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Block sanding question.
#1
So I had a few questions for all you body work gurus. I am block sanding this 71. I got half the roof done and the driver side quarter panel. I ended up sanding it with 220 grit and sanded through the primer in a few spots also found a couple pinholes. I am going to finish blocking the rest of the car with 220. Then what should I do?  So do I need to shoot the whole car again with primer then sand with 400 grit? Or can I just shoot over the areas that sanded through then sand with 400? And what is the best way to deal with the pinholes? Do I need to sand to bare metal then filler? Or just scuff primer and use  icing filler? Then prime and sand with 400? Any input is appreciated! Thanks for looking. 


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Kevin

1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]




                                                                                             
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#2
Hi Kevin,
It all depends on how straight you want the paint job to turn out. The more you prime and long block the smoother and straighter the finish (3 times around should provide outstanding results, if your body work under the primer is straight) First off I am assuming you are using a 2 part epoxy primer/surfacer/filler. If you are not, I would strongly recommend it. You should also be applying 3 medium wet coats in between blockings. This will give you the best results when long blocking your car. Looks like you are guide coating, that is the best way to read your work. You should do your first block with the 220 using at least a 6inch block (the longer the block the straighter the finish will be) and read your guide coat to see how flat the panel is. If you have low spots you should reprime and 220 again, If you have metal showing through you should reprime before any further sanding is done. It is a good idea to fill the pinholes with a light coat of glazing putty at this time then block sand those areas with 220 prior to applying your second coat of primer. Once you feel the panels are straight enough and the minor defects are addressed shoot another primer coat, guide coat and block with 320, if no metal shows through and no low spots are seen and no other defects are visible, wet sand with 400. Use the wet, glossy panel as a mirror and look down the side of the car, moving reflections down or across the glossy panel to see waves, dents or ripples. This will give you an idea of how the paint will look. If you see any imperfections and it bothers you, do another round of priming and blocking. A good rule of thumb is one sanding per coat of primer. I would not recommend block sanding multiple times on one regular coat of primer. With the exception of the 320 to 400 sanding as the 400 is meant to smooth out the 220 and 320 sanding marks only.
There are a few different ways to accomplish the same thing here and I hope more will chime in. This process has played a big part in me winning best paint on a few occasions. If you shoot a stellar coat of paint on a poorly prepped surface the finished product will look terrible and if you lay down a crappy coat of paint on a perfectly prepped surface it will look terrible. Patience is key in this whole process. And this process will test your patience!! I hope this helps!

movie stars with addictions go to the Betty Ford clinic,
I take my addiction to the Henry Ford clinic.Haha
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#3
Hi Kevin,

Happy to give tech advice, but a few questions first to help you nail it.

What product did you use?  - Brand and type.
How did you use this product? - as a primer or putty.
How many coats did you apply?
What substrate did you apply this paint over? - previous old paint/bare metal etc.
Why the need to long block the whole car? - does every panel have an straightness issue.
Does your product need an etch primer used first, if applying it over bare metal?
What paint will you be using for the final color coats? - 2 pack solid color enamel or   base coat/ clear coat or   2 pack solid with 2 pack clear on top etc.
Are you wet sanding or dry sanding your primer /putty to end up taking it to the color stage?

If you can answer all these questions for me, i can give you better, accurate  feedback and advice on  ending up with a good result.

Many thanks,

Greg. Smile

whistling LORD, MR FORD - JERRY REED
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#4
(03-01-2017, 05:41 AM)Thanks for the input fellas!   I will answer as many questions as I can below. Austin Vert Wrote: Hi Kevin,

Happy to give tech advice, but a few questions first to help you nail it.

What product did you use?  - Brand and type.      U-POL DTM PRIMER http://www.pbejobbers.com/repository/techsheet/ts0196.pdf

How did you use this product? - as a primer or putty.    HIGH BUILD PRIMER SURFACER
How many coats did you apply?      3 COATS

What substrate did you apply this paint over? - previous old paint/bare metal etc.     APPLIED OVER BARE METAL, 220 GRIT SANDED FACTORY PAINT, AND EVERCOAT EXTREME FILLER.  SEE LINK..   https://www.7173mustangs.com/thread-new-project-for-this-winter-71-mach-1?page=7

Why the need to long block the whole car? - does every panel have an straightness issue. I WAS ALWAYS TOLD TO BLOCK SAND ENTIRE CAR??  IM USING DURABLOCKS AND SOFTSANDERS IN VARIOUS LENGTHS AND CONTOURS. 6" - 24" LONG BOARDS.

