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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorbabs30
    • CommentTimeMar 9th 2012
     
    How do i know if my walls are lime plastered? Ive never seen it anywhere before and the walls are clearly a mixture of something :confused:

    Picture below shows hall (first room stripped bare) Some of the plaster have been taken off where it had blown badly.
    • CommentAuthorbabs30
    • CommentTimeMar 9th 2012
     
    another pic
  1.  
    If the top coat is pink, then its gypsum plaster
    If its White, most likely lime

    If the bottom coat is grey and very hard it's sand and cement, possibly with some hydrated [bagged] lime
    If its brown, black, white, or grey but not as hard then its some kind of lime mix, the colour resulting from the aggregate mixed with it.
  2.  
    It looks like lime in the pictures, though the pinky colour indicates it may have been patched up with a top coat of gypsum plaster.
    • CommentAuthorbabs30
    • CommentTimeMar 9th 2012
     
    Mike can i tell by the texture? Does it feel different?
    • CommentAuthortony
    • CommentTimeMar 9th 2012
     
    Looks like sand and cement undercoat so likely not lime plaster more likely waterproof plaster throwing off the finish then DIY patched up with filler
    • CommentAuthorbabs30
    • CommentTimeMar 9th 2012
     
    Tony if its any help the texture under the plaster feels rough and grainy while the plaster is smooth.
    • CommentAuthortony
    • CommentTimeMar 9th 2012
     
    when you tap the surface plaster does it sound a bit hollow in places?
    • CommentAuthorbabs30
    • CommentTimeMar 9th 2012
     
    No......it did on the bits that fell off but the rest is sound
  3.  
    Drop a small lump of the plaster into a water/hydrochloric acid or sulphuric acid solution to see if it reacts?
    • CommentAuthortony
    • CommentTimeMar 9th 2012
     
    Or vinegar
  4.  
    Posted By: tonyLooks like sand and cement undercoat so likely not lime plaster more likely waterproof plaster throwing off the finish then DIY patched up with filler


    Not necessarilly sand and cement. I have seen lime mortars having the float scratch appearance. What makes me think its lime is that the top coat seems mostly white, and white gypsum is very rare in my experience. Maybe its more common in Ireland, anyone?

    Plaster is not waterproof. Do you mean waterproof render?
  5.  
    Posted By: babs30Mike can i tell by the texture? Does it feel different?


    If its a lime mortar mix, then it is generally softer than sand and cement [though not always] Try making a hole in it with a teaspoon? Does it come away easilly and break down to dust?
    •  
      CommentAuthorJinni King
    • CommentTimeOct 6th 2017
     
    Boosting a very old thread here i know but... I just scraped off a bit of the existing internal render on our stone wall. It came away with using a spoon to scrape it off, and fizzed when I added vinegar. Does this mean it's lime or cement?
    • CommentAuthortony
    • CommentTimeOct 6th 2017
     
    They will both fizz.
    •  
      CommentAuthorJinni King
    • CommentTimeOct 6th 2017
     
    Yeah, I found a few sites saying that...

    Trying to decide whether to leave the existing internal plaster/render(?) levelling coat in place when IWI'ing,

    Builddesk gives them very similar mu values though, so does it really matter if it's cementious?

    It's inboard on a stone wall and will have woodfibre insulation/intello plus/woodfibre in service cavity/drylining inboard of it...
    • CommentAuthortony
    • CommentTimeOct 6th 2017
     
    vapour barrier or no barrier?
  6.  
    Are you using NBT Pavadentro? If so they will advise, and do a site visit if necessary. It's not fool-proof, but generally lime plaster is much more friable than sand/cement. If you happen to be buying from Ty Mawr they will give an opinion on a plaster sample you send them.
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