Hey guys, Im gonna be looking at starting prep and tackling paint on my moPar and was wondering the best way to go about prep, any input would be much appreciated thanks !! The car is very straight and rust repairs are done. The door skins are new and are only guide coating/blocking away from being ready. The quarters, roof and hood and front fenders are all super straight, clean and are painted in COB in a solid colour. I had metalled the car before so there is very little paint on the car atm and there'll be less when I take off the clear coats. My plan is to take the clear off the car down to the base coat using a DA and dry sanding. I may repaint/clear in the same colour but there may be a colour change, have'nt decided as yet. My questions are as follows : i. what grit do I start with on the DA? Should I use a long sanding board on the clear ? ii. what grit do I finish with to have a primer ready surface? iii. what is the next best step; reprime over the sanded base coat OR seal first, then reprime? I need a systematic, logical process to follow with regards to what tools, paper and approach would be best. Or is all the above bullshit and there is a better /faster/more professional way to go about this ? Havent painted a car for some time and things have changed. Any input would be a great help guys thanx !! Rat
If you use a DA, plan to re-prime and block the whole thing unless you're really good, disciplined, and have a really nice machine. The garden variety DA has more than just an oscillating action, the pad also wobbles up and down. Ever notice how one side of the paper gets more worn than the other? Dynabrades are exempt from that, but then that natural reaction to "edge out" problem areas comes into play. That's the discipline part of it. If you don't re-prime/block it's probably going to look like those cars you see that are so friendly every panel waves back at you I must say I'm a bit unclear as to what's exactly on it right now, not hip to "COB", but if you're repairing and going to the same color, and those areas are nice, yes you might want to seal and do a light prime with a quick block out and refinish to match. Overall, my best advice is to make every effort to keep film build to a minimum. Thick finishes don't last, they chip and crack easy, makes the car look "plastic" with cellulite that you can't remove no matter how hard you try. If you do seal, use near the whole "window" of no-sand time. Let it set as long as you dare before coating so it does the job it's intended to do, prevent excess solvent penetration. That's a few basics. If you can flop a pic or 2 up I'd be happy to get more specific later, but that might be REALLY later for you bein on the other side the world.
X's 2. more is NOT better in this case Use one vendor for all your prime/fill products. If done right any color coat should stick. Everyone has a favorite. I happen to like SPI http://www.southernpolyurethanes.com/. Great customer service - someone actually answers the phone. Read this before you start: http://www.southernpolyurethanes.com/perfect paint.htm
yes MORE is not better .One my first 6 timesresto I must have primed n reblocked 6 times the result was chipped door edges deck lid edges.Don't Da hand block with a 150 grit.higher grits just remove scratches.I like 150 reprime 3 coats wet block 400.paint.
Rat, I got back into a paint job after 25 years out of the loop. Just a few changes! Face and complete skin protection, yes. Peel away clear lenses on your mask, yes. Positive air supply, no question. The urethanes lay down nicely, if you do go w/a color coat, followed by clear. I rec. that you detail/sand all edges, reveal ends, places that once the gloss dries back, will show any prep 'holidays'. I'd use a regular block, over along board, unless you are trying flatten or contour a shape into form. In the final spray, do not re-visit the work till the next day! The fume retains it's strength for some time. Pimpin and Earl have some good tips in other threads.
I would definitely recommend not using a DA. I just finished building a 71 torino and had a similar issue. I stripped the entire front clip, doors, jambs, valances fender and quarter extensions, mirrors trunk lid and drip rails to bare metal. However on the quarters and roof I blocked the old finish with a long block with 80 grit then switch to 180 grit even though it was straight. 1 light to medium coat of sealer then 3 coats of primer. Guidecoat and Block with a long block with 320 dry then finish out with 600 wet on soft block or 800 wet if you're spraying waterborne base. With this process I ended up with 7 to 8 mils thickness. Factory on new cars is 4 to 6 mils. Posted using the Full Custom H.A.M.B. App!
I never prime or paint anything that has been sanded with less than 320 grit (will show sand scratches) and never jump more than 100 grit between papers for the same reason. I also don't put clear over anything that's been hit with less than 600 wet. Also, not a bad idea to use wax and grease remover before sanding anything. Apply wet, and wipe it off wet. And I would use a foam hand block for all the sanding in an alternating figure 8 motion.
There is nothing wrong with using a da if you 1: have a good da and pad. 2: don't run it at 10,000 rpm. 3: keep it flat.
It is a little silly unless you want to end up with 15 mils of paint and primer and end up with chipped edges. And just my personal preference.
