Best way to cut the urethane wave - Chevelle Tech
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post #1 of 15 (permalink) Old May 10th, 19, 1:04 PM Thread Starter
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Curt
 
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Best way to cut the urethane wave

I machine wet sanded 1000, 2000, 3000, then 3M Perfect it 1,2,3. The Perfect it #1 fixes a lot of flaws. Lots of time though.
I have my Chevelle trunk mirror smooth on the surface, but then the urethane wave underneath is awful.
I took the advice of several and dropped down to 600 grit (wet) on a small Durablock and then a 12" Durablock. The Durablock while wet sanding with 600 grit wants to "stick" to the surface and I have to force it to actually get it to move (sand). I feel like this is not the right way to do this. What say you guys?
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post #2 of 15 (permalink) Old May 10th, 19, 3:10 PM
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Re: Best way to cut the urethane wave

To cut urethane wave properly, I start with 800 grit and use a long block just as you would when blocking primer. Using a short block can create small valleys, further enhancing the wave. The key is long block sanding in diagonal directions to cut the highs off evenly, throughout the entire panel. You must have at least 3 good coats of clear to start with 800. Only light pressure should be needed to cut the clear with 800 grit. Lots of water with dish detergent added will help keep the paper lubed and clean. See pics in my garage of my black car and you will see what can be accomplished in home sprayed project
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post #3 of 15 (permalink) Old May 10th, 19, 4:54 PM
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Re: Best way to cut the urethane wave

Well, I say machine sanding will smooth the orange peel but but leave the panel wavy. You should only be machine sanding once you hit say 3000-4000 grit paper.

I also say, Durablocks are pure sh!t I'll repeat Durablocks are pure sh!t!

Go down to Home Depot buy some lexen plexiglass. Cut the lexen to various lengths, use that instead of Durablocks. I would also start with 600-800 grit. I also started using 3M or Mirka dry guide coat. Block the panel with 800 grit, dry it off, apply guide coat covering the entire panel. Now block with 1000 grit, this will TELL YOU when the 800 grit scratches are gone because the guide coat is gone.

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post #4 of 15 (permalink) Old May 10th, 19, 8:40 PM
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Re: Best way to cut the urethane wave

Quote:
Originally Posted by sevt_chevelle View Post
Well, I say machine sanding will smooth the orange peel but but leave the panel wavy. You should only be machine sanding once you hit say 3000-4000 grit paper.

I also say, Durablocks are pure sh!t I'll repeat Durablocks are pure sh!t!

Go down to Home Depot buy some lexen plexiglass. Cut the lexen to various lengths, use that instead of Durablocks. I would also start with 600-800 grit. I also started using 3M or Mirka dry guide coat. Block the panel with 800 grit, dry it off, apply guide coat covering the entire panel. Now block with 1000 grit, this will TELL YOU when the 800 grit scratches are gone because the guide coat is gone.
I begin cutting with 800 with blocks if needed. Wave is usually prevented by not hammering on the clear like an animal. Lexan and Pexiglass are two different products; but I get your point. Make your own blocks. I have dozens. Less expensive to get scraps from sign shops who make sign box faces out of both than deal with Home Depot. I was in the sign business before the restoration business. Decades of jobs and no wave.
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post #5 of 15 (permalink) Old May 11th, 19, 10:17 AM
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Re: Best way to cut the urethane wave

I knock down the wave before paint. Once panel is ready for paint, I re-do everything, dry guide coat, 400 dry on a long long block with very little pressure and it finds and destroys waves in the primer coats. Then re-guide coat, then 800 wet on a 12" block, I use a 2"x 2" durablock and the paper doesn't suction to the surface that bad, and then off to paint. At least you know the substrate is wave-free before paint.
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post #6 of 15 (permalink) Old May 12th, 19, 8:31 PM
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Re: Best way to cut the urethane wave

Quote:
Originally Posted by stanski View Post
I knock down the wave before paint. Once panel is ready for paint, I re-do everything, dry guide coat, 400 dry on a long long block with very little pressure and it finds and destroys waves in the primer coats. Then re-guide coat, then 800 wet on a 12" block, I use a 2"x 2" durablock and the paper doesn't suction to the surface that bad, and then off to paint. At least you know the substrate is wave-free before paint.
That's obvious but not the urethane wave in the clear that the thread is about.

