Sanding Grit Recommendations

      How fine is too fine between coats, for good adhesion? August 31, 2009

Question
I was just on the ML Campbell site reading up on something and came across their recommendation of finish sanding close grained hardwoods like maple with 120 grit. I usually start with 120 and go to 180 or 220. Is this just them covering their asses with regards to adhesion, or this the common standard ?

Forum Responses
(Finishing Forum)
From contributor B:
I always end with 120. Usually I start with it too - no need to go finer. I use a Dewalt 421 sander.



From contributor W:
As far as sanding goes I would finish with 150 or 180. If you sand with 120 and you like the results then stick with it! I always went finer.


From contributor G:
I use the MLC products also. I always sand to 150 - 120 is a bit to coarse for me. This is usually my starting point on solids, 150 on veneers. Unless you really sand ultra fine (400+) or burnish the surface, I can't see having adhesion problems. I also don't see over-sanding either. You can get the finish glass smooth at 150 grit so why would you want to spend the effort by going further, unless you are sanding endgrain to reduce stain darkening.


From contributor B:
Contributor W and G have it right. I always start with a worn 100 grit pad on an orbital sander, and finish with a fresh 150. A fresh 120 sounds a hair too rough, and might leave swirl marks on the wood that you might see with rubbing stain. Also, for large panels, like a refrigerator panel, or finished end, a 1/2 sheet panel sander kicks butt. I use that then pass over with an orbital. But yeah, sounds like their just covering their ass saying finish on 120. I mean hell, if 150 is too fine to get adhesion, what do you do when u sand your sealers, use 120? If 120 is required to get adhesion, then you'd have to sand your sealer with 120 too, unless its going to chemically bond.


From contributor J:
I can do that when I'm hand sanding with a block and going with the grain, like when I sand my raised panels before staining and assembling. Sometimes I do that and it makes the stain take better. But that's way too coarse for any of my sanders. So I guess it depends on what type sanding they're talking about.


From contributor A:
I agree with contributor G. MLC also recommends not passing 240 grit between coats. It's been the industry standard in auto finishing to sand 320 between coats. We primarily use MLC products, mostly waterborne with a little 2K thrown in here and there. We always sand 150 bare wood, 220 endgrain on raised panels, 220 after primer/putty, 320 between coats. Weve never had an adhesion issue in 12 years.


From contributor J:
120 is fine for oak, ash and hickory but maple and most everything else I take to 150 with the exception of walnut which I take to180 or even 220 if I'm going to stain it. The final grit depends on the wood and the end result I am trying to achieve. One thing to note however: different brands and types of paper can vary quite a bit within a stated grit size. For instance: Klingspor P33 120 is considerably coarser than 3M Gold 120 in my opinion.



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