Inliners International Forums General Discussion Body & Paint sandblast, soda blast, ?

I'm trying to decide how best to prep my truck for paint. I've read that a course grade of sandpaper will help primer adhear to the metal surface. My question is if you sandblast to remove all the old paint do you still need to "rough up" the bare metal? How about soda blasting? I've watched a car being soda blasted and it looks to me like the way to go. But, the surface of the metal felt smooth. Whats the best way to do it?

Sand blasting can very easily warp the body if not used by an experienced mechanic. Soda blasting is gentler to the thinner metal. A little sanding wouldn't hurt, but shouldn't be necessary. It's more important to thoroughly clean the body of all dust and grease/oil for good adherence of paint.

Dear Trident;

Light machine & hand sanding is the way most cars are 'preped' for re-painting.

There are several ways/methods of blasting. They are used only in extreme conditions and should only be done professionaly as sugested.

I would get several estimates from local body shops to learn more. No one can tell anything without seeing the vehicle.

Good luck, John M....

Trident ~

If you stop and think about it the paint that is on your truck is, and has been sticking to that smooth bare metal under it for years.
All that is necessary is some light fine sanding.

If you do feel like putting some elbow grease into your prep work, do NOT use course sandpaper, use something a lot finer than course.
Or your sand marks will show through when the sun hits it just right.

Like CatDog said, the MOST important thing is CLEAN DRY surface.

If given a choice I would go with the soda-blast.
It does not heat up the metal like sand blasting does.

Soda blasting won't take off surface rust. If you are removing paint and not trying to clean up rust then soda blasting sure looks like the way to go.

Gael

Gentlemen;

This Spring I will be experimenting in rust removal using a variety of methods.

One of these will be to "blast" with walnut shells (small bits)which is said to work well on "rust buckets" or areas to bad for just sanding/chemicals etc.

I ran Body Shops for several years & will post results here or in the 12 Port News.

Happy New Year, John M.....

there are many different views on blasting vehicles for paint prep,I am and have been in the media blasting buisness for close to twenty years now, and have blasted most everything you could imagine as well as used many different medias.soda blasting is a good way to clean body parts but extremely expensive and the soda must be neutralized afterward with chemicals as it is corrosive,walnut shell is not abrasive enough to remove rust and some paints,60 grit or finer silica sand works very well in the hands of an experienced blaster.Ed,it is not heat that causes distortion of the metal as most people think,it is the peening action of the media that compresses the metal,making it harder and dense causing it to expand outward,thus warping it.Think of a ball of dough,as you press on it,it becomes flatter and thinner but gets bigger as it gets flatter,the same happens to metal when blasted,a guy who knows his stuff can keep the nozzle far enough away to take the paint and rust off without peening the metal enough to distort.always hand sand the parts afterward to remove any sand particles that become embedded in the metal,you cant see them after blasting but they will show up in the paint if you dont,and always coat with epoxy primer as metal that has been blasted becomes more porous and is vey suceptible to rust if not treated properly.If a car body is completely stripped I usually blast them inside and out for around $500.hope this helps guys.my truck was blasted,even the rear fenders which are fiberglass were blasted with 80 grit silica.

Dear Jim;

I was planing to use the walnut shells "following up" with chemicals to neutralize the rust. Then using the epoxy primer you mentioned & wait to find defects before painting.

This vehicle was stored outside in North Dakota for about 40 winters. The rust is several thousands deep & I was worried about blasting clear through with sand.

I have yet to check with 'local' sandblasters as they are construction/home type folks & here we rarely see cars rusted enough for blasting.

Good advice you posted, John M...

The effectiveness of any blast media is a function of the weight of the particle and it's shape and hardness. The energy of the particle to knock off rust or produce a surface texture (yield metal) is partly a function of its impact energy (particle weight and velocity)just like a bullet. Walnut hulls and baking soda are soft and light so they do best when used for well aged paint and surface debris that requires minimal impact energy. Rust tends to be too much for it without prolonged blast times and excessive media consumption ($$$). Abrasive grits come in a wide range of screen sizes and one of these can be used to remove whatever you have on the metal without the metal distortion if used carefully. The blaster can also select a nozzle-to-part distance and air pressure to further balance the rust removal rate and metal distortion. A qualified blaster can select the proper blast media and size, air pressure and stand off diatance to do the job correctly. And to further complicate things, you need to know the nature of your primer to properly select the final surface texture. Paint adhers two ways: mechanical adhesion and chemical adhesion. Blasting produces the mechanical "tooth" and cleanliness allow for the chemical adhesion. Epoxy primers are generally applied thicker and have higher viscosities so they will cover the higher peaks produced by coarser blast media. And coarser media have higher removal rates (cheaper job)-although higher risk of metal distortion (uh-oh). So, use a good qualified abrasive blasting contractor! It is usually worth it. Learning on your "baby" is probably gonna hurt.

Don't forget to read the tech sheets before applying your epoxy. PPG, DuPont and SPI warn about soda blasting. It's a no,no.Period. Epoxy over bare metal sanded w/ 80 to 120 grit. sandblasted surfaces gone over with red scotchbrite to remove any imbedded grit. A very popular media is Starblast. It is only available in the US and it is I believe either a 3M or Dupont product. If you do decide to do some of your own sandblasting make sure its not silca sand. It will kill you. Read your tech sheets guys. If you have a question call their tech line that is what it is there for. Your paint job is only as good as your prep and what you put under it. This is the part of your restoration you don't try to pinch a few penny's.

Mr. Morgan is correct as: "blasting" of any type can cause more harm than good.

There are chemicals in professional use today that do a far better job.

PLEASE do the research, or pay to have it done like he mentions.