Sanding grit question

E

Elou795

I seem to be a bit confused here, I need to change the 2 passenger doors on my car but the new ones are not the same color. I know that I will have blend into the quarter and fender, for blending I was told that 1000 grit on an interference pad will do. For the 2 doors I was told use 600 grit or I would face adhesions problems. My question is why couldn't I use 1000 grit like I do for blending and as far as adhesion problems wouldnt I have adhesion problems when I blend to the fender?

I also might want to repaint the hood since it has quit a few chips so if the hood is not changing color do i use 600 or 1000?

Thanks
 
Lots of people do different things. Will base stick to 1000? Yes, it will. Would it stick better to 600? Probably so. I have been sanding blend panels with 1000 wet by hand, followed by a grey scuff pad, for over 30 years with no issues. I have recently started sanding blend panels with a sunmight 800 soft foam da disc, and they work well. The reason for a finer scratch on a blend panel, is the area where you blend the color will not have 2 coats of base, and 600 scratches may show with some colors like light metallics. Lots of variables, using intercoat clear as a wet bed to blend over, you can get away with 600, as you can with solid colors. Not all 1000 grit brands leave the same depth scratch, either. Hand sanding leaves a more aggressive scratch, in general, than a da. Wet or dry also makes a difference. 800 grit on a da would be fine to sand a blend panel or a complete panel, if you wanted to just use one grit. If it is thoroughly sanded and clean, adhesion will be fine with either grit, IMO. https://www.amazon.com/Sunmight-962...=sunmight+800&qid=1584798775&sprefix=sunmight
 
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If it's an older car, any sanding of the blend panel can change the color a little
when compared to the panel next to it..
Especially when the clear is yellowed a little. And most are.
Original silver panels will always look a little brighter when sanded and recleared.
I will only sand a blend panel with a gray scotch pad and sanding paste.
(for at least the last 12" of the blend panel next to the original painted next panel)
The more sanding you do the more likely it will look different when cleared.
You have to be thorough when doing it this way, every square inch must be
thoroughly scuffed and cleaned. Also, more coats of clear will affect the color too so the last
bit of the blend panel next to the original painted panel next to it needs less clear.
I usually only apply 1 coat of clear for the last 12" of the blend panel.
It's kind of like a swimming pool, the water is clear but the deep end always looks different.
 
First off have you ever blended anything before? If not then I'll try and describe the process. Everyone has their methods I'll tell you what has reliably worked for me over the years if I was doing the job. From your description sounds like you are working on a relatively modern car. Something with a factory bc/cc finish. I would wet sand the doors with 600. My blend panels I would wet sand with 800 grit. Sand the complete blend panel as you will clear over the entire panel. After sanding I like using Presta Scuff-Stuff and a gray 3m Scotchbrite pad and scuff all the panels including the blend panels. This ensures you get all the areas that you may have missed or couldn't get with the sandpaper. It also cleans the panel of any remaining residues and silicones.
Your are going to need to seal the doors. This should be considered mandatory. A mid gray is a safe choice for most colors. White for yellows and bright reds. Use a quality basecoat this will help ease the process considerably. When you go to your Jobber to get the color make sure you write down and bring along your VIN # of your vehicle. This will help the Jobber choose the correct formula for your car. This is important as their are many variants within a particular paint color/code.
Spraying. Seal the doors, fading out just as you get to the fenders and 1/4 panel. You want to slightly pull away while slightly feathering off the trigger. Basically you don't want to have a hard stop and start area on your sealer as that will show through the final finish.
After your sealer has flashed concentrate on getting coverage of the doors. Again feather off slightly with each pass, extending each pass farther into your blend area. Once you have coverage if your blend looks good you can proceed to clearing the complete job. If you can still see a transistion (look for color difference only, don't worry about gloss level or slight texture differences). One thing I do is to stand back and "relax" my eyes while looking at the blend. Take your RTS (ready to spray) basecoat and add some "blender" to it in the ratio of 1 part RTS base to 1 part blender. You can get blender at your jobber. Ask him for a pint or quart of it when you get your color. Depending on the color spray one coat over the entire replacement panels and blend areas or spray a coat on your blend areas. If you are new to blending doing the whole thing and blending out is the safer choice. Repeat if neccesary. If the color is close and you do it right you'll have indistinguishable blend. Then clear all the panels. Done. Unmask as soon as you can. Don't let your masking sit on it for any length of time. Especially tape on edges of moldings etc.
I wouldn't use 1000 anywhere as the adhesion risks are just too great. I've seen clear pull right off when unmasking something that the blend area was done with 1000. As far as sand scratches showing through the blend area that is not an issue with 800.
 
Thanks for the info guys, car is a 2014 cruze silver, one donor door is silver and the other is a light brown so I shouldn't have a problem repainting them bought it for my boy he turns 16 this week great first car 25000 miles salvage title both passenger doors and rocker were pushed in. I'm really good with metal work but I don't do enough painting to really remember what steps to take. I'm sure I'll have more question as I go.
 

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Sorry one more question when I wet sand the door with 600 and the blend panels with 800 can I use a da or by hand? Also if using da should I use an interference pad?

Thanks
 
Up to you. I always do my final sand wet and by hand. Blend I would sand by hand to ensure I didn't sand through on any edges etc.
 
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