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Body Work & Auto Paint Tips - Get Your Paint On
Bodywork Is Plagued With Pitfalls That Can Cost You Time And Money. We Asked The Experts For Their Advice On How To Stretch Your Restoration Buck.
Jun 1, 2009
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Body Work & Auto Paint Tips - Get Your Paint On
A common mistake when replacing a trunk floor is cutting it out and throwing away everything that's attached to it. Oftentimes, items like the gas tank straps and the trunk latch and bumper supports aren't included with replacement floorpans. While they are available from the aftermarket, the stock pieces are generally in decent shape since they're built from a thicker-gauge (sometimes galvanized) metal than the floorpan. Cutting them off and reusing them saves time, money, and headaches.
Here's a classic example of where a simple patch panel won't cut it. The quarter on this '68 Camaro has been hit at least once, probably more, and subjected to some hideous bodywork. "Something like this, with 1/2 to 3/4 inch of mud, is totally unacceptable. Anything more than 1/8 inch is too much," explains Austin. "Work like this is common with lots of backyard mechanics and even some shops because it's a lot easier to load a car up with $25-a-gallon Bondo than it is to learn how to replace a body panel. I always recommend replacing the entire quarter-panel because that enables you to take care of all the dents and rust at the same time. Patch panels can start cracking between the welds if you don't do it right. If you put a full quarter-panel on, you only have a tiny amount of filler at the factory seam near the roof, and the amount of money you save in labor can more than make up the difference in price."
This Camaro quarter looks salvageable from a few feet away but is nothing more than scrap. Although there is a sufficient amount of decent metal overall, there's rust all around the wheelwell lip and holes from a dent-puller behind the rear tires from a prior repair. "Don't be misled by the amount of overall rust-free metal in a panel. If there's a lot of rust or dents concentrated in one small area, then you can patch the panel," Austin says. "However, if there are small rust spots, dents, and holes spread out over the entire panel, then it's not worth the labor of trying to patch it. Just replace the whole quarter-panel and be done with it. That way you won't have to worry about new rust spots popping up six months after you finished painting your car."
Engine torque and normal wear and tear tend to twist a car's body over time. Even without a specialized lift, a few simple tools can help ensure that the body and frame are straight before removing any body panels. The first step is to support the car with jackstands at each corner near the pinch welds on the rocker panels. Next, hang plumb bobs from each corner of the car and measure to make sure the frame is straight. "Replace one panel at a time, because once you cut everything loose, it's really tough to line everything back up again," Austin advises. "Adjust doors to old quarters first, take note of the gaps, and use them as a reference point when attaching the new panel. Clamp everything down really well, and check door gaps and trunk gaps continually as you weld to make sure the panel isn't moving around on you. The last thing you want to do is have to cut a panel you just welded on back off for adjustment."
As with quarter-panels and fenders, floorpans can be patched, but replacing the entire pan offers several benefits. Patching up just one or two "quadrants" of a floor results in unsightly welds and seams. Replacing the entire floorpan ensures that everything between the toe board and the rear package tray area is rust-free. Furthermore, it's the only way to properly fix a trans tunnel that may have been butchered to fit a nonstock trans. "For a quality restoration, it just looks more polished and professional when you don't have welds running all over the place. When you replace the entire floor, it looks factory," says Austin. "Also remember to drill out and reuse the old seat risers, since they aren't included with replacement pans. They're much more durable than the floorpan and seldom rust. Reusing them is a good way to save some money."
A poor man's solution to rusted floors and trunks is to try and weld up each rust hole. Unfortunately, this Band-Aid fix won't last long. The floor will rust up again in no time.
Here's a nifty trick worth storing away in your noggin. If you narrow a replacement trunk pan before installation, you can position the lip directly over the framerail. Consequently, the seam is undetectable when looking underneath a car on a lift, lending the appearance of original factory metal. Likewise, cutting the trunk pan to the exact size needed, then butt-welding it in place, eliminates any metal that would normally hang down from the seam. "I want my replacement panels to look like factory originals. A lot of people these days have lifts in their home garage, so they're looking at the bottom of their cars as often as the top," Austin explains.
