[shine]

to prove a point several years ago i took a cheap siphon blaster at 40 lbs and made 1 pass down the middle of a sheet of 12 ga that i had left over. 1 pass and it curled half way. i have never used sand again. it only has to happen once to wrinkle your bacon. you might as well take a hammer to it.

[oldred]

Shine, I have told about ruining my Mustang deck lid so many times I am almost embarrassed to mention it again, but since you brought up the siphon blaster---I ruined the deck lid with a pressure blaster, I mean I DESTROYED the darn thing! I was told I didn't do it right(yep, certainly right about that ) so I then used a siphon blaster at low pressure to blast the inside of the drivers door because I was told that would be the safe way to do it---I lucked out because I found a good used door after I ruined the other one using the "safe" method. It took ruining two good parts to learn my lesson but I learned well and I will never attempt to sandblast sheet metal again!

[shine]

it's one thing to gamble on your own but i work on other peoples cars. i did my research before i started. can you blast with sand? yes. can you ruin metal ? yes. will the damn stuff kill you? yes. with all the media's avalible it's just crazy to risk all the stuff that goes with sand. if 10 bucks a bag is going to break you wait till you see the price of epoxy.

[oldred]

Obviously some have managed to do this with little or no visible damage but it seems like it would be a great deal more difficult to remove rust without warpage than just to remove paint since you would almost have to displace metal in order to reach down into the rust pits. I am not saying this is the case I am just curious about it.

[texczech]

Interesting idea with the electrolysis & molasses method. My question is -do these solutions deal with the old paint that's already on the old parts? If not, how does one safely get the old paint/primer & whatever on the old parts off, in order to get down to the original metal surface? Thank You.

[mitmaks]

lots of good info here

[krusty]

i always use paint stripper it messy but very effective

[foxracer1]

So what about acid dipping? Pro vs cons? What is the aveage cost? never heard about sand blasting warping panels. Seems completely possible though. good topic guys very informative.

[Lost in NJ]

I think some people missed the idea here.

A lot of people have this concept of using sandblasting to quickly remove the paint and rust. The problem is when you crank it up to do it fast you will increase the energy per unit area.

The good old syphon blaster. Well the problem there is no control of the sand in the stream. You are getting a lot of sand coming out of the syphon blaster so of course it is going to cause damage. A lot of sand at low pressure is just as bad as a little sand at high pressure. You are transfering more energy on to the panel. Lots of little hammers moving slower is just a bad as a few moving fast.


These guys are going to use sandblasting. I think it would be more productive to tell them how to do it right.

Also keep in mind most people are going to cause a lot of distortion when they try to weld in patch panels. Every weld is a shrink point.

[baddbob]

Lost in NJ, I agree. I've done enough blasting over the years to assure it can be done successfully. Usually the blasting I do is limited to inner structure, floors, door frames, firewalls, core supports, frames, etc. But I have also done complete exteriors without problems. The key is go slow with lower pressure, keep the valve at an angle, and maintain a good distance. It's all up to the operator, anyone can warp a panel in two seconds if they are careless. There's a blaster 50 miles to the west of me that does excellent work, I've seen some high dollar iron blasted there that was done right, perfectly clean, perfect texture, and no warpage. There's another blaster 12 miles to the east of me that warps everything that goes in his shop, leaves rust, and charges twice as much. It's all up to the operator.

[Jon]

This discussion has been added to the Body - Exterior Discussions category of the Hotrodders Knowledge Base.

Related resources from the Hotrodders Knowledge Base include:

Electrolytic Rust Removal
Basic details on how to remove rust using electrolysis.

Is Metal Crystalline or Molecular?
Discusses common misconceptions in describing the supposed "molecular" structure of metal as it pertains to automotive sheet metal and metalworking.

Blast Cabinet Design and Construction
Detailed descriptions and photographs of a custom-built media blasting cabinet.

Media Blasting Sheet Metal Automotive Panels
Very detailed description of automotive media blasting. Includes information on processes, hazards, damage to sheet metal panels, abrasive media properties, and advice on choosing an abrasive and a blast process.


--For the main page of the Hotrodders Knowledge Base, click here.

