Hi
>
>
> Cavity insulation has been fitted, but there is no waterproof membrane
> anywhere, resulting in the possibility of condensation and damp. So
> what is the best way to waterproof the surface of a healthily
> plastered ceiling?
>
>
> Regards, NT
Not sure why you would want to do this - AFAIK the ceiling should be able to breathe to avoid nasties in the plaster and the joists above. Again AFAIK you don't waterproof the ceiling of a bathroom, which gets pretty moist at times (far more than moisture not passing through cavity wall insulation). Checked the posting date and it was yesterday so presumably not AFJ?
When a solid wall is insulated using battens fibreglass and plasterboard, I gather it is important to use a vapourstop barrier on the PB to prevent condensation within the insulation, resulting in damp problems.
Am I wrong there? Thinking about it the insulation is on the other side of the PB so there shouldnt be a problem... I'm just not clear.
The other point is that I thought bathroom condensation would disperse faster if it did not get the opportunity to soak into the plaster - and this would also avoid plaster failure. Again I'm not really sure.
** 'Ang on a minute - now you are talking about walls! You originally asked about ceilings. Different rules for walls and ceilings. Ceilings (usually) hang from wooden joists, and if you trap damp in the joists bad things happen. When insulating a ceiling under a flat roof you have to leave a ventilation gap with good airflow above the insulation to keep everything nice and fresh. Also damp may not just pass up though the ceiling. Damp from above may pass down and evapourate keeping the joists above healthy.
**** New plaster takes quite a while to dry out - one reason why you are supposed to paint it with emulsion for the first 6 months or so, to let it breathe. Seems to me that putting a membrane between a solid wall and the plasterboard may be fine, because the new plaster could breathe and dry out, but sealing new plaster is probably not a good idea. I must confess that I am not totally clear why you use mebrane with a solid wall, unless the coldness of the wall draws in and condenses moisture, which is then held by the insulation instead of evapourating again as it would with just a plastered/rendered wall. Again this should not apply to a ceiling.
**
Bottom post as well so I am a top. middle. bottom poster :-)
hmm, vent gap eh. Someone scratches their head. This stuff was blown in after construction, so as for ventilation gaps... its anyones guess. I dont see any exterior vent holes either.
I saw a graph once that explained it. I dont think I could put it into words though! Basically condensation occurs in the inuslation without it.
Again this should not apply to a
Better than > Bottom post as well so I am a top. middle. bottom poster :-) side posting. Cheers!
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