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Priming for Paint - Prime TimeWhen your repairs are complete then comes the time to prime From the January, 2012 issue of Street Rodder By Kev Elliott
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If you’ve built a car before, or even had paintwork done on your daily, you’ll appreciate just how expensive the paint process can be. Long gone are the days when you could paint a car at home using nitro cellulose lacquer. Or are they? Lacquer paint may be a thing of the past in most states, but you can still paint a car in your home garage, thanks to Summit Racing’s two-stage urethane paint system. While you should have water... While you should have water traps and air filters in the air line, it’s always a good idea to have a filter at the gun too, and the Summit paint starter kit contains a couple of these DeVilbiss filters. It was about time I changed the one on my old suction feed primer gun anyway. The universal 4:1 mixing ratio of Summit’s system, whether you opt for basecoat and clearcoat or single-stage topcoat, is ideal for DIY painters, as the primer, clearcoat, and single-stage topcoat all use the same universal activator. Apart from which color to choose from the extensive range (custom colors aren’t an option) the only decision that has to be made is which activator to use. The fast activator is for use below 70 degrees F, the medium for between 70 and 80 degrees F, and the slow above 80 degrees F. What this means is that you don’t need a heated spray booth, and can paint in your home garage. Just select a reducer that matches the temperature range of the activator. Summit Racing also offers a special zero-VOC medium reducer for use in areas with strict environment compliance regulations, so check your area codes before ordering. If you live in California, this is especially important, as you could be breaking the law by painting your car yourself. However, Summit can’t ship certain products to some areas with strict environmental codes. Prior to priming, we used Summit’s wax and grease remover, though a surface wash is also available, as is a fish eye eliminator. This is more important for use when painting over existing paint that has been treated or polished with unknown chemicals, usually containing silicone. Summit also provided a painter’s... Summit also provided a painter’s coverall, and this half-mask twin cartridge respirator. Don’t be tempted to spray paint without a decent respirator; you only get one pair of lungs! As well as sourcing all our primer, basecoat, and clearcoat from Summit Racing, we also took advantage of their starter kit, as shown in our previous installment, which includes mixing cups, stirrers, masking tape and paper, paint strainers, and air filters for the spray gun. While we’re mentioning spray guns, although we used our old DeVilbiss suction feed gun for priming, we used Summit’s Pro Pack HVLP (high volume, low pressure) gravity feed guns for the basecoat and clearcoats, but more on that next time. For now we’re going to get the pickup in primer.  Summit’s own brand 2K urethane...  Summit’s own brand 2K urethane primer was used over the repaired areas and body filler. Mixed 4:1 with the universal activator, it has great high build properties, and although it’s claimed it can be block-sanded after four hours, I prefer to let high build primer cure overnight.  While I used a gravity feed...  While I used a gravity feed HVLP gun, again from Summit, who really were a one-stop source for this story, for the base and clearcoats, I used my trusty suction feed DeVilbiss for the primer coats. Applied without reducer, I sprayed four heavy coats of the urethane primer to attain a good high build. Of course the filler and metal were de-greased and blown clean of debris first.  Here’s where we left off in...  Here’s where we left off in the first installment, with the front fenders and passenger door repaired and ready for primer. The masking paper and tape came from Summit, while I already had the wheel covers. When spraying 2K paint or primer, mask or cover everything in your garage, as this type of paint stays “wet” in the air and will stick to whatever it lands on. I lined my garage, including the roof, with polythene sheets sourced from my local home improvement store, stapled to the rafters and walls.  Summit says its 2K primer...  Summit says its 2K primer can be blocked after three to four hours, I actually left it two days before sanding it with 80-grit paper. As with the filler, I used flexible long-blocks for this. Note the crosshatch pattern visible on the rattle can matte black guidecoat (arrows). Always sand this way and you won’t get grooves in the primer (or filler) from continually sanding in straight lines. Even after all the laborious sanding of the filler, there were still high and low spots in the primer. That’s where high build primer comes into its own. Don’t worry if you sand through the primer, as you’ll be priming again, though if you hit bare metal (or ’glass) and still have low spots, you probably didn’t prep the area correctly before priming.  With the steel rods removed...  With the steel rods removed from this style of block, they conform easily to the shape of the panel being sanded. Again, sand in a crosshatch pattern.  We should address the issue...  