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General: Parge coat advice

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    • CommentAuthorPaul_B
    • CommentTimeSep 12th 2012
     
    Went back to applying the parge coat by trowel rather than brush. I discovered the plaster sand contained quite a lot of larger pieces of around 3.5mm meaning it has created pulling and a parge coat thickness of around 3.5 to 4.0 mm. It means I'm going to have to leave the wall for at least 4 days before adding the insulation. Quite a bit of tidying to do tomorrow as well as moving the integrated vacuum pipe.

    Paul
      Trowel-Parge.jpg
    • CommentAuthornikhoward
    • CommentTimeNov 20th 2012
     
    Hi Paul,

    How has all your parging gone?

    I have done a bit as well for air-tightness to sections of wall that are not currently rendered or wont be in future (under eaves cupboards walls, gable ends where joists run parallel). I used a runnier single cream of 1 cement, 2 sand, plastersiser and lots of PVA onto dense block.
  3.  
    Just to add another option for parge coating

    I have used with success pre mixed lime based mineral renders (Parextherm or Baumit for example) and even Artex type products.

    I spread them on with a plastering trowel, very thin so that the trowel is scraping against the surface. Use a nice thick creamy mix and almost paint the wall with the the trowel. Dont put it on with any thickness, not even like a plaster finish coat.
    Wait for it to start to set and then I rub over with a car sponge. Works perfectly as a parge coat and one bag goes a very long way.

    The adavntage is that you dont have to worry about getting the mix right or choosing the correct sand etc.
    • CommentAuthordjh
    • CommentTimeNov 21st 2012
     
    Posted By: bot de pailleI spread them on with a plastering trowel, very thin so that the trowel is scraping against the surface. Use a nice thick creamy mix and almost paint the wall with the the trowel. Dont put it on with any thickness, not even like a plaster finish coat.
    Wait for it to start to set and then I rub over with a car sponge. Works perfectly as a parge coat and one bag goes a very long way.

    I can see that will give a level surface but does it also act as an airtightness layer when it is so thin?
  5.  
    Posted By: nikhoward1 cement, 2 sand


    why such a rich mix? Would a weaker mix be more flexible?
  6.  
    Posted By: djh
    Posted By: bot de pailleI spread them on with a plastering trowel, very thin so that the trowel is scraping against the surface. Use a nice thick creamy mix and almost paint the wall with the the trowel. Dont put it on with any thickness, not even like a plaster finish coat.
    Wait for it to start to set and then I rub over with a car sponge. Works perfectly as a parge coat and one bag goes a very long way.

    I can see that will give a level surface but does it also act as an airtightness layer when it is so thin?


    It gives a consistent smooth (with raised sand grain from the sponging), not flat surface, fills in all the holes etc. Definitely airtight over the block work and joints.
    • CommentAuthornikhoward
    • CommentTimeNov 23rd 2012
     
    Posted By: spoonandfork
    Posted By: nikhoward1 cement, 2 sand


    why such a rich mix? Would a weaker mix be more flexible?


    a bit rich i know, but i only needed to do a few m2, so 1 gauging trowel of cement, a couple of sand and i did not really need any more. also our local sands are fine or coarse, but fine is more like sharp and coarse is very coarse.

    they are all grey granite and a by product of the local china clay industry (whats is left when they wash the clay out), you dont get a buttery mortar like with red sand no matter how much lime or plastersiser you add, so you tend to make richer mixes to help bind the sand together a bit more.

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