Body sandblasting
 

We are preparing to begin restoring a 1930 Sport Coupe. Has anyone had any experience, good and bad, with having the body sand blasted??
I have a man who says they can do it fairly quickly, with no heat build up or warping of any kind. The body is in very good shape.

Thanks!!

Bob

Re: Body sandblasting
 

I've done some sandblasting and don't like it, but sometimes you have to. Keep sand away from chassis components if possible. Once I had a shop blast a good F-1 door for me. Came back badly warped which took hours to fix.

Keep air pressure low.

Re: Body sandblasting
 

Just got one back last week that was garnet blasted. I had never heard of using the garnet before but was very pleased with it and it wasn't a whole lot more money than sand. I've also used soda before and while its gentle on the metal, doesn't seem to have good results against old bondo. I will cast my vote as using sand as least desirable. Even if he doesn't hurt the metal, it is a real chore to get all the sand out of the body. My favorite is chemical dipping.

Re: Body sandblasting
 

I don't use over 45 lbs pressure, the finest sand (around here it is #50), what plans do you have for protection from rust on the newly sandblasted metal ---I have had good results with Picklex20, it has allowed me to do body work and welding without worrying about rust returning, some blasted parts have hung inside for 5+ years without rust

Anything mechanical will get sand inside---door latches, window regulators etc ---everything should be removed, glass can be damaged from 5 feet, even sand bounced off metal can etch nearby glass ---even the gas tank should be out so nooks can be blasted, the welting will need to be replaced anyway, if the tank is taken out later the rust that is hidden will be exposed, the garnish mouldings should be off.

The first time I had a body done someone else did it ----if the person you are thinking of says they will do it in their spare time while blasting a bridge ---run away

All metal that has been blasted should be treated for rust /primed the same day even if you don't sleep that night

Re: Body sandblasting
 

My neighbor just had his 1958 Morris Minor sandblasted and it came out nice. That has to be thinner metal than the Model A. I agree with Kurt about protect the metal from rust right away, because even humid air will start bare metal rusting. The local sandblaster offers primer paint for an extra charge.

Re: Body sandblasting
 

I would ask your guy for references from others who have used him to blast, then go talk to them.

Re: Body sandblasting
 

BTW, sandblasting the body of a car while it is on the chassis with the running gear installed is nuts. You really need the body shell off the frame, on a dolly, and stripped of the interior.

On the other hand, soda is OK for anything you can hose off afterwards, except
that it does not remove rust.

Doug

Re: Body sandblasting
 

Agree with Ray -- notice the (s) on his keen use of the term "references".

Displeased customers who paid for services usually can never hold back on their inner feelings & honest opinions, & will always tell it like it is.

The type of sand & the sand blasting machine is only a small part of the project -- the sand blasting operator is the major part of the project in order to determine how carefully this Model A project will turn out in the end.

Re: Body sandblasting
 

Here are some facts to understand about the blasting process.

First and foremost, warpage is NOT caused by heat.
To get heat warpage you need to get the metal up around 500 degrees. Not going to happen when you have a blast of expanding air. Keep in mind cooling done by air conditioning is caused by expansion of a liquid to a gas.

Warpage is caused by too much energy from the sand beating against the surface of the metal. Too much energy can be caused by to much velocity of small particles or too many small particles at a slower speed. So too much pressure or too much sand in the stream are what cause damage. I equate it to hammers. If one big hammer hits your head or a box of little hammers hit your head it is going to hurt real bad.

The damage is nasty. You are causing the surface of the metal to expand. That is why it creates a bulge towards the stream. There is no good repair for this problem as you can not shrink the just the surface. If you try to shrink the surface you will shrink the full thickness of the metal and now the back side is too short and the expanded surface is normal.

So in your discussions with the blasting people you need to ask questions. If they tell you it is heat that causes the problem then they just do not understand the physics of the process. Run away. If they tell you they control the pressure and control the amount of material in the stream then you are with someone that understands the process. The pressure and quantity are dependent on the media type.

My brother and I have successfully blasted 4 cars with 40 psi and just enough sand in the stream to be seen. It took a while, but NO damage to the sheet metal. We even tried to damage a piece of thinner French metal and could not do it.

Some of the cheap syphon blasters are bad because they do not regulate the amount of media in the stream. They will be more likely to cause damage even at low pressures.

Lastly, the golden rule of blasting.
The media will go everywhere and anywhere no matter how much you think you covered or sealed it. You will astonished by the amount of stuff that still comes out even though you think you got it all out.

Re: Body sandblasting
 

Ha HA 4 cars.. I have blasted 400 cars.

Blast at night and see the sparks fly, it produces heat , although the air stream cools it too.

Think again about air pressure and sand amount.

Think more about how the panel is stressed from its original pressing as to how it could and will warp to an amateur.

