How to fix runs/scratches in base coat?

MDPotter

MDPotter

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I'm a hobbyist at best when it comes to bodywork so I'm always making some kind of mistake. I was all geared up to paint fenders and doors this weekend but ran into some issues. I lost concentration for a split second and double coated a spot on a fender and resulted in runs in the sealer and I also discovered a couple pinholes. I put the fenders aside after sealing. No big deal, just have to take care of those two issues and resand and start over with the sealer.

What I'm not entirely sure how to fix is the issues in the basecoat on the doors. This is my first project using SPI basecoat so I'm still learning how to spray it and ended up with a few runs in one spot. The other issues are sand scratches. After I sprayed sealer, I saw some deep scratches in a couple spots so I wet sanded with 600 and sprayed the base but they're showing through. Also seeing some deep scratches in other spots. So my question is - can I sand these spots with 600 and reapply base over the entire area or do I need to reseal it and then base? I have grey 2K underneath the black sealer and it's going to be a couple weeks before I can get to it.

Runs in base
IMG_9517.jpg


Deep sand scratches from 2K blocking
IMG_9518.jpg


Sand scratches from sanding the sealer
IMG_9519.jpg
 
It looks like maybe you rushed to sealer before it was ready. Did you use guide coat?

I would take it back with 320 and guide coat. Then 400 with guide coat. Then sealer and base. If I need to denib sealer I use an 800 foam pad with a very light touch.

Keep in mind these are recommendations from a backyard painter.

Don
 
dhutton01 said:
It looks like maybe you rushed to sealer before it was ready. Did you use guide coat?

I would take it back with 320 and guide coat. Then 400 with guide coat. Then sealer and base. If I need to denib sealer I use an 800 foam pad with a very light touch.

Keep in mind these are recommendations from a backyard painter.

Don
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After I was satisfied with the blocking phase, I sprayed two coats of 2K followed by guide coat and 600 wet. I probably should start following my 150 blocking with 320 and then 2K and that would probably help with the big scratches.
 
sometimes those scratches happen because the paper picks up belly button lint like beads of paint. Does not matter what grit you use if you are using debris on the paper.
 
MDPotter said:
After I was satisfied with the blocking phase, I sprayed two coats of 2K followed by guide coat and 600 wet. I probably should start following my 150 blocking with 320 and then 2K and that would probably help with the big scratches.
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So you went from 150 to 600 wet? You can’t see anything wet sanding. You need to sand dry with a guide coat imho. I recommend 320 and then 400 right before sealer. No need for 600 wet or dry in my experience unless you are doing a light metallic or pearl.

Don
 
dhutton01 said:
So you went from 150 to 600 wet? You can’t see anything wet sanding. You need to sand dry with a guide coat imho. I recommend 320 and then 400 right before sealer. No need for 600 wet or dry in my experience unless you are doing a light metallic or pearl.

Don
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After blocking with 150, I sprayed two coats of 2K high building and then guide coat and 600 wet. It sounds like I need to hit it with 320 after the 150. I don't have any 400 paper, will 600 affect adhesion?
 
Those scratches are deep, they look like 80 grit. Did you use guide coat with the 150? I really recommend the dry guide coat, it is a backyard bodyman’s best friend. I use it on every round.

My suggestion is to slow down and make sure every grit removes the scratches of the previous grit. 320 is your work horse before sealer. I just use the 400 to open the urethane primer right before I apply sealer. No need for 600 wet in my experience and I have read others on here say the same.

Don
 
dhutton01 said:
Those scratches are deep, they look like 80 grit. Did you use guide coat with the 150? I really recommend the dry guide coat, it is a backyard bodyman’s best friend. I use it on every round.

My suggestion is to slow down and make sure every grit removes the scratches of the previous grit. 320 is your work horse before sealer. I just use the 400 to open the urethane primer right before I apply sealer. No need for 600 wet in my experience and I have read others on here say the same.

Don
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Yes, I used dry guide coat prior to blocking with 150. I'm going to change my process and go over the blocked areas with 320 prior to the next round of primer, whether that be for more blocking or for final surfacer prior to paint.
 
when it comes to sanding, i learned its best to change directions with every grit. sand in a ////////// direction with one grit then switch to a \\\\\\ direction for the next grit.
or vertical for one grit and horizontal with the next.
very easy to see if the sanding has completely refined the previous grit.
with a guide coat added, even easier.
 
In the pics you didn't get the first grit properly blocked out before moving to the next grit, it's easy to miss this in a shop with compromised lighting (like mine). But with 150 grit or worse scratches showing, you really need to block it all back down starting with close to 150/180 and dry guide coat like the others are saying. Use guide coat for every level of grit and level scratches as you go. If that were mine I would block the hell out of it with 180 through the base then two or three coats of epoxy and block 180, 220, 320, 400 with dry guide coat on every grit. It'll be ready for sealer and base after that.
 
Need a long thin block in that door handle - style line area, two hands very light pressure, straighten the lines, flatten the panel.
 
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Slofut said:
In the pics you didn't get the first grit properly blocked out before moving to the next grit, it's easy to miss this in a shop with compromised lighting (like mine). But with 150 grit or worse scratches showing, you really need to block it all back down starting with close to 150/180 and dry guide coat like the others are saying. Use guide coat for every level of grit and level scratches as you go. If that were mine I would block the hell out of it with 180 through the base then two or three coats of epoxy and block 180, 220, 320, 400 with dry guide coat on every grit. It'll be ready for sealer and base after that.
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My biggest mistake was not refining the 150 scratches - it was just too deep of a scratch to reapply 2K over and expect 600 to be the last sanding step. Other mistakes include not mixing the sealer right and just being rusty on spraying. I resprayed these parts this weekend and they came out great. I made sure my mixing math was correct and also was very careful not to double coat anywhere. I took care of the runs by blocking lightly with 320 once they were good and dry.
 
Wow, pretty serious shop for a hobbyist! Your truck looks great, was it as rust free as it looks in the first pic? Great find.
 
Slofut said:
Wow, pretty serious shop for a hobbyist! Your truck looks great, was it as rust free as it looks in the first pic? Great find.
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Building that shop was one of the best decisions my dad has made - we've worked on trucks, cars, tractors, dirt bikes, ATV's, you name it.

It had very little rust. Still had to do the typical cab rust repair for these trucks, but nothing on the doors.
 
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