Rendering Internal walls

Discussion in 'Builders' Talk' started by Julian1, May 19, 2006.

  1. Julian1

    Julian1 New Member


    Just had a small extension built and thinking of rendering the walls myself before getting a plasterer in to apply a coat of finish on top.

    Could anyone please advise on what type of sand to use and the proportions to cement. Do I have to add anything else to the mix. And finaly what thickness should be applied. The walls are in blockwork.

    Many thanks
  2. handyman 2

    handyman 2 New Member

    Are you serious??

    Firstly internal walls do not need rendering with sand and cement but a base coat of plaster is used instead such as Bonding or Browning
    Secondly, if you did render them then a finish coat of plaster would be nigh on impossible to get right as sand would inevitably break away from the render into the top coat as the plaster is applied

    Just get a Plasterer in from the start :)
  3. Are YOU serious Handyman?? what complete nonsense!
    It is absolutely fine to use a sand cement backing coat before skimming, though if they are thermalite type block it would be a difficult task in sand cement because of their pourosity. Better to dot and dab plasterboards in any case and the floating (backing) coat would need to be spot on if the skim coat is to be perfect whatever material you use.
  4. building control

    building control New Member

    make sure that with sand and cement render, it still complies with heat loss requrements?
  5. layiton

    layiton New Member

    Julian, its fine to render then skim(dont listen to handyman-his title says it all!!) but i suspect your a novice and you think that by doing the floating coat your saving money and helping the spread, but the floating coat is arguably harder to get right than the skim coat. Mess the floating up and no matter how good the skim your walls could be out of square,reveals all to cock and basically a 'handyman' job, good luck!
  6. cheltonian

    cheltonian New Member

    Agreed. Can't beat a sand cement render. I will always use this as a backing coat if possible.

    I have seen thermalites internally rendered, spreads used a lime/cement/sand mix
  7. M.I.G.

    M.I.G. New Member

    > Could anyone please advise on what type of sand to
    use and the proportions to cement. Do I have to add
    anything else to the mix. And finaly what thickness
    should be applied.

    so who's gonna answer his questions then?
  8. nearnwales

    nearnwales Member

    just normal building sand will do , at 4-1 sand and cement with a cap full of feb . But as the others say its not easy,

    If your right handed start at the top right lay it on about 17-20mm thick. And use your feather edge to rule it fill the areas that need it when all flat use to darby and when crusty use your float with nails in to form a key I use a 5 nails just slightly in .

  9. slapiton

    slapiton New Member

    lightweaght blocks will need a good soacking with a hose before applying sand and cement float coat with even a ****** out coat of p.v.a. on top. sand and cement is a better float coat than lightweight gypsum undercoats.
  10. Julian1

    Julian1 New Member


    Thank you for you advice its much appreciated. Could I trouble you again with one other thing. Presumably if applying a thickness of 17-20mm it will have to be done in two stages and scratch the first coat to act as a key for the second is that right?. Also, how is the final coat finished, smooth down with a float presumably before the skim can be applied?...Oops that 2 things I asked....

    Thanks again
  11. yorkshireboy

    yorkshireboy Member

    If I where you I would follow Robbo's advice and dot and dab plasterboards on the wall.It looks a doddle when you see a plasterer rendering but if you are a begginer you will not get it flat.
    The render should have a scratched finish to key the skim
    Out of curiosity why is everyone singing the praises of render undercoat.What are the advantages over a coat of browning/bonding ?
  12. nearnwales

    nearnwales Member

    The lads are right if I was my house I would dot and dap it. But if you want to float it float it :].

    You put only put a scratch coat on if it thick eg. stone work , but block work one coat will do.

    The advantages of render over browning and bonding is cheaper , less suction , easyer to mix , you can throw it back in the mixer . Don't get me wrong I love bonding for filling holes ect, just don't like floating with it .

  13. -chippy_john

    -chippy_john New Member

    Out of curiosity why is everyone singing the praises
    of render undercoat.What are the advantages over a
    coat of browning/bonding ?

    Possibly this?

    When I lived in London I did a lot of major renovation work for a large housing asociation. All the internal plaster was removed from the houses we worked on and replaced with sand and cement render, they wouldn't allow the use of Carlite Bonding or Browning because of it's tendency to soak up condensation. The finish coat was Sirapite(I think)
  14. dunc

    dunc New Member

    I am not a plasterer, its a real art. But I think rendering is the best way for the diy plasterer. You can work the render for longer and produce something good enough for the skim coat.
  15. handyman 2

    handyman 2 New Member

    :O -- Well I live and learn -- :O
  16. each backing has its own advantages and disadvantages s&c is good for situations of damp coarse use with a waterproofer in it and its a good hard background like gypsum hardwall as the bag says.whereas browning is soft and doesnt take knocks so well its all about the room in question in my eyes and what its use is as to what backing coat it gets.
  17. moe89

    moe89 New Member

    Hi mate,
    What's the purpose of backing render on to a block wall. Does it make the wall more soundproof???
  18. sospan

    sospan Screwfix Select

    Not quite, the backing render serves all sorts of purposes from evening out the walls and getting them flat, filling in gaps between the blocks / bricks, adding a little strength to the walls and making it look good. Typically people will either use a cement or plaster based product as their first and second coat and then use a finishing plaster.

    Really if you have a largish area to do, it is best to get a professional in only attempt it if it is a skill you really want to learn and are prepared for a few setbacks and less than perfect finish until you get good at it
    KIAB likes this.
  19. KIAB

    KIAB Super Member

    A scratch coat can be a cement render (old fashion nowadays) or undercoat plaster,like Thistle Browning,Bonding,Tough Coat,Hard Wall,etc,depending on the surface,some surfaces are low suction, others high suction, gives you a solid firm level base on the wall which is ready to provide a key for top coat plaster, known as finishing plaster.
    Last edited: Feb 9, 2017
  20. moe89

    moe89 New Member

    Hi mate,
    I'm new to this,,so plz bear with me....

    Can you use browning, hardwall or bonding over the plastering sand cement render, rather than using dot and dab plasterboarding.....

    Cause I hav bought a Victorian house. (internally has brick walls and stonewalls),

    the house has been rendered in plastering sand and cement, its in good tact... But my question is,, can you render over the plastering sand, rather than dot and dab it....

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