Sand Blasting, Body Prep, Wet Sanding, and Safety

by John Anderson

"I myself prefer to sandblast damaged areas, then Variprime them and hit the rest of the sound paint with a DA (Dual Action Sander). Prime the bus with a good sandable epoxy primer, guide coat it and then countless hours of blocking it out (this is where you and your bus really bond"

I'm no "pro" bodyman, but I do better work than most "professionals" around here. These are good, sensible suggestions in general. You want to avoid bare metal as a rule if you can--but sometimes you can't avoid it (like on the average condition crazed bus roof or if you really want to know what is under the paint, or if you feel there is too much paint on the bus).

I feel using PPG DP40, 90 (whatever color epoxy you want) after a good metal etch and conversion coat will be easily equal to what VW put on there 30 years back--so long as you had the metal as clean as VW did, and if you can coat everywhere VW did (the major failure problem). I like plastic media blasting, but the media is expensive. Check a local or regional industrial buying guide and try to find out where dealers are buying their product. Often you can buy a 200lb drum direct. I have also had very little problem warping panels with standard fine blasting sand so long as I don't dally in one spot, maintain about a 45 degree angle to the surface, and so long as you run the pot with a small nozzle and a bit lower pressure.

Sand costs $5-10 for 100 pounds, the plastic media around or in excess of $1 per pound. I run my Tip 99 at about 80-90 psi with a 7/32 nozzle, and my old DeVillbis military dual stage compressor can run it there all day long without loosing pressure. If I want a smoother finish I balance for more sand, more pot pressure, less acceleration pressure. Regarding the blocking and sanding, this is where I am right now. The windshield surround of the truck and 2 things make my life amazingly simpler. First, a foam rubber "Wonder Block (tm) by Motor Gaurd Corp": best sanding block for irregular surfaces like a bus I've ever found. I'd strongly recommend it, not for blocking flats, but because it is invaluable along the beltline, etc.

This is the third time I've used the polyester primer/surface and I can't say enough about this stuff. This is sprayable gold (in color and worth.) I'm using a gallon of product called Z-chrome Rust Defender. This stuff is amazing in what it can fill, in that it does not shrink, and it will spray over anything without lifting the substrate and it sticks. A couple warnings, spray it with a cheap gun, you need at LEAST a .070 tip, and you may want to thin it a bit with acetone. Doing this, it will go on heavy and smooth with no appreciable orange peel. I use it between two coats of DP40. It says to use it directly on bare metal, but I'm unsure since I trust the PPG epoxy beyond belief.

The Z-chrome is a savior for scratches, pinholes--all the stuff you would have used spot putty or a heavy laquer based surfacer for. You'll never worry that it will shrink back into sanding scratches. I did a large panel of the '90 a year ago with it, it is still perfect today. I pushed it to the limit: leaving bondo at 80-100 grit scratches beneath this, Z-chrome, then taking it directly to 220 dry, the second DP40 coat, and a 320 scuffing then topcoat. This stuff can save you so much time it is amazing. It's worth twice the $40 I paid for the gallon.

I'll also interject that I'm still ludicrously happy with my Sharpe gravity feed HVLP gun for my topcoat applications but I'm looking for an economical source for spare cups. My only gripe about the thing in general is the fact the cup holds much less than a quart. But I knew that going in, and I think the convenience of the gravity feed design as far as balance and size outweighs the negative. The "HVLP" functionality seems not entirely BS, there is a lot less bounce and paint goes noticeable farther. I like it better than my friends turbine which I always seem to spray overly dry.


All body work products have a little CYA litigious, US inspired warning reading something to the effect: only to be sold, mixed, applied by trained professionals using appropriate equipment etc. Now, this doesn't stop anyone round here (MD, PA, WV) from selling to anyone off the street, even with the HVLP laws that I believe are now in effect in MD. (On that issue as I said, HVLP is smart, works for you and the environment and I'm all for it.)

