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The proper amount of sanding

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  • Member since
    December 2018
The proper amount of sanding
Posted by Ted4321 on Tuesday, April 16, 2019 5:58 PM

Ladies and gents-

I hate to say it, but this is a beginner question.  What is the proper amount of sanding of parts in preparation for priming? 

I'm not necessarily referring to the edges or mating surfaces, that seems straight forward.  I'm referring more to the "faces" of parts such as wing, or body panels, or fuselage parts. 

What is the goal of sanding these areas and how do i know the job is done?  Run the gamut of 400 grit through 12000 to get nice and shiny? Or is 1000 enough?  

I'd love to hear your opinions and techniques. 

Thanks in advance. 

T e d

  • Member since
    August 2014
  • From: Willamette Valley, Oregon
Posted by goldhammer on Tuesday, April 16, 2019 6:15 PM

I just give them a good scuff with a gray scotchbrite pad. Just enough to get rid of the shiny surface. Since I work at a body shop, I have easy access to them.  Can get them at an auto parts store or auto paint supply store.  Not real expensive either.

They don't remove any detail, and leave a nice dull finish with some bite for primer.  Will also do a light scuff with them prior to color coat to give some bite to the primer.  Since I generally do aircraft and ships in flat paints, I don't need to worry about a glossy base like you need for finishes like alclad, but after primer and before a gloss coat should be the same. Though I'll let others chime in with their preferences for gloss stuff.

  • Member since
    December 2018
Posted by Ted4321 on Tuesday, April 16, 2019 9:03 PM

Thanks for the info Goldhammer.  I'll have to give them a rip. 

T e d

  • Member since
    November 2008
  • From: Far Northern CA
Posted by mrmike on Tuesday, April 16, 2019 11:51 PM

I hope you get a lot of responses 'cause there are many good builders here who offer many good tips. A lot of what I know I learned here; giving credit where it's due.

Sticking to surface prep alone, I believe that washing and rinsing all the sprues is a good idea. From there surface treatment is about what you have to work with. Some kits have nice shiny plastic while others will be more coarse. My favorite sanding product is 3M's line of foam backed pads, about 5" x 5" square, available at automotive paint stores. For the shiny plastic, the Microfine grade used wet is all it takes (I use the pads until they're bald). Superfine grade will buff down coarse surfaces in short order, again used wet.

Surface prep also has to do with the type of primer and paint products you use. Lacquers are very "hot" and bond to smooth plastic, enamels less so. Acrylics need a surface with more "tooth". It's always a good idea to try differant techniques on scrap plastic before doing it to the project you value...but I can't say I've always done that.

Maybe something I said will help; happy modelling!

mike

 

 

 

  • Member since
    May 2013
  • From: Indiana, USA
Posted by Greg on Wednesday, April 17, 2019 9:18 AM

goldhammer

I just give them a good scuff with a gray scotchbrite pad. Just enough to get rid of the shiny surface. Since I work at a body shop, I have easy access to them.  Can get them at an auto parts store or auto paint supply store.  Not real expensive either.

They don't remove any detail, and leave a nice dull finish with some bite for primer.  Will also do a light scuff with them prior to color coat to give some bite to the primer.  Since I generally do aircraft and ships in flat paints, I don't need to worry about a glossy base like you need for finishes like alclad, but after primer and before a gloss coat should be the same. Though I'll let others chime in with their preferences for gloss stuff.

 

I never really considered sanding parts prior to priming (short of some nasty plastic surface imperfection). You do make a compelling argument. Hmmmmm......

-Greg

  • Member since
    August 2014
  • From: Willamette Valley, Oregon
Posted by goldhammer on Wednesday, April 17, 2019 10:11 AM

I'll add that my go to primer is MM's 2981 gray laquer primer in the rattle can.

With the exception of Alclad, all my paints are acrylic.

  • Member since
    November 2009
  • From: Twin Cities of Minnesota
Posted by Don Stauffer on Wednesday, April 17, 2019 10:13 AM

Greg

 

 
goldhammer

I just give them a good scuff with a gray scotchbrite pad. Just enough to get rid of the shiny surface. Since I work at a body shop, I have easy access to them.  Can get them at an auto parts store or auto paint supply store.  Not real expensive either.

They don't remove any detail, and leave a nice dull finish with some bite for primer.  Will also do a light scuff with them prior to color coat to give some bite to the primer.  Since I generally do aircraft and ships in flat paints, I don't need to worry about a glossy base like you need for finishes like alclad, but after primer and before a gloss coat should be the same. Though I'll let others chime in with their preferences for gloss stuff.

