Is it necessary to sand in between coats?

Offline Joz

Is it necessary to sand in between coats?
« on: January 24, 2009, 01:56:50 PM »
I'm applying lacquer (aerosol) as a clear gloss finish. I didn't use a sealer. Do I need to sand smooth in between coats? How often? With what grit? To me it seems unnecessary except for removal of imperfections. What's your experience tell you?

joz

Offline tfarny

  • ******
  • 4,481
    • View Profile
Re: Is it necessary to sand in between coats?
« Reply #1 on: January 24, 2009, 04:34:58 PM »
I believe there are two schools of thought - sand lightly with 400 or so, or don't sand till the end. On the one hand, you want to not end up with a bunch of orange peel at the end of it all, on the other hand you could easily get a sand through, and it's a pain. I say just sand at the end, but I'm not a real expert.

Online Mayfly

  • ******
  • 5,475
    • View Profile
    • Link to my band
Re: Is it necessary to sand in between coats?
« Reply #2 on: January 24, 2009, 06:41:38 PM »
I've sanded between coats and ended up going through the finish.

Sand at the end -

be safe - sand later.

Re: Is it necessary to sand in between coats?
« Reply #3 on: January 25, 2009, 06:36:50 AM »
There are two main reasons to sand between coats.

1.  Promote adhesion between coats.  This is mainly an issue for curing type finishes that do not burn in (e.g. poly, acrylics) or finishes that have sat for a while.  In this case you are just lightly scuffing to break the surface.  Also, by adding some 'tooth' to the surface you slightly reduce the risk of runs.

2.  Leveling and filling.  By doing this in stages you safe a little time at the end, especially with finishes that can take substantially longer to cure as more coats are added (e.g. shellac)

I do not sand between coats of lacquer.  My approach is to have thoroughly prepped the the surface, grain filled, and have applied and sanded  enough sanding sealer to have a very level surface ready for topcoating.

Offline DangerousR6

  • Administrator
  • ******
  • 13,565
  • F.R.E.D.
    • View Profile
Re: Is it necessary to sand in between coats?
« Reply #4 on: January 26, 2009, 09:09:45 AM »
I've sanded between coats and ended up going through the finish.

Sand at the end -

be safe - sand later.
What were you sanding with mayfly, a belt sander...... :laughing11:

Just messin' with ya... :icon_biggrin:

Online Mayfly

  • ******
  • 5,475
    • View Profile
    • Link to my band
Re: Is it necessary to sand in between coats?
« Reply #5 on: January 26, 2009, 09:16:55 AM »
I've sanded between coats and ended up going through the finish.

Sand at the end -

be safe - sand later.
What were you sanding with mayfly, a belt sander...... :laughing11:

Just messin' with ya... :icon_biggrin:

Nah - I was using a planer.

Offline DangerousR6

  • Administrator
  • ******
  • 13,565
  • F.R.E.D.
    • View Profile
Re: Is it necessary to sand in between coats?
« Reply #6 on: January 26, 2009, 09:46:04 AM »
I've sanded between coats and ended up going through the finish.

Sand at the end -

be safe - sand later.
What were you sanding with mayfly, a belt sander...... :laughing11:

Just messin' with ya... :icon_biggrin:

Nah - I was using a planer.
:laughing7:

Re: Is it necessary to sand in between coats?
« Reply #7 on: January 27, 2009, 07:12:01 AM »
I've sanded between coats and ended up going through the finish.

Sand at the end -

be safe - sand later.
What were you sanding with mayfly, a belt sander...... :laughing11:

Just messin' with ya... :icon_biggrin:



Nah - I was using a planer.

Well, as long as it wasn't an angle grinder.

They're pretty aggressive.

Watershed

  • Guest
Re: Is it necessary to sand in between coats?
« Reply #8 on: January 27, 2009, 09:44:53 AM »
Depends on what you are using (paint) and what you want to achieve.
I agree, it's not "necessary", but it can have its advantages.

I really don't think there is a wrong answer here, but I am a fan of sanding back at the later stages of clear coat (as long as you are not using a belt sander, planer or angle grinder ;-)).
Sand too soon (first or second coat), and a sandthrough can be easy and become a real big pain.  After many coats of clear nitro (aerosol) without sanding, you are probably going to have some pretty decent orange peel buildup.  Once the lacquer is built up to that level, I have had sucess with sanding back partially and lightly using 600 grit (wet using naptha), manily to knock down the tops of the orange peel.  At this point I'd spray it again (on the light side), then hit it with some 1,000 grit (wet using Naptha) once it has had some time to cure.  That should get you pretty good and level with minimal chance of sandthrough.  The local auto parts store may sell 1,000 grit for sanding clearcoat.  Home Depot/Lowes will probably not sell it.

Good Luck,
James

Offline Joz

Re: Is it necessary to sand in between coats?
« Reply #9 on: January 28, 2009, 04:45:18 AM »


I see people use Naphtha here quite often. I'm unfamiliar with this stuff. I bought some from Home Depot but I'm worried about using something that I have no experience with. In particular, since the stuff is a thinner I just imagine it turning the coat into a gooey mess.

You're right about the sandpaper not being sold at HD or Menards. Weird. Feels odd going into an auto supply store to pickup music instrument finishing products. I wonder how a pine tree air freshener will look hanging from my tuning machines.

joz

Re: Is it necessary to sand in between coats?
« Reply #10 on: January 28, 2009, 05:14:31 AM »
Feels odd going into an auto supply store to pickup music instrument finishing products. I wonder how a pine tree air freshener will look hanging from my tuning machines.

When F started maiking guitars he walked into an auto supply store to pick up some cans of paint. That's the reason for the colors of the vintage Fenders - the cars of that period were in those colors. It's also the reason for the Nitro finish - the cars at the time were finished with Nitro. Should make you feel less odd...

Watershed

  • Guest
Re: Is it necessary to sand in between coats?
« Reply #11 on: January 28, 2009, 09:09:56 AM »


I see people use Naphtha here quite often. I'm unfamiliar with this stuff. I bought some from Home Depot but I'm worried about using something that I have no experience with. In particular, since the stuff is a thinner I just imagine it turning the coat into a gooey mess.

You're right about the sandpaper not being sold at HD or Menards. Weird. Feels odd going into an auto supply store to pickup music instrument finishing products. I wonder how a pine tree air freshener will look hanging from my tuning machines.

joz

Naptha:  I can see your cause for concern, but fear not, it will not harm a nitro finish, or really any other one that I'm aware of.  Same applies to mineral spirits.  I think it's great for wetsanding personally.  The advantage to wetsanding (I seldom sand dry), is no dust and the paper not gumming up.  The advantage to naptha over water is that water will likely cause the wood to swell, causing many many problems.  This swelling issue will be most pronounced anywhere a hole is drilled in the body. 

The stink is a drawback, but it's really no where near as bad as thinner.  Probably also should wear some nitrile, or similar, gloves.

They market the 1,000 grit sandpaper as being for clearcoat.  I suppose HD shoppers are not fans of a high gloss.

James