The Camaro Club (UK)

Its going to depend of hwat the type of paint you use and how you prefer to paint, you should get a tech sheet with it?,
With a 2k solid I normally use a 2 to 1 mix then reduce it by 10% which is fine for my guns.
To how much you should flat it depends on how thick each coat is layed down. Some peaople prefer to lay some coats down cut back with a 800 or so grit then flow coat to get an even flat coat but wouldnt advise this if your not used to painting a whole car.
As for polishing the finer you finish it the easier the scratches will come out with polishing I use a g6 then an american brand for the swirl marks. Try using a 1200 then 2000 then polish.
Oh also I prefer to polish after about 48hrs, normally no longer than a week as the paint is still a little soft its easier to work and sometimes you can heat the paint a little with the polisher at high speed to get a smoother finish. Then just rebuff when car is fitted up.

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Hi Ray, sorry I didn't reply to this sooner, but my lifes been totally manic these past couple of months & not had time to come on here very much.

Ok, reds can be a right pain in the butt, but even so, you shouldn't be experiencing the problems that you are. Reds by their very nature change colour as they darken..Period. You can also get what's known as "metamerism" with reds. The different manufacturers, use different pigments to make their own formulations to obtain a specific colour. In the manufacture process, these pigments have differing "strengths" of colour between the different manufacturers. Confused yet lol, ok have you ever seen a red car that looks to be one solid red?? Have you then seen that car under sodium street lights & you can see a difference in shade between some panels, normally looking more orange in colour?? this is metamerism, whereby the sodium lights can show that a different manufacturers paint has been applied, to that of the original (by "picking out" the different strength pigment in the mixing process).

So what has this got to do with you, you may well ask?? Well, as reds are curing the surface hardens & in doing so the pigments on the surface start to darken. Eventually, as the paint through hardens the red will become a solid colour, ie the same shade throughout its thickness. To be honest, if you stayed in there painting all day, I wouldn't have expected this sort of thing to happen. As has been said, it looks as if the surface of one layer of paint has hardened & cured fully, before the subsequent layers have "through dried".

Now I know that this paint has been on the car for some time now, so this really shouldn't be a problem. My car has between 6 & 8 coats on it, all sprayed over the period of about 6 hours & this problem didn't occur. I've never known it to happen between coats like this, it looks to me like metamerism, whereby a different paint or a different batch of the same paint has been used.

Did you use the same paint as was first put on the rest of the car?? The reason I ask is because you've not had a problem with the rest of the car have you?? Is the roof now painted with a different/new paint as opposed to the one used on the rest of the car? Did you use any of the older paint first to build up the colour & then coat over that with a new tin of paint??

If the answer to all of the above is no, then you've a problem with "pigment seperation". I've had a similar situation whereby I painted a car & when I came to flat & buff it, it came out all blotchy as soon as the fully cured surface had been broken through. That was down to there not being any "binders" added to the paint by the paint factors, but it gives the same result as you're experiencing. The reason I say "fully cured surface" is because paint, even when baked, fully cures surface first & then "through hardens afterwards" Unfortunately, people think that when a car has been baked, it's hard all the way through to the primer substrates, this is not the case. So, when you have an air dry situation like yours, the surface may be hard but the subsequent layers underneath are definately not as hard.

Pigment seperation can occur if the paint is over thinned when being sprayed on heavy. The pigments of the paint are able to "float" to the surface of the colour/paint & dry very quickly. Now you can maybe see where I was coming from ealier in this thread re metamerism. The pigments that "float" to the surface when over thinned, dry quickly & in doing so will be darker than the paint underneath it. Unfortunately, if this is the case, then even when the paint beneath the over thinned layer fully cures, it will not be as dark as the overthinned layer as the pigments have metamerised. The only cure is to repaint it I'm afraid.

As to painting over 1500 grit, I'd be inclined to hit it with some 600 or 800 as the 1500 won't give good mechanical grip to the new paint being applied. hth

cheers...Nige

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Too much power...not enough hands!!

