So here is our patient waiting to be smoothed out and put back into shape. We have an array of problems here including a couple of deep gouges surrounded by some nasty low spots.
It may be stubbornness, but when you work dents a lot you tend to get a feel for a few special body tools. Even though we picked up a body dolly and hammer kit from The Eastwood Company, we will mostly be using the old body hammer and heel dolly shown in this photo. It is very important to get used to using bodyworking dollies to give the sheetmetal a sort of backing when smacking it with a hammer. Not using a dolly for this will simply create more dents and a frustrating days worth of work.
You can actually figure out what dolly you need by laying it directly onto the surface you will be working over. You want the dolly to have a similar shape to the sheetmetal in question. For this panel we used our favorite dolly that matched the cowl's side panel perfectly. Using the body hammer on the inside of the panel first will work the low spots back out where you want the sheetmetal to be.
After you have popped the low spots out you may notice that the area now looks like it's bulging out too far. This is because every time a dent is created, it also creates a crown, or high spot, around the parameter of the dent. If the dent were shallow, we would simply use the dolly by placing it on the backside of the dent with a little pressure, while lightly tapping the crown down. This creates opposite pressures, but since the pressures are forcing the sheetmetal in and out, the shallow dent and crown have a chance to smooth out at the same time.
Unfortunately for this panel, it has enough damage that the sheetmetal has been stretched beyond being able to lightly tap straight. However, the same rules apply when working deep or shallow dents. It's the amount of energy you will be putting out that will change. After some serious pounding, we worked the panel to the point of no longer being able to see or properly feel where the remaining bad spots were.
To help us see the spots that still need further attention, we picked up one of our Dura-Blocks from the Eastwood Company and some of the heaviest grit sandpaper we had (25-grit) and used the factory Brookville Roadster red oxide primer as a guide coat of sorts. Basically we are looking for the first signs of bare metal. The bare metal areas are spots that still need to be tapped down with the hammer and dolly.
This is what the panel looked like after we blocked the primer down a bit. We can now easily see all the rough spots, including the extremely low spots.
We picked out one of the problem areas and marked where the crown of the original dent is and is still causing us problems. What you can't see here is the dolly on the backside of the panel and the pressure we are applying to it outward, while we use the body hammer to tap with light-to-medium-light pressure around the parameter, or crown of the dent.
Once you feel the area is back in shape enough to start filling with body filler, take the time to remove all paint and/or primer from the surface. Body filler needs to be applied to a clean and scratched surface. Since we aren't trying to grind a ton of metal off the panel, we use a disk of tired, worn-out 50-grit to take the primer off. Holding the grinder as flat to the surface of the panel as possible will prevent grinding too deep and will take a slight amount of metal off of any high spots that may have been missed with the hammer and dolly. Just don't forget how thin sheetmetal is by grinding right through it. We really only want to take just the primer off, leaving a clean, scratchy surface for the filler to bite into.
We're not sure if it's the "space age micro spheres" or not, but we love this brand of body filler. It seems to sand easily and hold up for a very long time. We have been using this filler for the past 15 or so years and haven't ever had any problems with it. At any rate, it is always nice to have a few sizes of body filler spreaders, a few old rags, and a can of lacquer thinner for easy cleanup.
When mixing mud (body filler), make sure to work it over and over until it becomes one consistent color of pink. If you still see streaks of filler and hardener, you will need to keep mixing.
When it comes to spreading the filler, try acting like a fine art sculptor. You may want to start off by spreading the filler in the deepest area first, but once those areas have filler in them, go over the area and slightly past the area in question with a nice, even skim coat. This way you will end up with a gradual feathered edge around the rough spots. For a small area like this cowl panel, we figured it would be easier to skim-coat the entire area for best results.
Always clean your spreaders with lacquer thinner, or another type of cleaner. This will become very important the next time you want to use them. The last thing you want is a chunk of old filler you never cleaned off chunking off into your fresh batch of filler. If you see this happen, stop and dig the chunk out before moving on.
By now the filler you just applied will be heating up and getting hard fast. There is a point just before the filler completely hardens that you can use a cheese grater to knock down the high areas of filler, while smoothing it out.
Using the cheese grater is fine in most cases, but if you have only skim coated the area with a thin layer of filler, the cheese grater tool may cut too deep into the filler. To keep from taking too much filler off at this point with a cheese grater tool, try using a tired piece of heavy grit sandpaper and a block...
...The filler will be soft enough to cut down easily, but hard enough to hold its shape. Also, using a block for this is like getting a jump on straightening the panel before you really start sanding and blocking it. Use a light hand when sanding at this point.
Once the panel is sanded down and you start hitting bare metal, this is the time to stop sanding that area and start thinking about either very lightly tapping these bare spots down slightly, or if you may need another blast of body filler. In our case the bare spots that showed up after sanding only needed a little bit more persuasion to be straight. After some tap-tap here and there, we applied one more very thin skim coat of filler. If you are still having trouble getting the panel straight after doing all of this, try spraying a guide coat directly onto the panel. Then lightly sand the area and watch the bad spots come to life. Keep repeating these steps until the area is ready for primer.