Body Work: Applying and Sanding Body Filler

After taking a pretty long break from my Corvette project to work on a few other projects around the house I’m now back into my restoration project. In the last update a few final tasks were completed to ready the chassis so the body could be lowered into place one last time. With this task complete there are now two major tasks remaining – bodywork/paint and the interior. Originally I was going to tackle the interior first. I figured that doing this first would reduce the likelihood of damaging the paint during the installation of the interior. However, I quickly changed my mind after thinking about how difficult it would be to keep the interior clean during all the body work and painting.

So, with this update I’m starting the bodywork process. I’ll admit this is a fairly daunting task. First, I’ve never been a big fan of body work and, second, I’m pretty worried about how the finished result may turn out. But, I figure like most other things I’ve done on this project with the proper research, the right tools, and a bit of patience it’ll all turn out ok. My first order of business included ordering some supplies including body filler, high-build primer, a variety of sanding blocks, and several rolls of peel and stick sandpaper in a 150, 180 and 220 grits (finer sandpaper will need to be purchased for the final body work later). Once the materials arrived it was time to get to work.

After doing a bit of research I purchased two types of sanding blocks. Dura-Blocks were first on my list whereas they were highly recommended by nearly all the sources I looked into. These blocks are constructed from closed-cell rubber that yields a semi-rigid block that has just a bit of flex. This semi-rigid consistency makes them great for block sanding. The kit I decided on included six different blocks of various shapes and sizes.

In addition, I purchased a set of Soft Sanders which are flexible foam blocks that come in a variety of shapes. These shapes are intended to mimic the curves, coves and ridges of classic cars to make the bodywork process easier. These blocks are quite flexible and are made of a foam material very similar to pool noodles. The kit I purchased had the 9” long blocks but you can get them in much longer lengths if desired.

With the new materials on hand the first item I decided to tackle was the rear tail lamp and valence panels. My Corvette definitely needs lots of bodywork throughout but I figured this was a good place to start. Previously I had completed some really rough body filler work, and also sanded down some areas of excess adhesive (blue areas in the photo below), but that was it. My current goal: fill over the blue adhesive and then finish out the lower corner of the tail lamp panel. Once this corner is done I’ll move across the full width of the tail lamp panel.

Since I’d already sanded the areas down they had a pretty good surface profile for the new body filler to adhere to. Therefore, I simply wiped them off with some pre-paint cleaner and started the process of mixing a small batch of body filler. For body filler I’m using Rage Gold by Evercoat which is a premium lightweight filler that’s easy to work with and sands with minimal effort. It is quite pricey but this is one of those areas where you definitely get what you pay for.

Mixing the Rage Gold is pretty similar to other body fillers. The main difference is that the hardener is blue instead of red. When mixing your filler an easy way to proportion the hardener is to place a round dollop of the resin 4” across on your mixing sheet. Then pull a ribbon of hardener across the dollop of resin going from one edge to the other edge. This should get you pretty close to the right proportions. Note that larger dollops of resin will require a slightly longer ribbon of resin while smaller dollops will require less.

One the two parts are dispensed mix the resin and hardener very thoroughly. It’s important that the filler is very thoroughly mixed such that it’s one consistent color free of any streaks or color variations. I use a putty knife to do my mixing but you can use your spreader too if you prefer.

  

Once mixed a flexible spreader was used to apply a thin, even coat over the seam between the tail lamp panel and the rear valence panel. For the first layer I like to go very thin and work the filler into the body panel – think of it as buttering a piece of bread. This ensures the body filler gets worked into the surface and maximizes bond. Once the base layer is thoroughly worked in an additional layer of filler is applied as needed to build up the surface. With the Rage Gold you have a working time of no more than 5 minutes so you need to work quickly. However, try to work neatly too which will save you lots of sanding time later. One trick to consider is taping off areas where you don’t want to get any body filler – especially in hard to sand areas. Spending a bit of time taping areas off is a lot easier than sanding off extra body filler (and yes, I’m speaking from experience).

