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Old 04-04-2019, 07:42 PM   #1
pwdcougar
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Block sanding. How am I doing?

Started block sanding the roof of my Suburban and wanted to get some advice as to how I am doing.

The roof was sanded with 80 grit sandpaper and an orbital sander, coated with an epoxy primer then SPI 2K. I'm using Norton Gold 220 grit sandpaper on a 30" Durablock. I'm sanding at an angle of about 30 degrees. Once I'm done sanding as far as I can with the 220 I plan on spraying on Featherfill and starting again.
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Old 04-04-2019, 07:45 PM   #2
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Re: Block sanding. How am I doing?

And more pics. I'm using SEM guidecoat too. There are low areas that are black. I'm sanding evenly across the entire top until they go away or until I hit the epoxy primer.
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Old 04-04-2019, 07:58 PM   #3
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Re: Block sanding. How am I doing?

Also after a couple passes I vacuum the sandpaper and the roof. Then I wipe it down with a microfiber cloth.
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Old 04-04-2019, 08:37 PM   #4
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Re: Block sanding. How am I doing?

It's best to sand in a x pattern...not just one direction....but it's looking good
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Old 04-04-2019, 09:00 PM   #5
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Re: Block sanding. How am I doing?

Quote:
Originally Posted by mongocanfly View Post
It's best to sand in a x pattern...not just one direction....but it's looking good
Greg I'm sanding this way \ going across twice then this way /twice then I clean the panel and the sandpaper.

Is that ok?
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Old 04-04-2019, 09:08 PM   #6
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Re: Block sanding. How am I doing?

Yep...I thought you were just doing /
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Old 04-04-2019, 09:33 PM   #7
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Re: Block sanding. How am I doing?

Close up.
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Old 04-05-2019, 12:03 AM   #8
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Re: Block sanding. How am I doing?

You're doing great! Why in hell would you ruin a great job of sanding your 2k with featherfill? If it's straight, paint it!
If it even needed featherfill, which I doubt, you should have used it before 2K...
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Old 04-05-2019, 07:26 AM   #9
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Re: Block sanding. How am I doing?

Well it has low spots all over the place. I can’t paint it with all the low spots.
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Old 04-05-2019, 08:10 AM   #10
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Re: Block sanding. How am I doing?

make sure your sanding block is a good 2x or more the length of the distance between high spots. When you sand side to side, you don't want the sanding block dropping in the low and cutting out the low. If it stays on top, it only cuts the highs.
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Old 04-05-2019, 07:00 PM   #11
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Re: Block sanding. How am I doing?

Quote:
Originally Posted by MP&C View Post
make sure your sanding block is a good 2x or more the length of the distance between high spots. When you sand side to side, you don't want the sanding block dropping in the low and cutting out the low. If it stays on top, it only cuts the highs.
Iím using a 30Ē Durablock and it feels like it is working well. Iíve also been varying the angle of my X pattern from 45 to 30 or so degrees.
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Old 04-06-2019, 01:07 AM   #12
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Re: Block sanding. How am I doing?

If you can block it flat with high build 2k urethane primer, there's no need for featherfill. Right?
If you can't block it flat with high build, then you have to put more high build on or go with featherfill...in which case you'll have to high build primer the featherfill because it's not meant to be painted because it's too hard to sand with finer grits and is too coarse and porous for paint.
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Old 04-06-2019, 08:51 AM   #13
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Re: Block sanding. How am I doing?

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If you can block it flat with high build 2k urethane primer, there's no need for featherfill. Right?
If you can't block it flat with high build, then you have to put more high build on or go with featherfill...in which case you'll have to high build primer the featherfill because it's not meant to be painted because it's too hard to sand with finer grits and is too coarse and porous for paint.
Thanks. In another thread I was told I could sand the featherfill with 220 then 320 wet sand with 600 and do the base coat.
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Old 04-06-2019, 09:24 AM   #14
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Re: Block sanding. How am I doing?

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Thanks. In another thread I was told I could sand the featherfill with 220 then 320 wet sand with 600 and do the base coat.
That's unfortunate.

Feather Fill is nothing more than sprayable bondo.... made by a body filler company. Feather fill has one benefit; it's ideal for large panels that are so far from straight to start with that spreading bondo by hand is not realistic or cost effective.

Urethane high build is made with very fine talc and urethane technology which doesn't shrink, is designed for final stage before paint and is made by most paint companies because of its widely known benefits.

Hopefully your roof is straight enough to not need feather fill. You're doing a great job of blocking. If you have the odd, slight low spot you can put finishing putty on them, sand it, then high build that spot without issue.
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Old 04-06-2019, 12:28 PM   #15
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Re: Block sanding. How am I doing?