You are correct about the panel bulges towards the blast, i do not understand what you say about you cannot repair this problem?

Blasting causes stretching, on a convex surface , it is quite OK, the stretching relaxes back. on a concave surface, it does not and it is buggered.

And who has 8 hours to blast a fender at 40 PSI?

Re: Body sandblasting
 

I'd rather strip and chem. Blasting is risky, but there's a lot more "safe" media to use today. I have 2 doors that are like 15X19 that were blasted in a cabinet. Not by me, and I adamantly advised against it. They're junk now, NOT repairable. Off to the coachbuilder...

Re: Body sandblasting
 

The Sparks you see are energy released as the quartz breaks and releases energy. I too have seen these sparks in the daylight.

This is not total heat energy being put into the metal. If that was so then you would NOT be able to touch the panel after you blasted it and the metal will change color. Keep in mind that heat shrinkage starts when the metal starts the blue color. You must get the whole metal into the plastic zone.

Think about the sparks you get when you press the igniter on the grill. That spark is generated by deforming quartz.

I can assure you that it does not take 8 hours to blast a fender at 40 PSI with the right equipment. It takes a day to do a full car and it is not as fast as one might like.

But hey, what could I know anyway.

Re: Body sandblasting
 

There is a professional sand blast outfit on the border of Rowan County NC, They do lots of Nascar stuff, chassis bodies everything... They did my Coupe and no distortion at all. If you read Flops posts you get an idea of how well the panels turn out. Last time I was there they had a complete 67 fastback ford mustang ready to go in and get blasted It was stripped and just a shell. I specifically asked about warping etc and he told me the only bad thing was the hood and roof ribs would leave "shadowing" as sandblasting does actually remove a little metal. I was very pleased with the stuff he did for me. Of course I brought him the pieces all striped, ie, loose quarter panels, cowl, subframe all in knock down form... I guess it depends on who you hire and if they know what they are doing?

http://www.bigrblasting.com/

Re: Body sandblasting
 

Not sure what you mean by shadowing, but I guess you mean you can see and feel the slight warpage where the ribs are under the panel.

This has not been warped and blown in from the outside.

It is stretching of the concave inner roof around the ribs and has sucked the metal in on each side of the rib where the expansion by sand hammering along with the mild heat generated has only affected the inner skin along both sides of rib.

Under the actual rib is untouched by blast or heat and so it remains original shape.
from the outside.

Concave surfaces are very risky to blast as you have to hope they relax back into shape after blast has passed over.

And never blast over any rib or thru any hole with an outside concave skin that will be hit.

Model A fenders inners are quite OK to blast as the pressing is a strong concave and inside the bonnet/hood tops are strong enough.

If I was doing a complete body.... my main concerns would be the bonnet/hood louvre edges as these are straight and an edge that can be warped easily...... the inside doors where there are holes to the outside skin, and inside the back phaeton tub , where there is a shallow concave and inner ribs.

Re: Body sandblasting
 

I had my slant window striped using Dustless Blasting that using fine glass and high pressure water. They came to the house. The door jams were OK and didn't need striping. We left the doors on and ducked taped the gaps. The hood was taken apart, all the glass was covered with heavy cardboard and bucked taped. the windshield was removed and the opening covered and taped. Removed the fenders and the running boards but not the splash pan. They were completely striped. all the wheels and motor were covered with old sheets. There was no glass dust in the car but there was some underneath that came off with my pressure washer. This guy was very good and could wright his name in the side of the car. He never got near the tape around the windows. Also, there was no problem with the louvers in the hood. I've had cars chemically stripe, sand blasted and sanded off, but this is the best yet. Go to Goggle and look up Dustless Blasting. PM me if you would like to see pictures.
John

Re: Body sandblasting
 

I used a 1" wide putty knife to demonstrate how sandblasting can deform metal. I used 90# of pressure and held my nozzle close to the knife. The blade curled right around. To restraighten it I blasted the other side.

Re: Body sandblasting
 

I would strip it first with paint remover. Then have it lightly sandblasted to remove what's left.

Re: Body sandblasting
 

my opinion on blasting is it all depends on the guy doing the blasting and if he knows / cares what he is doing .i have great success with my blaster and have never received a warped panel from him . stay away for the industrial people because they are used to blasting away on 1 inch plate . my blaster will not go crazy on a hood or decklid just a light dusting . i have 2 decklids in the shop now done by other blasters showing the exact pattern of the inner bracing . time to start shrinking !

Re: Body sandblasting
 

Flop, post a pic of one of your bootlids after you have lightly gone across it with a body file.

Do you have round indents on the outside that correspond to each inside frame hole?

Re: Body sandblasting
 

There are few methods that remove ALL the rust as well as blasting. Use common sense and it is a wonderful way to REMOVE rust.