Does your product need an etch primer used first, if applying it over bare metal?  NO. IT'S DTM.
What paint will you be using for the final color coats? - 2 pack solid color enamel or   base coat/ clear coat or   2 pack solid with 2 pack clear on top etc.          I WILL BE USING PPG GRABBER YELLOW 2 PACK BASE COAT AND PPG CLEARCOAT    (I BELIEVE IT'S PPG DELTRON??)
Are you wet sanding or dry sanding your primer /putty to end up taking it to the color stage? I PREFER TO DRY SAND WITH 400 FOR SOLID COLOR LIKE GRABBER YELLOW.

If you can answer all these questions for me, i can give you better, accurate  feedback and advice on  ending up with a good result.     THANKS FOR ANY INPUT AND ALL INPUT GREG. AND KEEP IN MIND, THIS GUY IS GOING TO DRIVE AND DRIVE AND DRIVE THIS CAR. NO SHOW CAR BEAUTY QUEEN, JUST A NICE GOOD LOOKING DRIVER.

Many thanks,

Greg. Smile

Kevin

1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]




                                                                                             
  Reply
#5
Kevin,

Thanks for the info - got it. The only thing i was not sure about was did you mix your UPOL as a spray putty, 4:1  or as a primer  4:1:1 reducer?   If you mixed it as a primer only, then that would not give you a very good film build to work with for blocking purposes, but three coats of spray putty is a good start.

OK, so here's my take on it all. Before you put the whole car into primer or spray putty, you would normally examine each panel for straightness and small dents etc. If you have a clean, straight panel so to speak, it becomes a waste of time loading primer filler onto that panel, and long blocking that panel for straightness. To any other unclean or not straight panels, well then yes, go for it. The UPOL product sounds like a very good versatile one too. thumb  So yes, i would first apply your three or four medium wet coats of spray putty to the necessary panels. BTW - Pin holing in the spray putty happens when you apply each coat too wet, and / or you apply further wet coats on top too soon before the last coat has flashed off properly. Next, for your block work, 220 dry is ok, but 240 would be better for creating less sand scratches. 240 works good for wet sanding the spray putty down. Using your guide coat as an indicator, your first block rubbing will reveal the state of each panel. It may show that you still have some highs and lows in that panel, after a good and careful block down,and therefore that panel needs more spray putty applied to it, and further blocking again. It may be that the panel blocks down first off with no highs and lows for example, and you have not sanded through anywhere on that panel. That is the ideal situation. If you have sanded through any where, then those areas will have to be spot primed  before the color coats are applied. So now, re putty any panels that need more filling up for straightness. If you have any pinholes in your spray putty, then you have a choice of filling them with 2 pack wiping putty, or spraying more 2 pack spray putty into them, wiping each wet coat in with your fingers to force the spray putty into the tiny holes. In both cases, you will need to guide coat and block sand down those pinholed areas with 240 or 220 dry. If you go the wiping putty way, then you will need to sand down the wiping putty first, then spray a couple of light coats of spray primer over your pin holed areas to  seal them off completely, and again, block down those areas.

Once you get to a stage where all your panels are nice and straight, and have the right amount of spray putty on them, and there are no spot rub throughs, you are now ready for the final sanding before the color coats go on. You said you will be using a base coat/ clear coat system. (solid color, non metallic). For best results, the final sanding down process should be a wet one, not dry. You start with a light guide coat, then you will be wet hand sanding down each panel with 800 wet and dry paper, not 400 grade. I will guarantee you that if you use 400 grade wet/dry paper on a metallic job, you will get sand scratch marks coming through and into your final clear coats. Even with your solid color base coat, you will still get some sand scratches appearing in your final clear coats. 400 grade is only ok for final wet or dry sanding, when the top coats will be  a solid color 2 pack enamel only. 800 wet and dry will guarantee NO sand scratch marks will appear in your clear coats.

So once the guide coat has been removed with the wet, hand sanding process, then that's it. You are now ready to apply your color and clear coats. Also, don't let water pool on any panel. As soon as you have finished rubbing any panel, then dry rag or chamois the panel off, removing all excess water. If you have rubbed through any small spots in any given panel, then spot prime them with one or two light/ wet coats of your 2 pack primer. THERE ARE SINGLE PACK SPECIAL SPOT PRIMERS ON THE MARKET THAT CAN TAKE CARE OF THESE SMALL RUB THROUGH AREAS. They are quick and handy for this type of application. Now move into your application of your color and clear coats.

