Paint fail question?

[BamaBus]

Can moisture from an air tank cause issues with the finish spray?

[banman]

Originally Posted by BamaBus

Can moisture from an air tank cause issues with the finish spray?

Absolutely! Just assumed the OP was using an inline filter before the paintgun.

[PNW_Steve]

Originally Posted by Danjo

What kind of cloth and what was the grease remover?

Microfiber and T-shirt all fresh out of the laundry.

[PNW_Steve]

I purged my tank and added an inline air dryer/filter before I started.

[sproutroot]

Originally Posted by sproutroot

Make sure that air hose is clean. You may want to just cover it with something for this job. They get dragged through every project you use them for, so they're usually soaked with all kinds of oils and metal dust.

I'd probably even wear shoe covers to prevent contamination during the painting process.

[Danjo]

What are you using to sand? Is it a vibratory sander? Is the paper wearing out to the backing on the sander?

[ACamper]

Did you use primer ? To me it looks like it needs a primer.

[TheHubbardBus]

Maybe my eyes or the picture, but I'm having a hard time seeing how something like that could even happen out of a spray gun. Those weird random patterns look like someone took a tree branch to your paint.



Any chance contaminates could have been dropped in the paint? Or that you hadn't thoroughly mixed it?

[PNW_Steve]

Yeah, it does look like someone drug a tree branch across the paint.

It occurred primarily in three spots. Not the whole roof.

Spots that we sanded through the existing paint got primer. Some small round spots and rivet heads.

There has not been much opportunity for contamination.

It's a mystery... Now, what to do about it? I can send it and shoot it again but I have no indication that the results will be different.

[TheHubbardBus]

I don't see how you could do that twice, Steve Whatever stars aligned to make that happen likely won't the second time around. The frustration, of course, would be still not knowing what caused it.

In most cases, I think you'd want to prime the entire surface, whether it was down to metal or not, unless you know that both the old paint & new are compatible.

I've been recently warned by the gent who repaired our cap dents to never use silicone, as it interferes with paint adhesion even after being removed from old paint. He claims that even bringing it down the metal may not be enough without thorough prep. Could those strange patterns be splatter-marks from some chemical compound that at some point got dropped/splashed/applied to those areas, soaking into the old paint?

If it were me, I'd bring those spots down to metal, prep, prime & go again.

[Danjo]

To me it looks like a kid drew on it with a crayon. That’s why I think contamination on the sander. When I was sanding with my electric orbital sander I noticed that when the edges of the paper wore, the backing pad would mark the surface.

[BamaBus]

I couldn't see the pics that well on my phone but after looking again I don't think it was a liquid. It looks to skip over and on top of the rivets which would leave me to think it was something dragging or rubbing. Is this just on the top or has some paint been applied to the sides?

[dwood443]

Did you clean the surface with acetone? I’d try that in a different area

[Booyah45828]

Are you sure the sher-kem can be applied over your existing paint? It says direct to metal on the website.

If paint is retreating, typically it's from some sort of contaminant. Whether it was on the surface and your prep didn't get to it, or it was put on after the prep, or is something inside the gun.

I like the hose dragging thought. I could see that happening easily.

I know when we painted mine we ran into that issue as well. I also had to paint the roof in my socks because no amount of cleaning of my boots would get the soles clean enough not to leave a mark on the prepped surface.

To fix it. I'd sand it back to the yellow. Wipe it with paint thinner and a lint free rag, then spray it with acetone and let that air dry.

Then shoot your paint on just those spots and see what happens.

[sproutroot]

remember that perfect prep will really suck the contaminants out of your surface leaving the pores wide open. it doesn't take much to screw up this surface. if a contaminant is introduced after prep, it will be a lot more potent than if the same contaminant had been introduced beforehand. the pores will eat it up.

I agree with what others have said, sand it down to bare metal and reprep. I would tape clean rags around the air hose wherever it'll touch the roof. I think that's more practical than trying to clean it. serious painters even have dedicated hoses for painting (mostly to avoid contaminants on the inside of the hose, actually). that's not my style, but it's probably the best way to keep things clean.