Despite all its benefits, a floorpan is a big honkin' piece of metal and therefore quite a bear to muscle into place. "The average floorpan weighs about 70 pounds, so it's definitely a two-man job and can be a bit of a struggle. The best way to shoehorn it in is through the passenger door," says Austin. "Make sure to remove the doors, steering wheel, and rear quarter glass before wrestling it in. The other option is to go through the windshield frame. This requires removing the steering column and rear seat brace as well, since the floorpan needs to be slid up and past the rear seat area in order to get the front of the pan to clear the firewall."
For those tempted to cheap out, this isn't the place to do it. The upper dash panel on this '67 Camaro is thoroughly rotted out. In fact this area is notorious for rust in Novas and Chevelles too. Anyone with moderate welding skills can replace this piece at home. However, it must be securely welded-not merely riveted-into place. As a section of the car that supports the front windshields, rivets could very well come loose during a collision, sending your glass flying into the air.
Most people have probably forgotten this by now, but many muscle cars weren't equipped with passenger-side rearview mirrors from the factory. This prompted many owners to buy cheap aftermarket pieces, and they often ended up in the wrong location. The prep stage is a perfect opportunity to weld these holes shut and reposition the mirror in the right location. Moreover, all handles, locks, badges, and miscellaneous trim pieces need to be removed as well, as it's impossible to sand around them.
Any time a car has undergone more than one paint job-or has major problems such as chipping, flaking, or cracking-it must be stripped down to bare metal. Failure to do so will compromise the adhesion between the car surface and the paint.
Once a car has been stripped and primered and most of the bodywork has been done, it's time to start fine tuning. Intensive blocking is a staple of any quality restoration. "After a car gets back from media blasting and is down to bare metal, it should be sprayed with a dark-gray epoxy primer to stop rust from forming. You then hit it with a 2K primer and start blocking," Austin explains. "By doing do, any time you see a dark spot it means that you've hit a high spot, which needs to be corrected. Without the epoxy primer base, you'd go straight to bare metal instead. Sometimes high spots are so subtle that you can't even feel them, so this is a great way to verify that the panels are flat. Blocking also removes scratches, pinholes, and other imperfections. This is the stage when low spots should be filled in as well." Block sanding shouldn't be confused with color sanding. It involves sanding down the clearcoat in two-stage paints, and the paint itself in single-stage paints, to remove orange peel, fine scratches, paint runs, and dust nibs. The result is an ultra-smooth finish.
Even with NOS or quality reproduction sheetmetal, there will be a gap somewhere on the car that's too wide despite prodigious alignment efforts. Since epoxy will pop right off, running a bead down the edge of the offending panel with a welder will close the gap right up. Austin prefers setting the gaps at a maximum of 1/4 inch. "The idea is to use a series of spot welds to avoid warping the panel, then filling the rest of the weld in. If you don't, the panel will get too hot and start rolling inward," Austin advises. "Then grind the weld down flat, and repeat the process if necessary. If you get it just right, you won't even need any filler."
The metal surrounding the rear windshield is also prone to rust, especially on vinyl-top cars. Unfortunately, replacement pieces aren't available. After the rusted metal on this Chevelle was cut out, a new metal strip was fabricated and welded in. The roof, on the other hand, was in perfect shape and required no work.
When looking over a potential project car to purchase, keep in mind that any area that collects leaves, dirt, or water is a hotbed for rust. The front windshield support area beneath the molding on this Nova is rotted out and will need to be replaced.
Managing airflow with a paint booth is critical in achieving a consistent paint finish. Poor airflow can cause blisters, since the top of the surface starts drying faster than the paint beneath it, forcing solvents to escape from the paint. Likewise, a proper booth also filters out dust, bugs, and other impurities from the air that could end up on your paint. Laws vary by state, but painting a car outside of a proper booth can result in fines of tens of thousands of dollars. "Either don't do it, or don't get caught," Austin quips.
