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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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  1.  
    An insurance claim has come to myself to sort....

    The claim is 'storm damage' but it is clear it is simply penetrating damp from poor external pointing being stone wall construction. The gable has now been pointed externally. We have hacked off all the internal plasterwork and render (1" thick) to the side of the chimney wall and found the mortar to have ~13% MC by Tony's favoured weighing method

    Desiccant dehumidifier currently in-situ. Should be dry this week.

    What is the best method of building up the internal render?

    Dot and dab?
    Lime render? If so, what mix?
    Sand and cement render with water-proofer?

    What is the best plaster? Standard thistle multi-finish?

    This is insurance work and as much as I'd like to be green in principle with IWI or similar the job needs doing. My usual plasterer has said to just use standard sand/cement with a waterproofing agent then skim as normal.
  2.  
    If I opt for a lime render, can someone link me to what products and what ratios for each coat?

    I have read 2 parts lime to 5 parts sand. But what lime does it refer to?
    • CommentAuthortony
    • CommentTimeOct 4th 2020
     
    3 sharp sand : 1 part lime putty for base coats,

    Neat lime putty for the skim,

    Ain’t easy but lime putty is available online
  3.  
    The rest of the room has wallpaper and paint unknown, surely making one section breathable is a pointless exercise?

    What about paints? Normally we just use a vinyl matt as a finish
    •  
      CommentAuthordjh
    • CommentTimeOct 4th 2020
     
    Various lime suppliers have been mentioned on here a lot. Many do courses that are worthwhile. Take advice from your chosen one.

    I hope you've pointed outside with lime mortar? Otherwise the problem may recur.

    The basic choice is between (a) lime putty/fat lime/air lime and (b) hydraulic lime.

    Lime putty hardens by drying and by carbonation. It's quite a slow process - a week or three - and needs to be watched and re-compressed whilst it is drying. Until it's good and hard it can be washed off by torrential rain. The advantages are that the end result is more flexible and won't crack as easily, and that you can keep any spare pretty much indefinitely in a sealed container. Even when mixed with sand etc. You can buy pre-mixes as well as pure lime from the suppliers.

    Hydraulic lime hardens by a chemical action, much like regular plaster. It will even set under water (hence the name). It's more rigid, and stronger and you have to discard any that's already mixed since it will just set. There are various 'strengths'. Setting takes a lot less time, but still longer than regular plaster.

    You mix the lime with an aggregate. This is often sharp sand, but you can also use chalk, which allows for a much finer finish. You also mix everything except the top coat (and sometimes even that) with fibres like horsehair or polypropylene to increase the tensile strength. If you mix fibre in the top coat, along with chalk, then you can burn off any bits that stick out afterwards. And sometimes there are magic additives. :bigsmile:
    •  
      CommentAuthordjh
    • CommentTimeOct 4th 2020
     
    Paint - Dulux Trade Supermatt is a good breathable paint. Clay paints are excellent - we have the Earthborn stuff everywhere.
  4.  
    Hi VE, although you say 'render' you mean plaster -internal - don't you? In that case it's not vulnerable to weather, but still to low temps if they exist.
  5.  
    Yes internal plaster

    The insurance only allow us to do the damage following the event, ie the internal repair only

    The policyholder has apparently re rendered the whole outside wall, it looks like it's been done in cement render.

    We've simply been tasked with hack off damaged plaster, dry the wall and reinstate...
    •  
      CommentAuthordjh
    • CommentTimeOct 4th 2020
     
    Posted By: VictorianecoThe policyholder has apparently re rendered the whole outside wall, it looks like it's been done in cement render.

    I'd turn down the work. You'll only be called back when the problem recurs.
  6.  
    It's not as easy as that unfortunately and as it pays my bill. I can only focus on the internal repairs so if I recommend lime plaster then that's what I'll do... At least I've done my bit to best practice
  7.  
    Are things happening v quickly? In your 1st post you said '' The gable has now been pointed externally''. Then in your penultimate post you say ''The policyholder has apparently re rendered the whole outside wall, it looks like it's been done in cement render.'' Same wall but things changing fast?

