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  • #1821627
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    riquet
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    Joined: 15 Sep 2010
    Location: North Tyneside & East 82 (not there often enough)
    Total posts: 2420

    Good morning all. I am at the point of finishing the loft area (crépis de chaux on the vertical walls and Laine-de-Bois under the roof + BA13).

    The other part of this renovation work is part of the barn in which we have created a wall (breeze blocks) built on top of a stone wall which is the wall of the cellar below.

    Similar to the loft, the roof area will be insulated with 200mm “laine-de-bois” with BA13 and all vertical walls receiving their coat of crépis de chaux …… except the new breeze block wall which is 9m20 x 5m20 to the apex. This room is a large volume that I have calculated to be @144m3.

    I will be heating this volume with a Morso (10.5Kw Danish wood burner) with 2m of single skin stove pipe before moving into an insulated double skin right through to above the roof area.

    My question concerns the insulation of the breeze block wall (which is now an internal wall). I intend to dot-and-dab some plasterboard with 40mm polystyrene. My builder (the one that puts the crépis de chaux on the other walls) tells me that with standard white polystyrene (€16.05 the board), I will get condensation between the insulation and the breeze blocks. He advises me to us the polystyrene “graphite” (€23.85 the board) which is the dark looking polystyrene type. Apart from having a slightly better insulating factor, I don’t see the point of using the more expensive version as for me, polystyrene is polystyrene.

    Do you have a different point of view? Thanks for your comments.


    #1821636
    mysty2
    mysty2
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    Joined: 29 Jul 2012
    Location: N/A
    Total posts: 9603

    I thought the grey one was more sound proof. Never heard of the white one causing condensation but i am self trained


    #1821637
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    mikej
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    Joined: 21 Jun 2011
    Location: Dordogne sometimes and Kent the rest
    Total posts: 5287

    Confused as to the positioning of the Breeze block wall, is it internal wall or the inside skin of a cavity external wall, if its an internal wall, why does it need insulating?

    Polystyrene is a closed cell structure and will not allow water vapour to pass if the joints are taped, any condensation will occur between the polystyrene and the plasterboard if that is dot and dab’d onto the polystyrene.

    I know that vapour barrier Polyurethane boards are available in France, but not sure on Polystyrene.

    Mike


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    • This reply was modified 06 Feb 2018 11:27 by  mikej.
    #1821647
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    Chanceux
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    Joined: 17 Mar 2010
    Location: Picardie
    Total posts: 13130

    I have experience of humidity totally destroying a placo doublage and creating a terrible health risk and it was in the commercial kitchen of my former hotel.

    Extruded polystyrene is indeed closed cell and impervious but the white doublage uses expanded polystyrene like consumer packaging.

    My place had been abandoned for decades so I dont know if the damp and mould had penetrated from the outside coming in or was the cooking vapours passing the placo/doublage and then condensing, what I do know is that the walls were black with mould from top to bottom including the mur mitoyenne which can only have been from internal humidity, the plasterboard fell off the walls and all the insulation billes fell to the ground in a great wave, it had completely decomposed, if I thought the mould on the placo was bad enough what was on the plastered wall behind hidden from view was appalling and a real health hazard.

    You will need to look into the subject and your particular situation, if the parpaing wall is at external ambient temperature then there will be a condensation problem to overcome, its all about the temperature gradient and the dewpoint from what I have read, my problem walls I redid with rails and placo with the insulation with pare vapeur, when I cut holes for new placo boxes and gaines I find the placo and the paper pare vapeur is dry but the wall behind can be running with moisture and in some areas the laine de verre is sopping wet.

    I am very glad that I did not re-use doublage whether black or white.


    #1821674
    loopski
    loopski
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    Joined: 23 Jan 2013
    Location: deux sèvres
    Total posts: 9778

    Good post chance.
    It all depends on the wall!
    Was a “damp course” installed between original traditional wall and parpaings ?
    Was the barn side of the parpaing wall fitted with insulation before enduit?
    Has the reidential side got a VMC?


    I would lie on top of the stairs and smell the cigar smoke of Castro.

    #1821789
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    mikej
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    Joined: 21 Jun 2011
    Location: Dordogne sometimes and Kent the rest
    Total posts: 5287

    The reasoning for interstitial condensation is best read up on to fully understand why it happens: https://en.wikipedia.org/wiki/Interstitial_condensation, although there are difference’s between a cavity wall and a solid wall and how you would approach the problem.

    Mike


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    #1821791
    loopski
    loopski
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    Joined: 23 Jan 2013
    Location: deux sèvres
    Total posts: 9778

    https://en.m.wikipedia.org/wiki/Interstitial
    ?


    I would lie on top of the stairs and smell the cigar smoke of Castro.

    #1821792
    loopski
    loopski
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    Joined: 23 Jan 2013
    Location: deux sèvres
    Total posts: 9778

    https://en.m.wikipedia.org/wiki/Interstitial_condensation
    A complete link is more helpful.!
    An activated clickable link is best of all.


    I would lie on top of the stairs and smell the cigar smoke of Castro.

    #1821829
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    riquet
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    Joined: 15 Sep 2010
    Location: North Tyneside & East 82 (not there often enough)
    Total posts: 2420

    Well, I am confused. Thanks for the replies however.