There are several methods of achieving a slick-looking undercarriage, but one the most effective is spraying it with an epoxy primer. Not only does it leave a nice satin black finish as if the car just rolled out of the factory, but mixing it with a hardener makes it resistant to chipping from road debris. The application is a single-stage procedure, so solvent popping isn't an issue. This particular epoxy is Glasurit Chassis Black.
If you don't have friends you can bum tools off of, tackling a paint-and-body project in your garage is a long-term commitment. The various tools of the trade in this one drawer-hole punchers, grinders, air hammers, drills, air chisels, and so on-costs several thousand dollars. That said, it could take several projects for an investment in tools to pay for itself for a DIYer.
Near the completion of any paint-and-body project, all cars look something like this. "This stage-after the metalwork is complete and the car has been stripped, primered, and block-sanded-is one of the most important," Austin stresses. "This is when you check panel gaps and perfect fitment before disassembling a car for paint. The last thing you want to do is have freshly painted panels rub against each other when you open the doors, trunk, or hood. It's very time consuming and a big pain, and the effort you put into a project at this stage can make or break the quality of your bodywork. If a panel doesn't fit right before paint, it won't fit after either. Bad prepwork is the biggest mistake DIYers make. Actually laying down the paint is only 15 percent of the job; the rest is prep. Any dents, scratches, or chips you see during prep will only look worse after they're painted."
Weatherstripping may keep water out of the trunk, but with no place for the water to drain, the lip that holds it in place will rust over time. Here, the bottom right corner of the lip has already been replaced, but the upper-right corner has not. The good news is that weatherstrip lips are readily available as replacement parts.
Although installing new floorpans requires removing the seat riser, it can be reattached as far rearward as your heart desires. For vertically gifted hot rodders, this means a precious few inches of additional leg room. Here, Austin split the seat riser in two pieces and welded a patch panel in between them to allow mounting the seat brackets farther back for a tall customer.
Regarding even the cars that command a premium price tag and are in decent overall condition, Austin says that 95 percent are rife with shoddy repairs. "The problem with buying a finished car is that a good body guy can hide a lot of imperfections that you can't see until you start disassembling a car. This doorskin should have been replaced in a prior repair, but it has a big hunk of Bondo in it instead. When you go to check out a car to buy, don't be shy about wrapping a magnet in a cloth and running it over the body to check for body filler."
There's more to paint selection than the number of stages in which it's applied. The composition of different paints varies dramatically. The simplest are single-stage paints, which have nothing in them but solid colors. Metallic paints, on the other hand, have aluminum shavings mixed in for that sparkly luster many people envy. They can be either single- or dual-stage paints, but most are only available in basecoat/clearcoat systems. Pearls are different paints altogether. They have mica particles mixed into them that reflect light from different angles. The result is a color-shifting effect as you walk around a car. Kandies, on the other hand, are applied by laying down a metallic base, then sealing it in with a coat of tinted clearcoat. As light penetrates the colored clearcoat, it reflects off the metal flakes, giving the appearance of depth. Applying kandy paint is a three-stage process starting with a basecoat of silver, gold, or white metallic followed by a transparent kandy tint, and then a clearcoat on top. Kandies are very laborious, require lots of experience, and are not recommended for the backwoods bodyman.
Reducers and hardeners must be mixed in exactly as directed in the paint manufacturer's instructions, or the consequences can be catastrophic. Their concentrations must be adjusted for changes in temperature and humidity as well. Straight out of the can, paint is like a syrup and must be thinned before it can be sprayed. Hardeners, on the other hand, are mixed into primers and clears to assist with curing. The exception is water-based paints, which are ready to spray right out of the bottle. Unlike urethane paints, water-based paints are nontoxic, so you can spray them without a booth. Some industry insiders believe that increasingly stringent state laws may someday phase out urethane paints in favor of their environmentally friendlier water-based counterparts.
Cheap paint guns can sometimes yield acceptable results, but high-dollar HVLP (high volume low pressure) guns are the industry standard. Not only do they help cut down on volatile organic compounds (VOCs), they apply a greater volume of material at lower nozzle pressures. That means more paint on the car and less overspray on the ground. Furthermore, they provide a wider spray pattern and operate at up to 90-percent efficiency compared to the 30-percent rating of standard paint guns.
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