cellotex on 9" brick interior cold walls to cure condensation/mould questions

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davo

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hi,
I have a problem with a rented property. Basically the cold walls facing the elements keep on suffering from massive mould growth all around the windows and the surrounding walls. This keeps coming back despite treating with anti-mould solutions/primer sealer/anti-condensation paint/anti mould paint etc.
I am told this is all due to condensation, but we have fitted humidistat fans, windows opened, heating on etc.
Have just spent a day and a half bleaching it all again. Main advice has been to put celotex 70mm insulation board on the wall, then baton over it, then put celotex plasterboard over the batons and skim.
I have several questions about the process, so please bear with me...

1. can the celotex be fitted straight on to the old dodgy and probably damp plaster, or do I have to hack off all the plaster - am worried if the latter is true because the wall is jerry-built and there isnt a flat brick in the place, all sorts of gaps and chunks and bumps - would probably have to fill it all in first.
2. Should there be an air gap between the exisiting plater and the celotex
3. should I do as per celotex website and cover whole wall then baton over it, or should I put batons on existing wall and put the celotex between them, then board over the whole lot
4. Do I have to worry about the mortar? the pointing is pretty poor, but I am told it wont matter
5. if the answer to 4 is yes, then do I have to rake it out and replace with lime mortar to let it breathe - read that standard mortar doesnt let it breath and so can cause issues
6. What should I use to seal it where it meets the ceiling
7. Can I get away with just fitting celotex on the walls that cause the problem, or do I have to put round the whole room
8. What percentage likelyhood is there that this expensive process will cure the problem and stop people from having to sit there in the freezing winter with the windows open
9. Is there a just as effective but cheaper alternative

Your reples will be much appreciated, thanks
 
Just doin some council spec jobs at the minute very similar to yours we are fixing tanalised battens over the old wall and fixing thermal bonded cellotex plasterboards to the batts , you could use a gypliner system if you like, there are number off way it could be done , but you seem to be on the right track, no need to do all the walls just the external facing ones ,
Were on to our third property doin this over the last month without any probs

Other option would be to fit a positive pressure system , work out about £800 fitted , but thats provided it is condensation and not pen damp etc
 
so are you getting away with only putting one layer of board on in total? - I thought we had to put 70mm either between battens or on wall with battens fixed to it, then put the plasterboard over the battens? Obviously your way would be much cheaper.
Are you having to do anything about the mortar in the brickwork, and the damp plaster on the existing wall or is it not necessary? what do you seal round edges with?
Finally do you have to go florr to ceiling, or should there be a gap at the bottom?

p.s. whats a positive pressure system? and how do I tell the difference between penetrating damp and damp/mould from condensation?
 
just thought of a big flaw in my plans ... the walls that I intend putting this cellotex or whatever on have windows in. If I intend to build it onto the existing wals then the walls would be so thick that they would protrude out past the level of the window ledges? - so do I therefore have to remove old plaster and go back to the brick? what did you do? or were you just lucky that there were no walls with windows in that you had to do?
Should the vent go under the window, or elsewhere and should it go right through the whole lot to the outside? - would that not breach the seal that we are trying to achieve and let the cold air in from outside and the condensation then starts again?
 
The condensation is caused by the air not being able to get out, dont worry about the windows you will just have reveals around the window and yes the vent will go all the way through.
 
thanks - so should I be going floor to ceiling with the 70mm cellotex (i.e taking off the skirting then battening over that then boarding over the battens), or would the other guys approach of just battening the old walls then putting the cellotex plasterboard on the battens be sufficient. Alternatively should I be hacking off the old stuff first?
Also, what about the mortar- do I just not worry about it and leave it? - will have to be repointed at some time soonish, and cellotex website sayss to not use ordinary sand/cement as it will trap the moisture, so recommend using lime mortar to enable it to breath...would you agree with that?
Finslly, where is the best place for the vent - up high? down low? under the window ?
 
warriorupnorth...
sorry to appear numb, but have checked out what a positive pressure system is, and I already have one fitted in the loft - hadnt heard it called that before. It doesnt appear to help much though, although the flat in question is ground floor and has fire door, so maybe the warm air struggles to get through? but then again that doesnt make much sense because the previosu tenant was moaning about the cold air coming in fro mthe corridor and tried to tape up the door to keep the cold out and the heat in!!
how do you deal with the windows and their reveals etc...I am losing about 3 inches on the walls and obviously this will take the board about an inch or so proud of the current window ledge/sill? - also, do you put thinner cellotex on the inside of the windows then join the thicker stuff from the wall to it over the batten? - do you use angle bead over the two where they meet before skimming, and do you put stop beads in the inside corners of the window reveals to guide the skim there?
 
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