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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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General: Lime plaster on plasterboard

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    So Im just offering this up as its the sort of thing people look for and I haven't seen it posted before...

    If you want to put a skim lime plaster on to plasterboard this is a tried and tested solution. Also works on any wall surface that you want to skim as part of a renovation. I came up with it because Multifinish plaster doesnt exist in France and the local plaster is shite for skim finishing because it sets very quickly.

    Prep the plasterboard or existing wall with 9 parts water and 1 part PVA glue which has sand mixed in. This will seal the wall and provide a mechanical fix. I wait until the PVA has set but still a bit tacky...

    then plaster on the skim coat of lime/sand plaster. Mix 1 part NHL3 lime with 1 part sand and mix together using the same PVA/water mix used for the primer.
    Use a fine, nice colored sand as it is this which will determine the final color of the plaster. Quartz sand can also be added.

    And thats it. Finish the plaster as you want, either flat finish with a trowel or bring out the sand using a sponge when the plaster starts to set after a few hours.

    If you live in one of those countries that uses gypsum plaster that sets within 20 mins, the missing ingredient you need to add to increase working time is trisodium citrate, a form of citric acid. You can also squeeze some lemon juice into the water as you mix the plaster. If you add too much the plaster wont set.
    • CommentAuthorMike1
    • CommentTimeMar 19th 2024
     
    Posted By: bot de pailleIf you want to put a skim lime plaster on to plasterboard this is a tried and tested solution.
    A long time since this was posted, but I may give it a try!
    Just wondering how thin you were able to apply it and how it's held up since?
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      CommentAuthorfostertom
    • CommentTimeMar 19th 2024
     
    I'll guess this converts lovely breatheable lime plaster into a vapour barrier?
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      CommentAuthordjh
    • CommentTimeMar 20th 2024 edited
     
    Posted By: fostertomI'll guess this converts lovely breatheable lime plaster into a vapour barrier?
    Depends whether you use vapour permeable plasterboard or not!

    BTW, if you don't want the yellowish colour of sand, you can use chalk instead. Various merchants sell bags of it.

    edit to add: "The gypsum core is inherently porous, but the plasterboard's facing layers contribute to its vapour resistance."
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      CommentAuthorfostertom
    • CommentTimeMar 20th 2024
     
    That's an alert - I've always 'known' that pbd is vap permeable.
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      CommentAuthordjh
    • CommentTimeMar 20th 2024
     
    Posted By: fostertomThat's an alert - I've always 'known' that pbd is vap permeable.
    You're the one that said it would make lime a vapour barrier?
  7.  
    Maybe the PVA glue makes all the difference.
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      CommentAuthorfostertom
    • CommentTimeMar 21st 2024
     
    As PiH says, it's all the PVA, not the pbd, that wd make a vap barrier.
    • CommentAuthorowlman
    • CommentTimeMar 21st 2024
     
    At such a low dilution, further diluted?/softened by the wet lime plaster, and weakened by the sand particles and the fibrous nature of the card facing layer of the gypsum core. Are you sure? :neutral:
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      CommentAuthordjh
    • CommentTimeMar 21st 2024
     
    Is PVA a vapour barrier? I see lots of reports of additives that can be used to increase its vapour resistance?
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      CommentAuthorfostertom
    • CommentTimeMar 21st 2024
     
    Just askin - keep replies coming.
    • CommentAuthorMike1
    • CommentTimeMar 26th 2024
     
    Posted By: djhIs PVA a vapour barrier? I see lots of reports of additives that can be used to increase its vapour resistance?
    Good question - and I can't readily spot an answer. Anyone?
    • CommentAuthorkristeva
    • CommentTimeApr 3rd 2024
     
    Surely you could just as easily apply some blue grit to plasterboard to provide a key for a lime skim?

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