I have 3 year old clear coat that still looks good. Problem is, when I color sanded I got some sanding marks in the paint. Didn't notice until I clear coated and buffed.
I would like to block through the clear coat and get the marks out of the paint and then clear the whole car again. Can I get away with this, or should I not take the chance?

Dave

Nope, if you break through the clear on a metallic you must shoot more color over it,not sure about a solid color.

Not 100% sure what you are really saying. First you need to know are the sand scratches in the paint(basecoat) or clearcoat? If they are in the base they got there because you used to aggressive grit prior to basecoat, you sanded the primer before its cure time or time to paint time or you even applied the primer on too dry, all of these can lead to sand srcatch swelling. The only way to remove srcacthes that are in the base is sand with 1000 grit reshoot base and clear. When doing this there is NO need to break thro the clear. In fact you want to avoid this, if you apply the new base to wet you can lift the pre-existing paint. All you need to do is DULL the shine for a repaint, NO NEED what so ever to block thro anything.

No amount of sanding and buffing will remove them if they are in the base.

Now if they are in just the clear coat, you used too aggressive grit to buff, didnt spend enough time buffing, buffing compund too aggressive all these lead to sanding marks in clear.

My first option would be start out with some buffing compound and a yellow foam pad. I use nothing but 3M products use the perfect3 system. Go over the areas with the compound. Then wipe any film off with a nice CLEAN soft towel, this removes any film left by the compound. Then apply some machine glaze and buff with the BLACK foam pad. Dont use the same pad with different compounds all you will be doing is mixing them together, allowing the rubbing compound to intermix with the finer cut machine glaze.

If that doesnt work then you need to wetsand with 1500 then work up to 2000 grit then buff. I prefer to use 1200 to 1500 first as it cuts so much faster and you get a smoother, level finsih compared to if you just went with 2000 from the get go.

I always try to go with the least aggressive method which would be the start out with the buffing, then try sanding and buffing

I'm not really sure if the scratches are under the clear or in the clear. Eyes aren't too good any more. I'll get some good reading glasses and take a look with those. Don't laugh, your turn is comming. ;)
My primer was over 30 days old and I used a sealer before the base coat. The sealer was a water base and I followed the directions exactly since I had never used the stuff before. Let it dry twice the time suggested on the can.
I think the scratches are in the base color. I let the base color cure 1 week. Then started blocking with 800. This seemed to work pretty well, but what I did not notice was occasional build up of just a dot on the paper. I know now it was from not enough water or no soap in the water. Live and learn. Didn't notice the spots. I did not go over it with 1500 because I was going to shoot the clear. Thought 800 was fine enough and it would leave a good surface for the clear to hold to. I blocked the clear after 2 days of cure time starting with 800 and going to 1500 and then 2000. Then I started buffing with a wool pad and 3M medium buffing compnd. Changed pads to grey foam and went to fine compnd. Followed up with polishing and then swirl remover and then wax. Shines like the dickens, but the deck lid has some lines in it. Not noticable unless the light is just right. But,I know they are there.
You guys have told me what I need to know, especialy you svet.

Thanks for all the info.
Good stuff.

Dave

Dave, what I see wrong is the sanding the basecoat. The only time you need to sand base is when you have some dirt or a sag, other then that there is no need to sand basecoat. If you do sand base YOU need to shoot a coat or two over the sanded areas, especially with metallic paint as you will disturbe the metallics and they wont look right, so you need to shoot one or two coats of base after sanding.

Sanding basecoat is probably the hardest thing to sand, every manufactors base will BALL up like it did on sandpaper no matter how much water or soap you got, it just does that.

Since you have tried to wetsand and buff the clear and still see the srcatches the only thing that will rid the srcatches will be a repaint. I Would wet sand the ENTIRE part with 1000 grit or even 800 grit. Apply one or two coats of base, then allow the base to flash off, most are around 30 mins to clear. Allow the base to flash then go straight to clear, no sanding the base just spray the clear.

If you use a tack rag before the base and inbetween each coat of base(make sure its dry) and beofre the clear you shouldnt have any dirt problems in basecoat. I cant recall the last time I sanded basecoat, if it was it was something like fly did the tap dance in it

OK, thanks for the info svt.
appreciate it.
I'm not going to do a repaint now.
I'll wait a year or two and fix some low places
that are bugging me now.
Then I'll do the repaint with the new info.

Dave