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post #7 of 15 (permalink) Old May 19th, 19, 9:07 AM Thread Starter
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Hey Sevt. You really opened my eyes to reality! I got a 12in x 12in half inch thick plexiglass block from Amazon for twenty bucks. I cut it in inch and a quarter strips and started on my hood. Wow! I did not realize the difference between the flexing of the dura blocks and not flexing of the plexiglass. I have a couple questions when you did the guide coat with the Thousand grit did you wet or dry sand it? Also when I hit the clear I'm going to have to re-spray some clear. Can I just sand it with the 800 and then spray? Thank you by the way.

Quote:
Originally Posted by sevt_chevelle View Post
Well, I say machine sanding will smooth the orange peel but but leave the panel wavy. You should only be machine sanding once you hit say 3000-4000 grit paper.

I also say, Durablocks are pure sh!t I'll repeat Durablocks are pure sh!t!

Go down to Home Depot buy some lexen plexiglass. Cut the lexen to various lengths, use that instead of Durablocks. I would also start with 600-800 grit. I also started using 3M or Mirka dry guide coat. Block the panel with 800 grit, dry it off, apply guide coat covering the entire panel. Now block with 1000 grit, this will TELL YOU when the 800 grit scratches are gone because the guide coat is gone.
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post #8 of 15 (permalink) Old May 19th, 19, 10:21 AM Thread Starter
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Quote:
Originally Posted by 65conv View Post
Hey Sevt. You really opened my eyes to reality! I got a 12in x 12in half inch thick plexiglass block from Amazon for twenty bucks. I cut it in inch and a quarter strips and started on my hood. Wow! I did not realize the difference between the flexing of the dura blocks and not flexing of the plexiglass. I have a couple questions when you did the guide coat with the Thousand grit did you wet or dry sand it? Also when I hit the clear I'm going to have to re-spray some clear. Can I just sand it with the 800 and then spray? Thank you by the way.

Quote:
Originally Posted by sevt_chevelle View Post
Well, I say machine sanding will smooth the orange peel but but leave the panel wavy. You should only be machine sanding once you hit say 3000-4000 grit paper.

I also say, Durablocks are pure sh!t I'll repeat Durablocks are pure sh!t!

Go down to Home Depot buy some lexen plexiglass. Cut the lexen to various lengths, use that instead of Durablocks. I would also start with 600-800 grit. I also started using 3M or Mirka dry guide coat. Block the panel with 800 grit, dry it off, apply guide coat covering the entire panel. Now block with 1000 grit, this will TELL YOU when the 800 grit scratches are gone because the guide coat is gone.
Also, the 6" velcro machile sandpaper (1000grit, 2000grit, 3000grit, and I also tried some 5000grit) seems to cause more random scratches than they smooth out. Is it because they are cheap? I got red label adhesives 10 packs for example. I dont recall the trizact paper doing that but it was $90 for 15 pads.
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post #9 of 15 (permalink) Old May 19th, 19, 12:32 PM
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Quote:
Originally Posted by 65conv View Post
Quote:
Originally Posted by 65conv View Post
Hey Sevt. You really opened my eyes to reality! I got a 12in x 12in half inch thick plexiglass block from Amazon for twenty bucks. I cut it in inch and a quarter strips and started on my hood. Wow! I did not realize the difference between the flexing of the dura blocks and not flexing of the plexiglass. I have a couple questions when you did the guide coat with the Thousand grit did you wet or dry sand it? Also when I hit the clear I'm going to have to re-spray some clear. Can I just sand it with the 800 and then spray? Thank you by the way.

Quote:
Originally Posted by sevt_chevelle View Post
Well, I say machine sanding will smooth the orange peel but but leave the panel wavy. You should only be machine sanding once you hit say 3000-4000 grit paper.

I also say, Durablocks are pure sh!t I'll repeat Durablocks are pure sh!t!

Go down to Home Depot buy some lexen plexiglass. Cut the lexen to various lengths, use that instead of Durablocks. I would also start with 600-800 grit. I also started using 3M or Mirka dry guide coat. Block the panel with 800 grit, dry it off, apply guide coat covering the entire panel. Now block with 1000 grit, this will TELL YOU when the 800 grit scratches are gone because the guide coat is gone.
Also, the 6" velcro machile sandpaper (1000grit, 2000grit, 3000grit, and I also tried some 5000grit) seems to cause more random scratches than they smooth out. Is it because they are cheap? I got red label adhesives 10 packs for example. I dont recall the trizact paper doing that but it was $90 for 15 pads.
It always amazes how some expect the cheapest what ever to preform anywhere near the professional grade. If the pro’s use them for awesome results then why do some people expect the cheapest items in the hands of inexperienced to yield anything but poor results.

