Bondo for body filler
My initial choice for body filler is Bondo. Bondo used to have a bad wrap in the 70s, mainly because people wouldn't apply it properly and it would crack, split or fall off. It's changed a lot since then and is very durable. It is a two part filler that you add a little bit of red hardner to the grey filler to activate it. It is only workable for about 10 minutes so you only mix a little bit at a time. I start with about a softball size and as I progressed I used less and less. Once it starts to harden, it will not spread smoothly. Throw it away even though there's a compelling urge to use up the last drop. If you use it past this point, you're making more sanding work for yourself and will most likely have to do it over again anyways.
Quite a few professional bodymen have advised me that Evercoat makes a very good filler that is nicer to work with then Bondo and its about the same price. I've since tried the Evercoat and found that it wasn't much different except that it was a greenish blue when mixed. I didn't realize it but I do use Evercoat Everglaze & spot Putty for finishing work and its a great product, so I'll definitely try the rest of their product line.
I'm doing the bodywork during the winter months and my garage, even though its heated, is about 50 degF which is below the rated working temperature for the filler. I keep the filler in my house so that its at a higher temperature and only bring it into the garage when I need it. I also let it cure for a longer time before I sand it. I found that at lower temperatures, it doesn't spread very good, it is too stiff. At room temperatures, it spreads very nice.
When it is cold, it takes a long time for the Bondo to cure. I have had to wait up to a week this past month as we had -20 degF weather and I can't afford to keep the garage heated when its that cold. If you try to sand Bondo that isn't cured yet, the sandpaper gets clogged very fast - within minutes. I thought that I had bought poor quality sand paper but the solution is to wait a day or two then it sands without clogging.
Now that it is summer, here's what I've found on mixing filler (Bondo or Evercoat). It is better to apply more hardner than too little. You want it to cure within 30 minutes. This way you can work with it quickly. The ideal progress of the filler is as follows:
Mixing boards and spreaders
Mixing board and spreaders
I purchased a plastic mixing board for a couple of bucks which resembles an artist's paint mixing board. It is well worth the money as it is very easy to hold and to work with. It is also easy to keep clean which in body work is next to godliness. After every time I mixed and spread the filler, I cleaned all my tools before I mixed some more filler. Otherwise, you'll get lumps in the filler which cause great havoc while spreading. I had a dedicated metal paint scraper that I used for scooping out filler from the can and which I mixed with.
Quite a few bodymen, take the extra time to clean their mixing boards with acetone after each use. They claim that even trace amounts of old filler can contaminate the new mix. Some say it causes the filler to take longer to cure or not harden at all. I would think that the opposite would be true but who knows. I'll give it a try - anything to improve...
My spreaders were used only for spreading filler. You can buy spreaders that are color coded for the correct color of properly mixed filler/hardner. This is handy when you are first starting out. The instructions are pretty vague on how much hardner should be added. I try to use the widest spreaders that I can so that I minimize any waves in the filler. I alternate in the pattern that I spread the filler too. I only put on a maximum of 1/8" at a time and give it plenty of time to cure. It says that you can start sanding after 15 minutes but my garage is on the cool side and I give it a complete day to be safe. Otherwise you clog up your sandpaper pretty quick.
Body filler file (cheese grater)
I used a body filler file for rough shaping of the body filler initially and taking off the excess filler before sanding. It's great as there is little or no dust generated and a lot of body work can be done before any sanding begins. It's a coarse instrument and used only for initial shaping. I first bought a cheap file and the handle broke off the first day I used it. A better quality tool was only a couple of dollars more expensive. Strangely, the cheap tool was in the automotive dept. and the quality tool was in the hardware section. You can get flat files or round edge files. The files are replaceable and are inexpensive. Besides the handle breakage, the quality file had a much better "cut" to it. I could noticebly feel the difference.
Dual Action Sander
6 inch Dual Action (DA) air sander
Sanding patterns compared
A must have is a DA air sander. DA stands for dual action and when referred to sanders, it means that it sands in a loop pattern as opposed to sanding patterns in one direction or a circle. The looping pattern prevents the sander from cutting too deeply into the surface being sanded. An example of a circular sander is a sanding pad on a hand drill. It'll leave deep grooves in the surface being sanded. Something you don't want to do as it adds more finishing work! An interesting note is that a DA air sander uses less air than in circular sanding mode. When purchasing any air tool, check the operating pressure (PSI) and the required air flow (CFM). The better the quality tool, the less pressure and air flow that will be required.
I used the DA air sander for coarse finishing (80 grit) after the body file. It quickly cuts down the filler. There's two adjustments on the DA air sander, one is air pressure. Set it for the least amount of air to do the job. The other locks or unlock the sanding pad. You want the sanding pad to free float and to be rotate offset from the center. The key is not to press down hard while sanding but to apply light pressure. It takes some practice to find the right pressure but then it works great! The DA air sander is only good for coarse finishing as there isn't enough control to prevent waves in the sanding. A longer flat tool is required.
