Skim Coat Tips and Tricks

Part 3: Filler Fundamentals for Uniform Fairing

By “Rotten” Rodney Bauman – Photography by the Author

When it’s used to describe body parts of a truck as shapely as the Chevrolet Task Force, the word “straight” makes little sense. Somehow words that pertain to the autobody trade tend to end up twisted. Take the word “skim coat” for example. No matter how loosely it’s translated, skim coat should never mean a thick slab of polyester filler.

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01 The initial filler work once cured is ridged filler
With initial filler work finished in short-strand, fiber-reinforced filler, we’ve also cheated our way free of oil can situation. Once cured, this is ridged filler.

Now, as long as we’re discussing weird words and polyester fillers, let’s get this out of the way, right away: Not all polyester fillers are “Bondo!” That’s only a brand name. You can use it if you want to, but for the skim coat job at hand, we’ve already coughed up the dough for Evercoat Rage Gold, which is among the higher-end fillers available today.

Read More: Shop Truck: 1955 Tri-Five Chevy Station Wagon

Our local parts store stocks Evercoat Rage Gold, but it’s currently costing $93.92 per gallon-size can. At the time of this comparison, the best deal we’ve found is $63.99 from Summit Racing. As we go here, the majority of tools and materials used are indeed Summit staples.

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02 We used fairing boards from Hutchins and Dura-block
So, here are a few fairing boards from Hutchins and Dura-Block. Some are modified, but the wooden paint stick is stock.

In our last installment, we stiffened a Chevrolet Task Force truck’s oil-canning roof skin. That was accomplished without further heating, beating, shrinking, and/or dinking with the stretched steel itself. That was accomplished by doing our initial filler work with a short-strand, fiber-reinforced polyester body filler.

As you may recall from last time, a crack was discovered in the passenger-side A-pillar’s factory-leaded seam. There, the ground-away lead was replaced with the reinforced filler as well.

03 Early model AFS unit is tunable board
Now this tunable board is an early model AFS unit. It and a longer 36-inch model were purchased in the ’90s directly from their inventor—who I really liked a lot.

Now, where were we, anyway? Oh yeah, our roof skin’s first round of filler work is finished, and it’s now ready for a skim coat. At our shop, like other good ones, skim coat means a very thin filler application. For fine-feathering purposes, a skim coat must extend beyond initial filler work. Since underlying smears sand at varying rates, the skim coat is our first opportunity for truly uniform fairing—at least ’til we’ve sanded through it, that is.

For our roof skin’s skim coat we’ll need a filler that’ll flow. Evercoat offers a number of low-viscosity skim coat suitable fillers. We’ve experimented with a few, but so far we always circle back to our versatile old standby.

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Read More: Second Time is the Charm: 1955 Chevy Bel Air

My own favorite all-around filler is Evercoat Rage Gold. Granted, it ain’t cheap, but then, neither are quality abrasives. If you choose to work with less-expensive fillers, you’ll burn through more abrasives. You’ll also work harder while doing so. Based on my own experience, it’s usually best to go on and spring for the first-choice filler—spendy as it may seem to be.

04 We use a mixing board but utilized a TE-31 Corrolla quarter glass
Last time, for smaller smears, we used a convenient tear-off-type mixing board. When a skim coat job demands it, a TE-31 Corrolla quarter glass still has its place.

For skim coat-reduction of Evercoat Rage Gold, we’ll add polyester resin to the mix for whatever viscosity feels appropriate. The downside is that extra resin makes the curing mixture extra sticky—at first. For that reason, we’ll begin sanding with previously used abrasives. Once the goo layer gives up, we’ll switch to fresh grit and continue on for accurate fairing.

Now, it seems like we may have discussed the “mud hog” before. If not, it’s sort of like an 8-inch version of a dual-action sander, although its action is somewhat less orbital—if that helps. At any rate, it’ll be the hot-tip tool for the first bit of fairing. For sharpest-possible accuracy, however, we’ll switch to employ a number of different flexible fairing boards, blocks, hand pads, and perhaps a good ol’ fashion wooden paint stick, too.