 

 

 

I never really considered sanding parts prior to priming (short of some nasty plastic surface imperfection). You do make a compelling argument. Hmmmmm......

 

I'm with Greg.  I never sand raw plastic.  I sand the primer to take out any dust particles or other imperfections.  Throughout the painting process I sand to keep smooth surface.  I can see when surface is good, and ready for next coat.

I certainly do sand seams that have been filled, and primer helps me to see if the surface is ready for painting.

 

Don Stauffer in Minnesota

  • Member since
    March 2003
  • From: Western North Carolina
Posted by Tojo72 on Wednesday, April 17, 2019 10:14 AM

I have to say that I never sanded the surface or washed my plastic parts to apply primer,the primer has always adhered with no problem as well as the paint coat.

  • Member since
    December 2018
Posted by Ted4321 on Wednesday, April 17, 2019 10:32 AM

Well these are all very helpful and interesting responses.  

I think my builds will be progressing much faster now.  Big Smile

Thanks everyone!  

T e d

  • Member since
    July 2014
  • From: Franklin Wi
Posted by Bakster on Wednesday, April 17, 2019 11:41 AM

My two centavos..

1. I do wash the plastic, usually before paint. Not only to remove potential mold release agents, but more so to remove any oils I left behind from my handling. Nacho chips--potato chips--chocolate bars--all the good stuff I may have been stuffing my face with adds to the problem too. Stick out tongue

2. I don't sand raw plastic unless there are imperfections. For better adhesion, maybe I should. Generally speaking--I have not had problems by not sanding. Will consider this more though.

3. Taking this a little further than the plastic question; I do wet sand the primer coat. Mostly--it knocks the grain down for subsequent paint layers. It's cumulative. So, each layer adds more grain to the finish. 

I am out of centavos. Now what.

  • Member since
    December 2002
  • From: Bury St Edmunds, Suffolk, England
Posted by Bish on Wednesday, April 17, 2019 2:09 PM

Tojo72

I have to say that I never sanded the surface or washed my plastic parts to apply primer,the primer has always adhered with no problem as well as the paint coat.

 

Ditto

Only sanding i do is seams and any rough patches and i have never washed a kit or parts, be it plastic or resin.

I am a Norfolk man and i glory in being so

 

On the bench: Airfix 1/72nd Harrier GR.3/Fujimi 1/72nd Ju 87D-3

  • Member since
    May 2013
  • From: From the Mit, but live in Mason, O high ho
Posted by hogfanfs on Wednesday, April 17, 2019 2:40 PM

Bish

 

 
Tojo72

I have to say that I never sanded the surface or washed my plastic parts to apply primer,the primer has always adhered with no problem as well as the paint coat.

 

 

 

Ditto

Only sanding i do is seams and any rough patches and i have never washed a kit or parts, be it plastic or resin.

 

Ditto #2

 Bruce

 

 On the bench:  1/48 Eduard MiG-21MF

                        1/35 Takom Merkava Mk.I

 

  • Member since
    April 2009
  • From: Longmont, Colorado
Posted by Cadet Chuck on Wednesday, April 17, 2019 8:05 PM

Another vote for no sanding.  I have never found it necessary, as the primer always adheres to bare plastic very well.  I don't wash it, either, the only exception being resin parts.

Gimme a pigfoot, and a bottle of beer...

  • Member since
    April 2019
Posted by united2019 on Thursday, April 18, 2019 3:00 PM

how about the Stainless Steel Model File Stick from http://www.galaxy-model.com?  Do they last forever?

  • Member since
    January 2013
Posted by BlackSheepTwoOneFour on Thursday, April 18, 2019 3:17 PM

I don’t sand before priming. Besides, I don’t see the need to. A waste of time actually...

  • Member since
    July 2013
Posted by steve5 on Thursday, April 18, 2019 3:22 PM

I think those sticks are sticks only , you have to stick on the sandpaper .

 

  • Member since
    January 2013
Posted by BlackSheepTwoOneFour on Thursday, April 18, 2019 5:12 PM

steve5

I think those sticks are sticks only , you have to stick on the sandpaper .

 

 

Yup. They're not like a nail file per say. Save your money on those. Buy the cheap sandstick in the beauty dept at Walmart. However, the finer grits you have to find at Hobby Lobby or online.

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