Paint surface prep and flash rust test
I am new to this forum and this is my first post. I have been going crazy over the past year trying to figure out what the best products or process is to prepare sanded or blasted body parts for painting. Phosphoric acid, Metal Ready, Rust Blast, PickleX 20, POR15, Rust Mort, Zero Rust, Hold Tight 102, Chlor*rid, Hold Blast, Evaporust, Master Series, Epoxy etc, etc, etc.....
I have experimented with several of these products and understand the difference between rust converters, rust encapsulators, etch primers, surface cleaners and so on. I also understand the need for a good base to start from like blasting or DA sanding. Where I have run into trouble, as I suspect many others have is ending up with a less than clean surface after blasting.
My example is as follows. I had the stripped down frame of my 1951 Dodge M37 (Power Wagon) blasted, and boy what a job - all clean everywhere. When I picked the frame up, however, I noticed a couple of finger and palm prints on several places on the frame. By the time I had the frame back in my workshop, I had added to the contamination by my sweat dripping on to the frame on a couple of place (90 degrees in my shop with 45% humidity). Now I needed to wait until the next weekend before I could dust, prep and spray primer. By that time the contaminated spots on the frame were sporting some nice flash rust (luckily no over-all flash rust bloom, just the contaminated spots).
I expect this is a fairly common scenario, so I have decided to do an experiment to test a couple of product and processes to see how I get the best results at eliminating or removing flash rust, and where I get the best paint adhesion.
I have twelve 6 inch by 3 inch 22Ga carbon steel test panels that are fairly well rusted (as you would typically find when doing a resto) that I am treating with a combination of the surface prep solutions mentioned above. All the rusted panels will first be sand blasted on one side, and DA sanded with 220 grit on the other side. This will be the starting point for all 12 panels. From there they will be treated by the various solutions and eventually primed with Master Series Silver, and top coated with 2K Urethane from TM9ordnance (specially developed for the military restoration folks with authentic military colors). The tests will identify the development of flash rust after the blasting and application of the various surface treatments, and how / if they effect paint adhesion (via cross hatch adhesion tests)
The reason I am posting now is to get any input or suggestions from folks to see whether there is interest in such a test or whether I am flying solo. Either way I will post the results when all is said and done. The test involves storing some of the panels in the unfinished state to see if flash rust develps, so this experiment should be done in about a month or so.
I have detailed explanations of the tests, the product and the procedures here:
I am open to any ideas, suggestions or criticism to help make this a valid and worthwhile test. Let me know what you think.
(here is a pictures of my primed and painted frame)
Last edited by asstor; 05-08-2012 at 03:41 PM.
This comparative testing has been done time and time again.
There is an ASTM standard test procedure called the 'salt fog test'. What they do is take standard coupons that are a spec panel, coat the panels with what ever product and score them thru the finish to bare metal, hang them in the salt fog chamber and read them periodically to chart when rust starts developing at the scribe mark and blistering sideways.
All one has to do is then find the B-117 salt spray numbers any product is willing to publish and go from there. ZR has documented 3000 hours for probably 20 years now and believe me when I say it works better the closer to the metal it's placed. I.E. don't put a convertor under it because the converted layer of "stuff" then becomes the weak link in the chain.....
Should be an easy search function to see who publishes what for salt spray numbers. If a product can do it then published numbers should be out there.....
Since I own a 52 M-37 that I took down and repainted in 87, I will tell you to forget sandblasting. If you absolutely insist on a media blast process go to waterblasting. There is no way in hell you or anybody will completely remove every bit of media residue from a M-37 post blast.
The second reason for not blasting the M is that there are already micro porosity caverns there and they are full of rust. Blasting only peens them shut, and it's just a matter of time till they find water & air so th rust can get back to work and begin spalling the paint.
There are about 3 ways you can clean up an M, and the most cost & time efficient would be to do phosphoric acid conversion properly.
Second would be to molasses tank the M in pieces but it will take time.
Third choice would be to electroplate the rust off which might be the least costly if you have the space to do it.
As far as flash rust is concerned, let it happen. Then use phosphoric acid to convert the rust layer to a good bonding layer between iron and paint.