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Housing - Renovation: Cavity Wall Extraction

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    Looking for a contractor to remove damp cavity wall insulation on a property in South Wales that has been retrofitted with EWI?
    • CommentAuthortony
    • CommentTimeOct 16th 2020
     
    It will dry out now , may take a while and empty cavities will negate the EWI if they are draughty, that would be normal too.
  3.  
    The water soaked the cavity following a roof leak and destroyed all the internal dot and dab plaster.

    We want to put the plaster back on but need to either dry the CWI and give a certificate or remove it..

    I'm not putting a warranty on it as it should have been removed when they did the EWI?
  4.  
    Hi VE, can you clarify? Are you saying that EWI was done when it was known that there was *wet* CWI in the cavity? If this is the case then that was arguably ill-advised although, as Tony points out, the CWI should ultimately dry out (although the speed and consistency of the drying-out will depend on the detailing and completeness of the EWI). If, for example, 'industry standard capping details' have left a cold strip along the top of the bedroom walls at the eaves, the top of the wall may take much longer to dry out.

    This brings us to a difficult issue re EWI on cavity walls. You'll find much discussion here and in other places about thermal by-pass 'leaving EWI out in the cold', and the attempts needed to ensure that this does not happen. Closing the cavities and, of course, closing the original cavity vents are obvious ones, but some leakage will remain. So... *although insulation is very rarely a draught-stopper* a lot of us suggest that CWI will go a small way towards reducing air movement - and thus thermal by-pass - in the cavity.

    So, if your CWI is absolutely *wet through* it probably does need to be taken out *but replaced by (graphite) EPS bonded beads*. I would not recommend leaving the cavity un-filled.

    As far as CWI removal it is a lot of years since I last tried to find a CWI removal contractor. At the time, from the replies I received, it became clear to me that none of the firms I contacted had a 'cavity hoover'. The installation job had maybe taken half a day off ladders, and the guesstimate for the removal job - removing individual bricks and 'poking it out with a stick' was over a week on scaffolding - a very different and much more costly proposition. Things may have changed now - there may be some sort of suction method, but never having seen it tried I wonder how easily soaking-wet agglomerated 'ex-fluff' would suck up a tube.
  5.  
    No the EWI must have been fitted previously but not known if any issues.

    The policy holder (insurance work) advised they had a roof leak that saturated the cavity. It's the last house on a run of 5 and takes all of the water and is felt roof

    We were tasked with redoing the internal plaster and decorations but advised to do so either the cavity needs to be dried (I'm not warrantying the drying as I don't think it should have been left in) or it gets extracted.... then we can do the repair works
    • CommentAuthorjms452
    • CommentTimeOct 17th 2020
     
    If it is insurance work you may be restricted but If it was my house I'd be focusing on a lasting solution for the roof.

    When you remove the cavity wall insulation (fibreglass?) the walls will still take a fair while to dry (weeks to months?).

    What is the EWI made of - phenolic won't like getting saturated.

    Posted By: Nick ParsonsSo, if your CWI is absolutely *wet through* it probably does need to be taken out *but replaced by (graphite) EPS bonded beads*. I would not recommend leaving the cavity un-filled.


    +1
  7.  
    While we await the insurers decision the customer isn't happy that they have two walls in the house exposed.

    I've reiterated to the customer that we can't reinstate the internal plastering and decorations until they make a decision as there's potential for water to track back across of it's still damp.

    Given the internal wall is now block, is there some kind of method to prevent any damp coming through?

    Perhaps foil backed PB mechanically fixed rather than with dabs? Just trying to figure a solution to what could take months to resolve....
  8.  
    Paint on tanking slurry? We have used it on 2 previous properties, both partially below ground - one about 5foot the other was up to the eaves at the back. The wall will not dry inwards then though.
    •  
      CommentAuthorfostertom
    • CommentTimeNov 5th 2020
     
    Tanking slurry - do you mean the Vandex type which grows crystals to clog up the masonry's capillaries, or the type which is simply an impervious coating? Don't know, but I guess each wd have different vapour transmission behaviour.
    • CommentAuthorcc64
    • CommentTimeDec 7th 2020
     
    I would suggest you contact the damp experts at https://www.safeguardeurope.com/damp/treatment

    I suspect they'll only insist the job be done properly i.e. first sort out that roof; then remove the wet CWI; if the internal blob and dob plasterwork was destroyed this was very wet indeed; maybe an opportunity to go through the similarly destroyed window reveals as access points for removing the CWI?
  11.  
    Posted By: fostertomTanking slurry - do you mean the Vandex type which grows crystals to clog up the masonry's capillaries


    Sorry, only just seen this. I think it was Permaseal (it was about 10 years ago now so I struggle to recall...!) because I remember you could get it in grey or white, so easier to distinguish between the 2 coats that are required.
    I do remember it claimed some sort of "breathability" which I found hard to believe, if this was the case then it was ideal, but the main thing for us was stopping the moisture from the ground coming through the wall to the inside!

    I also have a tub of KA tanking that I have used in some places on one of the outbuildings here. I picked it up from a DIY shed.


    from the Permaseal website:

    PermaSEAL Tanking Slurry is a single pack cement-based coating, consisting of Portland Cements, blended and formulated with quality graded aggregates and chemical modifiers. It is ideal for tanking cellars and basements, keeping them dry by effectively blocking water ingress. It is easy to use - you can apply it directly onto damp substrates with a brush.

    In addition, PermaSEAL Tanking Slurry contains an acrylic polymer that imparts improved strength, bonding and abrasion resistance. After hardening, PermaSEAL tanking becomes a vapour permeable and watertight coating capable of withstanding water pressure.

    Tanking Slurry Uses
    PermaSEAL Tanking Slurry can be used in the following situations:

    Tanking of basements and cellars
    Above ground damp proofing
    Sealing of tanks and ducts
    Internal and external waterproofing
    Lining of storage tanks for potable water
    Coating of brick and block work structures
    Using Tanking Slurry
    PermaSEAL cementitious tanking is mixed with water on site and applied directly to the surface by brush. It is safe to apply on damp substrates. It is specially formulated to enable excellent adhesion to construction surfaces.

    Our tanking slurry is available in two colours, white and grey. As a general guide, use one colour for the first coat then the other for the second coat which makes it easier to see if you have completely covered the surface.

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