Although I believe that DP40 recently changed to a slightly safer formulation for heavy metal reasons, MOST ANY GOOD EPOXY OR URETHANE PRIMER OR TOPCOAT SYSTEM WILL KILL YOU DEAD. Heavy metals, and worse, isocynates, ready to do nasty things. When you buy a product get the application literature and read it. I think it is law that it is provided, I know the MSDS has to be. Face some facts: buy a respirator rated for isocynates if they still exist (haven't seen one sold since the late 80's). It was rather expensive then at $80-$100. An average organic vapor respirator from Lowes for $30 don't cut it "by the book" for most systems. I know a lot of people who use them, but technically it isn't up to it.

The literature will tell you what NIOSH, MSA level respirator is needed and will likely suggest positive pressure instead of a respirator. This is a move I made a few years back as I am inclined to respiratory problems due to my foolish involvement with fiberglass dust during my MS research years. During sandblasting you should wear at least the $30 respirator and I've moved to using a QUALITY dust mask for mere sanding. The paint still has heavy metals and creates an extreme nuisance dust with fine sanding. I recently tried the N95 rated nuisance mask, about $20 for 20 at Lowes or $5 for 2 (you figure which to buy). These are 3M 8210? masks. Much nicer than the average cheapo dust mask, fit tight, dual layer-- fit so well that your breath doesn't fog your glasses if you wear them. That gives you a good idea, and you should be wearing them (glasses) when sanding, when painting with the respirator if you don't have a half or full mask. Wear a good hood during sandblasting (I wear hooded Tyvek coveralls taped at ankles and wrists too, since I don't like sand up my orfices.)

You've got one body, make the most of it. Decide what level safety you need to afford, take responsibility for yourself. A hobby positive pressure system is about $350. Your life is worth a tad more (or maybe not?!), but a lot of cars have been painted with mere dust masks even with urethane catalysts. Decide what you need, how much you intend to do, and obviously if predisposed to respiratory problems, DON'T do it, period.

That's all well and good, except maybe you're addicted--maybe you can't stop, because it is the only thing left in life you truly enjoy. Running your hand over the freshly finished contours of a nice bus, or a nice vette, or whatever. Or perhaps you like turning a wrench, or lying in the mud under the van with antifreeze running all over you (have I mentioned recently I hate my waterboxers?), or gasoline, or motor oil?

...These things get under your skin: buy a MIG and you want a blaster, by the blaster you need a new spray gun, buy the gun and you need that positive pressure system...

Painting Tips

I don't like turbine systems. I spray at least a van every other year and do touch ups on friend's stuff at least yearly. I have lots of hobbiest friends, one of whom bought a $750 3 stage turbine about 3 years back. We all spray it too dry with way too much orange peel. Even he does 50% of the time and he has tinkered with reducers, tips, etc. And we've had lots of people try it: guys who have been hobbiest painters for years, primarily with PPG enamels and urethanes.

Something I do like: my Sharpe gravity feed SGF HVLP gun. It's the best gun I've owned period--much better than my old Binks. Goes on nice, with good gloss, and actually does have some HVLP functionality. I paid $150, which was a very good deal. But Harbor Freight sells a DeVilbiss low end HVLP for this price and I just ordered their rip off gravity feed HVLP for $49 special to spray primer. We'll see how it goes.

I note when looking at an HVLP for compressor, I'd sort of shy away from "siphon feed" HVLP guns. It doesn't make sense: they need more paint at pressure whether by gravity feed or pressure pot (the SGF comes in both of these models and a "siphon" model for $40 less.) I bought this gun on a whim, didn't expect or care anything about its HVLPness, and have been quite satisfied and amazed. It won't put all the paint on the car, but sure puts a lot more on than even a quality, older siphon gun. It's the smoothest spraying gun I've touched, and I've recently sprayed the $350 Accuspray compressor run gun--it did nothing more.

Wet Sanding

Wet sanding is either between coats or as a final treatment. The idea is to sand off all the rough "orange peel" surface from a new paint job to make a perfectly level surface. Back in the 60's, 15+ coats of nitrocellulose laquer were put into a good job, with wet sanding between every 3-5 coats. Today one typically wet sands between coats only to fix an extreme error, or between coats of different colors or different materials (2 tones, clear coats, after primer, etc.) to rough the surface and give the new top coat "tooth" to stick to. It isn't always done then and in fact should NOT be done between coats of some systems. So mainly wet sanding is at the end, when all is sprayed.

