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    • CommentAuthordickster
    • CommentTimeNov 5th 2009
    Lots of useful discussion on breathable walls, membranes, interstitial condensation etc, but what happens when you paint your plasterboard walls with emulsion? Doesn't that create a non permeable "membrane"?

    Is there any info out there on the permeability of emulsion paints?

    Just a thought.
    • CommentAuthorCWatters
    • CommentTimeNov 5th 2009 edited

    PS: Some paint manufacturers claim their paints are "fully vapour permeable" which I would suggest is a virtually meaningless/impossible statement.
    The general rule for any construction whether breathing wall or not is that the interior surface should be the least pearmeable, each successive layer towards the exterior must be more permeable. The last layer on the exterior must be the most vapour permeable.

    This is one of one of those basic principles, construction 101.
    • CommentTimeNov 5th 2009
    Posted By: bot de paillewhether breathing wall or not is that the interior surface should be the least pearmeable
    why would that matter at all, in conventional thinking, if relying on a strong inboard VCL?

    Standard housebuilders' timber frame houses still now, as ever, reverse that principle, having unresistive plasterboard inboard and more resistive ply (OSB nowadays) outboard. That was blamed for the early UK timber frame failure scandal, which was 'fixed' by the addition of strong inboard VCL membrane, which allowed the reversed resistance gradient to function OK, to this day.
    <blockquote><cite>Posted By: fostertom</cite><blockquote><cite>Posted By: bot de paille</cite>whether breathing wall or not is that the interior surface should be the least pearmeable</blockquote>why would that matter at all, in conventional thinking, if relying on a strong inboard VCL?

    Standard housebuilders' timber frame houses still now, as ever, reverse that principle, having unresistive plasterboard inboard and more resistive ply (OSB nowadays) outboard. That was blamed for the early UK timber frame failure scandal, which was 'fixed' by the addition of strong inboard VCL membrane, which allowed the reversed resistance gradient to function OK, to this day.</blockquote>

    fostertom, like I said its the basic principle that you start from. VCL is just one solution that starts from this first principle, in the sense that the VCL is the least vapour permeable and everything afterwards should be progressivly more vapour open.

    Thats why the vcl goes on the inside and the building paper that goes on the outside is vapour open and not another sheet of plastic.

    Im suprised by your response, I thought this was a known given.
    But it could explain the confusion in the breathing wall thread.
    • CommentTimeNov 5th 2009
    No, I agree strongest inboard, generally weaker outboard, but that's not same as saying, as you did, that ea successive layer must be progressively more permeable. The latter is def not necessary in strong VCL situation (for as long as the VCL remains intact) and not absolutely nec either in breatheable situation.
    • CommentAuthordickster
    • CommentTimeNov 5th 2009
    Remembering my manners, thanks for all the inputs, but what exactly does VCL stand for?


    C= Closed?

    Vapour Control Layer
    • CommentAuthordickster
    • CommentTimeNov 5th 2009
    thank you
    • CommentAuthorCWatters
    • CommentTimeNov 5th 2009
    Something like EPS or foiled PUR foam is pretty impervious to water vapour (if installed correctly) so anything inboard of that might as well be an impervious VCL?
    • CommentTimeNov 5th 2009
    EPS (Expanded polystyrene - white or silver/grey bead board) is very permeable; XPS (Extruded polystyrene - coloured foam board) and all the other closed-cell plastics (with or without foil facing) are more or less impermeable
    • CommentAuthorwellburn
    • CommentTimeNov 7th 2009
    SO - What paint on breathable walls?
    I thought lime wash would be the best for my lime plastered walls. But am now being told that they will be chalky and leave marks on clothes. Also Lime wash will get dirty very easily. So I am looking for the most breathable and durable paint for my internal walls. Any suggestions ?

    Also all the stud walls that I have lined with Fermacell and skimmed with multi (as I couldn't get a suitable finish with the fine filler). So is there any point in buying a breathable paint for these walls/ceilings ?

    I would like to use lime wash as it seems the simplest and cheapest eco sound option, but I am concerned about durability and compatibility with multifinish.

    Any thoughts?
    • CommentAuthorJulian
    • CommentTimeJan 4th 2010
    I would reccomend a distemper - basically limewash with materials like tallow added. Still very 'breathable' but more resistant than limewash and less prone to dusting. I use distempers made by a local company in Dorchester called Rose of Jericho. They also make Claircolle which is basically a gelatine primer. Goes on before the distemper. With proper distempers you may find they have a limited shelf life.
    A bit late now but you could have skimmed with a lime finish instead of multi, with pigments etc. Job done.
    • CommentAuthorJulian
    • CommentTimeJan 4th 2010
    Womblepaul - do you mean you used the Fermacell fine surface treatment? I've found a float works well - I use a margin trowel.