We should address the issue of filtration before we get to the paint stage. I’ve had this DeVilbiss water and particle filter stashed in a box for about 10 years, ever since I closed my body shop, so I temporarily screwed it to my workbench and connected a Harbor Freight hose reel directly to it for this paintjob. I don’t intend to paint another car in my home garage anytime soon, hence the temporary hookup. While I have a regular in-line water filter as well, this dual assembly is of sufficient quality that I could use it to breathe the air if I had an air-fed mask.  The main body of my truck...  The main body of my truck was primed using a beige 2K high build primer about a decade ago, so I merely used the black lacquer paint I’d squirted over it as a guidecoat and sanded it as I had done the front fenders. Note also the floor is masked to prevent overspray as well as to stop dust blowing up onto wet paint.  Although I tried to spot all...  Although I tried to spot all the pinholes in the filler before I primed the panels, there’s always a few that will get overlooked. A little polyester putty soon had them filled. I’ve had this 3M putty for a long time, and it cures real quickly and is super easy to sand.  The few pinholes I found were...  The few pinholes I found were sanded with 180-grit paper. Up to this point all sanding was done “dry.”  I like to remove any masking...  I like to remove any masking and re-apply at this stage, as you’d be amazed just how much dust collects on masking paper, plus there’s a chance paint can flake off the paper where it’s heavier near the edges and land in the wet paint. Though the truck is almost completely covered in primer, on a car in better condition, this would really be the “spot primer” stage, where only any repairs are primed. Next the whole vehicle will get three coats of reduced primer.  With all repairs sanded with...  With all repairs sanded with 80-grit, and everything re-masked, I used an air line to blow away any dust left from sanding off the panels, using my other (clean!) hand to wipe as I went along.  After blowing the entire car...  After blowing the entire car clean, I used Summit’s Wax and Grease Remover to clean all the panels once again. Here’s what came off just one fender.  Once all the panels were thoroughly...  Once all the panels were thoroughly degreased and dry, a tack cloth was used to remove any final particles. While this is normally associated with the topcoat stage of painting, I like to use a tack cloth before final priming as well.  These mixing cups are provided...  These mixing cups are provided in the starter kit, and have various mixing ratios marked up the sides, making it real simple to mix the primer, activator, and reducer in the correct amounts.  Finally, we get to spray the...  Finally, we get to spray the entire car in one uniform color, three coats of the same high build primer, but this time reduced by 10 percent. These thinner coats will “flow” better and produce a smooth finish, easier to sand with 400-grit wet and dry paper.  I unbolted the rear of the...  I unbolted the rear of the front fenders and spaced them away from the main body to ensure primer covered the bolt flanges, plus this way the primer, paint, or clearcoat won’t bridge the gap.  Now comes the messy part!...  Now comes the messy part! After the entire car was given a light guidecoat from a rattle can, I sanded the primer wet using 400-grit wet and dry paper on a rubber block. Do not use soap in the water at this stage, just plain water, and ensure the bucket, water, and sponge are totally clean and free of debris. Note I masked the joint between the fenders and sail panels to prevent buildup of the primer/water solution in the joint. You may be wondering why my fingers are covered in tape too. Wet-sand a whole car without doing this and your fingerprints will disappear from the constant friction between sandpaper and skin. Go further and blood will seep from your thin-skinned fingertips for a couple of days. Not fun!  A flexible rubber block can...  A flexible rubber block can be used as a squeegee to wipe the primer/water solution away to check on your progress.  I primed the doors off the...  I primed the doors off the truck. While professional body shops have dedicated panel stands for this, a couple of cheap clothes rails can be employed for occasional use. Just don’t try taking them back in the house afterward!  On large areas I use this...  On large areas I use this foam-backed plastic block to wet-sand. It uses a half sheet of paper at a time, and really ensures a smooth finish. Again, sand with a crosshatch motion.  Normally I’d re-apply a guidecoat...  Normally I’d re-apply a guidecoat and re-sand with 800-grit for a basecoat and clearcoat job, or 600 for a single-stage paintjob, but the topcoat I selected has to be applied over a black base, so it was back to the mixing table (OK, my masking paper–covered workbench) to mix a batch of black primer sealer, again from Summit Racing.  Repeating the priming process,...  Repeating the priming process, here’s where we’ll leave the truck for this installment, covered in black primer sealer. After sitting for two days to cure, this was flatted wet with 800-grit paper. Note also, I wetted down the floor of my garage to prevent dirt blowing up as I walked around the truck. This also makes final cleanup easier as the primer and paint won’t stick to the floor.
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