Cheers Nige,

No worries, sorry that you're still going through electrical issues!!!
Thanks for the ideas, so most likely metamerism (sounds cool) or flash off time too much with too much thinner. A few people have advised since about it and reckon it's flash off time - i.e the lighter pigments flow to the top, the heavier to the bottom, creating a seperation of pigment. If a new coat would be applied soon enough, it would re-stimulate in a way and they would mix together apparently, but because i left it too long (about an hour thinking about it, in 30+ celsius) it must have set too far. So most likely this, as the data sheet i found says 15 minutes between coats.

Very good point about the paint - i actually did have buy a new 1 litre pot of red, same colour, same manufacturer, same shop, just took my old receipt in and asked for another litre. but maybe that could be causing it?

So far the issue has only occured on the newly painted roof, which was done 2 months ago. The rest of the car is 1 year old now, and the rear quarter didnt seem to have that issue. It was bloody hardened to sand though, couldn't imagine using 1500 on that, took 4 hours as it was I think if i respray the roof and sand it a few days later, i will use 1500 for that.

So the plan now is to hit the rest of the car with 1200 - due to it being pretty tough to sand, then if its all ok, move up to 1500 on a softer pad, then 2000 on a soft pad. If at that point everything on the car is ok, the roof will get resprayed. I wouldn't want to respray the roof and then start sanding the rest of the car to find that somewhere else has broken through after already having re-painted.

So that's the plan, still interested in thoughts, but it must be binding agents / flash off. I learnt my lesson with flash off and can fix my technique, but if its the binding agents, then thats bad news. May give you a call tomorrow Nige if you don't mind!

Found this cool article on paint issues, very useful, even has crossections of paint massively zoomed in, like the one pictured below.
http://paintrefinish.com/Paint-Defects- ... -Guide.htm
Cheers for now!

Ray

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Alritey so the update is that now that half the car is done, need to do a respray as the issue is slightly there in the rest of the paint. not as bad, very faint but still there. In researching, i found that DIY house painting has an issue known as "lapping", where the colours are different where wet paint is going over dry paint. http://www.mdrpaint.com/paint-problems/lapping.html http://www.sherwin-williams.com/pro/pro ... /index.jsp "Appearance of a denser color or increased gloss where wet and dry layers overlap during paint application."

Sounds like the issue i'm having! Also came across a car paint fault PDF from BASF which mentioned something about warping - they didnt show a clear picture but it mentioned something also about being caused from being painted too hot and incorrect flash times. So i guess that's what's caused this. Going to respray then and i have a question - can i paint over 1,000 grit scratches? Half of the car is done in 1,000, still need to flat the other half. Do i need to go back over with 600? or better to just go over 1,000 panels with a grey scotch bright?

Cheers!

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Personally, I'd go over it with 600, not only will it give it better paint adhesion properties, but it'll also be quicker & easier hth, good luck with it

cheers...Nige

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Too much power...not enough hands!!

Down to the shop we go for some 600 then

Did the fella manage to fix your pc in the end?

Cheers!

Ray

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Just a thought, could this be the paint reacting to layers beneath it? I want to it's a possibility but at the sametime, it's had about 8 layers of primers (4 primer layers, then sanded a lot, then another 4 layers of primer, sanded again) and apparently the primer also acts a sealer, so shouldn't effect the top coat. just a thought.

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Hi Ray the answer to your question is no problems with primer prep ect would show up different to what your problem i think you allready know the answer. As Nige has said flatt off with p600 /800 and away you go for round 2 unfortunatley. Make sure you get a data sheet with your paint and stick to it i would be tempted to get new activator and thinner to prevent any further probs ,keep up the good work Cheers Neil .

Cheers Neil, ye i just want to be sure. I've got one guy who is certain that without a doubt it's a reaction, but i've looked up paint reactions and they don't look like this. I even went to the paint supplier yesterday to see if it was maybe a paint fault and then said about a reaction, but they said it didn't look like a result of reaction. I tested something yesterday whhich was to sand back the rear bumper which i made from scratch from fibreglass so i know exactly what's on it and it had the same breakout, so it can't be reacting, because the rear bumper has no previous paint. the only thing in terms of reaction would be to the primer, but it's from the recomended system so i don't know.

