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General: Wot no peashingle bedding?

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  1.  
    • CommentAuthorcc64
    • CommentTimeApr 16th 2023
     
    Wot no pea shingle?
    I'm in the process of exposing the sub dpc walls down to foundation level on my early 1990 terrace in preparation for installing some EWI.

    In the process I've exposed several 100mm plastic drains. One superficial (~ centred about 300mm below GL) pipe taking low from a gutter downpipe, had some token peashingle (rounded not sharp), if nothing like the 100mm alaround as suggested by NHBC docs. The other two are soil/sewer, deeper (~80mm below dpc, 65mm below GL) have not a hint of any such bedding nor sidefill nor backfill - they're just embedded in rubbly subsoil. Has guidance changed or is this yet more corner/costs cutting in evidence?

    Each of these soil/sewer pipes has also been supported on bricks, again counter to current NHBC guidance ("Bricks, blocks or other hard material should not be used as temporary supports to achieve the correct gradients, as they may create hard spots which can distort the completed pipe run."). I despair.

    For reasons that probably don't need spelt out I'm reluctant to mess with the obvious deficiencies of these two; they've been in place for 30 years, not broken, so don't fix them.

    When it comes to infill time I can setup some temporary shuttering around each to reinstate 100mm pipe bedding gravel alaround each. Does that seem an adequate pragmatic approach to their otherwise inadequate installation?

    Lastly these two were left generous 550mm wide gaps to emerge through. These were filled with 3 applications of coarse (ie big aggregate) concrete. Each application slumped to protrude beyond the face of the surrounding blocks - not great for EWI skirt application. I've knocked off these protuberant bits but this does leave me with some fairly substantial voids. I'm thinking to fill these with non-slumping concrete. The cumulative experience here might have better ideas. Happy to hear these.

    If someone can tell me what photoimagesize is accepted here I can post a pic. It didn't like my phone default 3Meg photo

    Thanks
  2.  
    Posted By: cc64they've been in place for 30 years, not broken, so don't fix them.

    +1
    Posted By: cc64When it comes to infill time I can setup some temporary shuttering around each to reinstate 100mm pipe bedding gravel alaround each. Does that seem an adequate pragmatic approach to their otherwise inadequate installation?

    Yes

    Posted By: cc64Lastly these two were left generous 550mm wide gaps to emerge through. These were filled with 3 applications of coarse (ie big aggregate) concrete. Each application slumped to protrude beyond the face of the surrounding blocks - not great for EWI skirt application. I've knocked off these protuberant bits but this does leave me with some fairly substantial voids. I'm thinking to fill these with non-slumping concrete.

    The infill around the pipes should not be structural to avoid load on the pipes so infilling the voids can be done with anything you like and have to hand e.g. EWI adhesive when installing the EWI or squirty foam if you have a bit spare - 'cos it will be covered by the EWI anyway.
    • CommentAuthorcc64
    • CommentTimeApr 16th 2023 edited
     
    That'll be a lot of squirty foam...
    • CommentAuthorrevor
    • CommentTimeApr 16th 2023
     
    Posted By: cc64as they may create hard spots which can distort the completed pipe run."). I despair.


    Yes bricks are often used to set the fall that is ok as long as you take them out. It is how I did my drain falls setting bricks on edge to the 1:40 filling in between with pea gravel/ shingle/ pink stone remove bricks and backfill their holes. (Pea gravel is used because it does not compress. In cold climates like parts of the USA where they have permafrost they use that as the foundations of timber framed building with pea shingle on top and big baulks of timber laid on the shingle a solid foundation that has stood the test of time but now not so as permafrost melts with a warming world.)

    Where the pipes come through the wall there should be a lintel over in case of movement and a rodent proof barrier between the holes and the external back fill even if you have a solid floor as vermin can get into the cavity. So if you use squirty foam to fill the voids make sure that is protected as vermin will much their way through it. Some stainless steel mesh is ideal. Your EWI should cover it but better safe than sorry.
  5.  
    Posted By: cc64That'll be a lot of squirty foam...

    Not if you stuff off cuts of the EPS in first and then secure with squirty foam

    Posted By: revorSo if you use squirty foam to fill the voids make sure that is protected as vermin will much their way through it. Some stainless steel mesh is ideal. Your EWI should cover it but better safe than sorry.

    +1
    although vermin don't go through the EWI top adhesive coat with the glass mesh embedded.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 20th 2023
     
    Posted By: Peter_in_Hungaryvermin don't go through the EWI top adhesive coat with the glass mesh embedded
    That's an authoritative-sounding statement in what's been a long-running discussion! by 'glass mesh' you mean glassfibre i.e. the stahdard stuff embedded in the finish base coat?
    • CommentAuthorGreenPaddy
    • CommentTimeApr 20th 2023
     
    I've seen rats eat through concrete, which is why we've put crushed glass in the underbuild in the past, even added sheet steel facing, for an essential vermin-free project. Not convinced by a bit of f/g reinforcing mesh.
  8.  
    Mice can certainly get through cement mortar, don't think glass fibre mesh would stop them.

    I save up my offcuts of metal plaster beading, old nails, used hacksaw blades etc, and mix them into whatever goop I use to block mouse holes.

    Some people mentioned using concrete paving slabs, set on edge against the outside of the bottom of their EWI render, that would probably work if they were set tight against each other without mortar gaps between.

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