I have a textured ceiling similar to this:
Some of the texture peaks at 1/8", but it mostly peaks at 1/16". I am going to be applying a second layer of drywall with Green Glue in between and I want to know if all this texture has to be sanded down or scraped off before the second layer goes on.
The point of Green Glue is to create a flexible layer of never fully firm glue between layers of drywall, right? To absorb sound?
In which case, I think you'll need to first level the ceiling, then apply green glue, then apply your final layer.
Otherwise, if you green glue over top of the texture, you'll have high points in the texture that touch the new layer of drywall. That will transfer sound quite effectively - which you don't want.
Like Karl, I just riped the drywall out completely rather than trying to fix it in my own home. But if you go the pole sander route, then I'd measure out where the non-beveled joints are going to go (the 4' side of a 4x8 sheet) and just sand those areas, maybe 6" to either side of the joint. The drywall will bend in slightly at the joint and you fill the whole space with joint compound.
Also take a flashlight at a hard angle to see if you can find where the current joints are. Where you find the preexisting 4' ridges, sand them down. When you layout the new layer of drywall, stager the joints so you don't have two non-beveled joints on top of each other.
I would remove it, then your drywall sandwich has no gaps between it and will allow for better attachment. But its not popcorn so it may not be as simple as a scrape with a trowel.
If it is really a bear to take off, you could try a test piece without removing it and see how it looks and attaches. If the next ceiling is smooth, I would be somewhat concerned of noticeable peaks and valleys, but the only way to tell would be a test piece install.
It's not something you need to remove. However, how thick is the drywall that you're putting up? If it's 1/2 or 5/8", ok, but I'd be worried about how much weight you're adding. If you're putting up 3/8 or if you managed to find some 1/4", you're going to show every bump and ridge beneath it. You probably want to use half inch, and you might think about firring it out.
You still need to be aware of the slant of the ceiling to make sure that you don't bump outwards since that's hard to hide with compound. If you have to do anything, bow out in the middle of the board and then have your joints bow in.
I attempted to remove the same texture from drywall in my house, and it was a beast. i was using a belt sander with a 50 grit belt and it still wouldn't smooth down. I ended up tearing out the drywall and starting over.
