Topic: How Much MEDIA do I need to buy? What kind(s)?

[67gtasanjose]

I am preparing to blast the stripped down body (shell) of my 67 Coupe, mounted on the rotisserie. Areas needing blasted at this time:
 
* Roof panel (vinyl roof car, some rusting and pitting-minor)
* Both quarter panels (3-repaints, 2 are Imron Polyurethane)
* Taillight Panel
* Rocker Panels
* Engine Bay (inside/outside/underside)
* Rear Crossmember at Tailpanel (minor  surface rusting)
* Front floorboards (inside only-some deep pitting/few  small holes)
* Cowl area (inside through cut open access panels and outside paint removal-3 coats as above)
* Door openings of Body & Lower Door Post (A-pillar) also repainted once)
* Trunk Openings including Trunk Floor and Insides of Quarter Panels and Tail Panel (also repainted once)

I will be blasting the doors, trunk deck, fenders, hood etc at a later date, so I can buy more later as needed. A bit extra now is not a problem but I do not wish to have too much extra since we have much humidity around here and might not keep well once opened.

I am just trying to find out if I need like 100 lbs of this and 60 lbs of that... What to anticipate so I have it on hand.

I have a friend who does Monument blasting/etchings and he has equipment for the blasting. I have a 100lb sandblaster tank too and have built a wand attachment for going inside of the cowl area (should help make things easier there)

HELP (advise) WANTED! Neither of us have much experience in soda blasting so we are not sure what to expect. Youtube only helps so much

Thanks, Richard

*

[bryancobb]

That question's answer depends on so many variables, it's hard to say.  How thick is the paint?  Is it greasy?  How much undercoat or sound deadener is on it?  How much rust is there?  What capacity compressor do you have?  What type blaster?  Pressure-Pot or Gravity Fed?  What's your attitude toward your budget?  Do you have a fresh-air breathing blast helmet?  Silica sand is dangerous if you don't.  If blast dust is a a problem, black magic is the least dusty.

A rough estimate of media needed would be between (75 - 100) 80# bags for a whole car.  A higher capacity compressor uses less sand and is more efficient.  We have a HUGE system at the steel fabricator I work for.  It produces 120 cuFt/min @ 130PSI.  You could lean-out the sand to air ratio and still get quick removal.  My home system only gives about 15 cuFt/min @60 PSI.  It would take 5x the sand and 10x as long for me to blast a car, and it has so much vapor in the air stream that the car would almost rust immediately. 

The best product to use if you don't mind spending the money, is aluminum oxide.  Experiment with grit-sizes and pressure, WITH YOUR BLAST EQUIPMENT so that you get the "SURFACE PROFILE" that the primer manufacturer calls for in their Product Data Sheet.  (For example, if you use PPG DP74LF Epoxy Primer, blast with a grit and pressure that results in a surface profile equivalent to hand sanding bare steel with 80-180 grit dry sandpaper.)

Then...IMMEDIATELY CLEAN AND PRIME.  Do not allow microscopic rust to "bloom."  An air compressor with a "dryer" before the compressor, and blasting when humidity is very low will give the best result.  NEVER prime bare steel when the metal's temperature is within 5 degrees F of the "dewpoint".
If you do, the evaporation of the solvents in the primer will cool the metal below the dew-point and condensation will be trapped between the primer and the steel, and the paint will fail.

The New "Big Thang" is to hire it done with Co2 blast technology.  There's no residue except the paint itself.  No media "hits" your metal.  The Co2 blast superfreezes the paint and as it warms back up (instanly) it fractures and falls off onto the ground.


http://www.custom-aerosol.com/pdf/PPG-DPLF-epoxy-primer-product-sheet.pdf
http://www.ktagage.com/Product_Press-O-Film_Replica_Tape.asp

[67gtasanjose]

That question's answer depends on so many variables, it's hard to say.  How thick is the paint?  Is it greasy?  How much undercoat or sound deadener is on it?  How much rust is there?  What capacity compressor do you have?  What type blaster?  Pressure-Pot or Gravity Fed?  What's your attitude toward your budget?  Do you have a fresh-air breathing blast helmet? 

Brian, Thanks for your rather detailed response. To remove a few variables, I will break it down, best I can.

FOR PAINT REMOVAL:

THICKNESS: Looking to try and remove just the repainted material, as much as possible trying to leave original paint or at least "hit the brakes" as we arrive at the original paint. Not trying to go all the way to metal as much as we can. Original color is a much lighter color than the THREE layers of re-paint colors. Basically, the paint thickness is very thick (I have no way of accurately measuring the thickness).

GREASY: All grease has been removed from the engine bay and floorpans. We are NOT removing paint from the bottom side of the floor. We will do repair work and touch-up or repaint the underbody original surfaces.

UNDERCOAT and SOUND DEADENER We will NOT be removing any of the Undercoat/sound deadener. San Jose built car (no undercoatings applied at factory) that spent most of it's life in a desert (dry) environment.

RUST Very little rust needs addressed. Front floor boards on the insides, a little around the windows because of the vinyl roof and a little inside of the cowl area. (I have cut access holes under front fenders to get inside of the cowl)

COMPRESSOR Commercial grade compressor will keep 120psi up at full nozzle. No problem here.

BLASTING EQUIPMENT I would need to get details here, but the "friend" who owns the equipment works daily with it in the MONUMENT business. (his compressor) I also have a 100lb pressure pot that would be capable of doing any bead-blasting of rust. Our thoughts were to adapt the friends blasting equipment for SODA BLASTING.
Friend has resperator equipment and hood needed.