Life is too short for caring about every bodies else's stuff
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post #10 of 15 (permalink) Old May 20th, 19, 9:53 AM
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Re: Best way to cut the urethane wave

Quote:
Originally Posted by TechNova View Post
That's obvious but not the urethane wave in the clear that the thread is about.
Just my thoughts, the wave may originate in the 2K urethane high build primer and is misdiagnosed as a urethane clear wave, didn't think I was missing what the post is about.
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post #11 of 15 (permalink) Old May 21st, 19, 5:50 PM
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Re: Best way to cut the urethane wave

I use Red label abrasives for my 2x36 sanding belts, those are on par with 3M. But typically with abrasives you get what you pay for. I suggest 3M, Mirka, Norton and Klingspor. Couple years ago I bought the cheaper 3M sanding discs, more then half the cost of the 3M gold. I quickly learned that those cheaper discs did not cut as fast and wore out faster so my usage increased. In the end those cheaper disc costed the same as the higher priced ones because I used more discs and my time spent on the job increased.

Once you start using 3000-5000 grit you should start to actually buff the surface.

You block the panel with say 800 grit, dry it off, wipe it with dry guide coat then wet sand it with 1000 grit.


Quote:
Also when I hit the clear I'm going to have to re-spray some clear. Can I just sand it with the 800 and then spray? Thank you by the way.
Explain???

Currently working on How to videos and replacement sheetmetal panels

1970 chevelle getting Sliced and Diced Anything But STOCK
1970 chevelle SS455 not a typo its a BUICK BABY
1949 and 1972 chevy trucks
Pictures of my work

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post #12 of 15 (permalink) Old May 21st, 19, 7:33 PM Thread Starter
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Quote:
Originally Posted by sevt_chevelle View Post
I use Red label abrasives for my 2x36 sanding belts, those are on par with 3M. But typically with abrasives you get what you pay for. I suggest 3M, Mirka, Norton and Klingspor. Couple years ago I bought the cheaper 3M sanding discs, more then half the cost of the 3M gold. I quickly learned that those cheaper discs did not cut as fast and wore out faster so my usage increased. In the end those cheaper disc costed the same as the higher priced ones because I used more discs and my time spent on the job increased.

Once you start using 3000-5000 grit you should start to actually buff the surface.

You block the panel with say 800 grit, dry it off, wipe it with dry guide coat then wet sand it with 1000 grit.


Quote:
Also when I hit the clear I'm going to have to re-spray some clear. Can I just sand it with the 800 and then spray? Thank you by the way.
Explain???
once I use the plexiglass with 800 and guide coat with 1000, if I know I got into the paint, can I spray it with the clear right then or do I need to rough it up more with 400 or 600 for the clear to stick?
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post #13 of 15 (permalink) Old May 21st, 19, 8:26 PM
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Re: Best way to cut the urethane wave

Quote:
Originally Posted by 65conv View Post
once I use the plexiglass with 800 and guide coat with 1000, if I know I got into the paint, can I spray it with the clear right then or do I need to rough it up more with 400 or 600 for the clear to stick?

If you broke through the clear coat and exposed the color coat, then you will NEED to spot that area with base coat.


But yes 800 is fine for clear.

Currently working on How to videos and replacement sheetmetal panels

1970 chevelle getting Sliced and Diced Anything But STOCK
1970 chevelle SS455 not a typo its a BUICK BABY
1949 and 1972 chevy trucks
Pictures of my work

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post #14 of 15 (permalink) Old May 23rd, 19, 5:39 PM Thread Starter
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Re: Best way to cut the urethane wave

Quote:
Originally Posted by modern malibu View Post
To cut urethane wave properly, I start with 800 grit and use a long block just as you would when blocking primer. Using a short block can create small valleys, further enhancing the wave. The key is long block sanding in diagonal directions to cut the highs off evenly, throughout the entire panel. You must have at least 3 good coats of clear to start with 800. Only light pressure should be needed to cut the clear with 800 grit. Lots of water with dish detergent added will help keep the paper lubed and clean. See pics in my garage of my black car and you will see what can be accomplished in home sprayed project
Thank you
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post #15 of 15 (permalink) Old May 23rd, 19, 5:42 PM Thread Starter
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Re: Best way to cut the urethane wave

Quote:
Originally Posted by Grock-co View Post
It always amazes how some expect the cheapest what ever to preform anywhere near the professional grade. If the pro’s use them for awesome results then why do some people expect the cheapest items in the hands of inexperienced to yield anything but poor results.
Thank you. That was very helpful.
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