evenly. Clear phenolics and polyurethane coatings ought to be flowed onto the surface, as slowly and deliberately as possible.

For large surfaces, rollers spread coating films more smoothly and rapidly than brushes. A fully loaded 9-inch roller can hold enough paint to cover about 6 square feet of surface, compared with 1 square foot for a 3-inch brush. Like brushes, however, rollers have to be matched to the coating being applied. Natural lamb’s wool, For example, is unaffected by solvents, so it’s suited to volatile epoxies and polyurethanes. On the other hand, the fibers of lamb’s wool are likely to mat, and even fall out, after contact with alkaline latex paints. Use the charts below and opposite to choose the right roller for your work.

Specialized applicators for hard-to-cover surfaces include paint pads, which are helpful for areas too confined for the use of rollers, and lamb’s-wool painting mittens, which are used for wiping paint onto thin posts and rails. And some coatings are formulated to be applied with out any tools at all; they are simply poured onto a surface. Or, in some cases, the object to be coated is just dipped and allowed to drain.

CHART OF:

Fitting the Roller Fabric to the Paint

Surface: Coating | Smooth | Textured | Rough

= = = =

Alkyd| Lamb’s wool | Acrylic | Acrylic

Epoxy| Mohair Lamb’s wool Lamb’s wool

Latex| Polyester| Polyester| Polyester

Phenolic | Mohair | Lamb’s wool | Acrylic or polyester | Acrylic or polyester

Polyurethane | Mohair | Lamb’s wool | Lamb’s wool

Silicone | Mohair | Lamb’s wool | Lamb’s wool

---Choosing the roller fabric. To match a roller to a painting job, consider both the paint and the surface. The fabric of the roller cover must spread a paint evenly without reacting to its resin. It also must travel over a surface of a particular texture without matting or falling apart. Use this chart to determine the recommended roller fabric, then consult the chart on the following page to find the proper nap length.

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CHART OF: Matching the Roller Nap to the Surface

Surface: Smooth, Textured, Rough

Roller fabric

Acrylic

Lamb’s wool

Mohair

Polyester

-- Choosing the nap length. Once you have matched the fabric to the type of paint you are using, consult this chart to match the length of the nap to the surface being covered. In general, longer naps hold more paint, which makes them best suited for rough surfaces. For use on extremely smooth surfaces, such as wood paneling, special mohair rollers are available with nap fibers as short as 3/16 inch.

Special Tools for Special Situations

-- Coating rough surfaces. To work paint into the cracks and crevices of a coarse surface, use a rough-surface brush with nylon bristles that are not only thicker than ordinary, but split, or flagged, at the ends to carry more paint. Dip the brush squarely into a pan or roller tray containing about 1/2 inch of paint. Work it over the surface with an up, down and sideways spreading motion. For particularly hard-to-reach areas, such as mortar joints or the undercut divisions be tween shingles or shakes, tilt back the brush and use the narrow row of bristles on one edge.

-- Applying an ultra-glossy coating. To keep brush marks from showing on a mirror-smooth surface, use a sponge brush rather than a bristle brush. Submerge about half the sponge in the paint, then paint with short, steady strokes, taking care that you allow only the beveled tip to come in contact with the work.

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The Pour-on Polymer Coatings

1. Combining the components. Mix equal parts of resin and hardener in a disposable calibrated paper cup. Stir the batch thoroughly but gently with a clean wooden stirring stick, taking care not to introduce air bubbles. After two minutes of mixing, pour the thick coating over the surface to be covered—here, a butcher-block tabletop— working in a spiral from the outside in.

2. Smoothing the coating. Using a plastic- covered playing card as a spreader, gently distribute the coating evenly over the surface. Allow some of the coating to run over the edge, as in icing a cake; smooth this edge coating with a disposable sponge brush. Prick any large bubbles with a toothpick, then snare stray bits of lint with tweezers. While the coating is soft, breathe on the surface with your mouth open—the carbon dioxide will break tiny surface bubbles.

When the coating is completely dry, in two or three days, add additional layers if desired, until the coating is as much as 1/4 inch thick.

Dipping to Sheathe a Handle

--Sheathing an object in plastic. Suspend the object to be coated on a length of twine or wire, and slowly lower it into a can of rubber-base vinyl plastic coating compound. Withdraw the object slowly, about one inch every five seconds, and hang it to dry. Immediately seal the open can; escaping vapors could soften the sheathing, causing it to drip or sag. After about 20 minutes, dip the object a second time. Then allow the sheathing to dry thoroughly to a tough, pliable finish; this will take about four hours.