Hope that answers your questions Kevin.

Many thanks,

Greg. Smile

whistling LORD, MR FORD - JERRY REED
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#6
Great!! Thanks for the reply Greg!! A lot of good information in there. I did have a couple questions. And to answer one of yours, I did mix the U-pol primer to the 4:1 ratio and shot it with a 1.8 tip..... Its biggest one I had. I like this U-pol primer, it seems to sand out really nicely and easy.
Now that I am almost done dry block sanding with 220, I should prime any spots that I sanded through and hit again with 220. Once that is complete wet sand with 800?? Is that too big of a jump from 220? Will the 800 take all the 220 scratches out? I have a big roll of adhesive backed wet/dry 400. Should I use it after the 220? then go to the 800??
Also when I start my wet sanding I should use a spray on guide coat correct? The powder stuff won't work with water.
Thanks again for all the info Greg!!!

Kevin

1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]




                                                                                             
  Reply
#7
This is passenger side after about 4 hours of blocking last night. 
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Kevin

1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]




                                                                                             
  Reply
#8
Kevin, looks like your panels are coming out smooth. If you choose to spot prime your sand throughs (high areas) use a finer grade paper or you will just sand through them again. Try not to build the primer up on these ares or you will create a high spot that will show up in the paint, it is just meant to cover a bare area. I would recommend stepping down on your paper, such as going from 220 to 320 to 400 wet. 220 to 800 is too big of a step and you dont need to go that far since you are shooting a solid non metallic color you don't have to worry about sand scratches coming through. Your final guide coat can be sprayed on using a krylon flat black. Wet sand the panel until the guide coat is gone, if you see some scratches remaining spray more guide coat and wet sand again. Do not hand sand! Always use a block! If you just use your hand on paper you will create finger lines and make your paint wavy. One again check your panel when it's wet to make sure it is straight enough and wipe/blow the panel dry. Highly recommend that once the car is all sanded with 400 you should use a sealer immediately before you paint. This will keep any old paint and contamination from bleeding through. You can mix your UPOL to become a sealer. This will be a non sanding sealer and applied just before painting.

Here is one of my metallic paint jobs blocked twice with 220 dry and finished in 400 wet with a sealer and the paint was color sanded with 2000, 3000 and 5000 wet and buffed.


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movie stars with addictions go to the Betty Ford clinic,
I take my addiction to the Henry Ford clinic.Haha
  Reply
#9
(03-02-2017, 12:48 PM)6972boss Wrote: Kevin, looks like your panels are coming out smooth. If you choose to spot prime your sand throughs (high areas) use a finer grade paper or you will just sand through them again. Try not to build the primer up on these ares or you will create a high spot that will show up in the paint, it is just meant to cover a bare area. I would recommend stepping down on your paper, such as going from 220 to 320 to 400 wet. 220 to 800 is too big of a step and you dont need to go that far since you are shooting a solid non metallic color you don't have to worry about sand scratches coming through. Your final guide coat can be sprayed on using a krylon flat black. Wet sand the panel until the guide coat is gone, if you see some scratches remaining spray more guide coat and wet sand again. Do not hand sand! Always use a block! If you just use your hand on paper you will create finger lines and make your paint wavy. One again check your panel when it's wet to make sure it is straight enough and wipe/blow the panel dry. Highly recommend that once the car is all sanded with 400 you should use a sealer immediately before you paint. This will keep any old paint and contamination from bleeding through. You can mix your UPOL to become a sealer. This will be a non sanding sealer and applied just before painting.

Here is one of my metallic paint jobs blocked twice with 220 dry and finished in 400 wet with a sealer and the paint was color sanded with 2000, 3000 and 5000 wet and buffed.

WOW that looks great!!  Thanks for the tips and help!!!  I have been using various blocks in different sizes and contours to do all my sanding. About the only places I cant get is around some of the jambs and nooks and crannys. I have been using red scotch brite in those areas. Is that ok to shoot over or do I need to step down to the gray scotch brite?

Kevin

1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]




                                                                                             
  Reply
#10
Hi Boss,

Thanks for your input. Question - are you a professional , tradesman, auto spray painter or self taught?

Just wondering.


Greg.

whistling LORD, MR FORD - JERRY REED
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