Read More: Purpose Built Sport Truck: 1958 Chevy Cameo

At the end of our filler work marathon, this cab’s exterior will receive an application of epoxy primer, followed by three wet coats of urethane primer surfacer for finer fairing in the paint-prep stages. We won’t be using a “primer filler” from a ’gun with a fire hose fluid tip. Providin’ you’ll work your polyester filler of choice far enough along, you won’t need the big ’gun either.

05 Skim Coat needs the Evercoat rage gold resin to reduce desired viscosity
The shape of this experienced palette is ideal for larger skimcoat applications. Here Evercoat Rage Gold is resin reduced to the desired viscosity.
06 Extra resize slows the curing process thinned down filler flow
It’s cool in the body stall. Extra resin slows the curing but we’ll move quickly just the same. Smeared firmly at first then further finessed, the thinned-down filler flows.
07 we removed the extra resin goo on the mudhog
Before complete curing we’ll sneak up with spent 40-grit on the mudhog to remove the extra-resin goo. So, how does this flatfooted tool find fairness on a convex panel?
08 We only use the mud hog as a time saving shortcut
In our shop, the mud hog is only used as a time-saving shortcut. The final fairing is always done by hand. Here for the larger expanse, the AFS board is our buddy.
09 We use a trusty hand pad from Motor Guard to help shape it
Still using 40-grit for now, we’re alternating back-and-forth between tools. Here for the most rounded corners, the curly old Motor Guard hand pad has the needed shape.
10 For these drip rail areas the stick is perfect
You can have a box of blocks and longboards, too, but without a wooden paint stick, you’re underequipped. For these drip rail areas, the stick is an invaluable tool.
11 Harbor freight offers a magnet for your blowgun to secure it safely
Youngsters won’t yet relate, but up-and-down from scaffolds to floor level for a blowgun gets old. So, with a Harbor Freight magnet, we’ve fashioned a handy blowgun holster.
12 Body work basics requires feeling for imperfection
At this point we like what we see, but seeing ain’t enough. As we were taught back there in body school we’ve got to feel our work as we go to know.
13 It_s important to also visually inspect for imperfection
But let’s not sell eyesight short. When we’re seeing shiny metal in deep sand scratches that’s a good indication that our feathered edges will end up undercut.
14 We achieved uniform fairness thanks to Evercoat for Metal Glaze 416
We’ve already achieved uniform fairness. The deep sand scratches won’t require a second skim, thanks again to Evercoat for Metal Glaze 416.
15 We like to call this cramcoating since we are cramming Evercoat 416
If I could name this step myself, I think I’d call it “cramcoat.” I’m not going for build, I’m only cramming Metal Glaze 416 into my sand scratches.
16 Once fully cured the cramcoat gets hit with 80 grit then 120 grit
For our fully cured cramcoat we’ll take the first few strokes with 80-grit on each block and board we’ll use. Then we’ll switch to 120-grit when the spreader trails are leveled.
17 We apply dry guidecoat to check for imperfections
To monitor our progress, let’s apply a dry guidecoat. This will make any low spots, pinholes, or sand scratch imperfections stand out visually.
18 We use a finer 120 grit abrasive
Here we’re using the same tools as before but now with finer 120-grit abrasives affixed. When the dark guidecoat is no longer apparent we just might be done.
19 we take longer strokes now in a cross hatch pattern
We’re taking long strokes on the larger expanse, in an evenly alternating cross-hatch pattern. Pointed fingers denote the direction of this particular stroke.
20 Metal glaze 416 feather in small ripples we sanded our skim coat to an earlier fill
At this corner only, we’ve come back with Metal Glaze 416 to feather in a small ripple where we sanded our skim coat through to an earlier fill. This is working.
21 Skim coat is a very thin layer and gives this panel a good feel
As it’s intended to be our skim coat is very thin. Here we see some transparency, and feathered edges transition smoothly. This panel feels good and it’s nearing primetime.

Harbor Freight Tools
(800) 423-2567

Summit Racing Equipment
(800) 230-3030

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