How to do Basic Body Filler and Paint Work [by: Halloweenking]
Hotrodders Bulletin Board: Knowledge Base: Body-Exterior: Articles
The hardest part of bodywork is using filler, the rest is pretty basic.
There are a few basics to learn before you actually use filler. When mixing a two component filler try not to use too much hardener. If you do, this will cause the filler to crack under the extensive heat of the chemical reaction. If it doesn't crack, it is sure to be brittle and won't last very long. A small ribbon of hardener across the diameter of your filler is more than enough. Try not to make too much at one time, because as we all know, time waits for no one.
A good smooth flat mixing board is good to have, you can make one from glass, marble or Lexan. Cut it to size, then drill a few holes on the sides for gripping. Using this, you can easily scrape off the previously hardened filler without wasting a whole sheet of cardboard.
Using Filler, technique #1: Prep the surface before applying filler. When working with large areas (bigger than 3"x3"), always scuff down the the metal at least 3" around the affected area. Use a body hammer on all high spots. When using filler, you have to be quick and you can't be "skimpy". Don't be shy with the filler when trying to correct an imperfection. Apply filler 2-5 inches around the affected area (when a dent is made, sheetmetal stretches, so the area around the dent is affected as well). Apply the filler liberally to the affected area, let set (until the filler is firm to the touch but not totally hard). See Working with Filler, technique #1.
Using Filler, technique #2: If applying filler to a surface where a bodyline is present there are a few tricks to doing it but the easiest is as follows:
You need a roll of scotch tape (I use 3M, but any will do). Tape down a 2" long part of the tip of the tape to the center of the bodyline and stretch the tape at least 6" from the other side of the affected area, this will be used as a guide or template to where the bodyline once was.
DO NOT continually press down the tape as you work your way to the other side of the affected area, this will void the whole purpose. You may smooth tape after you attach 2" of the tape to the other side, securing it to the center of the bodyline, then smoothing it. Apply filler to the side of the tape which is centered in the bodyline, wait till jelly-like and peel off tape, this will put a "lip" on the filler where the line used to be. Apply filler 5" below the "lip", this will give you a straight smooth line. Let harden until firm to the touch, but not completely hard. See Working with Filler, technique #2.
Working with Filler, technique #1: After letting the filler reach this firm state, it's time to start sanding (it's perfectly fine, it's easier to start before it fully hardens). Have a sanding block ready with your desired grit paper (36-40 for prep and excess filler, 80 for shaping, 120 for scuffing/smoothing, 220 for smoothing, and 400-2500 for wet sanding).
DO NOT sand without a sanding block, this will unevenly distribute pressure, causing "waves" in your bodywork. When sanding a smooth surface (no bodylines, etc.), always sand the whole area, 1-2" past the filler. Never sand one area for any length of time, as this will cause a low spot. In any sanding, sand in an "X" motion 5 times one way, 5 times the next. This crisscross motion will lessen fatigue and work the filler faster. Work filler until you're satisfied. Applying filler may have to be repeated, it's normal. When you become satisfied, you should have been using a smaller grit paper to smooth the area (working from 36-40 to 120). See Prepping for Paint.
Working with Filler, technique #2: Now it's time to start sanding after the filler has reached this tacky state. Use a sanding block with your desired grit paper (36-40 for prep and excess filler, 80 for shaping, 120 for scuffing/smoothing, 220 for smoothing, and 400-2500 for wet sanding).
DO NOT sand without a sanding block, as this will unevenly distribute pressure, causing "waves" in your bodywork. When sanding to create a bodyline, use the "X" motion (criss-cross) but only one side of the line at a time so you keep the straight line intact. Sand 5 strokes above, 5 strokes below. Work your way from 36-40 to 120 grit until you're properly satisfied with the line and its smoothness. Always sand the whole area, 1-2" past the filler, never sand one area for any length of time, as this will cause a low spot. In any sanding, sand in an "X" motion 5 times one way, then 5 times the next. This criss-cross motion will lessen fatigue and work the filler faster. Work filler until you're satisfied. Applying filler may have to be repeated, it's normal. See Prepping for Paint.
Prepping for Paint: Now that the filler work is completed, it's time to get ready for the paint. After the filler has cured and you're happy with the results, it's time to seal the filler. Using a good sealer is essential to your paint. If you don't use a good sealer, your body filler will "show through" because it will absorb your primer and paint, causing a discoloring mark, and any oils that might have been absorbed by the filler from your hands or the air could ruin your paint.
Prep the surface by using a degreaser or a mild dish detergent like Palmolive or Dawn. Wash the surface down, and let fully dry. Wet the floor of your spraying area, make sure it's properly ventilated, and then squeegee the floor so there will be no splashing up on your fresh sealer.
Mix and spray, then coat fully. Let cure and wet sand with 400 grit on a sanding block, paying careful attention to bodylines and edges so you don't wet sand through. After wet sanding the area smooth, wipe it down with some tack cloth (rinsing with clean water and a rag works too) and then with some Scotchbrite to remove the wet sanding residue and to scuff the surface.
Prime with your desired primer, then let cure. In a crisscross motion, apply a different color primer to the entire surface, then let cure. After the surface is completely cured, wet sand with 400 grit on a sanding block. This will sand off the alternate color of primer you applied but the areas that are low will still have residual residue of that alternate color. Fill with your choice of filler or spot putty, sand smooth and prime again. The alternate color primer can be applied and sanded off more than once but is not needed.
Wet sand the fresh primer with 400 grit on a sanding block. Clean off residue and scuff with a fresh sheet of Scotchbrite. Prep your spraying area for paint, then clean the surface if needed (optional). Make sure the spraying area is well filtered, the floor is wet but squeegeed to prevent splashups (unless you're using a downdraft paint booth -- some bodyshops and trade schools will rent the booths). Also, have a good filtered mask or fresh air system (FAS).
Never spray on a rainy day, or with temperatures below 72 degrees F. When spraying, keep your wrist straight -- move with the gun, never stretch. Paint a section at a time (rear, middle, front or vise versa), never side by side, as this will cause the car to look two different colors because of the time the paint set.
Spray 6-8" from the surface. Don't move slowly, you build up paint that way. Spray a few light coats just to cover the surface, a light mist, then a heavier coat for the last shot to coat and make one uniform smooth coat. Let the paint flash in between each coat, usually 5-10 minutes depending on paint, then let the last coat flash for about 15-20 minutes and clear. You can color sand between each coat of clear, but it's not necessary. Let the paint cure (ask your supplier about the cure time for that paint before buffing).
After the paint's cured, buff to a smooth glossy finish, use some swirl remover, and sit in your driveway on a beach chair with some sunglasses with a big smile and waving at the passers-by.