When i showed the paint shop what had happened they were baffled too ( i was hoping they've seen it before). they kept saying that when i was sanding i may have got too far. they said "you've probably gone through" which i don't really understand. the 4 layers should be one consistent colour, and if i went through it should hit primer and that's it. They were kind enough to give me the PPG reps number so i called him today and he said he's not come across it either and said most likely i've gone through, again, don't understand what that means. They all thought 1,000 was too harsh (but the paint is pretty hard, i tried a panel with 1,200 and did take a bit longer)and recomded 1,500 (i tried 1,500 too but took forever to get rid of orange peel on an area). So the PPG rep recommends to flat it to 1,500 then machine polish and get in touch with him afterwards to see if that fixes it. I was gonna buy a machine polisher at some point anyway so moved that timeline forward and should have one here by the weekend and will try out a section. Though, i am growing fond of the matt red look

Personally i'm thinking that it's pigment seperation on 1 of 2 levels.

Option 1 - looking at it from 1 layer of paint = the pigment within the layer seperates out, so the lighter weight pigment (the darker colour) raises to the top of the layer and the heavier weight pigment (the orange) sinks to the bottom. Therefore, you don't see this seperation because it's still one conitnous layer.

Option 2- multiple layers - Either as above, multplies with each layer painted OR each layer itself is fine - 1 layer is perfect in colour mix throughout, but it's the application of a new layer that is causing the below layer to "kick up a stir" and reactivate due to the solvents. So therefore the bottom layer is now flowing and the pigments can move arround and then each layer has light bottom and dark top. sounds like a fashion show now. In other words, the bit where the 2 layers are incontact, the pigements seperates out. Almost like looking at the sea - the wave is blue but the top bit reacting with the air is white.

These seem the most logical explanations - each layer has a dark and light side, kind of like stacking jammy dodgers ontop of each other. you break away the top of the biscuit and get the jam, you break trough the jam and the get the biscuit, hence the light / dark as you keep sanding down.

So there is still one question that remains which is the all important one. Why would it be doing this? Would it be too long / short flash off? bad chemical mix i.e too much thinner or too fast hardener? maybe too many coats? they were a little shocked when i said 5 coats. they said the data sheet only say 2 as it's a high solids. I tried to explain that being an amatuer i'd need an extra layer or 2 for sanding as i don't wana break through to primer as i'm still inexperienced in flatting down and machine finsihing.

The data sheeet is below, if it's worth anything

http://www.hex.co.uk/tds/nexacv/nexav0930.pdf

So there's the predicament. I will repsray in the next few weeks while the weather is warm. (as long as it's sunny the garage will stay about 5 degrees above the outside temp) so i just need to understnad what it could be, before i go in again and waste money on more paint and more time on prep and paitning to make the same mistake again. I appreciate there's a lot of possibiluites out there as to a cause, so just trying to use logic and narrow it down as much as possible

Thanks!

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Hi Ray if you read the last paragraph of Nige,s answer i think he is dead right, over thining to long flash off time = problems.when you get your new paint hardener and thinner make sure you get plenty then if you need to repair anything in the future you have a good match with the paint thats on your car .What i do is tip all the paint (after a good mix ) into a plastic bucket and make sure you get all of the paint /pigment out of the tin then mix paint from there into a big paint mixing cup ,(one with all measures on the side )stick to the tech sheet for mixing use a fast hardener&thinner .I have also been told not to put on so many coats and ive had no problems ,you need plenty of paint on to flatt off properly P.S 1200 is ok to flat off with if you need to .PPS try not to look any further into your paint probs i think you have got some good answers and it can drive you round the bend .Cheers Neil Get cracking and keep up the good work .Just been rereading through Niges comments and it gave me a thought you say you mixed the paint by the pot full aprox (NOTHING TO DO WITH PAINT RATIOS )but would it be possible that the paint in the tin has been mixed in the tin different ly still leaving pigment to be mixed in later giving you slightly different shades to each coat?????? :crazy:Was the paint stood for any time (in the paint tin )before using.