The Essentials of Fiberglass: Part VI

Contrary to popular belief, there really are people out there who actually like finished cars. There's a yet more radical bunch that prefers an even, consistent color and shine. Yeah I know it sounds strange, but it's true.

So considering we're discussing fiberglass in automotive terms, we're going to make the assumptive leap that some of you would actually like your fiberglass repairs and fabrications to resemble the nice areas around them. It's the kind of thinking that keeps us on the cutting edge.

As you'll recall, last month we laminated a really simple part over a really simple foam shape. True to our "just enough resin" school of laminating, we ended up with a really strong and rigid part. As part of that same school, we also ended up with a rather coarse finish--a surface that doesn't exactly do paint justice.

So we're showing how to make that raw, cob-rough 'glass shine like it was nobody's business. We compiled some of the information and experience from our man J.B. Donaldson with the information and experience from our well-versed PPG paint wizard Andy Ganderton. We took all our kooky notions and laid them on Carl and Alan Brunson over at Carl Brunson Refinishing and Restoration in beautiful Las Vegas, Nevada.

But before we get into the particulars, we're beholden to emphasize a few of J.B. Donaldson's major principles that make the difference between a pleasant finish and rhinoceros skin. First of all, "you want sufficient time (for the laminate) to de-gas," Donaldson said. As fiberglass resin cures, it releases styrene. The more the cure, the less styrene there is to leave the laminate. "Use your nose for that one; that's what it's there for. The less it smells, the more cured it is. You don't want it (resin) to outgas to the subsequent primer level; it'll wreak havoc with the finish. Give it at least three to four days (at ambient temperature) or a little less if you can get the temperature higher."

Also, "always read the label," he said. "It sounds stupid, but most of the problems come from people not reading the label," which, in most cases will list chemical compatibility. "You don't want to use a system that will react with fiberglass," Donaldson said. As for precautions, "talk to your local distributor...they hear all sorts of whining and complaints about products. Not only do they deal with people like us, but they hear what painters have to say. They (distributors) can tell you what works and what doesn't."

We tried a few things before officially starting. First, Ganderton recommended knocking our surface down with an 80 to 180-grit pad and blowing on a coat of resin-compatible K-38 High-Build Primer/Surfacer to fill all voids and consistencies.

While the K-38 worked fairly well, we found it might not have been the best remedy for the application; the K-38 didn't fill the voids between the glass fibers quite like we wanted it to. To fill the gaps fast, we broke out one of Donaldson's aces in the hole: Morton's Eliminator polyester spray filler. Remember when we mentioned plastic body filler was basically polyester resin with a thickening agent and an accelerating agent mixed in? Well, this is basically lower-viscosity sprayable plastic filler. It creates a moisture and solvent barrier, so material applied over Eliminator cannot penetrate or separate it from its substrate.

Eliminator magically erased all major pitting and pockmarks in one application. It even let us block-sand the panel with ease. As for primers to avoid, Donaldson said to steer clear of resin and lacquer hybrids; they'll shrink much like straight lacquer primer. Use your nose on this one; if it reeks of lacquer, keep looking. Incidentally, after we admitted how rough our piece was to Ganderton (after we finished the job, that is), he said he would've recommended Omni MX 241 primer for its heavier bodied properties (it's similar to the Eliminator we used, according to Ganderton).

The polyester primer's the foundation that really let the K-38 shine, so to speak. What the polyprimer didn't fill, the K-38 did--including sanding marks and a few small voids left from the first coat. In short, this is one really bitchin' primer/surfacer that happens to sand like butter. Brunson blocked it down with 320-grit paper, applied another coat, and blocked it one last time with the 320.

He then mixed a paint cup of PPG Concept DCC acrylic urethane with some DT-870 reducer (65- to 80-degree ambient temperature) and DCX-61 general-purpose hardener. One coat and we knew we had our combination. As the second coat settled on the surface, we couldn't believe our eyes; it was gorgeous. At that point we'd wished we'd made something worthwhile other than some silly old scoop housing.

But we did this for illustration's sake anyway. At this point we've got a finish good enough to pull a mold off of so we can make yet more useless square lumps that could serve as hood scoops. That's probably our next encounter. Until then, dig in and paint away.

Straight, No Chaser
Without digging around it's pretty tough for even some professionals to spot the difference between pretty good and really good bodywork. On the other hand, your half-blind grandma can spot the difference between pretty good and really bad bodywork. We've heard the latter called friendly bodywork, as in "it waves at ya!"

Luckily enough, it's pretty simple to obtain professional results, it's just a matter of preparation--specifically block sanding. It's one of the things that separates the good from the best. It really deserves a story of its own, like the story on block sanding in this issue, but we can still address it briefly here.

Block sanding is pretty simple: build up an area with high-fill primer, then knock the high spots down with a sanding implement that acts on as large an area as possible. The high spots go back to their pre-primed status, but the unsanded low areas eventually build to match the high spots. When the primer on the high spots gets thin, simply blow more primer on and keep knocking the high spots down 'til the panel feels straight.

As you can imagine, there's a mechanical element to it. One tool that fits the largest area possible on one panel might work radically different on another. For example, convex panels like wide and long sanding tools. Narrow and convex tools work well on concave panels and details. Use judgement on this one.

There's proper technique, too. A long, narrow sanding tool, when plied the tool's length down a panel, will cut a mean groove in the tool's shape. However, rake that same sanding tool diagonal to its shape on a panel, and you'll affect a greater surface area and hopefully flatten the area. Alternate directions often in a biased pattern (not perpendicular), and the results get even more consistent.

Our man Alan Brunson did just that with an old pine paint stirrer. It's really a pretty simple thing, it just takes thought and a lot of elbow grease. Think of the panel's general shape. Then break into that dusty crevice in your mind called your imagination and come up with a good tool.