On Jun 2, 11:52*pm, "george [dicegeorge]"
wrote:
NT wrote:
On Jun 2, 4:09 pm, "Dave Plowman (News)" wrote:
In article
,
* *NT wrote:

Stuffing mineral wool in tight puts pressure on the ceiling, and over
a fair area it adds up to quite a lot of force. I wouldnt. As long as
there isnt a damp problem there I'd be more inclined to go with
papercrete, its denser, has a finer porous structure, and stiffens and
damps anything its in conctact with.
Mineral wool has f-all effect on sound transmission. Once you've got rid
of direct air borne paths you need to add mass. Plasterboard etc is
probably the easiest/cheapest way.

Any of the following would help: rigidity, mass, damping.

- Sand adds damping and some mass
- Plasterboard adds some mass
- Papercrete bonds to all around it, stiffening and damping. Mass
added is the end user's choice, it can be anything from very light to
very heavy.
- mineral wool damps thin PB, but doesnt add any mass or rigidity.

NT

But if we put papercrete under the floorboards, above the downstairs
flat ceiling,
isnt it very flammable?

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.

And wouldn't it absorb moisture from the damp kitchen steam below

theres plasterboard between steam and papercrete, so no

and from occasional leaks

any material in there will absorb water if there are leaks. Not
normally a problem though.


and stain the ceiling below?

[g]

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