    To mikej, I want to insulate that wall because I believe it will add to the comfort of the room and keep the warmth in when the wood burner is on….. Am I wrong? Are you suggesting to dot-dab a plain plasterboad and skim with plaster? (that would save me money ….)

    The breeze block wall was built inside the barn therefore, on the other side of the wall is the barn which has 2 x huge sliding doors leading to the outside world.

    To loopski, the breeze block wall was built on top of a 2m high/70cm thick stone wall of the cellar below. This stone wall is 100% above ground. No damproof applied when building the breeze block wall.

    Thanks for you comments.


    #1821861
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    mikej
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    Joined: 21 Jun 2011
    Location: Dordogne sometimes and Kent the rest
    Total posts: 5287

    If I understand you correctly their is another room (barn) on the other side of the wall you wish to insulate, if that is the case I would hard plaster the blockwork wall on the habited side and insulate the barn side of the wall, but beware of the condensation issue on the barn side of the wall, I would not use dot and dab plasterboard anywhere that was in my house, IMO plasterboard should only be used on a ceiling, good for a quick bodge up job, read Chanceux post above.

    Mike


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    #1821893
    vic evans
    vic evans
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    Joined: 25 Apr 2015
    Location: Brittany 29
    Total posts: 4066

    I would not use dot and dab plasterboard anywhere that was in my house, IMO plasterboard should only be used on a ceiling,

    I’m not advocating dot & dab pb but would say that when I bought this stone house 1 1/2 lounge walls had been ‘done’ with 50mm polystyrene/pb sheets using this technique. One wall was totally external & the other a party wall between barn & house. I don’t know how long ago they had been insulated but would guess at at least 20 years.

    My immediate thoughts were ‘possible damp problem’ so I removed sections to investigate & as all walls were perfectly dry with no signs of mould I not only replaced the removed sections but finished off the 1/2 done wall in the same manner.

    Twelve years on I removed another section to board in a fireplace & still found no sign of damp with damp meter readings no different to walls where I have removed the plaster & re-pointed the stonework.

    Lucky? Maybe. I’m certainly no expert in these matters & the technique does go against everything I’ve read  but it certainly seems OK here.

     


    The power of accurate observation is commonly called cynicism by those who have not got it.

    #1821915
    mysty2
    mysty2
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    Joined: 29 Jul 2012
    Location: N/A
    Total posts: 9603

    This reply is at Vic and mike, not often I have a pop at mike and have met him :bye:

    Most new French houses have plasterboard used as dividing walls and exterior walls. I have heard people before saying PB should only be used on ceilings but  would disagree with that.

    You get buildings that are damp and putting PB on the walls will go bad but like vic, I have boarded out houses in France for over 20 years and never had a problem.

    I did say on here a few years back a customer contacted us to ask what product they could use on plasterboard to stop the mushrooms coming through, they had plaster boarded their cellar :yes:


    #1821975
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    riquet
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    Joined: 15 Sep 2010
    Location: North Tyneside & East 82 (not there often enough)
    Total posts: 2420

    mijej you are correct and in the meantime, I have been thinking too ….. I will get non-insulated plasterboard on the inside (to be skimmed appropriately), and insulate the other side of the wall inside the barn (lattes, some form of vertical hanging insulation and something to finish on the barn side.

    Just behind where the wood stove goes, I will have bricks against breeze blocks. This will be plastered too. I will then fit a large piece of metal off the wall to act as heat-shield.

    Question. I am getting a fair bit of finishing plaster delivered for that job, most likely more than I will need. Anyone interested in buying what is left? House is in 82250. Thanks.


    #1821997
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    mikej
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    Joined: 21 Jun 2011
    Location: Dordogne sometimes and Kent the rest
    Total posts: 5287

    Pop away mysty2 from you I don’t mind.

    The density of the wall is important with all these things, if as in most case’s the walls are permeable and solid then interstitial condensation will in all probability not happen, when you have a true cavity wall which will prevent the moisture from getting to the outside skin the water vapour will condense somewhere, hence the need for a vapour barrier.

    My dislike of plasterboard on walls stems from being an older gentleman and remembering how real trade plasters worked, they where artists in their craft, there are still some around, but the last one’s I encountered where Polish.

    Mike


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    #1822210
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    premierowner
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    Joined: 29 Oct 2015
    Location: near geneva
    Total posts: 60

    <p style=”padding-left: 30px;”>Graphite or white wont be the variable that causes or does not result in moisture problems.</p>
    Outside insulation is better but not always an option. There is moisture in the air and when the air gets colder it cannot hold that moisture any longer, I.e. rain. The same happens with condensation. The moisture will settle on cold surfaces and for that reason you must work clean with inside insulation. Otherwise you have cold spots in the corners for example and then moisture condenses at those spots and mold will result.

    Work clean with inside insulation ro ensure that no air flor and moisture can get behind insulation where the outside wall,after insulation, will be colder. Focus on the edges of the plasterboards and also the joints. In addition, use cable guide for electric cables as styrofoam can result in a chemical reaction, although slowly, with the protective cable housing of the wires.

    Ensure that there wont be too much humidity in that room and you should be fine with the cheaper boards.

     

    I used a combo of insulation foam glue and plaster glue foe fixing those board in a room I insulated like that.

     


    love working on our new old house.

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