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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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General: Acrylic v Cement v Lime renders

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  1.  
    Hoping for a civil discussion of the advantages and disadvantages of each. Anyone care to raise their heads above the parapet?

    I'm particularly interested in establishing physical properties and how these justify liquid/vapour permeability ; *breathability* etc.
    • CommentAuthorShevek
    • CommentTimeMar 8th 2013 edited
     
    Do any of these (or any other options) avoid the formation of cracks? What are elastomeric coatings, for instance, and can they be applied to EPS?
    • CommentAuthorMike George
    • CommentTimeMar 8th 2013 edited
     
    Posted By: ShevekDo any of these (or any other options) avoid the formation of cracks? What are elastomeric coatings, for instance, and can they be applied to EPS?


    Hi Shevek, exactly the kind of things which need to be discussed. We could do with experts in product/coating/ mortar type putting forward the case for each.
    • CommentAuthorjamesingram
    • CommentTimeMar 9th 2013 edited
     
    Certainly no expert on such things , other than personnal experiance of using the various products as a jobbing builder .
    From BS12524 Building materials and Products,Hygrothermal properties, Tabulated design values.

    Renders / water vapour resistance factor /DRY/WET
    gypsum sand /10/6
    lime sand /10/6
    cement sand /10/6

    So no difference there.
    In practice many poorly informed plaster/renderers add water proofer additive to sand/cement render (often 4/1 in my experiance) which no doubt changes things.
    6/1/1, sand/cement/lime without additive , I beleive is the correct/better mix, perhaps weaker ?
  5.  
    From tables in Breathability: The Key to Building Performance by NBT
    http://www.natural-building.co.uk/images/downloads/Breathability_in_buildings.pdf

    Vapour Permeability (r) is offered ( unsure how this relates to water vapour resistance factor in BS12524)
    cement plaster 100
    lime plaster 75
    clay plaster 40
    • CommentAuthorMike George
    • CommentTimeMar 9th 2013 edited
     
    Hi James, Thanks for the link.

    Edited

    The conversion is actually quite simple if you look at the excellent illustration here http://builddesk.co.uk/wp-content/uploads/2013/01/vapourResistances.pdf
    It's the raw data such as that in the NBT Table that is hard to come by . .

    Regarding the data given by NBT, the numbers do not tally (See images below)with data in BS12524 (unless my maths are wrong) The NBT sorces of these data is unclear from the paper.

    Right or wrong they are in the same ballpark however and when you consider the range of these values I see no justification for any argument that one kind of render is significantly different to another in terms of vapour permeability What we don't have is numbers for the acrylic/mineral renders in order to be able to make a comparison...
    •  
      CommentAuthorfostertom
    • CommentTimeMar 9th 2013
     
    Posted By: Mike GeorgeIts the raw data such as that in the NBT Table that is hard to come by
    Has anyone asked NBT Neil for his raw sources?
  8.  
    The Referencing on the NBT paper is not the best

    These are the sources listed under the NBT table

    sources: Bablick, Federl (1997): Fachwissen für Maler und Lackierer, Stamm Verlag, Köln
    CIBSE 1999 Guide A: Environmental Design
    Product technical sheets: Various

    Googling them yields nothing. Though the Guide A will be easy to find when I can grab my copy
  9.  
    As someone interested in the overall environmental impact of building materials, I'd be less keen to use acrylic based products on the assumption that disposal at end of life would be environmentally more problematic than (esp) lime mortar. The valley I live in is full of ruined old cottages whose lime pointing, in many cases, has just dissolved benignly into the landscape leaving nothing but a pile of native stone.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMar 9th 2013
     
    Posted By: Henry Searshas just dissolved benignly into the landscape leaving nothing but a pile of native stone.
    Is it really benign, bit on the alkaline side isn't it
    • CommentAuthorTriassic
    • CommentTimeMar 9th 2013 edited
     
    Posted By: SteamyTeaIs it really benign, bit on the alkaline side isn't it

    But dosn't nature naturally buffer the alkalinity, will an acrylic resin break down naturally? Probably not!
    •  
      CommentAuthordjh
    • CommentTimeMar 9th 2013
     
    Posted By: SteamyTeaIs it really benign, bit on the alkaline side isn't it

    Not especially once its carbonated - but that's the point really, acid rain needs to be neutralised.
    •  
      CommentAuthordjh
    • CommentTimeMar 9th 2013
     
    Posted By: fostertomHas anyone asked NBT Neil for his raw sources?

    Stable door, 600 mm bolt, horse. I guess Ecobuild would have been a good place to ask many questions like this of the great and good.
  14.  
    Posted By: SteamyTeaIs it really benign, bit on the alkaline side isn't it


    That's welcome round here, where the pH is seriously on the low side...

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