--For more information on the Hotrodders Knowledge Base, click here.

--For information on becoming a Hotrodders Knowledge Base Editor, click here.

[Ultra Al]

[QUOTE=Lost in NJ]There is some very important information left out of all these posts.
What pressure, relative sand density and angle was being used in each case?

Very good point NJ. Obviously if you use Black Beauty under hi pressure you will destroy sheet metal. Ottawa silica out of a good pressure blaster with a 1/8th nozzle and a good air supply will work. I have it on pretty good authority that before beads were used the white Ottawa silica was used in cabnet blasters.I wouldn't give you a nickel for a siphon blaster. My .02. AL

[guitarboy123us]

Well having been a shop manager at a firm that started out almost 20 yrs ago plastic media stripping and aluminum oxide blasting of every thing form rust hulks to ww11 aircraft parts made out of aluminum I have to say , both the last two posters were and are correct, this is a very feasable way to remove paint filler and rust, but if you don't have alot.........ALOT!!! of experience, and don't know the quality or reputation of the shop you are considering do your blasting............find another way! There is way too much room for error and too many variables involved. Hell, even the bracing structures on the inside of panels can cause weird warping effects because of one part being rigid and one area being a "floating "surface.
Depending on your area, you could contact my old shop......and inquire about prices, these guys as I said, handle everything form aluminum bodied Cunninghams(rare british aluminum bodied, dodge hemi powered cars from the 50's and 60's)to big steel structures, they have seen it all, and this includes vettes and plastic panels from the flexible bumpers and filler panels on new cars to the frp found on most cars andtrucks today!
call U-spray inc. 262 781 8884, ask for Dean, tell him john h sent you. these guys are the best! Bar none..........and if they feel it is a bad move, they'll tell you..BEFORE the part is ruined...........very professional.

[jim..]

Quote:This thread is not a "How to sand blast", sure there are ways you "can". This thread is about WHY sandblasting will warp sheet metal.

Yes I agree with that,BUT,all of the technical reasons aside,the main reason is that most people don't do it properly or use the right media.
I've been in the sandblasting and painting biz for over fifteen years and have done dozens of cars for other people as well as my own,the trick is to use a light sand such as silica and no larger than 60 grit(even 80 or 100 grit if it will flow thru your pot).
Stay back far enough so the sand has lost enough inertia so as not to peen the metal,but still hits hard enough to wear away the paint and rust.
Removing rust is easier, as it is hard and chips away easily,paint is resilient and absorbs the energy of the sand particles and takes longer to remove increasing the likelyhood that the blaster will get impatient and move closer to speed up the process,thus damaging the metal(I've done it )
I also stay away from any large flat areas such as centersections of the doors,roof,trunk or hood,but any areas with rigid body lines can be done,and those are the hardest to hand sand anyway,around headlites,rocker panels,door posts,roof perimeter,dash,kick panels,floor,inside trunk,engine compartment etc.
Don't discount it as a fast easy way to take a car down to bare metal,just have an experienced knowledgable person do it,even a painter can screw up a car if done wrong,that doesn't mean all painting is bad.
Done right it could save hundreds of hours in labor.

My sandblast unit is portable mounted on a tandem axle peterbuit truck,4 cylinder ford deisel 200 cfm compressor,800 lb. sandstorm pressure pot,feeding an 1.5'' blast hose into a number 4 or 5 nozzle,even with an industrial size unit as this it can still be done safely.

[Da Tinman]

we don't need myth busters on this one here's the proof. this chassis got an update and was sent of to get powdercoated,, the coaters had it blasted by another shop. The steel had been in the car for 6-7 years, was skip welded to the chassis and was still very straight. The guys that did the coating had never done a chassis car before and didn't realize it wasn't supposed to look like this so they coated it. I had to remove all the warped stuff and build all new stuff, without screwing upi the powdercoating on the tubing. It had to cover all the area that were messed up grinding down the welds, and pop rivet down. Looked good when finished. But was an expensive, time consuming fix.

I realize the guy that blasted it is an absolute freakin meathead, most blasters wouldn't be this "gentle" but it can and does happen on a daily bassis,, be careful of who you trust with your stuff!!!