The Stovebolt Site Forums The Shop Area Paint and Body Shop After Sandblasting

after i sand blast my frame and body parts. what should i do? i plan on Zero rusting the frame and expoy priming the rest but the sandblasting is going to take some time and i heard expoy primer should be used within a certain amount of time. should i prime the body parts with regular primer until i can get all the parts cleaned and expoy primer them all at once? does anyone know of a good expoy primer, filler, and paint that is all compatable, because i heard this could be a promlem too, compatability.

Unless you plan on doing this full time - I would only get the frame blasted. Then deal with it first and get it done. Then strip the other parts.

Don't sand blast any part of the body unless you use light weight media (small sand / low pressure) or you may warp the panels. You can blast the heck out of running boards and fenders, but door skins / cab panels / hood will all look like heck if you blast them.

Goat Rancher, I sandblasted my entire truck, frame, cab, fenders, bed and interior and I DID NOT have any problems that you mentioned. Did you ever have the same problems that you mentioned from sandblasting? This keeps coming up here and I don't think I just got lucky, just use comman sense. Get the old paint and rust off and get the hell out of there, don't linger too long at the same place. I think the problem here is TOO much preasure and TOO long at the same place if you are distorting the metal.

Go here to see pics of my finished procuct.

I had the problem with a hood - oil canned it good trying to get undercoating off the inside that the previos owner had sprayed on it. I have also looked at several Chevy trucks from '34-'36 that had hoods and doors sandblasted and they were all warped beyond saving.

A local powder coater also destroyed an electrical cabinet we sent to him to have powder coated. He sand blasted the heck out of it and the doors and sides balooned out almost like he had pressurized the enclosure from the inside.

An AD truck has lots of compound curves that hold their shape well - blasting the bed sides and top of hood would be the most likely to create problems if you got carried away at all.

Goat Rancher, right back at you again, I sandblasted the top of my hood the sides of the bed the doors you name it, like I said before,
"USE COMMAN SENSE"!!!!!

. . . tell you what, I'll help you with your spelling if you help me with my sandblasting technique.

Using too high of a pressure and too course of a sand can most certainly distort sheet metal panels that have little or no crown.

Knowing that alone can usually be enough information to help in the "use common sense" arena.

Commercial sandblasters that do frames, trailers, heavy stuff, etc., are USUALLY the people that end up hurting light sheetmetal panels because they're used to doing stuff that can handle the heat and pressure. Often, they don't readjust their setup for a sheetmetal job.

The combination of the high pressure and friction of the sand hitting the metal can cause enough heat to actually cause the metal to expand, and then with the pressure, stay distorted after cooling. Hood panels from cars from about, say, the early 60s with a frame under them are a good example. Use too high of pressure, and you'll be able to see the outline of the hood frame in the outer skin. The unsupported areas get distorted. The door skins from our '53 AD project were distorted by a commercial sandblaster when he sandblasted the INNER panel, and blew sand inside the door at the bottom where the hinge access panel had been removed. The heat from the sandblasting drew the doorskin low in the area of the access panel, causing difficult to repair damage that wasn't necessary.

Flat panels are the most susceptable to distortion, because contour helps provide strenth to the shape. A hood, roof, back of a cab, or bed sides, should all be handled with care.

A good alternative would be to have your panels media plasted. The heat generated is much less with the plastic media. Unfortunately, it is not aggressive enough to clean up anything but the lightest rust.

If you go with sand, I would suggest white silica sand #1 for flat panels, while fine brown sand would do very nicely on areas with crown. The brown sand is more aggressive, and will clean faster. It's also less expensive.

You can apply your epoxy primer directly to your sanblasted metal. If you exceed the time limits, it only means that you'll have to sand the primer before you apply anything on top of it. My advice on what to do after sandblasting is to apply "wash primer" to your clean bare metal, and then do any necessary repairs prior to epoxy. It is self etching, and will protect your clean metal from flash rusting. If you exceed the time limits on it, it is less work to reapply some more and THEN apply Epoxy primer right over it, than it is to sand the epoxy and recoat.

All products have a "window" in which they can be recoated, and they're all different depending on the paint, and the manufacturer. Choose your product line, and become familiar with their tech sheets. Modern paint materials have health related concerns, too, so make sure you understand what they are, and how to protect yourself. I've heard sad stories about people not protecting themselves while spraying paints.

It's best to stay with one product line, but not imperative. It is crucial, though, to not intermix different manufacturers products together. I use Martin Senour wash primer, epoxy primer, 2K primer, but I use PPG colors and clears.

OK, that got kinda windy. Sorry.

Tim
Stellar Antique Auto Restorations
KS
http://www.geocities.com/stellarrest/LinksPage.html

Metal Man gets an "A" for speeling.

OK - now for the REAL reason for warpage when blasting . . .

Sand blasting is a great way to remove coatings from any kind of material. In addition to removing coatings, another mechanism is at work that places the surface into compression.

A similar process that achieves the same type of compressive stresses is shot peening. This is often done to parts that will be placed in cyclical loading (compression/tension) like a piston rod. The shot peening places the outer surface of the rod in compression (thus placing the core metal in the rod in tension). This balance of forces prevents surface defects from forming a crack because the defect is kept in compression.

Any time you place a material in compression, you improve fatique life dramatically - that is why high tension cables are passed through concrete bridge structures to form pre-stressed beams.

Back to sandblasting - when the heavy sand media impacts the surface of the metal, it does not create enough heat to amount to squat. The real mechanism that is creating the warp is that the surface is placed into compression and therefore it will bow toward the sandblasting gun. This technique was used in the early days to assist in the formation of cowls and wheel pants on early aircraft except instead of using sand - they used very small steel shot.

SOooooo . . . in short - sand blasting works great to remove old paint and surface rust from stuff, but - it comes at the risk of metal deformation.

AD - you were lucky - OR - you are not as discerning as others in recognizing warped panels. My guess is that it is a combination of both. Either way, you have a great looking truck by the photos you have posted . . .

Goat Rancher, I can assure you there was no metal warping on my truck metal. There is a gage "I do not know the name of it" that can measure the amount of bondo or other filler between the paint and metal. That gage cannot find more than 1/8 of filler in my truck, except where body panels were put together at the factory, we did it on my truck. Hey, I have one of the best body men in the business and I did the blasting. He proved to me how much bondo is on the truck. Now, what can I say?

To all, about the misspellings/typos in the above posts, "I am sorry"!

Goat Rancher, thank you for the compliment on my AD!

Maybe without sandblasting your truck would have needed no bondo? Less bondo? Less work?

i got alot of information from this post. i will sandblast the entire truck if warpage does not accure and i will let you know how it comes out. thanks Tim for the info on the product line available for the primers and paint. i will be attemping this project alone and plan on finishing within two years. a frame off restoration. thanks for your help as i will be calling on it again in the near furture. does anyone sell patch panels for the front fenders you know the section closest to the ground front and back mine has some rust thru areas there. thanks again.

Why not use a "Strip-It" disk from Sunchaser Tools? These work great on panels. Faster than blasting and no warp problems. http://www.sunchasertools.com