We thought we'd gotten all the rust taken care of, but after painting and striping the 48, bubbling has shown up on the roof and one door. Has anyone got a suggestion on how we can attack these areas without taking the car apart or doing a total repaint? I've been told to soda blast it and I've been told that soda won't get the rust out. I've been told to use walnut shells and also told that they will pit the glass. I've also been told to sand and grind the bad areas as much as possible and then use Por 15 as a base coat to seal the metal. Any advice would be greatly appreciated!
I would use a DA, get it back to as much clean metal as I could then seal it with resin like you use for fiberglass. feather and repaint.
You need to find out why the paint is bubbling, most often it's rust coming through from the reverse side. If so, it will need to be cut out, welded, finished and repainted.
Get it down to bare metal in those spots ( glass blasting would be ideal) and treat with phosphoric acid metal prep. I've used a prep called Ospho but there are plenty of different brands out there. Recoat with an good epoxy primer to seal. Repaint and blend bad spots. Easy to say, not so easy to do to a finished paint job. My .02. Good luck. Keep us posted. Posted using the Full Custom H.A.M.B. App!
Yep, all the above, except for Beaner's fiberglassing idea (sorry PnB). You need to blast the area, and those small isolating blasters might keep the mess to a minimum. Just grinding will still leave the "live" rust in the pits, and it may come back again. But you might also find the rust is coming through from the back side, and you will need to cut the bad sections out and replace with new metal. THIS IS WHY PEOPLE NEED TO CLEAN ALL THE RUST OFF A CAR BEFORE PAINTING! It will come back. Rust never sleeps.
Don't sweat it, it was something that I learned from Mr Roth and it has always worked for me. granted I don't own anything today that I owned 40 years ago.
Its rust that we didn't get totally out of the pits when we initially did the prep. Even though it was wire brushed and treated twice with Jasco p What are the odds that soda can get rust out of the pits as opposed to using walnuts, glass beads or something else? I really want to avoid having to take the car apart because of using a really aggreaaive media.
Soda won't clear the rust from the pits. Will not do it. If you soda blast plan on acid etching the pits and neutralizing the acid. There an on going debate on soda causing paint adhesion issues as well. I don't know how many pits you have, a spot blaster may work well, or take forever. At the minimum plan on stripping the paint on the entire roof to see what you're dealing with.
i'd use naval jelly and a small pick to scrape it once its loosened by the naval jelly until its clean
I've used rags saturated with vinegar covered with plastic for smaller area treating. Sometimes a small drill bit at high speed with at a steep work angle to bust up the crap in the bigger pits. Beaner, I've heard of the resin trick before but it was stressed to be that it be the epoxy resin. Not sure how epoxy resin differs from epoxy primer but that was from an old timer who probably isn't up on all the latest.
Guys, I'd just like to add a little info about this fiberglassing idea. Basically, fiberglass and bondo are the same chemicals. It's just that bondo has extra talc and fillers to give it body, and none of the strands to give it strength. So, if bondo still allows moisture to creep under it and rust from behind, wouldn't regular fiberglass resin do the same thing?
It certainly begs a question, but FG isn't bothered by water and talc is. I'm pretty sure I've seen FG repairs stay put while the metal rusts into oblivion from the backside & I've seen bondo bubble into golf ball proportions while the metal shows only a pin hole.
I realize the bondo is weaker with the fillers in it, and fiberglass is stronger. But they both seem to allow rust to creep under them and spread around on the metal surface. And if the moisture is coming from the backside of the metal through a pinhole of rust or a pinhole in your weld, the fiberglass or bondo will only last a short while before the bubbles appear again.
I'm not going to pretend to know what happens on the molecular level. But talc, a mineral made up mainly of the elements magnesium, silicon, and oxygen. As a powder, it absorbs moisture well and helps cut down on friction, making it useful for keeping skin dry and helping to prevent rashes. It is widely used in cosmetic products such as baby powder and adult body and facial powders, as well as in a number of other consumer products. So here's a substance that's has it's major claim to fame listed under the ability to absorb moisture, & it contains it's own oxygen. Steel oxygen and moisture = rust. I agree that FG or bondo on less than a stellar surface will eventually fail, A bondo repair on rust or pinholes might last 6 months and then the bondo rises off the surface face into bumps. A FG repair might last 6 years while the metal supporting the FG disintegrated.
any suggestion here that does not involve blasting the area to clean bare metal is incorrect. taking a shortcut has cost you once, why would you want to try another one with the risk of having to do it again a 3rd time? without seeing the damage and assuming it is indeed rust causing the bubbles sounds like the spot blasters would be the way to go.
Nope. That is why it works. Fiberglass resin is not nearly as porous as mud, perhaps because it doesn't have the extra fillers and talc added. You don't use the glass fiber just the resin and it does seal it up. I have tried it and it has worked for me, but like I said I don't own a car that I have built 40 years ago. Alchemy look at it this way, and this is just between Alchemy and me so mind your own business. If you sand a vette and paint it all is good, unless you break through the glaze then the paint gets sucked up by the glass mat. As long as the top glaze (there is another name for it) stays intact you can paint it once you break through it you are screwed. The reason that you can paint it is because it is not porous unlike the glass that is underneath.
The top coat on a fiberglass part is called gelcoat, and it's just the same resin as in the glass, but no strands, and a bit of color added. Without the strands it is probably a bit more solid, so no microscopic holes to soak up the paint. All this said, PnB and 31Vik and I have really stolen this fella's thread. I'll stick by my method: Get the metal clean to the bone, and then you have no reason to encapsulate rust. You will sleep well at night.
There is nothing wrong with your method. And thanks for the right word Gelcoat, I couldn't remember. Anyway no need to argue I apologize for the hijack (I didn't intend for it to become an argument)
i have never seen or had luck with fiberglass resin sticking to metal and was always told to put a layer of bondo on first then the fiberglass. i have also mixed resin in with the bondo [long time ago] to get the filler to a thinner, smoother, substance. blast or cut away rust, weld metal solid, fill using a quality filler [if necessary] prime, paint.
Thanks for all the info and education. We've decided soda won't be the way we go. Looking at glass beading the affected areas then covering with Por 15 and going from there.
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