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Renovating a semi-detached house. On the shared wall, the builder mortared gypsum board to the cinder-block (first and second floor, each 8' tall x 30' long).

Tools I have considered:

  • Belt sanders and air-hammers seem like they would be exceptionally slow.
  • Grinders might be marginally faster, but might damage the cinder block.
  • A demolition hammer might be faster per minute, can an average dude hold one up long enough?

Is there a better (faster / less tedious) approach I haven't thought of?

  • Why do you want to remove it? – brhans Aug 14 '18 at 11:46
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    You could just stud out the wall and lose the half inch or so. You'll save yourself a ton of time and headache that way – The Evil Greebo Aug 14 '18 at 12:28
  • @brhans, previous owner did not maintain the house at all, so I've removed all other gypsum in order to eliminate stink. This is the only remaining example, and though the house smells 95% better, the stink remains. I would rather invest the time and energy than use a sealant and hope. – Duncan Aug 14 '18 at 18:00
  • @TheEvilGreebo, agreed, that would be my approach in most circumstances. In this instance, I don't feel like it's an option. – Duncan Aug 14 '18 at 18:49
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Unfortunately it won't be mortar but drywall adhesive; the so called 'dot and dab' in the UK, and it can be the very devils underpants to remove. It's not particularly hard but it is very 'grabby' and absorbs impacts, which means it sticks really, really well.

I use a small electrical breaker with a blade chisel. Work at a really shallow angle to the wall and tackle each dot (or dab lol) at a time. The shallow angle will protect the block-work and in theory get behind each clump of adhesive. They rarely come off cleanly (like mortar might come off a brick for example) as it's too soft.

Expect a solid band of adhesive at the top and bottom.

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For anybody who stumbles upon this, I took two approaches... maybe three.

1 -- I rented a demo-hammer (two-handed electrical device, 10a, excellent when taking tile off subfloor). That approach lasted ten minutes. The hammer I was using wouldn't activate without sufficient pressure on the bit, and I could only get over that threshold by pointing the hammer relatively straight into the wall -- risking the underlying cinder-block wall. It was also heavy and loud, which pissed off my neighbour (semi-detached house).

2 -- I used a 7" grinder with a concrete-grinding cup. This worked well, though obviously generated insane levels of dust. The dust is very fine, which clogged the filter bags very quickly. No-name bags would clog and then burst, clogging the filter; name-brand bags would clog and lose flow but at least they didn't burst. Once they lost suction, most of the dust remained in the air near the tool. Eventually I gave up on the vacuum and worked blind. I relied on feel and sound to know when I was grinding gypsum and when I was merely smoothing the cinder-block. I did approximately 20m2 myself, then hired a contractor while I went to my day-job.

3 -- When the contractor wrapped up, I used a one-handed air hammer with a 3" blade-chisel, as recommended above. This was excellent where gypsum remained, which was only at the edges. It was the best because I could get under the wire mesh, instead of grinding through and showering myself in shards and molten droplets.

All three methods created a lot of noise.

The grinding created a lot of dust, and eventually the dust was sent out the window with a series of fans. This was good for the first day, but on the second day someone mistook the clouds of white dust for smoke! I had departed for the night, so five fire trucks attended before someone told them where to find the trades key. After that, I called the FD dispatch desk to warn them I would be grinding.

I hope nobody else ever faces this issue -- much easier to just tear the house down. :)

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