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Housing - Renovation: Sandstone interior wall prep method help wanted

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  1.  
    Hi guys,

    Hopefully someone has done this before and can guide me along.

    I am looking to refurbish an 1800s sandstone rubble filled gable end interior wall which has been chipped back to the sandstone.

    For warmth we are thinking of adding a wood fibreboard.

    I'm also wanting to use timber to section the wall into manageable "bays" as its quite a large area to do in one go.

    What method do I follow,

    do I need to dub the wall out then stick the wood fibre on to the bare stone to give me a relatively flat surface and then create the "bays" ?

    Or, Do I slurry the wall first, then use the adhesive to fix the boards ?

    Hope that makes sense.

    Thanks in advance
    • CommentAuthorjfb
    • CommentTimeJul 12th 2021
     
    For woodfibre IWI you really need to get to a flat finish so that there are no voids when fixing the boards to the wall with plastic pin fixings (not adhesive). So dub out the wall and then another flatening layer (so all stone is covered). The render also acts as an airtight layer.
    Use hydraulic lime rather than cement for behind the boards and as the finish. There can be slightly different methods for finishing render but normally it goes on in two layers and has a 4mm plastic mesh sandwiched in the middle.
    • CommentAuthorJonti
    • CommentTimeJul 12th 2021
     
    Can you explain a little why an internal wall needs insulation? Is the room on the other side not heated or something similar?
  4.  
    ''Can you explain a little why an internal wall needs insulation? Is the room on the other side not heated or something similar?''

    I'm guessing that as it's a 'gable end' the 'internal wall' refers to the *interior face* of an *external* wall.

    Davycrocket, can you explain the sectioning up into 'bays'. I can't quite visualise it unless the timbers are to form a full-thickness thermal bridge.

    As per jfb, dub it out first. If you like 'wobbly' walls you do not have to go for flat. We did a rubble-stone wall in 100mm total wood-fibre laid as:

    - 2 or 3 coats lime plaster to smooth out the lumps.

    -20mm W-F buttered with 10mm toothed coat of lime, hammer-fixed.

    - 40mm W-F 'dry', joints staggered. Hammer fixings.

    - Further 40mm WF 'dry'. Hammer fixings.

    Mesh all joints (as they are not T & G), toothed coat plaster, mesh, 'wet on wet' coat to hide mesh as far as possible. Further coat when 'wet-on-wet' has stiffened. This one can be trowelled up as finish if desired. Final 'polish' coat if desired min 2-4 days after previous coat.

    We used Baumit plasters. Not cheap but lovely to use.

    Dubbing (thick): RK38

    Base/coarser finish: RK70

    'Polish': Kalkin Glatt (?RK30)
    • CommentAuthorDavycrocket
    • CommentTimeJul 13th 2021 edited
     
    <blockquote><cite>Posted By: jfb</cite>For woodfibre IWI you really need to get to a flat finish so that there are no voids when fixing the boards to the wall with plastic pin fixings (not adhesive). So dub out the wall and then another flatening layer (so all stone is covered). The render also acts as an airtight layer.
    Use hydraulic lime rather than cement for behind the boards and as the finish. There can be slightly different methods for finishing render but normally it goes on in two layers and has a 4mm plastic mesh sandwiched in the middle.</blockquote>

    Thanks jfb

    So if I'm reading this correctly because the wf is fastened rather than stuck on, can I take my time adding the two finishing coats over the wf, or am I still constrained by time ie not letting the plaster base layers dry out before adding the top coats. ( its a large wall and i'm no spring chicken)

    Tia

    Edit.

    I think Nick Parsons has confirmed ? that I will be constrained by time.
  6.  
    <blockquote><cite>Posted By: Jonti</cite>Can you explain a little why an internal wall needs insulation? Is the room on the other side not heated or something similar?</blockquote>

    It's a gable end mate else I wouldn't bother.
  7.  
    <blockquote><cite>Posted By: Nick Parsons</cite>Davycrocket, can you explain the sectioning up into 'bays'. I can't quite visualise it unless the timbers are to form a full-thickness thermal bridge.</blockquote>

    I wanted to create sections / bays with timber approx 2 metres wide with 38 x 19mm or thereabouts to help me get the wall fairly straight. (I'm hoping to get a good flat finish)

    I'd use a Darby from timber to timber then remove them when applying the top coat.
  8.  
    <blockquote><cite>Posted By: Nick Parsons</cite>Mesh all joints (as they are not T & G), toothed coat plaster, mesh, 'wet on wet' coat to hide mesh as far as possible. Further coat when 'wet-on-wet' has stiffened. This one can be trowelled up as finish if desired. Final 'polish' coat if desired min 2-4 days after previous coat.</blockquote>

    Reading that I am constrained by time from fixing the wf to application of the top coat ?

    I was hoping for a break in between coats:sad:
    •  
      CommentAuthordjh
    • CommentTimeJul 13th 2021
     
    Posted By: DavycrocketReading that I am constrained by time from fixing the wf to application of the top coat ?

    No, normally when you apply multiple layers of lime plaster, you wait until the first coat has stiffened up before applying the second one, to avoid slumping.

    But there's a special case when you're putting a mesh in lime. Some instructions tell you to put a coat of lime on, then push the mesh into the top of it, then finish that coat and wait for it to stiffen up before applying the next one. But frequently that will cause a weakness in the lime, with the upper coat tending to pull loose. So the idea is to apply a very thin coat, then immediately apply the mesh and follow that immediately by a second very thin coat (i.e. wet on wet) so as to form a single thicker coat with the mesh embedded in it.

    There's no particular time constraint from when you put the woodfibre up to when you start putting the lime on top. Just as there's no particular maximum time from when you put the initial scratch coat on the wall to when you put the woodfibre on top.
  10.  
    That's great thank you.

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