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I have worked at a shop that has won multiple awards including pebble beach for paint every one has there own opinion and what thay Like all high build primer‘s have talc in them some people say they don’t like the slick sand or feather feel because they are full of talc thay call it spray on Bondo hard to sand and you can’t paint over it or it has to be top coated non off this is true if you read the instructions I have used it for twenty years O shrinkage O Die-backs I am the one that said you can sand it down to 600 and I will stand behind it I see cars we panted 15/20 years ago that look like thay were panted yesterday I have not seen a spot putty that did not shrink and if you have used Bondo you’re urethane primer it’s not going to stop diebacks it works fine on straight stuff body shops use it it’s good for production it cost effective but this is my opinion and experience
I read the TDS on feather fill....has anyone else?
Where does it say you can paint it?

There's short cuts and experiments that many put these products through, but unless the TDS says it's ok, it's not.

My many years in the business and factory trained on fillers and several paint companies have taught me this...nonr ever said you can paint body filler.

There's the right way, then there's improv... I chose the manufacturers reccomended procedure over years of experiments.

For clarity, I said finishing putty, not glazing putty which is lacquer based and is not a product I was use anywhere.

Good luck with your project OP.
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So when is this "Old enough to know better" supposed to kick in?

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Old 04-06-2019, 03:39 PM   #16
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Re: Block sanding. How am I doing?

I have a little bit of SPI 2K primer left. Can I just spray the low spots or should I get another gallon and do the entire roof?
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Old 04-06-2019, 08:08 PM   #17
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Re: Block sanding. How am I doing?

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I have a little bit of SPI 2K primer left. Can I just spray the low spots or should I get another gallon and do the entire roof?
There's no harm in spot spraying primer if you do it right.
One such method is to spray three coats, the first being the smallest area, the second a little larger area, then a third a little larger area yet.

If you run out, you run out...then go buy more. There's no reason to spray the entire roof, unless you're selling primer.
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Old 04-06-2019, 10:10 PM   #18
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Re: Block sanding. How am I doing?

Quote:
Originally Posted by Foot Stomper View Post
There's no harm in spot spraying primer if you do it right.
One such method is to spray three coats, the first being the smallest area, the second a little larger area, then a third a little larger area yet.

If you run out, you run out...then go buy more. There's no reason to spray the entire roof, unless you're selling primer.
Got it! Thanks again!
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1969 Mercury Cougar Standard 4 speed
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Old 04-17-2019, 08:09 PM   #19
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Re: Block sanding. How am I doing?

Well the main portion of the roof finally has no low spots. I've been sanding with 220 and plan on moving on to 320 after spraying on the guide coat. One question: is there a going to be a problem in the areas where the epoxy is showing through the 2K?

Thanks

Paul
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Old 05-13-2019, 09:41 PM   #20
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Re: Block sanding. How am I doing?

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Originally Posted by nsb29 View Post
Only if you sand through to metal if that happens spot those places in with a reduced primer and then 600 The whole peas
Please explain this. I am blocking my parts now.

Here is what I have done....if you see any errors please lemme know

All pieces were sanded down to the metal...not blasted...sanded ( I know)

I put 2 coats of epoxy then 2 coats of 2k high build.

Blocked with 80g...found the low places then added filler ( Rage Gold) and blocked down with 80g. Once I thought it was straight I sprayed 2k primer again and blocked with 180 then 220 ( the stage Im at now)

I have burned through some areas down to the metal, not big areas more like the size of a quarter on some places.

I plan on spraying 2 more coats of high build then blocking with 320.

Thoughts?
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Old 05-13-2019, 11:00 PM   #21
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Re: Block sanding. How am I doing?

If you've got bare metal, then it needs epoxy on it..do the spots you hit bare metal look like high spots?...if so then you've got some more body work to do
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Old 05-13-2019, 11:30 PM   #22
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Re: Block sanding. How am I doing?

Not so much high...more of edges...around corners etc.
Will epoxy be fine over the 2k primer? Can I spot the bare places or do I need to spray the whole panel again?

Last one ..after the epoxy and block with 320 do I spray 2k again or can I go to color then
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Old 05-14-2019, 12:08 AM   #23
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Re: Block sanding. How am I doing?

The epoxy will be fine over the 2k. You can just spot the epoxy over the bare medal and then reprime with 2k. You can not block sand epoxy.
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Old 05-14-2019, 12:14 AM   #24
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Re: Block sanding. How am I doing?

Epoxy only works on bare steel. You can overlap the 2k urethane in the adjacent areas with zero negative effects.

The next stage is tricky because if you high build and sand too much, you can burn through the epoxy again. If you do, and the panels is otherwise perfect, you can paint. A tiny area of unprimed epoxy is acceptable to some. If not to you, epoxy prime and paint wet on wet.
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Old 05-14-2019, 12:22 AM   #25
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Re: Block sanding. How am I doing?

Quote:
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Epoxy only works on bare steel. You can overlap the 2k urethane in the adjacent areas with zero negative effects.

The next stage is tricky because if you high build and sand too much, you can burn through the epoxy again. If you do, and the panels is otherwise perfect, you can paint. A tiny area of unprimed epoxy is acceptable to some. If not to you, epoxy prime and paint wet on wet.
Ok....Do I need to sand with 80g before I epoxy. It is currently down to 220g
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