But if we put papercrete under the floorboards, above the downstairs flat ceiling, isnt it very flammable? And wouldn't it absorb moisture from the damp kitchen steam below and from occasional leaks and stain the ceiling below?
[g]
not at all. The behaviour of papercrete in fire varies depending on the mix. The worst mixes wont support a flame, but can very slowly char over many hours if exposed to severe flame, the better mixes won't. Since even the worst mixes take severe flame to get charring its not a real world issue, unless its used for structural support.
theres plasterboard between steam and papercrete, so no
any material in there will absorb water if there are leaks. Not normally a problem though.
I suspect it wuold if the OP forgot to drain it off before placement. Even if it did, just paint over, not much of a challenge.
NT
I'd see if I could afford lead sheathing rather than the first plasterboard layer. G around the joints in the wood and the bricks with a lot of resin glue fired from a mastic gun. Wet the wall first. The damp has a positive effect on the reaction. It is an acrylic similar to that used on skate boards if you want to look it up.
Lead or some dense sheathing is expensive but you only need it at the toilet and other noisy parts of the wall. It has amazing sound brrier properties unavailable to rock-wool or -sheet. If you can find something simialt steel sheet or somesuch, that might help but nothing matches lead for some frequencies. You will still need as much space as possible for the studwork and plasterboard with a layer of wool between.
You'll get away with 3 x 3 and if you lay everything on thick membrane to seal it that will be an asset too. Fit the lead to the stud work and pop it in place. You might want to leave the rest of the waal where you scrimped on lead, unplastered so you can take the wall down some time in the future to apply more lead.
It's all very expensive and the reason terraced houses are so much cheaper than almost anything else on the market. It is a matter of buy cheap spend dear.
Lead is highly rated, but extremely expensive. Neoprene may be a reasonable alternative - it provides mass and natural dampening capability.
In damp areas really avoid plasterboard, use at the minimum moisture resistant or the various cementboard products (think aquapanel is the most expensive, there are cheaper offerings and cementboards are heavy).
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