Brushing Up on Paint Basics - BodyShop Business

Brushing Up on Paint Basics

Whether your paint technicians have been with you two months or 20 years, a quick refresher course on the foundations of paint mixing and application is always time well spent.

They can make a ’57 Chevy shine like new and bring the splendor back to a ’71 Beetle. But instead of a top hat and a wand, these magicians simply need a can of paint and a spray gun.

These magicians are paint technicians.

But regardless of whether your painters have logged one year or 20 in the collision repair industry, everyone can use a quick refresher in the paint department. In this article – rather than explain how to create a blend on a 2001 Navigator or add a pinstripe to a ’66 Mustang – we’ll take a look at the foundations of paint. We interviewed a number of training center managers, as well as veteran paint technicians, to provide an inside look at paint basics. Some techniques are straight out of a 2001 training manual, while others are tried and true. In either case, we can all learn from a review of the basics.

Recipe for Paint
Paint consists of three primary ingredients: solvent, resin and pigment. Each plays a vital role in the productivity of the paint:

  • Pigment is one of the primary elements. It sets the color of the paint and is responsible for weathering/corrosion resistance.
  • Resin determines the type of paint adhesion and is important in the paint’s durability, gloss and drying capabilities.
  • Solvent is responsible for not only the application and drying characteristics of paint, but also atomization and evaporation.

While paint has these three primary elements, a number of additives are also included in the formula. These additives include driers for controlled, uniform film formation; levelers for flow and texture control; anti-skin for stability; plasticizers for controlled flexibility; and hardeners for improved gloss and durability.

The paint’s ingredients determine how it dries. And typically, paint dries in one of two ways, depending on whether it consists of lacquers or urethanes. Each paint type begins as wet paint film. Lacquer, however, dries as a soluble film through solvent evaporation. In layman’s terms, “soluble” means the product has the ability to return to its original state. For example, dirt is a soluble substance. If water is added to dirt, it has the capacity to dry and return to its original state – dirt.

Enamels and urethanes, however, dry as an insoluble film and can’t return to their original state. For example, concrete is an insoluble material. If water is added to concrete, it cannot return to its original state after drying. In paint, enamels require oxidation and polymerization, while urethanes require two-component polymerization.

Measuring & Mixing
The first step in paint application involves proper mixing of the ingredients. A training center manager I spoke with noted that many technicians – even experienced ones – get confused when mixing. He stressed the importance of following the directions on the product label and of always using the activator, hardeners and solvents recommended by the paint manufacturer.

When mixing paint, there are two primary types of mixing:
1. Three-part mixing includes the mixing of the resin, the solvent and the hardener. Each ingredient must be thoroughly mixed at each stage.

2. Two-part mixing involves mixing the paint and the activator. Likewise, after each material is added, the ingredients must be thoroughly mixed.

A vital solvent in paint mixing is the thinner (for lacquers) and reducer (for enamels). The purpose of these solvents is to thin out or reduce the paint to the proper spraying viscosity. The appropriate thinner/reducer depends on five things: the product, air and surface temperature, humidity, air movement (over the surface being sprayed) and the size of the repair.

Today’s solvents are no longer rated by the evaporation speed. Instead, they’re rated by temperature – typically listed from low temp to tropical. Another training center manager I spoke with explained that the various evaporation speeds of different solvents aren’t simply to make the paint dry faster or slower, but to make it perform consistently – regardless of changing spray conditions.

Using the proper solvent for your spray conditions allows the paint to atomize into small droplets, wet the surface being sprayed (providing adhesion), flow out to a smooth appearance and then flash off once the flow has been accomplished.

How important is it to choose the proper solvent? It’s crucial. A solvent that evaporates too slowly will cause the paint to run or sag; a solvent that evaporates too quickly won’t flow properly.

Another important part of paint mixing is the hardener/catalyst/activator, which initiates or speeds the cure of a two- or multi-packaged product. Some are used to enhance the performance of a specific product (acrylic enamel hardener), while others are a necessary component without which the product would fail to cure (acrylic urethane hardener or polyurethane activator).

As with the thinner/reducer, accurate measurements must be made of the hardener/activator to ensure optimum product performance and long-term durability. For example, adding too much results in a slow-curing product that eventually becomes brittle and prone to cracking.

Proper Prepping
The product is selected. The solvents are mixed. So you’re ready to apply the paint, right? Wrong. Before applying any product, prepare the surface.

The first step is to wash the vehicle with hot, soapy water to remove water soluble contaminants, including dirt, mud, tree sap, brake dust and road salt. As you wash the vehicle, pay particular attention to all cracks and crevices such as around moldings and other trim. Says a veteran paint technician: “The best product we’ve found in removing water soluble contaminants is a 1-to-1 mixture of Mr. Clean and hot water. It’s inexpensive and works just as well as specialty automotive products.” (And leaves the surface as clean and shiny as Mr. Clean’s head.)

