Sometimes you can't catch a freaking break. Picked up my cab from the blaster. On the way home got it in a pop up shower...(10% chance of rain my ass).... So now what?
Take it back and see if the guy will give you a quick dustover for a $100 or so............... Weathermen are basically useless if you actually think about what they say. Basically if there is no chance of any rain anywhere approaching your area, they can get that right.......usually. If the horizon (radar) shows a front approaching and there is 100% chance of rain they can get that right. Now the rest of the time they tell you there is a chance of rain and give you some phony % number. Usually their viewing area is 1,000 sq miles or more and sure enough someone in that viewing area will get rain, even if its hundreds of miles from you. Think about it, when they phrase it as "There is a % chance of rain, basically they just said " I don't know if its going to rain or not" They flash their fancy weather radar on the screen and use a lot of fancy terms........but basically they told you nothing!
Don not use products on blasted metal before primers, reblast or sand rust off, you should sand with 80 grit any how.
was it sand blasted or Dustless blasted?, if dustless they should have enough rust inhibitor mixed in the water to hold off flash rusting for 72 hours.
It appears that the OP's situation is a little like the bare panels on my Suburban that have been stripped for years, mine is/was sporadic light surface rust mostly from body oils/handling, his seems to be so light that it is more tarnished than a significant rust issue and yes heavy rust needs to be converted whereas I used Rust Mort as a light cleaner/ etching acid. Rust Mort, at least the formula (green, water like) that I've had for years is not left on to dry but only put on for fifteen/twenty minutes and neutralized with water. It is possible they have changed the formula, mandated by regulations and the like. This was done twenty five years ago and could stand a freshening up, steel wool dipped in Rust Mort has worked great for me but like I said it is not left to thoroughly dry as It does leave a thin white residue, by the way, don't do this over concrete without rinsing it off. I touched up the hood some years back due to many handlings by people that feel compelled to run their hands over bare steel. The three piece louvered hood on my roadster has also been treated with the same stuff.
Here's what I have used in similar situations... mix up a 10% solution of Ospho to alcohol. Spray a wet coat, it will dry fast. If the light surface rust disappears it will have been converted to iron phosphate which is good to paint over. It may even have a slight iridescence.
My trucks PO blasted the cab and fenders but they flashed before he sprayed a primer coat over the top. I did not want to blast again as the cab is thin enough already so I stripped it with scotch brite on my buffer/sander. whatever the method you choose, it must come back off. Might as well get to it
Deoxidene (muriatic acid) is what I'd use. Dilute with water, rub it on an area at a time and wipe over with a wet rag. Blow dry and prime.
Ospho in a spray bottle…. I have it in the garage and it comes in handy. Just don’t breathe in the spray!
They add a product called "Hold Tight" into the water that is used in the dustless blasting process. The stuff is pricey so often times there may be a "tendency" to not use the formulated ratio to accomplish 72 hours rust free. It is suppose to buy you enough time to get the panels/ body into epoxy. I like to get epoxy on the underside/ inside of the panels first, where all of the super hard sanding would be. If you have them wash it down real good with the water/ hold tight mix you can/ should prime without wiping it down ( inside of panels) . The outside of the panels/ body i hit with 80 then prime. If they screw you on the hold tight ratio you got real problems.
Blasted panels should be DA'd with 80 grit before epoxy anyway. To either lay down the rough surface or rough up a smooth surface depending on what blasting process and grit was used. DA the car. Wipe down with your choice of etch solution, neutralize per instructions, wipe down with panel prep, shoot epoxy. Yes - I know some epoxy manufacturers do not suggest acid etch products.
Personally, I would not use any type of acid. It gets into seams and is pretty tough to neutralize there. Plus you are adding even more water to rinse. Wasn't water the original issue? Just sand it (dry) and wire brush as Lloyd said and go.
Ospho. I have been using it for about 4-decades, by the instructions. I have been painting over it for just as long, and have never had a problem.
Gimpys, My primer (kirkers) recommends using their etch. It goes on with a rag or light spray. Says to let it fully dry and then wipe with pre cleaner. Is that similar to your process???
I am unsure what the chemical composition of the product you mentioned is. Do you have a link to the MSDS sheet?
No but it is phosphoric acid. I was curious if you lets the ospho dry? And then rewipe it? Or do you wipe it off while still wet? Do you apply filler over the ospho prepped surface?
Apply. Leave it to dry. Ignore it until it is time to apply primer. When that time comes, do standard prep for primer, an immediately prime.
I'm on four Decades of metal prep never had a problem. Metal prep is generally 22 /35% phosphoric acid , converters on 40% +. both usually contain at small amount of alcohol And a small amount of EB solvent which is a detergent type cleaner. I tested some epoxy over converter and it did delaminate over over a converted surface. A metal prep will clean up that little bit of rust and if you nervous wipe it down with DENATURED alcohol afterward NOT water . After that follow the directions of whatever brand of epoxy primer you using as far as pretreatment Body panels in the photographs look plenty toothy for paint to adhere to. If the product data sheet recommends grinding with 80 to 180 Grit then do it. Epoxy primers are usually used to promote adhesion When we painted cars with black lacquer we never went lower than 220 because if you did you would get sand swell marks all over the place. Well times have changed I guess.
As far as body fillers go you're better off putting it over the epoxy or urethane primer than bare metal. Production body shops put body filler On bare metal. In areas that use salt on the roads the rust will form under the body filler around the three year mark. good luck
I agree with others who are saying blasted sheetmetal really should be sanded before primer anyway, I'd pound on this with 80 grit DA pads until I'd hit everything I could hit and then wire wheel/brush the rest flat and prime. I would only resort to some of these other methods if I absolutely could not get it clean enough for whatever reason with the sanding and wire-ing.
Just grab a scotch bright pad and give it a quick bump where the rust is appearing. Dry it out good air works good for that, and prime it. Here is a thought that I am sure that most are not thinking about. Back around 1980 when the calif govt was dropping malathion to kill Mediterranean fruit flies. It was eating though paint wholesale. I helped a friend that contracted with the state to renew the paint on those cars, they had to be taken down to bare metal which we did with paint stripper then pickled the bare metal with muriatic acid. Now here is the real kicker in this process. The last thing that happened before beginning the paint job was washing the bodies with capias quantities of, wait for it, wait for it, water. yea the same damned stuff that falls from the sky. you all stress over the most minor crap.
I have to wonder about a lot of this prep work. I would think after a car is blasted and just wiped down it should be ready to paint if no bodywork is needed.