Rob H
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Registered: 28th Oct 00
Location: Staffordshire Drives: Astra SRi
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Had a go at spraying my bumper the weekend. All was going well untill the paint started to react in a couple of places, and finished with a few big patches where the paint has all bubbled  . Really have no idea what has caused it the primer/filler primer that ive used on it has never reacted at all, and i was spraying onto that. Also ive now rubbed that area down and tried spraying filler primer over it, but that reacted too .
Any ideas?  .
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Rob H
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Registered: 28th Oct 00
Location: Staffordshire Drives: Astra SRi
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Bumper before spraying
Bumper with the reacted area below the lower grille
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M333KS D
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Registered: 15th Mar 04
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if you have used any celulose basted sprays anywhere in or around your garage (like back to black etc) then the paint will react and you will struggle basically to spray it no matter what you do!!!
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Colour-Tec Coachworks
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Registered: 18th Dec 03
Location: Winners of Max Power Live 2004 - Best Bodywork of
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quote:
Originally posted by M333KS D
if you have used any celulose basted sprays anywhere in or around your garage (like back to black etc) then the paint will react and you will struggle basically to spray it no matter what you do!!!
That doesnt cause a reaction... thats causes seperation, commonly known as fish eyes.
Reactions are caused by chemical problems... a really common reaction in painting is when coats are applied to quickly. When painting anything there is a set time needed between coats... this time is called "flash off time". This is basically the time needed for the solvent in the paint to escape fully before the next coat is applied. If u apply a new coat over a coat which hasnt fully flashed off... the new coat will trap solvents underneath... they will try to escape through the new coats... causing a reaction in the paint surface. Other reactions can be caused by a mis-match in paint types and chemicals... theres millions of reasons for reactions... the only way to find out is to completely break down exactly what you did step by step from prepping the bumper for primer all the way through to the last coat of paint when the paint reacted.
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loo_goblin
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Registered: 14th Jul 04
Location: Horsham, West Sussex
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i could because of silica from synthetic oil etc in the air
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infinitycorsa
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Registered: 3rd Apr 02
Location: Stourport-on-Severn, Hereford and Worcester
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u can still borrow my compressor if u wanted rob, but you would have to fetch it m8 
looking good mind.
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Rob H
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Registered: 28th Oct 00
Location: Staffordshire Drives: Astra SRi
User status: Offline
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quote:
Originally posted by Colour-Tec Coachworks
Reactions are caused by chemical problems... a really common reaction in painting is when coats are applied to quickly. When painting anything there is a set time needed between coats... this time is called "flash off time". This is basically the time needed for the solvent in the paint to escape fully before the next coat is applied. If u apply a new coat over a coat which hasnt fully flashed off... the new coat will trap solvents underneath... they will try to escape through the new coats... causing a reaction in the paint surface. Other reactions can be caused by a mis-match in paint types and chemicals... theres millions of reasons for reactions... the only way to find out is to completely break down exactly what you did step by step from prepping the bumper for primer all the way through to the last coat of paint when the paint reacted.
This is the thing, theres nothing to my knowledge that is specific to those areas to cause the problem. Ive rubbed down the areas where it reacted, filler priimered them and that reacted too, only that reacted around the edges by where all the different layers of spray have been exposed. Think im gonna have a go at using white plastic primer and trying that, but after that, im stumped .
Tris, ive already got a compressor mate, ita bout 4 foot long, 1 foot diameter, and has got a 1.5HP motor on it, so its pretty adequate for what i need. Also im looking to buy a new spray gun as the one im using is a little too small to do the whole bumper (only got a quater litre hopper  ). Some half decent looking ones in Machine mart for about £20-30 so i think i'll invest when i get the chance to pop into one .
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G_Man
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Registered: 4th Dec 04
Location: Darlington Drives: Seat Leon Cupra R
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when my wing was sprayed it reacted, quite badly, just sanded it back to bare metal, then re sprayed it all, obv u cnt sand a bumper back to bare metal, but you know...
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1600power
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Registered: 22nd Apr 04
Location: Shropshire Drives: 1.6 16v Sport
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this sort of reaction is caused by applying fresh paint on2 something before it has properly had time to dry. Apparently its caused by the solvents in the paint underneath trying to escape but they cant and get trapped until finally the paint goes like crazy paving, trashing the fresh paint in the process.
My advice is spray the primer and leave it for at least 1hr prior to colour coating especially if its a cool day.
I do a fair bit of spraying and have seen this a few times in my own work and sure enough its normally down to me being to eager to get the colour on!
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Rob H
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Registered: 28th Oct 00
Location: Staffordshire Drives: Astra SRi
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hmmm. The primer underneath had been on for days All i'd done is spray on the colour, although we had to keep re-filling th spray gun as its too small. Being 2 pack it was drying quite quick, so maybe thats the problem? That said it still doesnt account for why the filler primer reacted .
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Greasemonkey
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Registered: 17th Apr 02
Location: Drives a Tractor
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if ya using cellulose paint with 2 pak then there is ya problem they dont mix
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jr
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Registered: 20th May 02
Location: Kent
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quote:
Originally posted by Greasemonkey
if ya using cellulose paint with 2 pak then there is ya problem they dont mix
i was considering saying this but feared for looking stupid if i was wrong
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Greasemonkey
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Registered: 17th Apr 02
Location: Drives a Tractor
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lol, im betting his filler primer is cellulose and he is spraying 2pak over the top, this you can get some sort of a stopper though to spray between the 2 otherwise the filler primer will have to come off completely, had problems with this on my old motor, i sprayed my M3's my self on got scratched in an accident and the body shop said they had a nightmare respraying it cos it was reacting with everything
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Rob H
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Registered: 28th Oct 00
Location: Staffordshire Drives: Astra SRi
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Are you sure about the 2 pack and cellulose thing? Talking to the bloke in the shop when i was buying it, 2 pack IS cellulose based anyway. I know that acrylic and cellulose is dodgy when you try and spray them together though.
What i still dont understand though, is why the paint only reacted in some parts. Look at the parts. By the time i sprayed it the bumper was pretty much covered in either Filler primer, or normal primer out of a spray can, which is cellulose based.
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austen
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Registered: 9th Jun 07
Location: midlands
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did you use an adhesion promoter?
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Steve X16XE
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Registered: 31st Dec 06
Location: Barnsley, South Yorkshire
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Check the date when this was first posted 
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austen
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Registered: 9th Jun 07
Location: midlands
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no!
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