I'm sorry this happened, man. for what it's worth, you don't have to fix it if you don't want to.

[PNW_Steve]

Originally Posted by TheHubbardBus

I don't see how you could do that twice, Steve Whatever stars aligned to make that happen likely won't the second time around. The frustration, of course, would be still not knowing what caused it.

In most cases, I think you'd want to prime the entire surface, whether it was down to metal or not, unless you know that both the old paint & new are compatible.

I've been recently warned by the gent who repaired our cap dents to never use silicone, as it interferes with paint adhesion even after being removed from old paint. He claims that even bringing it down the metal may not be enough without thorough prep. Could those strange patterns be splatter-marks from some chemical compound that at some point got dropped/splashed/applied to those areas, soaking into the old paint?

If it were me, I'd bring those spots down to metal, prep, prime & go again.

You are preaching to the choir I don't allow silicone within 10'of the bus.

As far as paint compatibility, I checked with SW and I am good there.

I cannot see any contamination occurring during or after my prep. There just is no opportunity where the bus is.

The alternative is that I failed to remove contamination that was preexisting. If that is the case, what to do after washing twice, dreading twice and sanding with 120grit on a DA sander?

[EastCoastCB]

I'd go for like a 220 grit. No need to go to metal if its compatible with the paint.
Its just a total pita to get ALL the surface decontaminated and keep it that way.
I say just sand the area down and wash it and rise it like hell and try again. Make sure its all bone dry before reapplying.

[sproutroot]

I just have one more question on my air hose contamination theory. I'm still assuming you were walking backwards while painting, so the air hose wouldn't have ever touched the first 3 or 4 feet that you painted. Is there any of this pattern going on in that area?

If you have no faith that the second try will work, do the first coat in small sections. 4x4, 4x8, something manageable. IF the contamination is getting introduced while painting, this will help a lot. On the other hand, if you're correct and there's something that you aren't getting off during prep - at least you didn't do the whole dang bus again.

[PNW_Steve]

Originally Posted by sproutroot

I just have one more question on my air hose contamination theory. I'm still assuming you were walking backwards while painting, so the air hose wouldn't have ever touched the first 3 or 4 feet that you painted. Is there any of this pattern going on in that area?

If you have no faith that the second try will work, do the first coat in small sections. 4x4, 4x8, something manageable. IF the contamination is getting introduced while painting, this will help a lot. On the other hand, if you're correct and there's something that you aren't getting off during prep - at least you didn't do the whole dang bus again.

Good suggestions.

But, I have already taken action. I hope it works

I took the bad spots down to bare metal. As soon as the rain stops I am going to prime the bare spots and shoot another coat of paint.

[Budbrother]

Hi Steve

I was a professional automotive paint for 20 years. You have what they call "fish-eye" That means when you washed it with a wax and grease remover you probably didn't change rags and the silicone, wax, grease worked to the edge of the cloth-making streaks of the contaminate. When you do your wipe down with a wax/grease remover you need to use a wet rag and a dry rag change up your clothes with a new one every so often, and most important you MUST use a dry cloth and dry the wiped spot don't let the solvent dry on the bus roof that's where the contaminates concentrate. Also use loads of the solvent to break the wax and grease up making sue to dry it after. To fix the problem let the coat of paint you have on it dry completely, 24 hrs. Then Scuff it (the streaks) with a fine sand paper to knock down the edges of the "fish-eye". ( Then wash again with wax and grease remover, but lightly this time with clean rags. Your first coat of paint should go really light so it dries quickly, this will bridge any residue left. Let it dry, at least 30 minutes then another light coat and again 30 to 60 minutes. Dry to the touch using the knuckle of your finger, then you can put on a thrid wet coat on for shine this should solve the problem. Happens all the time.

I don't agree with air contamination or hose dragging the look is completely different. I am confident in my analysis of the problem. I have seen it happen many times in my 20 years as a refinisher.

Cheers