final sanding before paint ? - Chevelle Tech
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post #1 of 18 (permalink) Old Jun 10th, 08, 11:08 PM Thread Starter
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Sam
 
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final sanding before paint ?

I've been blocking on my car for awhile now and I believe the car is as straight as I can make it.Anyway on my last round of blocking I used 220 and dry guide coat that's how the car sits now with no burn throughs. I'm letting the car sit for a couple days and I plan on going over it again lightly with 220 to be sure.I'm gonna lay down a couple more coats of primer and move on to paint.This is where I'm not sure how to proceed,I've tried searching for info and it seems everyone's using 400 or 600 grit and some say wetsand and some say dry.What about technique should I use all the same blocks I've been using and the same pattern or could I use smaller blocks?I'm just not sure which way to go,any advice would greatly be appreciated.
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post #2 of 18 (permalink) Old Jun 10th, 08, 11:25 PM
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Bill
 
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Re: final sanding before paint ?

Apply 2 wet coats of sanding primer, to fill those 220 scratches, then block it wet, with a 4 inch rubber block and 800, till it's flat, with no orange peal.
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post #3 of 18 (permalink) Old Jun 10th, 08, 11:39 PM
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Re: final sanding before paint ?

I just started using SPI products and they say to use their epoxy, thinned down for a final coat before color, a 'sandable' sealer. That makes good sense to me and I plan to do that.

I undestand that it fills, creates a barrier and a superior surface to apply color to.

Anyway, I always wet sand with a squee-gee about a square foot at a time, closely looking at the work and making sure there are no deep scratches or imperfections. I ALWAYS find some too. Much better to find them at this time than at any later. This is no time to be in a hurry. It's the final step in the preparation for paint, the most important aspect of a quality paint job.

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post #4 of 18 (permalink) Old Jun 11th, 08, 1:01 AM
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Re: final sanding before paint ?

if you use a sealer now it will make the your primer surface shine, more like a color would then you can see any inperfection, it real easy to get blinded by the primer gray, many times people will use different colors of primer, during the blocking, gl
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post #5 of 18 (permalink) Old Jun 11th, 08, 5:03 PM
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Re: final sanding before paint ?

Just a thought:
You may have enough primer on there now to just apply more guidecoat and step your grit down to 400 for solid colors or 600 for metalics. There's no sense in repriming unless you need more build, it should take nothing to cut those 220 grit scratches out and prep it for sealer or paint. Another plus is less product, less chance of shrinkage, less work, less money spent, less chance of urethane wave (yes it happens in surfacers) and if your sealing with epoxy there's no problem if you get any sand throughs on your surfacer. Guidecoat will show when your 220 scratches are gone. Bob
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post #6 of 18 (permalink) Old Jun 11th, 08, 9:12 PM
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post #7 of 18 (permalink) Old Jun 11th, 08, 11:43 PM
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Re: final sanding before paint ?

Either. They both have advantages,some prefer wet, others-dry.

I prefer wet for the final sanding and the benifits are: no dust (health), less paper & faster (no loaded paper), and it also has a natural cleaning effect (oils float on water)
disadvantages: wetsanding sludge to cleanup, dry time before recoating, promotes corrosion on areas that are not protected.

Dry sanding you're able to use PSA paper which is nice, no sludge, no dry time before recoating. Does not promote corrosion. Disadvantages: slower bcause fine grits will load up fast-plan on spending time blowing the paper clean as you sand. Lots of fine dust. More paper used
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post #8 of 18 (permalink) Old Jun 11th, 08, 11:55 PM Thread Starter
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Re: final sanding before paint ?

Thanks guys for your input.It just seems odd you spend some much time blocking with long boards only to finish with a short one.So should I be sanding on an angle or straight with the panel?
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post #9 of 18 (permalink) Old Jun 12th, 08, 12:40 AM
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Re: final sanding before paint ?

At this point your shape should be straight if you used long boards and good sanding patterns. Now that you're going to shorter blocks it will be more important to be consistant with your sanding patterns because if you spend too much time in one area you'll create a wave. Use an x pattern and start at one end of the panel working evenly to the other and then back-make swipes across the panel then back untill the guidecoat is gone, sticks, hoses, and soft pads can be used in areas with a lot of contour. Then when all the guidecoat is off follow up with a good rubdown with grey scotchbrites- two stacked together gives enough support so you don't create any divits from finger pressure, run the scotchbrites lengthwise with the car whenever possible. JMO
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post #10 of 18 (permalink) Old Jun 12th, 08, 7:16 PM Thread Starter
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Re: final sanding before paint ?

Thanks baddbob71 for the info exactly what I needed to know.I've read about people scrubbing the car before paint using ajax?Reason I'm wondering about that is because once my car is final sanded,it's going for a ride on the trailer to the body shop where i'm painting it.I know once there I'll need to clean the car,thinking I could rub it down with the grey scocthbrite and cleaner?
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post #11 of 18 (permalink) Old Jun 15th, 08, 7:09 PM
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Re: final sanding before paint ?

just a little tip i got from a house of kolor seminar i went to this year,jon kosmoski said if i dry sand to use 320 grit for my final grit before applying my sealer over my 2kprimer then paint my base/clear.phil
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post #12 of 18 (permalink) Old Jun 15th, 08, 7:12 PM
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Re: final sanding before paint ?

oh yeah jon said you want a good mechanical bite ie: the 320grit but what does he know hes only been doing custom paint for about a hunderd years! lol! lol!
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post #13 of 18 (permalink) Old Jun 15th, 08, 9:21 PM Thread Starter
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Re: final sanding before paint ?

thanks for the tip,I don't plan on using a sealer.
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post #14 of 18 (permalink) Old Jun 16th, 08, 7:39 AM
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Re: final sanding before paint ?

Quote:
Originally Posted by snake2k View Post
Thanks baddbob71 for the info exactly what I needed to know.I've read about people scrubbing the car before paint using ajax?Reason I'm wondering about that is because once my car is final sanded,it's going for a ride on the trailer to the body shop where i'm painting it.I know once there I'll need to clean the car,thinking I could rub it down with the grey scocthbrite and cleaner?
No, I wouldn't scrub it with the scotchbrite and cleaner. Just do the soctchbrite thing at home so it is ready for paint and clean it as normal at the paintshop prior to painting. The Ajax scrub works well but requires some good rinsing and plenty of dry time.
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post #15 of 18 (permalink) Old Jun 19th, 08, 12:33 AM Thread Starter
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Sam
 
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Re: final sanding before paint ?

baddbob71,sorry for the delay in replying I greatly appreciate the info.I tried sanding my car in 400 but had some burn through to the epoxy so I went and layed two coats of a dark gray surfacer.I was using yellow before and with the gray the body line down the side of the car stands out and there's some areas that aren't right.Is it possible to block down the line with 220 to straighten it up and go right to 400 without causing any waves?
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