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MG MGB Technical - Cutting back colour coat - cellulose
|I've finished painting the doors , boot and bonnet of my roadster. I've cut back the top coat on the boot after three weeks and can't seem to avoid scratch marks in the paint even though I'm using plenty of water with a little detergent and progressively finer wet and dry. I get a nice even matt finish but when I compound it back the marks are still there. It's as if a bit of grit has gotten under the paper even though I am using clean water. I'm getting just a bit frustrated! I'm pretty sure the marks are not in the primer. The finish colour coat was pretty even with no sign of any marks. But not good enough to compound directly.|
Admittedley the foam pad I am using is for final polish so I need a coarser pad. What compound do I need for initial compounding?
You didn't mention what grit paper you are using. I haven't done lacquer for a long time, but I remember using it on a motorcycle in the early 70s. After multiple coats and sanding between every three coats, I sanded the final coat with 600 grit wet. Then I compounded it, and after all the work it was pretty disappointing. Then I waxed it. After waxing, it was great, and I could comb my hair in the white, let along in the black.
|C R Huff|
600 grit is what I start with. Moving up to 1200 or 1500 grit.
|Ok....started afresh. Fresh water (with a bit of detergent) new 600 grit and 1200 grit wet and dry. Rubbing down paintwork with light pressure for a few strokes. Paper has spots of paint on it which need rubbing to come off. Looks like these are the culprits. Scratch marks in paint which do not compound out (I've used a tin of rubbing compound...about the coarsest I could find instead of the G3 I have used in the past). So what am I doing wrong. Do I need to leave the paint for 6 months to harden off even more? It was 3 weeks ago that the last coat went on. I may be down to the last layer or two of topcoat now!|
Is it 1200 and 1500 that are getting paint choked? I have never used anything finer than 600. Last time I did this was for my Healey 100-6 and Triumph Tiger. At that time I had never heard of anything finer than 600. If it is the finer ones that are choking, maybe try going straight from 600 to compound.
If you are serious that you may be down to the last coat or so, maybe you need to consider shooting some more? Not what you wanted to contemplate I'm sure.
|C R Huff|
What Charley said. 1500 is unnecessary and 1200 is more than enough before compound but try stopping at 600.
It does sound like the paint is still a bit soft but it shouldn't be by now. Did you allow enough time between coat for it to flash off properly?
I used Farecla G3 compound and got a great glass like finish before wax.
|I've only done the "bolt on bits" so far (boot bonnet and doors). I shall start on the main bodywork this weekend. I just wanted to sort out the finishing before getting on to that. I allowed time between coats for flashing off (well over 30 minutes) and only painted when the temperature was over 15 degrees and humidity below 60%. I have been able to get rid of the marks by using frexh rubbing compound quite often. G3 just wasn't coarse enough. I think maybe the paint is still too soft which is perhaps why it marks easily and why the paper clogs. I shall leave the other pieces until I have finished spraying the body. That will give another few weeks to harden off. I've hung them up from the roof of my shed which gets pretty warm when the sun shines on it. Should give them a slow bake! (assuming we get some sun!). I'll stock up on fresh 600 grit paper.|
|I sprayed both my MGs in cellulose and polished in two weeks. Rub down with superfine grade paper with plenty of soap. I then machine polished with Farecla g3. Using a machine polisher and spraying the surface with water to dilute the g3. I have a mirror finish on both my cars without any problems. I suspect that if you did not spray the machine pad with water prior to polishing the car that this might be the cause of your problems|
This thread was discussed between 03/06/2014 and 10/06/2014
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