Collision Repair Training | United States
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Current Events/News: Advantage Online: 2002 Archives
ROLL-ON PRIMER-SURFACER
February 4, 2002 -A new process used with an existing material is getting attention. Roll-on primer-surfacer, as the name implies, is applied using a roller and a roller pan, similar to painting a wall (see Figure 1). Roll-on primer-surfacer can also be applied with a brush. It sounds simple, and it is. Applying a refinish material with a roller or a brush, as opposed to a spray gun, offers some obvious benefits:
Primer-surfacer is currently the only refinish material available as a roll-on, because it's the only material where any minor imperfections can be sanded smooth after application. Due to the mechanics of having to physically roll or brush on the material, it's best to use this product on small areas, like spot panel repairs. Like regular primer-surfacer, roll-on primer-surfacer can be applied over properly prepared original or previously repaired bare steel, aluminum, and almost all rigid plastics. This is not a direct-to-metal material. Bare metal areas require application of a spray-on primer. One major difference is that there's usually no need for a sealer, eliminating one step. This advantage is the result of new resin family groups whereby base adhesion, innercoat bond, and topcoat holdout are all provided. Since these products are not tintable, additional coats of basecoat or transparent single-stage colors may need to be applied. Preparation The same basic preparation steps must be followed as with regular primer-surfacer, including cleaning, sanding, and applying corrosion protection. One of the biggest advantages of using roll-on primer-surfacer is that there's no need to mask large areas to protect from overspray. Masking is usually only required along the edges of panels. Roll-on primer-surfacer is a two-part product, and the hardener does contain isocyanates. Wear the proper respirator when mixing and applying the material. Application
Following the product maker’s steps, mix the proper ratios of the primer-surfacer and hardener (see Figure 2). The rollers and brushes are available from the product maker. A different brand of brush or roller can be used, but they must be solvent-resistant. The brush can be simply dipped into the container and applied. If using a roller, the material is poured into a roller pan. Different roller naps will apply different thicknesses. Normal application is 1–2 mils per coat. Apply the first coat over the exposed repair area only. Wait the proper flash time, then apply a second coat extending out slightly further than the first coat. If needed, follow with a third coat extending out slightly further than the second coat. Apply all coats in the same direction. Do not roll the material on in a crosshatch pattern. Rolling or brushing should be done at a normal speed. Going too fast can capture air bubbles into the material, causing pinholes (see Video).
Avoid leaving ridges on the ends of the roller or sides of the brush. This uneven thickness can cause improper layering of the material. One major result of this is, even after sanding level, the topcoat causes a swelling of the primer-surfacer where these ridges had been. Roll-on primer-surfacer has a short pot life, as short as 30 minutes, so mix only what’s needed. The roller or brush can be cleaned with solvent immediately after applying the last coat, or discarded. The primer-surfacer can be force-dried after a flash or purge time of about 10 minutes. If using conventional heat, bake at 60° C (140° F) for 20-30 minutes. If using infrared heat, medium-cure bake for 20 minutes. Normal air-dry at 20° C (70° F) is about 2-3 hours. Sanding is recommended in two stages. Start with P320 grit dry or P400 grit wet, followed with finish sanding with P500 grit dry or P600 grit wet. Any bare steel or aluminum exposed during sanding must be retreated and recoated. Sanding of this product seems similar to other primer-surfacers. Always use a foam pad or rubber block to create a smooth, flat surface. Conclusion This new process for primer-surfacer offers an alternative with some built-in benefits. While roll-on primer-surfacer is not intended to replace all spray-applied materials, it is a handy alternative for small repair areas. Investigate the advantages and possible applications of this new material. You may find that this new form of primer-surfacer can improve use of space, increase productivity, and reduce VOCs.
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