Soda blasting a plastic model?

There's a particular brass locomotive I have my eye on at the moment, but it's painted for a railroad I don't model. This MRR Magazine thread says soda blasting works well for stripping paint from brass.

http://cs.trains.com/mrr/f/88/t/192286.aspx

I've been toying with the idea of either having it blasted with baking soda by a local company or doing the blasting myself to remove the old paint, then repainting it for a road I do model. I also have a Atlas undecorated SD35 that a previous owner painted in a rather thick and oddly shiny CNW-inspired scheme...



I removed the fuel tank and soaked it in good ol' 91% isopropyl alcohol for about 2 hours. The paint softened enough that I could take it off the larger areas with my fingernail through a nitrile glove. However, a brush did nothing to remove the paint from the nooks and crannies. I have some Testors E.L.O. somewhere that I could also try, but as I was thinking about the brass loco I had a thought: Has anyone tried soda blasting a plastic model to take off old paint, and if so, did it damage the details underneath?

Badger and Harbor Freight sell affordable media blasting guns that can use baking soda and run off of a bog-standard air compressor. I don't see the point in buying a blasting gun if I use it only once on a brass model, but if it can take the paint off of plastic models without damaging it it could pay dividends in saving time and the hassle of disposing of used chemicals.

 

while soda will remove the paint from your plastic loco as well, it may --depending on pressure -- be too aggressive for plastic material, and -soften- small details ...
plastic is quite a bit softer than brass

 

Nobody recommends making the experiment. But everybody would be interested in seeing the results if you do!

 

I have done this many times, using a simple air eraser. The only problem is that sometimes it isn't aggressive enough. A large box of baking soda from the grocery store should get the job done.

And, to state the obvious, I suggest you do it outdoors.

 

Interesting. What PSI do you normally set the air eraser to when you're working on a plastic model?

 

Whatever it takes to get the job done. I start out around 25-30, but am not afraid to go up to 50 -60 if needed. If it's thick paint like Bachman I'll even use the abrasive they sell.

You really have to work to damage the plastic. This woks to get stuff out of nooks and crannies. If you are scared start out with cornstarch.

 

And don't be afraid with Badger's abrasive on brass, it can give the brass a bit of tooth for better paint adhesion.

 

What is the humidity where you live?

I live on the Gulf Coast of Florida and I've tried baking soda many many time with an air eraser. It works.... sort of. But then it clumps. Long story of frustration.

I finally went with pure silica (sand) ground to a fine fine powder. I bought a 25 pound box off ebay. Used about half of it over the years. I love it. It NEVER clumps.

So..... many people report great results with soda. But I wonder if climate has something to do with it. For me at least, it wasn't worth it.


Also.... I agree with those who say that soda could potentially harm plastic too. It has more to do with pressure and technique. Some people use fine glass beads (I've never tried that).

At any rate, get off as much as you can with soaking techniques. Use the highest concentration alcohol you can find (have see it at 99%- but 91% is OK). Pour out old and use fresh. Scrub with a medium toothbrush. Soak some more. Scrub some more. You may get more off that you think you can.

 

Try to find someone in your area that has a Vapor Honing machine. We have one here and it makes any plastic look like new. it is a pressure water and baking soda pressure is about 45 PSI but the flow is 45 gal a min. we put in 10 lbs of soda to 40 gal of water. It works perfect.

 

To show how gentle it is, here is a photo of a Carburetor float. You can damage just by scratching it with your fingernail. It cleans the brass and the outside coating with no damage to the surface.
This is not a machine for the hobbyist it takes 3 phase power, 40 CFM of air and it was about 6K with the shipping. But it does one hell of a job.

 

it's a lot fancier than the small blasting cabinet i use for soda .....maybe takes three pounds ...
a larger one [takes truck rims] is used for sand, uses three to ten pounds of that ...

 

We got it to clean CVT clutches for Kawasaki and CanAM ATV and UTV's. It was a gamble getting it, but WOW what a job it does with NO damage to anything. You can put your hand in it and spray them and it feels just like water running on them. We do have big blast cabinets that would wipe out plastic in a few seconds. We even put plate glass in it to test it and no marks on the glass.

 

@u18b, I live in Massachusetts, so dry and cold right now, hazy hot n' humid in summer. I've messed up paint removal with liquids in the past which is why I found soda blasting to be intriguing. I'll likely need a stiffer brush for getting that thick paint on the SD35 out of the nooks and crannies.

@DASH 95, that Vapor Honing machine is a leeeetle out of my price range, but there are plenty of media blasting services in my area. I have a few buddies who are active in road racing and autocross who would likely know who has machines like that.

I'm in no rush with any of this, so I will chew on it for a bit more. Thanks for the advice, everyone!

 

I think u18b needs a moisture filter on his compressor, or perhaps use CO2 instead of air.

 

Hi Bill. I use pure bottled Nitrogen. So as dry as it can get.

Where I live on the Gulf Coast, the humidity is between 70-100% all year round.
Today it is 100%. Average annual rainfall is 65 inches- which is subtropical.

 

Looks like you're doing as well as you can do.

Were I you, I would be considering relocation.