[gtobird]

I painted the hood for my 68 Bird and used PPG DCC9300 single stage starlight black paint. Under that is DP90LF that I used as a sealer coat and under that is K36 primer surfacer. The topcoat as been dry for about 6 weeks now, so the paint is pretty hard at this stage.

Yeah, I know some of you like to cut the paint when it is soft. I've had good results cutting and polishing with it hard, but now I have a issue.

During wet sanding of the paint, I found an error that I must have made in my final blocking (of the K36 surfacer) on top of one of the hood scoops (in back of where the scoop insert is). The error was small enough that I thought maybe I could block it out of the paint. No such luck. After getting the surface perfectly level, I ended up cutting into the DP90LF and exposed a small area of the K36. The exposed DP90LF area is about 2" in diameter and the K36 that is exposed is about the size of a dime.

My question is, do I really need to re-seal the exposed K36 and DP90LF area with more DP90LF before shooting more DCC 9300 paint? If you follow the DP90LF P-sheet, yes you have to do this for spot repairs, but I really question if this is necessary for such a small area.. If it must be, then I will do it. I have a boat load of time in this black paint job and it needs to be look perfect and hold up.

Regards,
Old Joe

[400 4spd.]

No, you do not have to seal that spot. Of course you do have to shoot the entire panel again because you won't be able to spot it in.

[gtobird]

Originally Posted by 400 4spd.

No, you do not have to seal that spot. Of course you do have to shoot the entire panel again because you won't be able to spot it in.

I figured that since the area was on top of the scoop which has a major contour, I should be able to just shoot the top of the scoop area, recut and buff. This is single stage, so why won't I be able to do that? Does the black paint leave an odd looking blend area?

[nytrainer]

400 4spd knows the deal...while the idea of painting what you've already finished isn't great think of it as a chance to block down the hood and essentially "flow coat" the hood. Hood will look even better than it does now. That's the only solace I can offer you.
Single stage can be "blended" somewhat with the right technique and supplies like blending solvent, etc...but not right on top of your hood. Always have to worry about rolling back the blend edge.
On high end paint work I routinely flow coat the clear which (you probably know this) means after the car (or panel(s)) are based and cleared and when it is dry you block the entire vehicle with 800-1000 and reapply 1 or 2 coats of clear. Flows out so nice without peel you can cut with 1500 step up through 3000 and just polish.

[gtobird]

Originally Posted by nytrainer

400 4spd knows the deal...while the idea of painting what you've already finished isn't great think of it as a chance to block down the hood and essentially "flow coat" the hood. Hood will look even better than it does now. That's the only solace I can offer you.
Single stage can be "blended" somewhat with the right technique and supplies like blending solvent, etc...but not right on top of your hood. Always have to worry about rolling back the blend edge.
On high end paint work I routinely flow coat the clear which (you probably know this) means after the car (or panel(s)) are based and cleared and when it is dry you block the entire vehicle with 800-1000 and reapply 1 or 2 coats of clear. Flows out so nice without peel you can cut with 1500 step up through 3000 and just polish.

Yeah, I've done what you are both suggesting when I had bigger mistakes. This one hurts because the error was pretty small. Live and learn. At least I started to wet sand the paint in the problem area first so I didn't cut and polish the entire hood and discover this last. The truth hurts.... Before I painted it, I was thinking about shooting more K36 and blocking it one more time, but it was so dang good that I thought I could maybe skirt danger this one time. Stupid is as stupid does..... I won't do that again on a black car.

Thanks
Old Joe

[400 4spd.]

nytrainer is thinking along the same line that I am. It should be even slicker after sanding and reshooting with a coupl of coats. If I were repainting the hood, I would sand it slick with 800 or 1000. Because it's not a metallic, I would lower the gun pressure (to cut down on overspray) and get the offending spot covered with 2 or 3 coats about 5 minutes apart. That way you're not dumping four or five coats on the whole hood because of needing to hide the dime sized spot.

[gtobird]

Originally Posted by 400 4spd.

nytrainer is thinking along the same line that I am. It should be even slicker after sanding and reshooting with a coupl of coats. If I were repainting the hood, I would sand it slick with 800 or 1000. Because it's not a metallic, I would lower the gun pressure (to cut down on overspray) and get the offending spot covered with 2 or 3 coats about 5 minutes apart. That way you're not dumping four or five coats on the whole hood because of needing to hide the dime sized spot.

Part of the hood is already sanded with 1500. Is that okay, or should I re-sand with 1000 grit to give it more bite?

[nytrainer]

I wouldn't sand it with anything greater than 1000. I'd be more inclined to use 800. Try wrapping that grit around a paint stick and use diagonal strokes. Your getting it ready for respray that way with the added bonus of getting the hood flatter. I feel that's necessary on the older cars to help flatten the urethane wave anyway.

[gtobird]

Generally speaking, I don't have issues with getting the paint flat or urethane wave as I'm pretty practiced at cutting urethane. My mistake in this case was not applying a last coat of K36 and blocking one more time prior to sealing / painting. I block the paint with wooden sticks or PVC pipe (for concave curves) and 400 to 600 grit first, depending on how much wave and orange peel I see, then move to higher grades. I have 4 coats of paint on the hood and I'm pretty careful not to block too far with the 400-600 grit. In this case, parts of the hood were already completed all the way to 1500 grit. I just need to understand if the 1500 grit surface is too fine for the next coasts of paint to stick properly. If so, I can lightly re-sand to a coarser grit, but would like to avoid doing that if I don't have to.

I'm curious about whether you use a DA with 1500 grit and up after you hand block with wooden sticks. I get excellent results by hand sanding the paint all the way through to 3000 grit. I've even gone to 5000 grit in areas where machine polishing isn't practical. The only time I use a DA is on a truly flat panel like a deck lid and that's after I have blocked it by hand with the coarser grits first.

My biggest problem with bodywork and painting is that I do it infrequently, so I need to re-educate myself every time. I'll never be out of the learning mode, but my results are good because I'm patient and would rather put the time in to get it right even if it means doing something twice. Now don't ask if I ever had to do it three times..........

[nytrainer]

I still would use 1000 grit. Being a fresh respray you could argue there still may be a open chemical bond but I would still want the mechanical adhesion of 800-1000 grit as well.
I have used a DA (3/32 throw which is a tighter orbit than a regular DA) with the interference pad with 1500 - 3000 but you have to be extra careful regarding dirt, etc making "pigtails" in the finish. You can "feel" it when doing it by hand but with the machine you wont know there was a bit of grit/dirt until the pigtail appears. I use a filter on my water line to guard against that.