WTF ? rust emitting gas bubbles under my bran new paint

[68 & 00 GT]

well my 68 is (I mean was) almost completely done late last week. My car used to have a vinyl roof on it, and it has been plaguing my project from the beginning. When I pulled the vinly roof off years ago the roof was completely covered in rust. I sanded, treated, and had it painted about 3-4 years ago. It was a very shotty deal at that point knowing it was all only temporary as I knew I'd be re doing it right later on. Well all that rust came back in random spots all over the roof slowly over the years. Not that I was at all surprised, but it bubbled the paint, and looked like the moons surface. The rust for the most part is not deep, and the roof is still strong. This time round a few areas around the top of the rear window were cut out, and replaced w/ new metal. The roof was sanded down treated, sanded down treated over and over. Then a filler that dried, and looked like aluminum was applied to the entire roof. Sanded out smooth, then primed, base coated, clear coated, color sanded, and buffed out. Everything looked flawless. Until... They set it out side on a hot sunny day or three, to let the paint cure / dry whatever and bubbles started forming all over under the paint. He says they dont understand why, but are preparing to strip it down to try and figure it out, and start over.

Anyway -
I talked to a buddy yesterday whose dad used to own a body shop and he asked me if they baked the car - I'm like huh ? He says the car needs to be baked to pull all the gases out of the rust, and the gases coming out are causing the bubbles. I say then why was ther not gas bubbles before only rust bubbles, he says the gases were going into the metal, and are now coming out. I never heard anything like this before. Can someone verify, or tell me what needs to be done, or what is happening so I can have them fix it right this time - Does it need to be baked ? If so how ? How long / much etc..
Any ideas / suggestions wanted.
Please help
Thanks guys -

 

[Pakrat]

OH man, that bites. I have never heard of such a thing before, sounds awfully screwy though. My only suggestion would be that you consider getting baked, it'll helop ease the pain.

 

[66 BLAKE 96]

Sorry to hear that man.

OH man, that bites. I have never heard of such a thing before, sounds awfully screwy though.

I've never heard that before either.

My only suggestion would be that you consider getting baked, it'll help ease the pain.

 

[68 & 00 GT]

lol

just want my car back really They had it since early March

 

[67CoupeDriva]

Well you don't say who is doing the body and paint work but in general, all of the products being used should be from the same manufacturer and be designed to work together as a system, and applied by someone that knows what they are doing. Otherwise there is a pretty high risk of chemicals reacting and lifting the paint. And it should always start with shiny, bare steel.

 

[68 & 00 GT]

they can't really start w/ shiny bare steel b/c it could grind my roof too thin, and the heat could also warp it.

 

[RajunCajun]

My roof had serveral holes and pitting from vinyl roof and which made the roof very thin and weak so i just used a huge fiberglass matte on the underside and applied resin fully through it worked fine for me now the roof is solid and doesnt move , still rust on top of roof but ill be getting to getting rid of that soon enough if it turns out to weak ill just cover the whole top of roof in the same matte to and do the same either way it will be strong,

just something to consider

 

[Ozsum67]

Shiney metal is really the only way to go. Why not buy a new/old top off of a Coupe and weld it on?

 

[68 & 00 GT]

I wish it were that simple. No one sells sections of roof sheet metal. To cut the roof off, and weld another one on would be about impossible to get it to line all up. From what I understand w/ my roof cut off things would shift.

 

[68 & 00 GT]

 

[6Stang7]

Well rust is the result of oxygen molecules bonding to iron, so gas will be released during the oxidation process. What did you treat the rust with? Chemically treating metal is a great way to prevent rust, since you cut off the oxygen source, so I am thinking that something wasn't done right here.

-Shaun

 

[68 & 00 GT]

I have no idea what he treated it w/. I'll call him shortly and ask. I'm going to have the PPG guy go have a look at it. Maybe one of the chemicals had a reaction w/ one another

this sucks -

 

[RajunCajun]

I wonder if it wasnt initally rust but a chemical as mentioned that bubbled the paint that sounds so much like acid bubbling the paint and then with baremetal shown it rusted so it appears as if rust was the cause

 

[mdjay]

Wow bummer buddy...