Finishing DA and Inline Sander
Woodworking finishing DA sander
An air inline sander saves your strength!
The air inline sander is a great tool for quickly cutting down the new epoxy based fillers. I alternate between the air sander and finishing DA sander cause it is flat surface and it is easier to get a uniform finish. It's usually considered a woodworking tool and not an autobody tool. It works for me. I use 80 grit paper and very frequently, smack the paper to clean the dust off. The paper lasts a lot longer this way. I take long strokes and sand in constantly alternating motions: vertical, horizontal, diagonal. This way, the area starts to conform to the rest of the body shape. I constantly feel the surface of the work to feel for high and low spots. I've found that the sanding dust can give false impressions of low and high spots so I constantly wipe off the surface. I've also found that after sanding for a while, my hands lose their sensitivity to the surface so I take a break and go do something else. Must be the vibration of the sanders..
Long Board Sander
Long flat sander
I use the long flat sander horizontally
The flat block sander is used before priming and after to make sure everything if flat
There comes a point where you can feel the dips and bumps but not see them. This is when you start to use a long flat sander. I found that since there is so many round corners, a flexible long flat sander works. Unfortunately, there is only one long flexible sander that I found and it didn't flex very much. I did find a generic short 8" flexible sander which is sold pretty well everywhere under every brandname like Bondo. It costs anywhere from $3.50 to $10.00 depending on where you buy it. Basically I found it to be too short and too stiff. It didn't have any rubber backing which I really didn't like. Too easy to gouge the bodywork. All in all, it lasted one day and broke.
Flexible Long Board Sander
Generic 8" flex sander that you can buy anywhere
After one day of hard use, it broke on the right hand side
I figure that I can make a longer and more flexible sander (about 10" long)" using the handles and sandpaper clamps from the broken pieces. So I found some flexible white plastic, rubber for backing (mouse pads work well). The big problem was which glue to use to glue everything together.
The pieces ready to be put together for the new improved flexible long sander
The flexible sander is great for the curves, easily bends and follows the contours
The original handles/clamps are on top, some unknown flexible white plastic that I found and some semisoft rubber for backing. After trying 5 different glues (contact cement, rubber cement, abs glue, crazy glue, carpenter's glue), I found that PVC glue worked the best for glueing the handles to the white plastic board as long as you roughed up the surfaces with 40 grit sandpaper. Initially, nothing seemed to stick the rubber backing to the white plastic material. Either the adhesive stuck to the rubber or to the plastic but not to both. I made a little test jig and tried 14 different adhesives and let them cure overnight. Permatex Back Silicone Sealant was the winner and stuck the best to both- its a silicone based sealant by the way.
I originally used ABS cement to glue the handles together and it softened up the plastic which allowed the rivets for the sandpaper clamps to pull through. So I countersunk some screws and screwed on the clamps that way. I decided to try PVC cement instead and it works much better than ABS cement. The new improved flexible sander is such a nice tool, I'm giving it serious thought about manufacturing them (when I get my car finished of course...).
I also liked the cushioning action of the rubber so much, I glued some on to another store bought flexible sander which improved it a lot. I just won't try to bend it around such sharp corners so that it breaks when I use it.
Glazing or Finishing Putty
Evercoat Everglaze & Spot Putty (1 lb tube used up)
After the filler is shaped and sanded to almost a perfect shape, I use a finishing putty to finish the surface. There comes a frustrating point when you can't seem to get the filler any straighter. That's the time to spray on some primer and a coat the complete surface with a very thin coat of finishing putty. The finishing putty sands easy and smooths out any small dips and ripples.
In addition, the filler is rather coarse and has some small airholes in it. The finishing putty fills any airholes, scratches and smoothes the surface. It is easier to sand than the filler so it is much easier to final shape the work. I change to a 120 grit sandpaper for sanding finishing putty. I used a complete 1 lb tube for two coats on the roof so you don't need much. I figure the thickness was less than 1/64" in most places - just enough to smooth out the dips and cover the scratches.
Came across a novel method of shrinking high spots using a shrinking disk that is easily made. I made mine out of an old stainless steel pot lid - I punched out the lid knob hole to 7/8" so that it would fit my 7" grinder's chuck and backing plate - done!
The Incredible Shrinking Disk
The incredible shrinking disk!
The basic idea is to use a stainless steel disk on a grinder to warm the high spots (takes about 4 to 6 seconds), then immediately douse the high spot with a wet rag. You want it hot but not hot enough to turn blue. Take your time, repeat as many times as it takes and in a couple of minutes the high spot is gone. It works great!
The Metal Shapers website has movies and great info on the shrinking disk so I won't repeat it here. You have to do a little searching to find it under the Learning Center - Metalshaping 101 link
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Copyright Jan 2013
Hot Rod High