Knauf Vs Rockwool acoustic wadding

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Building a false wall to separate bathroom from one bedroom, looking at which type of acoustic insulation to put in the gap. Retail prices- Rockwool 100mm slabs are about 4 times the price per cubic metre than Knauf 50mm acoustic on a roll. Anyone got any views on the performance difference? (There are other parts to the sound reduction- acoustic board on one side, cement backing boards on the other, might even splash out on green glue)
 
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Anything on a roll is surely much less dense than the rock wool slabs, so I’d be wary. I’ve not used knauf acoustic roll and I assume it’s a beefed up version of loftroll, but it’s still likely to be much softer/less dense construction than the rock wool which holds its shape, can be cut to panels and isn’t really a wool-like substance. I didn’t think it was particularly expensive either last time I bought it but then that was pre-apocalypse…
 
Ta- yes thinking on I need to compare the density not just the volume. The Rockwool comes in at about £12/sq m cover at 100mm, it's only a small wall so prob go with it for your valid reasons above
 
You seem to be comparing 100mm or rockwool with 50mm of the other product o_O

Anyway, TBH, despite the spec's on paper, I doubt you will notice any difference between insulation and none let alone different types of insulation. But 50mm of Rockwool would be normal - slab or roll.

Consider acoustic plasterboard (blue) both sides instead.
 
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Yeah, reckoned the slabs (being a bit denser) would do better than normal rockwool. Yes blue pb on the bedroom side, heaviest tile backboard I can find on the bathroom side :)
 
I recently pulled the plasterboard off a stud wall that divided a bedroom and bathroom in our house to find an empty void! (which wasn't unexpected) as it sounded hollow, Anyway I filled it with 75mm rockwool acoustic slabs and an extra layer of acoustic plasterboard. It was a faff but it has made a difference.
 
I recently pulled the plasterboard off a stud wall that divided a bedroom and bathroom in our house to find an empty void! (which wasn't unexpected) as it sounded hollow, Anyway I filled it with 75mm rockwool acoustic slabs and an extra layer of acoustic plasterboard. It was a faff but it has made a difference.

A couple of years ago my stepson asked me to fit a rad towel rail in his bathroom. I started drilling holes in the plasterboard as I looked for voids to run the pipes up. I soon discovered that the walls were 25mm plasterboard with 9mm plasterboard glued to either side of the 25mm.

I refused to hang the rad off it, he got annoyed. Fortunately he moved house.
 
I vaguely remember back in the day you got double plasterboards (when you bought them you had a pair with the edges taped together, good side in, presumably to protect them in transit?). This was in the 60s :)
 
I wasn't aware they did 25mm plasterboard.

I am pretty sure it was 25mm. The walls were framed with 1*1 timber, i.e. the thin timber was screwed to the floor, plasterboard screwed to one side, strips of the 25(?)mm glued to that and then another layer of plasterboard screwed to the timber on the other side of the wall.
 

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