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How To Block A Car Bodywork - Get It Straight
Block Sanding For The Beginner
Mar 31, 2010
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Hermosa Beach, CA
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How To Block A Car Bodywork - Get It Straight
Here are the goodies we ordered from Summit Racing. The key components to a blocking job will be the blocks. Since the body has multiple curves and various flat panel sizes, we picked up a block assortment kit made by Dura-Block. The kit features a standard, 1⁄3, 2⁄3, full size, round, and scruff blocks. Most of the time you will want the block to stay rigid and flat, but there will be a few areas that will necessitate the need for a flexible block and this assortment will fill both of those needs. For the sanding duties, we grabbed a roll of 80-, 150- and 220-grit papers to stick on the blocks and a roll of 80-grit for the dual action sander (D/A). To fill the low spots, a can of Rage by Evercoat body filler will do the trick. This lightweight body filler has great spreading and sanding properties, thus eliminating the need for cheese grating or sanding with coarse papers. We also picked up a can of guide coat and a box of 3M grinding discs just in case we unearthed some bad rust.
The first step is to assess what is under the paint, primer, sealer or whatever might be on the body when you start. A piece of 80-grit strapped to the D/A will be the best way to find out. Also, when using a D/A make sure to keep it flat to the surface and let the sander do the work; you won’t need to push down very hard. What you are trying to do is feather out scratches and chips to see what is underneath. If the fender is new and has the black E-coat, then all you need to do is scuff with 150, since we are working on old stuff we didn’t get 150
After the fender is sanded, take the paper off the D/A and hand sand all the edges. This is one area you don’t want to forget for the best results possible.
After being blown off with compressed air the fender can be primed. The primer we are using here is a high build 2K with a 2.1 VOC rating, which is the max for us here in California. At press time, all of Summit’s primers had a higher VOC rating so they couldn’t ship them into California, but now they fall into compliance. Back to the primer at hand, this stuff is designed to go over bare metal and still be a high build. It was mixed 4:1 before being poured into Vic’s DeVilbiss PRI gun with a 1.8 tip. He applied 3 heavy coats, 10 to 12-inches from the panel being sprayed with a 50-percent overlap on each stroke/pass.
While Vic was waiting for the primer to dry (two hours in our case), he cleaned his spray gun. Vic said, “Clean the gun ASAP, as the catalyzed primer only has a pot life of one hour. After that a simple clean job will turn into a scrubbing and chipping nightmare.” After the primer had dried, the area was dusted with the guide coat.
With some of the 150-grit stuck to the medium-sized block, Vic began sanding. You will want to sand diagonally at roughly a 45-degree angle between the top and bottom bodylines of the section of the panel you will tackle first. After about six swipes go the other diagonal direction again from top to bottom. This creates an X-pattern, which produces the best results and prevents the block from creating gouges.
As the guide coat comes off, high and low spots will reveal themselves like this high (on the left) and low (on the right). The idea is to sand out all of the low spots without breaking through to bare metal. If you break through to the bare metal, it’s time to add filler or get the hammer to tap the high spot down.
The guide coat will show your eyes the high and low areas, but your hand will also be a good tool to assess how bad they actually are. If you can feel it with your hand you will defiantly see it once it’s covered in shinny paint.
Here are two excellent reasons to have a good assortment of blocks. The ’65 Chevelle features a tight concave area that runs along the top of the body that the round Dura-Block is perfect for. When using the round block continue with the X-pattern but rotate the block, like twisting the throttle on a motorcycle, as you sand. There is also a concave area on the top of the fender near the windshield that was too tight for the thick block we were using on the side, so the thin block will flex enough to get into that space.
Running down the center of the fender is a bodyline that you will want nice and straight. The best way to ensure this line is perfect is to lay a piece of tape along
one side of the line—the top in our case. Make sure the tape is straight as possible as you stick it down.
Now use your block and sand up to the tape. The tape will prevent you from removing material that it’s covering. Sand until all the guide coat is removed.
Remove that tape and lay a piece along the other side of the line and repeat the process.
When you have the guide coat off, pull the tape to reveal the straight bodyline. If you can’t get all the guide coat off before you break through to bare metal, then you will need to hammer the low area of the line up or build it up with filler.
For high spots where there are no low spots next to them, you will need to use a hammer to move the metal down. Tap lightly around the perimeter of the high spot first then tap down the middle. Don’t get all macho when swinging the hammer it won’t take as much muscle as you think to move the metal this little amount.
Now it’s time to mix up some Rage to fill in the low spots. Before you pull any out of the can, slowly mix the filler. Don’t mix it aggressively; that will just produce a bunch of air bubbles. Pull out a couple of blobs that will make about a 3-inch diameter spot on a non-porous mixing board.
Kneed the Cream hardener to mix the contents before laying a 11⁄2-inch long bead on the filler. Mix in the hardener completely with a plastic spreader until the color is uniform.
Spread the filler over the low spot as smooth as you can. The more you lay filler the better you will get at it, which will save you some sanding time. As you can see Vic spread the filler well beyond the low spot, this put enough material on the panel that you can sand off to make the area flat again. The bigger the low spot the larger the overage you will need to spread. Also, if the filler starts to harden while you are spreading it, just stop and let it dry. You can always knock it down with some sandpaper and try again if need be.
Once the filler is dry (about 20-minutes) start blocking with 80-grit. Don’t put a lot of pressure on the block as you sand in the X-pattern. You are just trying to catch up with the surrounding area that was already blocked and it’s pretty easy to take off too much material.
Once you are close (you can tell by running your hand over the area), spray some more guide coat and switch to 150-grit.
It only took a few passes with the block to remove all the guide coat without breaking through to bare metal. That let us know the low spot is gone.
Now the surface is ready to be primed, guide coated, and blocked again. This final blocking will be done with 220-grit paper on the same blocks used throughout the process.
If you have followed the steps, the last round of blocking should look like this. The guide coat is gone and there are no bare spots showing. Now just repeat these steps on every body panel and you will be ready for paint. If you are planning on a single stage paint job then just spray some sealer over the 220’d finish. If you are going with a two stage (basecoat/clearcoat) then you will want to remove the 220 scratches with some 400 and then remove the 400 scratches with 500. Then you will be ready for sealer and then your basecoat.
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