MORE or OTHER Very clean engine bay that had a couple rattle can repaints. Last repaint (with engine out and fenders off) Easy-Off oven cleaner was used to strip MOST of the previous engine bay paints off, then repainting with rattle can Krylon. This should be a rather fast cleanup in the engine bay.
underside of engine bay, front structure is all clean of grease and dirt. Very minor surface rust in select areas where the factory primer/sealer was either thin or worn away. Also a light cleanup. No serious work needed there.

A rough estimate of media needed would be between (75 - 100) 80# bags for a whole car.  A higher capacity compressor uses less sand and is more efficient.  We have a HUGE system at the steel fabricator I work for.  It produces 120 cuFt/min @ 130PSI.  You could lean-out the sand to air ratio and still get quick removal. 





We should be good on the high capacity compressor, so should need "LESS", is that then about quantity of about 75 80 lb. bags of Soda? I'm not sure if this is the way to read your reply here.

I understand about the immediate rusting issue and thank you for comments on dewpoint as that is a really important point to consider when working with fresh bare metal.

Aluminum oxide might be a very nice option, though probably a bit cost prohibitive for me.

I'm starting to think if this is too much for me while still holding down a day job. I am self-employed, not making a fortune and walking a tightrope of budget and available time. I cannot CLOSE for a week to get-er-done, not that easy.

Thinking of how to do this without compromising the quality of the end product and without loosing "the farm".

Thanks so much Brian, your info is much help.

Richard

[bryancobb]

Sounds like you could probably cut my quantity in half if you use silica, based on your limited scope.

I am absolutely ignorant of soda.  No experience.

Unfortunately, there's no way to "do this right" without spending bucks, or time.  If you have lots of time and no money, you can mechanically remove the paint very cheaply but it's slow.  It does give superb results and if you do about 4 sq ft at a time, scuff with 120 sandpaper, and immediately prime that 4 sq ft patch with DP epoxy before rust bloom occurs, you can save a LOT of money.

Here's my first few sq ft I did before my helicopter project interfered with my Mustang project.  It looks like factory new sheet metal.  It took me 4 or 5 hours with a stainless cup brush on a $30 Harbor Freight grinder.

[ruppstang]

IMHO you are making a big mistake not removing all paint to bare metal especially when the car is all ready striped to a bare shell. Most paint products will not guarantee their product over another. If there ever is a problem you know the blame will fall on what was underneath. Also while the under carriage looks great for a 47 year old car it will not look that good on a newly restored car.
Just my two cents.
Marty 

[1969 Cale II]

For what it is worth, I have been doing the odd resto over the years, I am no expert, I don't run a shop even though some think I should. I have a 100lb pressure pot and I use silica sand from Menards. I only blast the curvy areas, not the flat sheetmetal. Floors, engine bay, trunk area, door jambs, etc. The flat areas warp too easy from the friction heat of the sand, but works great on all the other areas. Wear a respirator, that's super smart. Do you plan on blasting out side and letting the sand fly? You can get 2 cycles from silica, then it turns to dust. As long as it is not humid(don't if it is) you should not have trouble with rust. I have a water trap for moisture(make sure the trap is a distance from the compressor so the air can cool before the trap). It is a good idea to blast and then paint as soon as possible. I have parts that were blasted months ago and they are not rusty or painted even. I use around 500lbs of sand on a car, depending amount of surface rust.
Chris

[67gtasanjose]

IMHO you are making a big mistake not removing all paint to bare metal especially when the car is all ready striped to a bare shell. Most paint products will not guarantee their product over another. If there ever is a problem you know the blame will fall on what was underneath. Also while the under carriage looks great for a 47 year old car it will not look that good on a newly restored car.
Just my two cents.
Marty

And thanks also to everyone who has helped in this post. We are going to give the soda blasting a "try" and see how it goes. There are areas that will need a bit more than soda blasting and as I said before, I have that 100 lb blaster also. (silica or glass bead is available AND a few good respirators)

Thanks also Marty, I certainly respect your input and advice but possibly I am misunderstood here. The point I was trying to make is to STOP the BLASTING PROCESS of paint removal at the factory paint (Hitting the brakes there). There have been 3 repaints on this car. I wish to be sure and get good adhesion to the original metal or at very least, the original body color. I have always felt removal of ALL of the paint, all at once, was too much of an invitation for rust to develop before getting a sealer onto it.(due to available time) I can resume stripping, (by blasting, sanding or chemical) panel-by-panel to the bare metal and sealing each panel as I proceed. I do NOT have a whole week of dedicated time available or a few thousand dollars to throw at it to have somebody else do it for me (or I would). My largest concern, since September is here already, is that I wish to get all the repaint off SOON and to protect any of the bare metal surfaces from rusting over the winter months. It may be April before I can do anything else extensive, but my goal for this year was having all of the repainted areas stripped down, all rusty areas blasted clean, the bare metal sealed and the floor pans repaired & sealed. (any painting on the undercarrage to be done at a later date). The rotisserie is on loan, I do not know how long I can keep it at this time so my urgencies are in getting everything I can done while it is on it.

The "jury" (in my head) is still deliberating on how much I will strip the undercarrage down. The thoughts at this time are still to try and color match it and touch-up first (this year) and if not satisfied, to (possibly next year) shoot the whole floor again. The extent of undercarrage repainting will be determined after all body work is finished above the rocker pinch welds.

Richard

[hughnews1]

i alwys use Oshpo after blasting    cheap and no rusr