wet sanding a deep scratch and repaint?

[gcorolla99]

Help.

I have some deep scratches to my car, and bare metal has rusted. I'm planning on sanding it all the way down with a 5 or 6 inch rotation sander. I'm thinking that I will sand about 8 inch in diameter. Then spray primer. let dry, spray color, let dry, then spray clear coat and then wet sand at 2500 grit to smoothen out the surface.. What do you think would be the result of me sanding with a 2500 grit to smoothen out the surface? Will it run it and make it dull? I'm thinking of then putting on buffer to make it shine again.. will this work?

Notice I'm planning on sanding an 8 inch diamter..I want the final paint to match the surrounding paint. Color is black. I hear that professionals typically will spray the whole panel, but is it absolutely necessary??

thanks,
Gordon

[fishexpo101]

If you are going to sand out an area that is 8" in diameter - my suggestion is to paint the whole panel to ease color matching. If the paint is metallic (metal flake black) - I would highly recommend just repainting the whole car, unless you have experience in color blending - as it will look very obvious that there is a repair point. Biggest problem you'll run into is that the rest of the paint has seen some environmental damage - the clear may be faded, damaged quite a bit.

Depending on what you use to initially sand out the scratches and how much blending you plan on doing - 2500 grit will make the clear coat look dull and hazy. But you can use some polishing coumpound with a machine and buff that right up (assuming the rest of the clear on the panel is OK). Do what you need to get rid of the rust (don't want to risk having rust push the new paint out). Try and not use any grit any coarser than 400 grit before you shoot paint. You might have to use 80 to 220 grit to get the rust out, but "feather" the repair area with 400 grit and up to reduce your workload.

If I was planning to do that sort of job and have several 8"-10" diameter "patches" - I would fix the rust, shoot epoxy primer (protects metal / prevent further rust), do any body work (fill gouges if needed), shoot a few coats of primer sealer, shoot 3-5 coats of color, shoot 3-5 coats of clear. Wet sand with very fine grit, machine polish, seal, wax. Of course - use appropriate/compatible products and wait the appropriate amount of time before you work on the paint.

Also keep in mind that many non-metallics or single color paints do NOT have clear on them. I know Toyota's white paint is this way, I haven't heard about black paint and how they treat it. Easiest way it to test on the intended repair area. Very lightly wet sanding the finish, see if any color comes off on a clean towel. If not - then you have the two-stage paint (color + clear) otherwise, it is the single stage paint.

[gcorolla99]

Hi,

Well, some spots about about a quarter big.. and some are deep key scratches.. I really don't want to paint the whole panel.

If I were to do what you suggested, but at the very end, WET sand it at 2500 grit, and even if the clear coat gets dull, but once I buff it, won't it be fully shiny [this is what I really want to know]? Will it be so shiny that it will match the other part? Let' also assume the black paint matches. Let's assume we have a line that runs about 12 inches.

I don't want to sand and dig into my keyed scratches before I know the answer to the above cuz I don't want to ruin it.

I'm trying to sell this car for $6500, so I really don't want to let the pros do it..

Thanks,

Gordon

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Originally Posted by fishexpo101

If you are going to sand out an area that is 8" in diameter - my suggestion is to paint the whole panel to ease color matching. If the paint is metallic (metal flake black) - I would highly recommend just repainting the whole car, unless you have experience in color blending - as it will look very obvious that there is a repair point. Biggest problem you'll run into is that the rest of the paint has seen some environmental damage - the clear may be faded, damaged quite a bit.

Depending on what you use to initially sand out the scratches and how much blending you plan on doing - 2500 grit will make the clear coat look dull and hazy. But you can use some polishing coumpound with a machine and buff that right up (assuming the rest of the clear on the panel is OK). Do what you need to get rid of the rust (don't want to risk having rust push the new paint out). Try and not use any grit any coarser than 400 grit before you shoot paint. You might have to use 80 to 220 grit to get the rust out, but "feather" the repair area with 400 grit and up to reduce your workload.

If I was planning to do that sort of job and have several 8"-10" diameter "patches" - I would fix the rust, shoot epoxy primer (protects metal / prevent further rust), do any body work (fill gouges if needed), shoot a few coats of primer sealer, shoot 3-5 coats of color, shoot 3-5 coats of clear. Wet sand with very fine grit, machine polish, seal, wax. Of course - use appropriate/compatible products and wait the appropriate amount of time before you work on the paint.

Also keep in mind that many non-metallics or single color paints do NOT have clear on them. I know Toyota's white paint is this way, I haven't heard about black paint and how they treat it. Easiest way it to test on the intended repair area. Very lightly wet sanding the finish, see if any color comes off on a clean towel. If not - then you have the two-stage paint (color + clear) otherwise, it is the single stage paint.

[fishexpo101]

Wet sanding with ultra fine grit (generally 1200+) on clear is one of the ways to restore the shine in weathered finishes. The touchy part will be not cutting all the way through the clear coat - assuming it has clear on the finish.

Once you cut all the way through, the only way to fix it, is to reshoot the clear on the whole panel. Hazing the finish like that can be easily polished out with a machine. You could do it by hand, but will be tough work. Straight rotary buffers should be left to the pros, a good quality dual-action buffer, on the the other hand, will be quite difficult for someone to accidentally burn through the paint. This is assuming that you will end up polishing the rest of the car - since it would look odd to have one clean/shiny panel and the rest of the car looks "off".

You don't have to sand the surrounding area with a deep key scratch. One way to approach it is to use a fiberglass finish pen (sort of a spot sander) to remove any surface corrosion in the scratch. Fill with touch up paint - enough to slightly over fill the scratch. Then either very lightly wet sand (block it to prevent digging into the surrounding finish) or use a good quality polishing compound to cut off the excess color there - then seal and wax. You don't even need to put clear on something like that - the repair will be hardly noticeable.

The ones that are smaller, don't spread the repair area out too far - try and keep it localized around the damaged finish. There are tricks to limit overspray on the area without having to shot too much paint. I won't get into too much detail - but basically use an old airbrush trick of shooting color through a hole in some hardstock/plastic/cardboard, etc. That way you can keep the correct distance away from the finish to lay up correctly, while limiting the coverage area of spray. A smaller repair area will be easier to blend in than on that is 8"-10" in diameter.

With all painting - the prep is the most important step - I'd say it is probably close to 90%-95% prep and 5%-10% of actual painting. Lots of info on this online - to get the most successful repair, do the proper prep work.

[Kenshin]

i got a quick question if my car has burn paint from the what can i do to fix it is kind a white color my car is black metallic i got the problem in the roof and trunk thanks.

[fishexpo101]

You mean the black metallic has a white haze or white "chalk-like" contamination on the surface? Sounds like oxidation to me - burn through in paint, is when you completely sand or polish through the clear coat and into the pigment or color coat. Only way to fix that is to re-shoot the clear coat.

If it is just oxidation, clean the area well first, then clay bar it. That will help remove any surface contaminants. If it still looks hazy or chalky - you will need to get some polish and rub it out. Machine is the easiest way to go - you can do it by hand, but will be a lot of work. Work at it a little at a time until you remove the haze.

This also assumes that the paint still has enough clear to work with. If the finish is heavily oxidized or damage - you may have no choice but to repaint. If you go far enough that black paint shows up on the bonnet for hte machine or your polishing cloth - you just burned through the clear. Only recourse at that point is to repaint.