Polystyrene Backed Plasterboard

Status
Not open for further replies.
M

matchstick

New Member
We have recently renovated our house and have noticed that condensation if forming in the two alcoves and fireplace in the lounge. There is no damp penetrating from the outside and the alcoves are very cold so that's why I think it is condensation. The external walls are around 18-20 in thick stone, but the alcoves and fireplace are just brick (no cavity wall). We've bought some polystyrene backed plasterboard to line the back of the alcoves and fireplace (not in use) but don't know the best way to fix it to the wall. We aren't going to plaster the board, just paint it so we can't really screw it in place. Can we use dot and dab or will it not stick to the polystyrene?

Also, I've read somewhere that the polystyrene backed plasterboard actually worsens the damp problem? If so will we need to install a vapour barrier?





Thanks, Mark
 
Yep just dab em on, your supposed to baxk it up with a couple of mushroom type fixings , in case of fire but thats up to you, alternatively use mf or tomber studs/laths and screw em , but then you got to think about plastering or dry lining
 
So dot and dab is ok then.

What about the damp though? Will the polystyrene make anything worse, or will it cure the problem?


Thanks, Mark
 
The wall will then be warm, so in theory the condensation won't form. It may also be due to lack of air circulation.
 
Dabbing or screwing boards may be a cover up solution but idealy you should consider using a lime based or breathable plaster to cure condensation.
It would require base coats and top coats but would be a long term solution.

Insulated boards will hide the condensation and the finished surface may not show any visible signs but the cavity created by dabbing will still allow vapour to condense, leading to water running down the back of the polystyrene and onto the floor/skirting.
 
So what your saying is you have some cold spots. Just how bad is it . Is the fireplace open ,condensation is more to do with air flow .
 
Nice one, a genuine question from a genuine punter for a change with some good answers to follow, personaly i think vapour barrier is needed but Chriss will be a long sometime with his valued expertise in this field.
 
Removing existing problem plaster before dabbing the boards is something else I think should be said.
As TonyM said, airflow will normally cure condensation.
if there have been windows replaced without trickle vents or chimneys bricked up without ventilation then this is normally the result.
 
Thanks for the advice


The chimney stacks have been totally removed, but the roofer took out some bricks from the chimneys for ventilation in the loft.

The windows have trickle vents but we closed them through the winter becasue it was so cold - stone walls take a long time to heat up!

We don't want to remove the plaster if it is in any way avoidable because we've just finished the renovation and the house is for sale

Thanks again, Mark
 
If like you say condensation is the problem and not penetrating damp etc then you are on the right lines with the insulation method , condensation generally occurs on solid brick/stone walls that have no cavity or any external insulation , the masonry acts like a giant heat-sink as soon as the warm moist air internally hits the cold substrate hey presto moisture droplets form (bit like when a warm front meets a cold front and you get fog/mist) so if you place an insulated barrier between the hot and the cold then this will prevent condensation forming on these surfaces, but this will then migrate to the nearest cold spot (generally windows) this is then when you need to start taking passive ventilation (be here all night) in effect creative a positive pressure system internally so as to force damp air out (negative pressure externally) This whole scenario is created when employing modern building techniques/heating systems in older un insulated property's ie gas fires, central heating, double glazing etc and of course the way we live ie drying clothes, cooking, bathing,breathing etc breathing alone for two average adults produces one and a half pints of water every eight hours so add that to wht is produced by sweating , belching, wind and that produced by gas appliances, cooking, washing etc so all this combined in an airtight property it's no surprise there are so many problems.
So just replacing your old lime plaster with new lime plaster for breath ability is not the answer it will still condensate. SO INSULATE IT and maintain some passive airflow
 
Ok thanks warriorupnorth, thats explained it perfectly
I'm going to put it up this afternoon

One more question - can I use a MS polymer grab adhesive like stixall, sticks like sh*t, serious stuff etc?

Thanks, Mark
 
matchstick said:
Ok thanks warriorupnorth, thats explained it perfectly
I'm going to put it up this afternoon

One more question - can I use a MS polymer grab adhesive like stixall, sticks like sh*t, serious stuff etc?

Thanks, Mark
Click to expand...

Not sure mate ask the board manufacturer, some ahdesives react with the eps or phenolic backing so best check
 
If it's only small areas, use Dryfix foam to stick the boards. It sticks like s**t to a blanket, and goes off in minutes.
 
Jesus Warrior! where did you learn all that fela! i might have a go at reciting some of that when i next get asked about a window wall thats got some condensation!

Will impress the pants of a customer and ill charge em an extra £20 fo doing f**k all and just re-skim it lol

Zombie:RpS_thumbup:
 
Status
Not open for further replies.

Share this page

Back
Top