Drywalling - sand once, or after each coat?

Discussion in 'Remodel Forum & Blog' started by Fistor, Jul 12, 2009.

  1. Fistor

    Fistor Geotechnical Engineer

    Messages:
    48
    Location:
    Vancouver, BC
    Hi -

    This is probably a silly question, but I have seen differing opinions on drywall sanding... should drywall be sanded after each coat, or only once, after the final (2nd or 3rd) coat of mud?

    Thnx!
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,917
    Location:
    New England
    If you're really good, yo umight not need to sand.

    I try not to do much of this, so my experience may not be the greatest...I'd sand after each coat to expose any potential bubbles so you could fill them in next time. A wet sponge can be used if you don't use a setting type and is less messy.
  3. dgold

    dgold Product R&D for a powertool manufacturer

    Messages:
    82
    Location:
    Carlsbad, CA
    I'm NOT good at finishing drywall, so if you're like me, here's what I've found works best:

    I use setting type compound (20 or 30 minute I think). Invariably, I mix more than I need and try to get it fairly smooth with just the knife. Then I sand and do it again -- each time with a wider and wider knife.

    Personally, I think the setting type compound is the greatest thing ever. Once you get the hang of mixing it, it really saves time, because it dries so fast and lets you keep moving. You can also take a blow dryer to it and it'll set even quicker.

    As a landlord, it makes great spackle too, because by the time I've filled all the holes, everything is dry and ready to be painted.
  4. iminaquagmire

    iminaquagmire DIY Senior Member

    Messages:
    207
    If you're asking this question, you'll probably be hard pressed to even be able to put second coat on without sanding first. I've done a lot of drywalling in my house and everytime I say I'm going to hire somebody. Everytime I end up doing it myself and doing a lot of sanding.

    Be very careful on using the setting type compounds. Some dry extremely hard and are near impossible to sand. I use USG Dust Control in the gray bucket. It works well for taping and topping and the dust is heavier so it settles where its sanded instead of wafting everywhere you don't want it.
  5. dgold

    dgold Product R&D for a powertool manufacturer

    Messages:
    82
    Location:
    Carlsbad, CA
    I didn't know that about the setting type compounds. What I buy is from USG and is labeled "Easy Sand" I think -- so maybe it's improved versus what iminaquagmire has had bad experiences with. It's no more or less difficult to sand than the regular USG "lightweight" stuff in the bucket with the green cap. I just like it because I don't have to wait for it to dry, in 30 minutes or so, it's ready for sanding and another coat if necessary.

    Here's what I use.
    Last edited: Jul 13, 2009
  6. Fistor

    Fistor Geotechnical Engineer

    Messages:
    48
    Location:
    Vancouver, BC
    Thanks for all the replies, guys!

    I decided to go with a minor sanding after the first coat, just to remove the obvious lines and any minor bump, plus a quick overall sand. The second coat is now drying, so we'll see tomorrow how it looks. Because this is my first time drywalling, I plan to spend a lot of time on the finish sanding, as I don't want to accidentally take off too much.

    Yeah, iminaq, I also am using the dustless mud. I imagine that the pros would probably have reasons not to use that stuff, but it is working pretty well so far.

    While we are on topic, any advice or suggestions for drywall primer, prior to painting? I assume that it is much like any other primer, but for drywall... or is there as wide a range of primers as there are muds?
  7. patsfan78

    patsfan78 Web Development | HVAC

    Messages:
    33
    Location:
    Maine
    After each coat for the best results.

    It could actually take less time too. If you only sand once after 3 coats, that's a lot of mud to have to smooth out.
  8. GabeS

    GabeS Remodel Contractor

    Messages:
    294
    Location:
    Brooklyn NY
    After the first coat, I take a 6 inch knife and SCRAPE the ridges and bumps off. I do this step quickly just focusing on major stuff. Then the second coat goes on with a 10 inch knife. After that sets, I use a pole sander and 80 grit doing a few quick passes(not going crazy here). Now I have a smooth surface, but with very minor indentations that need to filled(there should be no high spots, bumps or ridges at this point). Now the third coat goes on with a 12" knife. When you apply the 3rd coat you put on the compound on and then take it ALL off with the twelve inch knife, leaving a nearly perfect finish.

    After third coat dries, you can either very lightly pole sand it (with 100 or 120 grit), or take a damp sponge and rub out the imperfections lightly. If it's a small area like one room I use the sponge. If the area is bigger I use a pole sander with fine grit.

    If you want to go crazy, after you are done with all the steps above, take a flashlight and shine it down the lenght of the wall or ceiling and it will expose EVERY minor imperfection left over. Then use a fine grit sanding sponge(the gray ones) and fine tune it. You CANNOT get a more perfect job this way.

    Good luck.
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