Thoughts on media blasting of steel fenders/body

[hursst]

Hello,

   I'm seeking some opinions regarding media blasting of steel fenders/body panels.  I'm restoring a 1960 MGA and  I'm at the point where I'm chemically stripping most of the paint off (top layer tested positive for lead) and it's more convenient when it's rainy and cold.  However, most of the panels are rusty, especially on the insides of the fenders and body, although it's mostly light surface rust.  Paint stripper won't help, it needs to be media blasted.  (FYI, I hand stripped and sanded the aluminum doors, hood, and trunk).

 

   The opinion I'm seeking is how I should blast them.  I have a home blaster and use garnet sand, but my main concern is heating up and warping the panels.  I've heard this my whole life from various folks.  I also went to my favorite blaster shop and they say that it's no problem and they blast cars all the time with no warping.  I forgot ask which media they use.  I will have to have the body blasted professionally, as it's too big and time consuming to do myself with my amateur equipment.

 

   I was thinking of blasting the detached fenders at home with garnet sand, then farming out the body to the shop.  What are some opinions on whether or not I will warp my fenders if I do them at home and what are some opinions on which media should be used on the body when farmed out?  Are there any other things to consider?  Thanks!

 

-Chris

 

    

[Bhigdog]

Warping is not caused by heat. Its caused by the media actually peining and stretching the metal. The way to avoid that is never concentrate the blast in one area and always blast at an angle with as low a pressure as possible. Curved areas are fairly safe. Big flat areas need caution but are very doable with common sense......bob

Edited January 25, 2019 by Bhigdog (see edit history)

[Ben Bruce aka First Born]

 

  Media blasting is never "needed"  .  I sanded and wire wheeled mine.  And it is much larger than your car. A lot of work? Sure was. Gotter done, though.

 

  Ben

[39BuickEight]

It’s like painting.  Don’t concentrate on one spot and you’re fine.  Move evenly across the panel.  My entire car was media blasted by myself and my father in his driveway using a $500 compressor, the 5 gallon blaster that Harbor Freight sells, and Black Beauty abrasive from United Rentals.

[hursst]

Thanks for the replies.  I think I'm okay to do some sandblasting at home, then, now that I have some more information from all of you. 

 

I wire wheeled and sanded my last car, which did work, but took forever and physically destroyed me.  It took way too long and was physically exhausting.  Chemical paint stripping combined with sandblasting will be significantly faster, far less physical activity, and I do need to blast, as every portion of my car has surface rust and a few pin holes that need to be explored and a wire wheel and sanding will not get it down to perfect bare metal and remove all rust from these areas.  Also, there are many nooks, crannies and corners on this car that a wire wheel will not fit into.  Both the inside and outside surfaces of the entire body need to be stripped to bare metal.

[Ben Bruce aka First Born]

Wouldn't a body size tank full of citric acid be great?  

 

  Ben

[hursst]

I looked at having it dipped, but there's not one near me, it's too cost prohibitive.

[MochetVelo]

I really prefer to send body parts out to be stripped, as I dislike that job. That can be easy or hard, depending on where you are. Here is a mobile stripper in VA.

 

Phil

[26-25Buick]

I agree keep the nozzle moving and the the pressure down and there shouldn’t be a problem regardless of the media type. And yes there will be some heat generated, the energy from the media hitting the surface has to go somewhere but by moving the nozzle it never gets excessive. High pressure water blasting also heats the surface for exactly the same reason.

A couple of other pointers if you’re doing the blasting at home make sure you thoroughly clean all oil & grease off of the car where you’re blasting before you start. Blast cleaning will not remove it but will push it in to the surface gving you poor paint adhesion. Don’t be tempted to recycle your grit to save a few bucks either as it’ll be full of rust and old paint and the last thing you want to do is embed these contaminates back in to the surface you just cleaned. Blast shops can recycle grit as they have the equipment to remove the contaminates. Also if there is any chance there is road salt present be extra vigilant about washing before blasting.

Unfortunately even if you buy new media it’s not always clean. We’ve seen batches of “new” garnet  contaminated with clay and a Black Beauty substitute with a high salt content. Checking for clay and rubbish is an easy test. Take some media and put it in a pill bottle with some water and give it a shake and see what settles out. The water should be pretty clear after about 5 mins. Try and see what you get.

[jan arnett (2)]

Chris as Phil said send the whole thing out to be dip stripped including the fenders.  It is the only way you will get into the nooks and crannies.  Make sure the metal is thoroughly neutralized.   Be ready to prime (epoxy) the body as soon as you get it back then you can take your time with body work.

Jan

[Zimm63]

I have blasted quite a bit of sheetmetal over the years, including my MGA in the 70s.  While the MG was done by others, I use a pressure pot from Eastwood and a 5HP/60 gallon compressor now.  Echoing others, lower pressure, smaller orifice on the blaster to compensate for less air, keep an angle, and most importantly use fine material.  For sheetmetal, I use extra fine which is 000 I think.  Its been a while.

 

Even more important is get and use a high quality respirator.  Breathing the dust is bad news.  I have always worked in the open and didn't go to an air supplied hood, but would think about it if I was working in an enclosed area.  A dust mask is not good enough.  I also used a large tarp with the work in the middle to recover the sand for reuse.  It will wear out, but can be used more than once.  If you are worried about lead paint, the spent material could be toxic.  

 

Go slow, take your time, and you can get good results.  

 

 

[hursst]

Thanks again for all the pointers.  The mobile service is fairly close to me, so I may give that a try for the body in the spring, when I can primer it right after.  I tried blasting a fender today and it worked quite well.  I have been recycling the media, so I should start using fresh media for now on for the important parts.  Didn't even think about that.  I think I'll hit that fender again quickly with fresh media in case I contaminated it.

 

I blast outside only and have been using one of those "nice" 3M dust masks with the breather in the middle.  My full respirator won't fit under the blast hood I wear.  I'll have to rethink, maybe that's not good enough.

 

I tested the original paint with a lead test today and did not get any lead, so it looks like the repaint has lead, but the original paint underneath it does not.  I've been chemically stripping the repaint off as to limit any contamination.

[kings32]

I have been blasting for years many whole cars large parts . Never have seen warping . I use a large compressor { compressor size has nothing to do with warping its the pressure }  I use about 110 LBs With alarge Maco Blaster  . Have done panls on a 1916 Overland ,  1972 MGB this summer . I It is dirty job , I use a pressure fed helmet  off a second compressor . Kings32

[chistech]

I had my 32’ Olds dustless blasted (water with glass beads). It’s a woman that owns the business, she also does the blasting, and she does a great job. The time it would take me to set up my blaster, go buy the sand, blast it, clean up the area, then put everything away I can easily spend somewhere else. As far as warping I have seen this first hand and couldn’t believe it actually. I restored a 83’ Chevy blazer and I blasted the X frame sheet metal support on the backside of the hood. I DIDN’T blast the top of the hood. When we started working on the top of the hood which was rust free and without any dents, we couldn’t understand why the hood had waves in some places. We ended up figuring out what happened. While blasting the framework on the backside of the hood, the stream of blast sand that would pass by the edges of the framework was hitting the backside of the hood. When we looked at the hood at just the right angle and in the right light, you could see the waves mimicking the shape of the edges of the backside framework. I ended up using another hood as there was no way we were ever going to get that hood waveless. 

      With that said, I have a large blast cabinet and blast the majority of what I work on. Metal that isn’t rusty or rusted I use wire wheels or paint stripper. I will often give a light blast “dusting” to the pieces for better etch primer adhesion.