COB=clear over base... You sound clued up already so heres a refresher for everyone. If using 2 pack products at home it can be difficult without having a bake oven or at least few infrared heat lamps, I wouldn't wet sand as primer is porous to aid adhesion of the paint which is less so (hence waxing paint, fill the microscopic pores to stop water breaking it down) and wet sanding can drive moisture into the pores causing adhesion problems later on, ever seen them tiny bubbles under old laquor paint jobs? Well lacquer clogs sandpaper because it dries by solvent evaporation so it never gets really hard which is why it's wet sanded, no need to with 2 pack... If you want it to look good and straight and dont wanna bare metal it yes still key the whole panel for primer and prime the whole thing dont spot prime it and If you wanna keep the car I usually get it to steel, metal finish it deoxidine it then either epoxyurethane or dp40 it and put a coat of surfacer on to key for filler, then if it needs bog or a skin of filler key the primer with 80 grit on your DA, I reckon if you put bog over the steel and put your hands all over it to feel if it's straight you're introducing moisture that can turn to rust under your repairs later on, unless you use gloves, and body fillers nowadays have good enough adhesion over primers..the reason people grind the paint off before using fillers is a throw back from when enamels and lacquer were used and if you didn't get the paint off the thinner in the new layers of primer etc would re activate the paint and cause it to fry up around the repair making them unsightly rings some of you guys would have seen... Anyway... Do your body fillering if you need it, then finish it to 150-180 grit, all over the panel, that'll key up the rest of the primer and sand out any coarse scratches in the filler, you can use a DA for this and over your filler but use an interface pad, it's a 1/4" thick foam pad that goes between your hook it and the DA.. And like is mentioned above get a variable speed one and use it sorta turned up maybe between 1/4 and 1/2 way not on full tit, Then 3 coats of primer filler OR spray bog, then if you want it straigh as a die block it with 180 grit then 3 coats primer surfacer which is mixed at a thinner ratio, then block with 240 grit then go over with your DA with your interface pad and some 400 grit dry, you can go over this with base coat and wont get sand scratches or sink back...Be sure to guide coat between every sanding stage, and use your shop vac attached to the sander.. Don't be tempted to use accelerators in the harder or more harder as this will mean free isocyanates that have no paint particles to cross link with and it'll stay soft and take longer to dry, and if you over harden paint it can end up greasy as they evaporate to the surface... If you're using a supplied air respirator make sure your compressor has a good moisture trap etc as you should anyway because you don't wanna breath that crap in, and make sure your carbon filter in the respirator is good too, you CAN use a cartridge filled respirator as long as you keep an eye on the carbon cartridges and change them regularly but bear in mind isocyanates in catalised paints are tasteless and odorless (basically a version of cyanide) and seep in through your eyes, and if you are using catalised paints at home for the love of god use a respirator not one of then dust masks because if not you'll most likely be in hospital that night with water on the lungs... Also bear in mind prep work will make or break a job and a pro body shop guy can often notice a wavy panel like you won't be able to because they have experience on their side day in and day out.. A lot of guys try saving a buck by doing the prep work themselves then blame the paint shop who they get to squirt it in their booth when it fails and doesn't look as good as they'd hoped from a home prep job, don't prime straight over 80 grit scratches or you'll get sink back I promise haha. This is my opinion from my years as a painter, there are probably many guys here that'll disagree or have other opinions, if anything i hope to give you more food for thought for you to make your own mind up about which way you go, this is just the way I've done it and never had any probs, Flash times for primer too id use 15 mins or till the last bit you primed isn't wet anymore and I'd use a gravity fed gun with at least 1.7mm setup at probably... Around 1.5-2 bar air pressure at the gun, make sure your compressor has enough free air delivery to keep up because theres nothing worse than doing a job and having to stop to wait for it to build up air pressure but if anyones using air shop tools theyll know that anyway haha..but use a test panel to try it all out, as long as you're comfy
Also, if you're doing a solid color, you don't need to clear over base, you can put a couple coats of medium solids DG (direct gloss) over final sanding with 320grit and it'll be all good. PPG IS the shit too! Haha, or DuPont have a high solids DG that covers in a tack coat then one full wet coat... and has probably the nicest smelling reducer I've smelt
i think he was lookin for simple answer....id block with long board...180...longer better...marine boards are great...then you know its straight...then prime with couple coats high build...final block with 600 wet for metallics...400 if solid color...single stage or b/c..
Yea all good, by no means was I tryna be "that guy" haha, the infos bound to be handy for someone?... Short answer, buzz with 240 and wet on wet it with dp40
Kiwi; Thanks for several pearls, not too mention the reasons behind the safe practices. The paint science fellow from Langley once gave a talk on the stuff at UVA. He worked in a 'mix' of atmospheres and chemical reactions, a lot (it was) to chew on, in short order, I think your explanation helps.
The safest thing to practice is V E N T I L A T I O N. Simple enough to wear a good respirator and cover your skin and all, but it's that short moment afterward, when the shop "looks" cleared out of fumes or overspray. It may be cleared but the car is still "gassing out", purging the really damaging stuff into the air and that instict to stand there and look at your good work... Get the air moving and changing. You'll be better for it whether you're in OZ or the county next to me.
Damn Kiwi, I agree on most of your points but have you ever heard of a comma? Geez My eye balls are falling out trying to read your essay. Thanks for your response anyway!
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