Surface Rust Removal From Undercarriage?

[cmholm]

Abstract: Is walnut or other "soft" blasting media fiberglass-safe when cleaning surface rust underneath? 

Mea cupla: When I bought my Avanti in Oz, it appeared free of visible rust when I crawled under the car. Driving it on salted roads maybe four times one winter in Yorkshire, UK earned me a patina of rust over most of the exposed steel. Now that I'm in Arizona, I'm not likely to make my boo-boo worse, but I'd like to get the rust off. 

Short of having someone lift the body and go to town on the chassis, I'm wondering if anyone has experience getting their car blasted with a soft media to clean things up. In the post Undercoating removal, @Stacey mentioned using walnuts and plastic beads on Corvettes back in the day.

Question: Has anyone had success blasting light rust off the bottom of their their Avanti?

[Stacey]

Plastic and walnut will remove the light surface rust, but not actually clean the metal to white clean rust free. I also used to use extremely fine glass bead at low pressure to totally remove the rust. Low pressure to us was 15 to 30psi being shot out of a 1/2 inch nozzel at high high volumn. It would kind of wash the substrait and not dig in or harm the surface material. I had a 800 cfm compressor that was able to run 4 blast hoses at once.

if your rust is light surface, using a abrasive pad of some type to remove the loose rust and then using a rust converter, navel Jelly type or POR-15 and then coating the metal would work without going through the expense of jacking the vehicle up high enough to gain a "shooting angle" and blasting the bottom. I'm in Arizona also and had thought of opening a blasting company like I had in Michigan, sure seems like there is a need for gentle cleaning of vehicles for those restoring them.   

[Stacey]

Sorry I missed you, just spent the month of Feb in Tucson at the KOA RV park sitting in the warm sun thinking I wish I had my Avanti Convertible down there with me... 

[1inxs]

You can soda blast to remove the rust, but what I prefer to use is oxalic acid in a spray bottle. The objective is to keep the surface that you are derusting wet for a continuous 15 minutes. Then you rinse thoroughly with clean  water. Follow up with a rustoleum type paint.

I purchase mine here https://www.amazon.com/gp/product/B0147IFKBY/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&psc=1

[Stacey]

Soda blasting has its own set of issues, you must wash the soda dust that has impregnated the metal with soapy water to remove that film. Otherwise the overlay of primer/paint has no bond. Years ago they were using that method of blasting to remove the paints and primers from GM, Ford & Chrylser cars. I got to reblast hundreds of vehicles to stop the peeling paintand then be repainted. The orignal blasting prices the soda guys were charging was just a tad less than what I was charging. Once the cars had issues, they all (the soda blaster companies) closed up and disappeared.Soda blasting was originally set up as a grease removing system, it worked well for that.

[1inxs]

In my near 50 years in the automotive industry, I’ve dealt with the issues of chemical stripping, sand blasting and soda blasting. Each method requires their own set of precautions to avoid a paint failure. Luckily I’ve never regretted the outcome and my customers were pleased with the results. While I suggested soda blasting as an alternative to the light surface rust the OP is experiencing, soda blasting is typically only used as a paint, primer, body filler and light surface rust removal, it’s not effective at heavier rust. For this reason I recommended the oxalic acid method for the undercarriage. It is effective at rust removal/conversion and easy to neutralize. 

[cmholm]

@Stacey, @1inxs, thanks for your responses. I think I'll start by checking for anyone in Tucson who might be able to do a soft blast, and regardless follow up with a DIY application of oxalic acid.