Spraying nightmare

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ppyvabw
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Spraying nightmare

Post by ppyvabw »

I'm trying to spray the tops of my wings and the front on my MGB. I'm using cellulose, and I am working outside which is not ideal, but I have nowhere else. I haven't covered it over between coats because I thought a bit of rainwater on it was preferable to a dirty great tarpaulin over it.

I squirted the etch primer on the bare metal and fibreglass wings, then built up with yellow primer putty and sanded back until I was happy with it, then sprayed on the grey primer. For the most part it's gone on ok and looks good, but at the front, a few hours after I had sprayed it, huge cracks appeared in the grey primer. I sanded them back and resprayed, but more cracks kept appearing in different places: still only at the front. So I have set to sanding the whole lot off on the front to have another go, weather permitting.

There's only two reasons I can think why this has happened. Firstly, where I have chased the water out from any crevices with the airline, there may have been muck and grease in it, although I have tried my utmost to work as meticulously clean as possible. Or secondly, where I have sprayed the more complicated shapes around the front, too much paint has built up and cracked as it cured. I think my paint and thinners are ok, because on the wings it is absolutely fine.

Does anyone have any suggestions about what may be causing my problem, or what I can do to stop it happening. I really need to get it done before the weather gets so bad to make it absolutely impossible and before it damages the rest of it.
Last edited by ppyvabw on Sat Sep 14, 2013 11:51 pm, edited 1 time in total.



DaveEFI
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Post by DaveEFI »

Cracks are usually due to laying it on too thick, or dissolving the layer below.
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ppyvabw
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Post by ppyvabw »

DaveEFI wrote:Cracks are usually due to laying it on too thick, or dissolving the layer below.
Ought I forgo the primer putty?

chodjinn
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Post by chodjinn »

That's a shame, same thing happened to a friend on mine the other week on his mgb sebring. Bought a brand new spray gun and forgot to clean it out first, so there was minute amounts of oil in the paint. Celluose too, and he's having to hand sand it back, absolute worst nightmare for a new spray hope you get it sorted.
RIP MGB V8 .... served me well as a learning curve.

R32 Skyline V8 .... this one is gonna be a monster!

ppyvabw
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Post by ppyvabw »

chodjinn wrote:That's a shame, same thing happened to a friend on mine the other week on his mgb sebring. Bought a brand new spray gun and forgot to clean it out first, so there was minute amounts of oil in the paint. Celluose too, and he's having to hand sand it back, absolute worst nightmare for a new spray hope you get it sorted.
Cheers mate. Finished sanding back at the crack of dawn this morning and got the etch primer back on. Hopefully I'll be able to get some more done tomorrow, but to be honest though, I'm on the verge of saying f*** it, and having a body shop do it. It's impossible outside in the current conditions. It's done nothing but chuck it down today, and the next few days look no better. It'll be bubbling up and pealing off within a fortnight.

chodjinn
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Post by chodjinn »

Get the oxide/etch on and leave it unil the weather is less moist! As for spraying, I've found that 2-3 mist coats work a hell of a lot better than 1 big coat. Although saying that I've never used cellulose paints before .... will be doing when it's time to spray my MG!
RIP MGB V8 .... served me well as a learning curve.

R32 Skyline V8 .... this one is gonna be a monster!

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Post by katanaman »

Havent seen you say you have but don't sand the etch primer. It can and usually does cause reactions. Cellulose is a PITA, it reacts at the drop of a hat, cellulose is also a really aggressive solvent as well so as said if you put it on too heavy or too fast it melts your primer coats and the paint slips/cracks. Painting outside and leaving uncovered just adds to the hassle. There could be anything in the air landing so always use panel wipe between coats.

ppyvabw
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Post by ppyvabw »

katanaman wrote:Havent seen you say you have but don't sand the etch primer. It can and usually does cause reactions. Cellulose is a PITA, it reacts at the drop of a hat, cellulose is also a really aggressive solvent as well so as said if you put it on too heavy or too fast it melts your primer coats and the paint slips/cracks. Painting outside and leaving uncovered just adds to the hassle. There could be anything in the air landing so always use panel wipe between coats.
Hi Marki,

I did as it happens unwittingly wet-flat the etch primer, but I don't think that was causing my problems: for certain reasons I think it was crap primer. Anyway, I got the colour on because I've been in a rush to finish it, but it looks crap. It'll do for now though until I can either get the garage cleaned out and have a proper go at it myself next summer, or have the whole car done by someone who knows what they are doing!

DaveEFI
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Post by DaveEFI »

IMHO, cellulose is the easiest paint to spray at home. I've not used two pack due to the dangers of it without the correct safety equipment. And the cleaning out of the gun, etc, needed.

But like everything else, there are different qualities of paint. I bought some cheap plain black online, and it was rubbish. Went to a proper car paint supplier locally, paid twice as much, and got the results I expected. You can get very very good results with cellulose - after all it's what everyone including Rolls used for many years.
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