I think you could find a replacement roof, line the sucker up and eliminate this once and for all. Keep us clued in...

 

[zookeeper]

Are you positive it was caused by the old rust? I've seen tons of repainted rusty cars, and while the rust sometimes comes back, I've never heard of it emitting gas. It sounds like "solvent pop" to me. That's a condition by putting the clear on while the base is still too wet, or by putting the clear on too heavily, therefore trapping the solvents under the clear. Since solvents "gas out" while the paint dries, and it has to go somewhere, it either bursts thru the outer clear, causing a pinhole looking pit, or bubbles under the clear, looking like a rust pocket. Whatever it is, sorry to hear about it, it's gotta be frustrating.

 

[67GTA-FB429]

Have you considered making it into a convertible??

 

[fastcoupe68]

This is not caused by your rust if it occured with in a couple of days of it being painted most likely a chemical problem. the solution I suggest is to media blast the roof with aluminum oxide if there was any remaining rust. Then do an epoxy primer sealer then do your body work over top of this then prime seal and paint. No more problems

 

[Hack]

I'm really sorry to hear about this. The good thing is that you paid someone to do the work. If it's any kind of reputable shop, they will make it right for you. They should have plenty of technical resources available for figuring out where they messed up, and then making it right.

 

[3spd on floor]

is a vinyl top out the question? it would mask any imperfections in the roof. my roof has a bit of orange peel starting, and come painting time, if its rusty at all, i'm going to vinyl it.

 

[oboebrian]

If they are small moon craters/pin holes ranging from about a millimeter to 2-3 millimeters in diameter then zookeeper hit it exactly on the head with the solvent pop. Also solvent pop can come when you don't mix the paint correctly or if you have some oil still on the surface (i.e.if someone touched, breathed, or coughed near to the car). The only thing you can do is strip just the paint off and start over. make sure the painter is very conscious about the flash and dry times along with mixing the paint correctly.

Here's some articles I found on the subject:

http://www.pfonline.com/articles/109806.html

"Guide to Solvent Pop
(This guide has been adapted from "Spray Paint Defects: Their Cause and Cure"

By Gerald L. Schneberger, Ph.D., PE)
Solvent popping, or pinholes, appear when solvent evaporates so quickly from a wet film (paint) that the increasingly viscous liquid paint is unable to flow into the resulting void. Here are common causes of solvent popping:
Temperature: High oven temperatures heat wet film too quickly, causing the solvent to vaporize. Film cannot flow into resulting voids fast enough.

Solvent Blend: Too much low-boiling solvent (thinner) may cause popping during flash or upon entering the oven. Conversely, too much high-boiling solvent may result in popping near the end of the oven—when solvent boiling point is attained.

Film Thickness: Wet paint film that is too thick may cause popping because it contains too much solvent. Solvent that doesn't flash may boil in the oven, resulting in popping.

Spray Distance: Too-close spraying causes extra solvent to reach the surface. Increasing distance lets droplets lose more solvent into the air.
Flash Time/Line Speed: Increasing flash time or decreasing line speed may lower amount of popping, resulting in solvent loss before part heats up.

Air Pressure: Higher air pressure causes more solvent loss into the air. Popping may be reduced, but an undesired thin film coating can result because of greater overspray—meaning less paint is applied.

Paint Pressure: Too-low paint pressure causes small paint droplets and greater solvent loss into the air. Popping may decrease, but a thinner film may result because less paint is applied.

Air Velocity: Low air velocity can make popping occur because of slowed solvent evaporation. Too much solvent may remain in the film when entering the oven. "

From Sherwin william's website:

http://www.sherwin-automotive.com/reference/troubleshooting_guide/solvent_popping/index.cfm

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