Once the water soluble contaminants have been removed and the vehicle is dry, use a solvent cleaner to remove solvent soluble contaminants such as grease, oil, road tar and waxes.

The final step is sanding. Another training center manager told me that because sanding techniques have changed so much over the last 10 years, wet sanding is nearly a technique of the past. He noted that thanks to improvements in dry sanding paper, body fillers, polyester putties and vacuum sanding systems, dry sanding is easier than ever.

Once the vehicle has been properly sanded, it can be taped. Taping is also very different than it used to be. Today’s coatings have more film build and better film integrity than previous coatings, so it’s easier to bridge paint around areas such as tight moldings and door handles.

Guns & Roses
The final step in the refinishing process is setting the high-volume low-pressure (HVLP) spray gun and applying the product. The training center mangers I spoke with said that properly setting a spray gun is one of the biggest problems for technicians and that HVLP guns starving for air are a leading cause of most paint-related failures. Problems like air entrapment, solvent pop, orange peel, die back hazing and shrinking can all be caused by insufficient air supply.

To properly atomize high solids urethane, as well as low VOC coatings, HVLP guns must maintain the recommended 10 psi air cap pressure. To check air cap pressure, you need air cap test kits, which are available through the gun manufacturer. The kits are simply one or two air pressure gauges mounted on an air cap to check internal cap pressure. A two-gauge cap kit will demonstrate pressure changes between the air horn and the fluid nozzle chamber area, depending upon the fan pattern position. With the fan pattern at its widest, the gun provides maximum pressure for atomization. If the fan pattern is decreased, atomizing energy is greatly reduced. The fan pattern must be adjusted to suit the painter prior to setting the inlet air pressure, which will ensure the proper 10 psi internal cap pressure.

Once you’ve set the spray gun, you’re ready to paint. Keep in mind that painting should always be done in the direction air in the booth is moving. This minimizes the amount of overspray over the fresh paint and ensures better gloss, durability and distinctness of image.

The final step in the refinishing process is buffing the vehicle. A veteran painter I spoke with recommended using a dual action sander (DA) with an interface pad and 1,500-grit sandpaper when buffing. He also stressed to always clean the vehicle prior to sanding and to clean it again before buffing. Remember to never use worn or dirty buffing pads, and never use paint sealant on fresh paint – this will hurt the long-term durability of the finish and cause the paint to lose gloss.

Building On the Basics
While the art of refinishing vehicles has been around for years, there are always new techniques to learn – as well as a few tried and true ones to remember. Whether your painters have been with you two months or 20 years, be sure the all-important basics of paint mixing, preparation and application aren’t forgotten. Creating the perfect blend on that 2001 Navigator can only be achieved by building on the basics.

Writer Dave Ketner is learning center manager for Sherwin-Williams Automotive Finishes Corp.

Mixing Tip No. 1:
When painting large jobs, mix small amounts as needed so the product won’t reach the end of its potlife (which could affect the sprayability of the paint).

Mixing Tip No. 2:
To achieve the best gloss, always use the proper solvent for the temperature, job size and airflow of your spraybooth.

Sanding Tip:
When sanding, never skip more than 100 points in sanding grit. If you do, you could polish the scratch rather than remove it, possibly causing your paint to sink later.

Taping Tip:
Paint manufacturers generally recommend removing tight-fitting parts to refinish them. If the parts can’t be removed, use outlining tape at the end of refinishing. Outline the part with tape, making a tail at the end. This will make the tape easy to remove before the paint dries and will eliminate any bridging problems.

Spray Tip No. 1:
Another way to check for adequate air supply is to spray a test pattern on masking paper. See how much pressure is needed to achieve proper droplet size. Set the pressure at the gun to be 5 psi higher than needed and hold the spray gun trigger open for two minutes. Check to see if there’s a pressure drop. If there is, you need to eliminate any air robbing restrictions and/or increase compressor size.

Spray Tip No. 2:
Gun-mounted diaphragm regulators rob air pressure. If possible, use a wall-mounted regulator and connect the hose through one low restrictive quick disconnect (QD) at the gun.

Spray Tip No. 3:
Never overlook the fluid nozzle size of your gun. There’s a limit to how much paint an HVLP gun can atomize. Don’t exceed this limit by either having too large a fluid nozzle or having the needle adjustment open too far.

Avoiding Mixing Mistakes
What’s the biggest mistake paint technicians make when using mixing ratios? According to one training center manager, it’s using weight, not volume. He says that paint manufacturers typically state mixing ratios in parts, by volume. For example, a mixing ratio of 4:1:1 normally means four parts of the base product, one part of thinner/reducer and one part of hardener. But many times, especially when using a digital scale, technicians will use weight rather than volume. For example, they’ll use 400 grams of the base product to 100 grams of thinner/reducer to 100 grams of hardener. But weight doesn’t equal volume, so using grams won’t give you the proper end result. If your techs use a digital scale, it’s possible to receive weight measurements from a paint manufacturer via microfiche or computerized mixing.

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