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Tim S

coughed up some electrons that declared:

wrote:
Tim S wrote:
coughed up some electrons that declared:
John Rumm wrote:
wrote:
John Rumm wrote:
wrote:
Hi

Cavity wall (brick & block) with a slightly narrow 1.5" cavity,
any advice re cavity filling it? What fill, if any, would work
with such a cavity? Any tips on diying it?
Do you want to insulate and existing wall, or is this insulating
a new one as it is built?

Its an existing wall, and making holes in it to fill it is no
problem.

Any of the normal loose blown in or injected cavity wall insulation
products then...

I thought most of them needed blowing in, I dont have the equipment.
I'd be looking at pour in, and polystyrene bead is the only one I
believe that can be done with. Are there any others? Any specific
bead size, coating, etc? The issue Tim mentioned of beads pouring out
of holes shouldnt be a problem.

NT

If it were me, I'd go with the beads if you really want to DIY it.
Making some sort of wide channel out of ply or thick cardboard and
pouring them on that and using it to direct them over the wall leaf
into the cavity might help - I guess there'll be a lot of volume of
beads.

Would you be doing this from inside of out?

inside

If I were paying, fibre seems OK, but glued beads might be better from
a damp tracking POV (though I've never seen damp in the walls and the
outside is unrendered brick).

the wall is damp, and will stay so, but I cant see poly beads making
it worse. I think unglued ones would be an insurance policy though,
just in case. I have heard of the odd case where CWI made the damp
much worse, and needed to be removed, but IIRC those were from water
running down inside the cavity, which doesnt happen in this case.

NT

I realised something else too, theres a balanced flue duct going
through the wall for a 3kW cast iron heater, so almost 3kW going
outside through that. Is that compatible with polystyrene bead? I
guess I know how to find out.

NT

Does it run no more than warm to the touch in the bit you can get at? And is
it concentric? Any heat shield where it goes through the wall?

It's not going to take much to melt polystyrene