    Tempted to agree with djh, but if he/she really has 'locked up' the outside wits/c render, maybe you can still help *the structure* with lime, but you might not *cure the problem*
    •  
      CommentAuthordjh
    • CommentTimeOct 4th 2020
     
    Posted By: Victorianecoit pays my bill

    You are asking for advice on how to spend extra money on tools just to save tax and you're worried about the income from one job? It will end up costing you more than you make, since the cement render will continue to absorb water and the lime is likely to be permanently damp. How will you fix that?
  8.  
    I wouldn't fix it, so long as the 'reinstatement' part is done correctly then the cause of the damp isn't an insured issue?
  9.  
    Is it not a case of 'Perfect being the enemy of the good'?

    While the ideal is to have fully breathable walls, inside and out, is it not the case that by at least fitting breathable materials on the interior of the house, it lets any moisture in the wall escape into the room? This can then be vented via extraction (ideally a MHRV system). Also, lime based products are naturally anti-fungal.

    Our property is solid wall sandstone with external cement pointing. We have problem areas inside with damp and mold growing on gypsum plasterboard inside. However, where we have removed it and replaced it with lime plaster and clay based paints, the damp issues have been eradicated.

    If funds allowed, I'd obviously opt to replace all the external pointing and internal plasterboard with lime, but until I win the lottery I'll continue to fix one room (sometimes one wall) at a time.
  10.  
    Is lime render/ plaster easy enough for a plasterer who has never used it before?
    • CommentAuthorjfb
    • CommentTimeOct 5th 2020
     
    Depends on the plasterer - many will only really be doing skimming so won't be as comfortable rendering.
    Those that are comfortable rendering should be able to use lime but many won't have done so and may be hesitant to do so. Its not that different to cement rendering, it just takes longer - needs to stay damp while going off, usually have to wait longer before rubbing up and longer between scratch/finish coats.
  11.  
    Desiccant dehumidifier been in place for a week, mortar still showing as 12.5% moisture content

    Indicative of existing ongoing q issue. My thoughts as mentioned by others are to walk away?
    • CommentAuthortony
    • CommentTimeOct 8th 2020
     
    How was the 12.5% measured?
  12.  
    Sample taken and weighed

    Sample put in oven at 120c for 1hr then weighed, then another hr and weighed until no further change

    Calculation made as follows:

    Weight before drying - Weight after Drying
    ---------------------------------------------------- x 100
    Weight before drying
    • CommentAuthortony
    • CommentTimeOct 8th 2020
     
    πŸ‘ I have never seen a wall that wet 😒
  13.  
    What calculation do you use?
    • CommentAuthorjfb
    • CommentTimeOct 8th 2020
     
    how is any guttering/tiling above the wet wall?
    • CommentAuthortony
    • CommentTimeOct 8th 2020
     
    I use the same as you there are variations on the theme
  14.  
    It's a ground floor wall in question. Either way we just get asked to remediate the damage ie. Hack off, redry and redo

    As much as I'd like to investigate the problems etc and would actually like to help out I don't get paid for it and the insurable would never cover it
  15.  
    Posted By: VictorianecoIt's a ground floor wall in question. Either way we just get asked to remediate the damage ie. Hack off, redry and redo

    As much as I'd like to investigate the problems etc and would actually like to help out I don't get paid for it and the insurable would never cover it

    If you continue with this job IMO you should put a disclaimer in writing stating (in your opinion) the problems otherwise when/if the work fails 6 months down the line they can't claim poor workmanship
    •  
      CommentAuthordjh
    • CommentTimeOct 9th 2020
     
    Posted By: Peter_in_HungaryIf you continue with this job IMO you should put a disclaimer in writing stating (in your opinion) the problems otherwise when/if the work fails 6 months down the line they can't claim poor workmanship

    +1

    I'd also make sure that copies went to both the insurer that's funding the work and the occupants of the house who have to live with it.
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