Media Blasting Underframe On Car?

[Bingster]

In looking over my '47 Desoto the other day, I see it has more rusted spots than I thought.  One of the things I'd like to do is paint the underframe, but I need to remove the rust.  I've media blasted the floor pan, etc, off the car but I wonder about the wisdom of doing that for the frame while it's on the car.  Wouldn't the media get in places where it shouldn't?

 

A frame off is not in the cards, but I'd like to arrest the rust (call the sheriff!) to prolong the life of the frame.  What do you think?

[Don Coatney]

The frame has already lasted 60+ years. Just paint it and report back to us 60 years from now on how it looks.

[BigDaddyO]

P.O.R.-15 or equivalent.

[Bingster]

I understand perfectly what you're saying.  But if I was to media blast it, would it hurt anything if I masked carefully?

[Young Ed]

I think if you really want to do something get after it with a drill and a wire wheel. You'll be under there a while but it will solve the media issue. Then paint with POR15 etc

[Bingster]

Yeah, a wire wheel was my first thought.  I guess I'm gonna have to buy a two poster lift to really get under there.

[suntennis]

Media blast the underside of the car and do not sand blast. I am working on a car now that I had media blasted on all the underside with body on and the front with body and engine removed. Media blasting will remove underseal and rust but will not damage rubber. If the engine and trans are still in the car, you car protect areas that have seals by covering them with duct tape. Keep in mind that when everything is clean, someone will have to get under the car to paint or coat the raw metal to prevent rust. If you do this it will not be easy unless you can have the car a few feet off the ground. When my car was done the blaster used a chain hoist and lifted the front end of the car about 4 or 5 feet off the ground.

Edited September 1, 2014 by suntennis

[dlrides]

Wire brush/wheels or water soda blaster, anything else is asking for disaster.

[Plymouthy Adams]

suntennis, on 01 Sept 2014 - 11:43 AM, said:

Media blast the underside of the car and do not sand blast. I am working on a car now that I had media blasted on all the underside with body on and the front with body and engine removed. Media blasting will remove underseal and rust but will not damage rubber. If the engine and trans are still in the car, you car protect areas that have seals by covering them with duct tape. Keep in mind that when everything is clean, someone will have to get under the car to paint or coat the raw metal to prevent rust. If you do this it will not be easy unless you can have the car a few feet off the ground. When my car was done the blaster used a chain hoist and lifted the front end of the car about 4 or 5 feet off the ground.

Media...just refers in general to the abrasive being used in the operation..you must define it a bit better when describing the actual operation..granted most assume sand as the media but you have other forms of grit/abading substances like, glass, slag, walnut shell, soda and the list goes on..

[Plymouthy Adams]

using sand or other media is not asking for trouble...it is however a process and series of steps one must take in order to do the job effectively and will allow proper cleanup after the fact...it is not however something to just wade into unknowingly...if you were to really go on and read the full blurb on soda blasting..you will find it as every bit a hassle as any other form of media..the added after the fact steps you must accomplish makes this often not the better choice....soda would be best reserved to softer substrates like aluminum and yes fiberglass..

Edited September 1, 2014 by Plymouthy Adams

[Bingster]

So as far as an abrasive,  glass?  Walnut shells?  I just need something to get most of the major rust and not leave a big mess, although I guess anything will leave a mess.

[Plymouthy Adams]

if you are not wanting to have a mess...do not recommend an at home blasting operation....farm it out..BUT..farming out will be risky as they know only high pressure and wide open sand flow..holes and warpage is not a primary concern to most blasters..they just get the rust/paint gone..it's your baby after that...if you are wishing to do this with the door glass in, interior in place and engine in place..you going to have some very major sand problems..oh it can be done...but you have to know what you doing and how to prep the car for those operations..it is best that you do this before rebuilding the door anti rattles and such, if you have no intent to do the rebuild of the doors..you may wish to pass here..if engine is still in the car...seal it off and wrap in plastics and then wrap it in an old blanket and wet the blanket during blasting and keep it wet throughout the process and even during the removal of the blanket..double and triple layering with duct tape the cracks and such along the body, glass etc is advisable, also while blasting use of a hand held shield to protect from direct sand flow to the taped are is a plus..further..it is only the fact that you are using low pressure and low sand flow that is going to make this home operation successful..

 

I have sandblasted beneath cars with sand with no problems...here are pics of my 54 as I blasted it in the back yard.. since this car I have built a knock down portable back stop for blasting car bodies that is made for easy erection and take down and also have a dedicated sandblast building for smaller items complete with dust collection system..I add this as you need to know that the mess for blasting is very much everyhere if you are not careful

Edited September 1, 2014 by Plymouthy Adams

[Plymouthy Adams]

the basting operation as done this past Friday in the blasting building I set up...

[Bingster]

Very nice!  I've blasted parts off the car as well, and it works out great.  I may go the wire wheel route

[48Dodger]

1 • I like to use different size wire brushes with a putty knife on the end.

2 • Then go back and clean again with the wire wheel.

3 • If you need it, blast the frame with sand. Otherwise skip it. (the frame won't warp like door panel can)

4 • Use the Por-15 designed for frames ( that's all they used to have, but have grown to other products with the por-15 label)  

5 • The idea of Por-15 is to paint over the rust.....but if you get it uber clean, shoot Epoxy Primer /Single Stage color with a hardner. 

 

Now.....if you are doing this with the car all together.... skip #5 

 

These are my unpublished, totally bias thoughts and attitudes based on the dirt in my eye, callus on my eblows and the holes in my shirt.

And the ever increasing bald spot on my dome...lol

 

48D   

[Bingster]

Thanks for the info!

[Lloyd]

I sand blasted and painted at a metal fabrication plant for 7 years. A big problem we had to watch when blasting was ricochet. Some things were not meant to be blasted. Blasting the frame below the car while still attached with any media will direct the media to other parts. Like floorboards, suspension... Floorboards are thin, 16 gauge I believe and will not take the pressure the frame will. Also despite type of media you will still end up with finer articles as it hits the steel and disintegrates - sand, walnut shells, glass... You would need to really, really protect areas.

 

I would recommend wire wheel and elbow grease. Actually if you look at it there really is not that much frame to do. It could be prepped in a day, maybe two then painted.

While I had my front end off and engine trans out I went ahead and prepped the frame and suspension. First pressure washed it, used a putty knife to scrape the tough grime then pressure washed it again, then hit it with a wire wheel then used a smaller wheel on a drill. Sprayed some rust converter on it, let it sit overnight then used good old spray cans - zinc based primer and rustbond paint. I will be doing the rest of the fame the same way.