    Bot - can you say a bit more about pigments please? What works well and what sort of priming would the fermacell need? DG27? SBR? Or something else? I have used boiled flour and water on gypsum and cement substrates.
    Bot - its funny never thought of that... a bit of the woods and trees going on.

    Yes tried the Fermacell fine surface treatment and it didn't work for me. So skimmed with multifinish.

    Julian many thanks will look into it. Does the distemper really breathe as well as lime wash ?

    Also has anyone any experience with the NBT 'contract eco' and 'trade emulsion' ?
    We have used Livos Dubron matt emulsion on skimmed plasterboard. Its an absolute pleasure to use and smells lovely of orange oil, covers well and goes a long way. Did 2 coats on bare skim, and have refreshed it twice in some places in intervening years without problems.

    Would probably use just limewash now that I have used it elsewhere, but don't know about the chalking - can't see it being a problem except underneath the coat rack.
    • CommentAuthorRoger
    • CommentTimeJan 5th 2010
    Limewash made up of 50% lime putty and 50% water, with a slug (5%?) of linseed oil should resist flaking and brushing off.

    Several thin coats better than a couple of heavy ones. Worked OK for me on skimmed plasterboard but sticks better to lime plaster.
    • CommentAuthorEv
    • CommentTimeJan 5th 2010
    Distemper is slightly more robust that limewash, and yes, Rose of Jericho.
    • CommentAuthorJulian
    • CommentTimeJan 5th 2010
    Yes, distemper should give you the same 'breathing' characteristics as limewash but more robust surface.
    • CommentAuthortomsusweb
    • CommentTimeJan 5th 2010 edited
    The following table from Neil May's Breathability paper is helpful:


    because the emulsion layer is thin it's still more 'breathable' than the plasterboard.
    • CommentAuthorJulian
    • CommentTimeJan 5th 2010
    Very useful tomsusweb, thanks.
    Many thanks all. I think I will go for lime wash on all surfaces. And put some oil in as Roger suggested in Kitchen and high traffic areas.If I get bad marking etc etc I will then coat with a distemper. After putting 6 tonnes of lime mortar/putty on the walls I really want to maximize breathability!
    Consider also claypaint - very nice to work with, as its non irritant, and gives nice matt finish, I washed over with a pigmented scumble and it looks nice. rubs off a bit when fresh, but tough as anything in a few weeks.
    Beeck make a big range of excellent paints and their technical data sheets include water vapour permeability data.

    All forms of limewash and whitewash (chalk) and clay paints and silicate paints are highly vapour permeable, even when linseed oil is added to form an emulsion. It's the acrylic and alkyd resin paints (the modern stuff in the DIY sheds) that have lower vapour permeabilities.
    I've had some caesin distemper from rose of jericho for my lime plastered walls. So far it has been very good.

    I've used this as some new internal walls have been gypsum plastered plasterboard adn the clour match is super on the two surfaces and this paint is the only one which will do both types of surface well.
    • CommentAuthorAMc
    • CommentTimeJan 8th 2010
    Another vote for distemper - though I've painted it on an old previously external exposed brick wall as opposed to lime plaster it still needs to be breathable.
    Too early to give its breathability a test but it certainly doesn't flake or chalk on brick or sections of standard gypsm plasterboard.

    Mine came from Little Greene - ordered online.
    • CommentTimeJan 10th 2010
    This was in my comic this week, early days though.


    'GROWING grass on your roof and other attempts to make homes carbon neutral are mere "green bling". So says Rachel Armstrong of University College London (UCL), who suggests that her smart paint can turn buildings into carbon sinks.

    Armstrong created the paint by dissolving salts and esters in oil droplets. Repeated coatings react with carbon dioxide in the atmosphere to produce calcium carbonate - which is the main constituent of limestone - and alcohol. The resulting "biolime" will provide extra strength and insulation, she says. How much CO2 could be removed from the atmosphere in this way has not yet been tested.
    The paint would react with carbon dioxide in the air to produce 'biolime', which could help insulate homes

    Armstrong wants to adapt the technique for use underwater to create an artificial limestone reef beneath Venice to stop the city sinking. She will present her work at a workshop at UCL's Bartlett School of Architecture next month.'
    • CommentAuthorRosemary
    • CommentTimeJan 10th 2010
    And another vote for claypaint. Wholesome, easy to use and the claims that it absorbs a degree of moisture seem to be valid.
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