Some systems are made to go on rather dry with much sanding necessary, though most enamels and urethanes spray to a good gloss with only overspray and problem areas requiring work to build gloss. The hobbiest who doesn't do so well or the cheap pro job can be drastically improved by wet sanding. Specifically speaking, one starts with 600 grit silicone carbide wet/dry or finer paper on a softer backing block. Soak the paper in a bucket, then start sanding along contours in 1 direction only (unlike when blocking down filler with cross hatch). Do the entire car, then go to a finer 1000, then to 1500 grit. As you sand you frequently dunk your paper and block in water and use a sponge or a squirt bottle or a hose to keep rinsing off the fine sanding debris. Always keep the surface flooded and never let buildup gather on the paper (this is why you do it wet instead of dry, and you change paper frequently). To get things perfectly smooth you use a "guide coat" technique. To do this you shoot a contrasting color (say black on a red paint) compatible spray paint or the like thinly all over your freshly painted bus, like grafiti. The contrasting paint will be on the mountains and the valleys of the orange peel in the real paint. When you finally sand to the point all the contrasting paint is gone, you know you have leveled all the paint to perfectly flat.

BUT!!!! This isn't to be taken lightly: depending on how much topcoat is on the car to begin with, it is VERY, VERY easy (even for an experienced painter) to sand too far and go through into the primer or even to bare metal, particularly on edges and bends and all the contours of a VW bus. And if you do that you are in trouble. It will require extensive spot repair to remedy. This is complicated by the fact that water tends to pool with all the sanding remains along those surfaces and you don't even realize you are through until you rinse again. Smooth the flat surfaces and mentally sand on an edge or against some body feature (say 1/10 of the amount you think you sanded on the adjacent flat panel). Always use a backer of some sort (eventually you realize how to do it bare handed but until you do, you risk sanding too thin under where your fingertips press). Sometimes a backer is worse up against a sharp all gets complex.

Then you've got to ask, "What do I really want, show paint on a bus?" A late bay comes with healthy orange peel right from the factory. Do you intend to over-restore? Now most resprays will be slightly rougher, even after buffing, but not much. So for most people a light color sanding of only problem areas (runs, bugs, or really rough orange peel from overspray or the like) is what is probably sensible, followed by a good buffing. The secret to shine is mostly in the final buffing with a quality professional compound on a foam pad. This is for the final coat. For initial cutting I like a wool pad. Even a cheapy professional buffer (the $50 WEN is good value for more than a couple of cars compared to $120+ for a Milwalkee, DeWalt, etc.) is far more likely to make your car look how you want it to look: shiny, but not perfectly smooth. 50's and 60's VW paint is a bit better done and smoother than the later stuff. If you want perfection you can work for it, but be ready to pay the price. This is all largely what makes the difference between the $1000 job and the $5000+ job on your friends '67 corvette.

Wet sanding of primer and initial old material in the 220 to 400 grit wet range is commonly done as well for preparation to topcoat, seal, or prime. Wet sanding is better in many respects because the paper lasts longer, but it gets stuff wet. This is a problem if you again go to bare steel, and water isn't fun at times like winter, etc. The sludge that runs off carries a light dust to nooks and crannies of the van that can cause paint separation later. The most important thing with any job is to wash with good soap and water and then auto degreaser before you ever touch the van to even do body work. Also do this after you have everything done and are ready to put on any paint coat (i.e. before each prime, each seal, each topcoat, where you have sanded prior.) Again this is what costs money, a guy who knows what he's doing takes his time.

Don't be afraid of wet sanding your van. But realize that it is best to get the hang of it on something you put little value in (a beater) before you attack your pride and joy. Be prepared for the possibility you mess it up and be ready to deal with it. Back in high school we painted a friends '70 Blazer with car paint and brushes (!). We started at 320 and went to 1000 grit, then buffed it out and it looked...well, as good as a lot of $500 paint jobs! But it wasn't really cost effective. A final note: buy quality paper at a good paint supply store. Shop around and find who has the best prices. A foam rubber block called a "Wonder Block" is great for final sanding.

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