Once you’re finished applying body filler you can remove any excess filler from your spreader using a paper towel and some brake parts cleaner or other solvent-based pre-paint cleaner. This gets all the extra body filler off and allows your spreaders to be reused.

After about 10 minutes the body filler had started to “kick”. At this point I used some 80 grit sandpaper to knock off any obviously high spots of body filler while the filler was still fairly soft. It’s much easier to complete rough sanding at this stage than when the filler is full set. Just be sure to use coarse grit sandpaper. Otherwise your paper will quickly become clogged up. After about 20 minutes the body filler had fully cured so I loaded up my 11” Dura-Block with some 180 grit sandpaper and got ready to start sanding. I could have started sanding with coarser sandpaper but I realized it had been quite a while since I’d done any body work. Therefore, I figured going with a finer grit sandpaper would minimize the potential of sanding too much too quickly. Basically, I decided to use the slow and steady approach here. Besides, the body filler sands pretty easy so the 180 grit paper worked well for me. With my sanding block in hand I set to work on the body filler sanding in an “X” pattern. Using this crisscross pattern is an important aspect of sanding body filler and blocking body panels and minimizes the potential for flat spots. Start out by placing one hand at each end of the sanding block. Now place the block flat against the body and slide the block across the surface at a 45 degree angle. Do this several times and then repeat but going in the opposite angle. Be sure to steadily move across the body panel as you repeat this pattern to avoid creating any low spots in the body panel. The only time you should stay in one spot while sanding is if you’re trying to knock down a high spot. This is the basic pattern you want to follow. Avoid using a simple back and forth pattern – you’ll end up creating a flat spot. In the photo below you can see I’m using my 11” Dura-Block – the largest sanding block that would work for this area – sanding at a 45 degree angle by moving the block from roughly 10 o’clock, down to 4 o’clock, and then back to 10 o’clock. After making my way across the valence panel I then switched to sanding in the other direction – from 2 o’clock to 8 o’clock, to create the required crisscross pattern.

In the photo above you can also see I’m wearing a respirator. To say this is a messy and dusty process is an understatement to say the least. You really don’t want to breathe in all the dust if you can avoid it, it’s just not healthy. A simple dust mask would suffice but I prefer to go one step further and use a respirator since it does a better job. After making an initial pass at sanding the rear valence panel the exhaust trim piece was test fit in place to make sure the profile was accurate.

The overall fit was pretty good but I decided to do just a bit more sanding to get things as even as possible. In the photo below you can see the low spot (the dark green area) just above the sanding block. Sanding everything else to get down to this level would have required sanding well into the fiberglass panel. That would obviously be a no-no so I ended up applying another thin layer of body filler to this area to build it up. This is pretty typical – body work is a bit of an iterative process.

Here’s the drivers side of the tail lamp and rear valence panel after sanding. You can see the edges of the body filler are well blended into the surrounding panel – the feathered edges have a milky appearance. In addition, there’s no perceptible change in the surface profile when I ran my hand over it. A tip for checking the smoothness of a body panel with your hand is to place a piece of paper towel between your hand and the body panel. It significantly improves your ability to feel changes in the surface.

  

With the lower corner of the tail lamp and valence panel complete it’s time to move onto the rest of the body work. It seems this bit of work represents only about 1/100th of the body work I need to do on the car so it appears I’ll be doing a lot of sanding over the next couple of months. Once this initial body work is complete I’ll apply the sanding primer and start the process of block sanding the entire car in preparation for final paint. Stay tuned for more updates in the near future. While I usually don’t do a lot of work on the Corvette in the winter (the garage gets pretty cold) my goal is to make my way through much of the initial body work in the next few months. If you have any questions about this update, or a project you’re working on, navigate over to the Corvette Restoration Forum and ask! I’m there fairly often and, together with the other great forum members, you’re sure to get some great feedback.