Silicone carbide vs aluminum oxide sandpaper?

Discussion in 'Finely Finished' started by goodchicken, Jul 14, 2019.

  1. goodchicken

    goodchicken TDPRI Member

    Age:
    43
    Posts:
    63
    Joined:
    Oct 8, 2018
    Location:
    US
    I've heard some kinda confusing opinions.

    One is to start with aluminum oxide coarse grits and finish with silicone carbide fine grits.

    Another is to never use silicone carbide for wood.

    Aluminum oxide always seems more expensive, if anything can be taken from that.

    One thing I'm trying to defeat is those tiny scratches that are easily missed until the finish reveals them. I start with no lower than 80, sometimes 100 or 120. Then go 150, 180, and finally 220.

    I haven't been really paying attention to material or coatings so far, just grits. Having some mixed results, although my technique doesn't always seem to be the problem (could be wrong there).

    I like bare/dyed wood finishes, so I haven't been adding anything that would really fill and scratches and would be fine under an opaque finish.
     
  2. IMadeYouReadThis

    IMadeYouReadThis Tele-Meister

    Posts:
    206
    Joined:
    Jul 4, 2018
    Location:
    Somewhere in the Rockies
    I'm not an expert on finishing and I personally don't have any experience with comparing those two types of sandpaper side by side. Sandpaper is just sandpaper in my world. I do, however, know that before applying a finish you can go over with mineral spirits and it will reveal just about every flaw visible under most finishes.

    You could take a few pieces of similar scrap wood, go through the finishing process with different grits and materials of sandpaper, and put a finish over it to see what works best.

    Of course, I've only finished 2 instruments in my life. Take it for what it's worth.
     
  3. aerhed

    aerhed Friend of Leo's

    Age:
    60
    Posts:
    2,395
    Joined:
    Dec 24, 2016
    Location:
    Boulder, WY
    There are two ways to have scratches. You either just put them there, or you left them there.
     
    Jim_in_PA and dan40 like this.
  4. W.L.Weller

    W.L.Weller Tele-Holic

    Posts:
    540
    Joined:
    May 20, 2014
    Location:
    Queens
    Try a final pass with 360? I don't know that the chemical composition of the abrasive matters that much for wood. But I'm not in the abrasives or wood finishing businesses.
     
  5. goodchicken

    goodchicken TDPRI Member

    Age:
    43
    Posts:
    63
    Joined:
    Oct 8, 2018
    Location:
    US
    You've never heard of gremlins?

    I thought the material didn't matter other than probably just durability, but I've heard otherwise. Never hurts to get other's opinions though.
     
  6. Vizcaster

    Vizcaster Poster Extraordinaire

    Posts:
    5,078
    Joined:
    Sep 15, 2007
    Location:
    Glen Head, NY
    I think the bigger difference is what's available retail. Silicon carbide in my experience is almost always wet-or-dry paper, and aluminum oxide is for papers that have to be used dry. Wet-or-dry paper is readily available in very fine grits used for rubbing out finishes, and I've never seen it cheaper than aluminum oxide.

    I prefer 3M Frecut Gold aluminum oxide paper for the finer grits because I prefer to sand finishes dry rather than wet.

    Klingspoor is a good online source for good quality but not necessarily expensive paper. There are other exotic abrasives (aluminum zirconia for example) that fit other purposes like staying cool when smoothing metal, which you don't need for general woodworking. There's also plenty of choices for the backing especially if you're using a random orbit sander (I prefer heavier backing so the paper can be re-used).

    Also remember if the paper clogs up with pitch or resin from the wood, it will create a hard spot on the paper that can cause scratches.
     
    goodchicken likes this.
  7. Peltogyne

    Peltogyne Tele-Afflicted

    Posts:
    1,960
    Joined:
    Oct 29, 2012
    Location:
    Northern California
    I suspect the criticism of silicon carbide is the potential to leave dark grit behind that can be visible if it gets in the grain. I've had issues with it on maple.
     
    goodchicken likes this.
  8. old wrench

    old wrench Tele-Holic

    Posts:
    885
    Joined:
    Feb 2, 2017
    Location:
    corner of walk and don't walk
    The short answer is that alumina oxide is more durable in the larger grit sizes. Silicon carbide is actually harder and sharper, but it fractures more easily, which makes it more useful when the grain size is smaller to start out with.


    I can tell ya one thing for sure - sandpaper quality has improved dramatically in the last 20 or 30 years! :)

    Most of the improvement has been in the backing material and the adhesive that fastens the grit.
    Better quality control has also led to more consistent grit size too, which lessens the chance of deep scratches from stray oversize grits.



    The most common sanding problem I've had is ending up with scratches that haven't been sanded out.

    I'm probably preaching to the choir again :), but the best way to avoid scratches is to follow a sequence with progressively finer grits and to completely sand out the scratches left by the previous grit.

    On metal, it's easier to see when the previous scratch pattern is sanded out because you can alternate your sanding direction with each grit which makes it very easy to see when you've scrubbed out the scratches from the previous grit.

    On wood, it's a little more difficult to see the scratch pattern because we usually sand in line with the grain. On a small piece like a guitar body or neck, when it looks like I've scrubbed out the previous grit's scratches, I'll usually vacuum the wood dust off of the piece so I can see more clearly. Wiping the piece off with naptha or mineral spirits will give a much better view, too.

    Good lighting and 20/20 vision (either natural or corrected) is pretty much a "must" if want good results.

    And then there is patience ;), an elusive but necessary component to the sanding process.





    Best Regards,
    Geo.
     
    goodchicken likes this.
  9. goodchicken

    goodchicken TDPRI Member

    Age:
    43
    Posts:
    63
    Joined:
    Oct 8, 2018
    Location:
    US
    Think I'm gonna use a combination of Naphtha and better lighting (the shop's lighting is gonna get upgraded) to limit these issues.

    My vision is very bad, and it is actually hard to see at certain close ranges. I'm not sure if that's a big deal, but maybe another reason to go ahead and get Lasik lol!
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.


  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.