Need some sanding advice

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PostPosted: Sun Jan 16, 2022 5:44 pm
The car was taken down to bare metal, then 2 coats of epoxy primer, then filled then 2 coats of high build primmer. In the end the car will be painted a colour that is just a shade darker than the epoxy.
This a problem I run into a lot and I'm never sure how to proceed. I've block sanded the entire car with 220 and you'll see from the pics I have broken through to the white epoxy but there are still a few little low areas.
So what is the best way to proceed? I'm temped to fill those little lows, sand again the spray another layer of primer, or could I just prime it again and hope the primer fills in those lows?
After the next layer of primer I would usually sand again with 220 but is it possible to start with 320 instead?
Thanks,
Chris
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PostPosted: Mon Jan 17, 2022 1:06 pm
if you can feel it, it might need some filler. you can use the 2-part spot filler. its really hard to tell without being there and feeling it with my sensitive hands. one thing is, you might shoot some hi-build on it and it won't be enough, BUT the filler will get it. after you block down the filler then spot spray these areas with your hi-build and block. I would use your 220 bocking the filler you want to cut it flat not round it off. you might also just go over the 220 profile with some 320 just to smooth out some of the 220. you can wrap the 320 around a folded scratch pad or a soft sanding pad and make 3-4 light passes over the 220 scratches just to smooth it out some more, get rid of some of that 220 profile. (remember to use a guide coat)
Jay D.
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PostPosted: Mon Jan 17, 2022 3:03 pm
Thanks Jay, yes I can just feel the lows with a finger, so I'll add a little filler to those.
As you can see in the pics I've broken through down to the epoxy in few places so I think I will need one more coat of primer to have enough height so I can get it down to 600 grit without breaking through again.
I have blocked it out with a set of acrylic linear blocks I made, they are so much better than the hard foam blocks I was using.
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PostPosted: Mon Jan 17, 2022 3:39 pm
Just looking at those pic.s and blowing them up somewhat.... are you sure you are getting enough 2k on there? Those blocks you made, while cutting very level, are kind of aggressive. Maybe you need some more "build" of the 2k to stop this from happening in the first place.
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PostPosted: Mon Jan 17, 2022 7:12 pm
DarrelK wrote:Just looking at those pic.s and blowing them up somewhat.... are you sure you are getting enough 2k on there? Those blocks you made, while cutting very level, are kind of aggressive. Maybe you need some more "build" of the 2k to stop this from happening in the first place.

Maybe, but I used an entire gallon of HB primer and got 2 coats on everything.
But you're right, these blocks really cut fast. I have to buy more primer tomorrow so maybe on the next and hopefully final coat I'll slow down each pass a bit and let it stack up.
Thanks

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PostPosted: Tue Jan 18, 2022 9:39 am
So now you know these are trouble spots, do the overall but get these areas with more build this time.....
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PostPosted: Tue Jan 18, 2022 11:13 am
grannyknot wrote:
DarrelK wrote:Just looking at those pic.s and blowing them up somewhat.... are you sure you are getting enough 2k on there? Those blocks you made, while cutting very level, are kind of aggressive. Maybe you need some more "build" of the 2k to stop this from happening in the first place.

Maybe, but I used an entire gallon of HB primer and got 2 coats on everything.
But you're right, these blocks really cut fast. I have to buy more primer tomorrow so maybe on the next and hopefully final coat I'll slow down each pass a bit and let it stack up.
Thanks


Two coats is not really much build primer depending on spray gun tip size.
I use regular build primer but shoot it through a 2.0 tip and start with 3 coats. Guide coat and sand to remove guide coat. If I start seeing primer before all the guide coat is gone, I scuff off the guide coat with a maroon Scotchbrite pad and shoot another couple of coats and repeat the guide coat blocking process.

Most of your build primer ends up on the floor as the panel gets blocked straight.
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PostPosted: Tue Jan 18, 2022 1:23 pm
:goodpost: :goodpost: i like to repair all my problem areas like what you have, then just spot spray these areas with a couple good wet coats of hi build then guide coat and block. keep at them until they are perfect. then if you want shoot the complete project and do you final sanding.
Jay D.
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PostPosted: Tue Jan 18, 2022 2:30 pm
^^^^^^^^^^^And what the guys said here is what I was getting at.... You really have to "work" 2k off the surface and apply more until things level up and magically you stop breaking through. Guide coating is the key to working 2k......
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PostPosted: Wed Jan 19, 2022 8:40 am
Thanks, more primer, good advice.

Next problem, some areas I can achieve a fairly smooth surface spraying the primer on but some areas the surface is pebbly and as rough as 30 grit, not sure what I'm doing wrong on those pebbly areas. By the time I sand down to the bottom of the pebbles there is no primer left and I've reached the layer below. The tech sheet says to use 1.8-2.0 tip and I'm using a 1.8, the gun wants 30psi at the tip and that is where I have it set, I'm not thinning it out at all just straight 4:1
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