Quick question about render...

  1. julianf

    julianf Member

    Messages:
    3,988
    Location:
    devon, uk
    I need to render an external wall.

    It's currently bare thermolite blocks (light aerated block)

    I'm thinking -

    Pva it.
    5mm or so 4:1 sharp sand / cement mix
    Render mesh
    Another 5mm of the same mix over the top.

    All applied together (ie wet on wet)

    Is that the right sort of idea?


    I can plaster gypsum fine (I'm not a pro, but I've done more than one friends place also) and I'm fine with lime, but I've just never done cement render.

    Thank you.
     
  2. 8ob

    8ob Forum Supporter

    Messages:
    4,129
    Location:
    moscow on thames
    Dont know the correct answer but the last house I built was thermolite inside and out, plasterer used silver sand/cement on that.

    Bob
     
  3. tommy dunlop Member

    Messages:
    119
    uk south east
    hi what size is the wall
     
  4. julianf

    julianf Member

    Messages:
    3,988
    Location:
    devon, uk
    Small. Single story, not more than, maybe, 3mrts long? I mean this is off the top of my head, but it's not much of a job.

    Why do you ask?
     
  5. angellonewolf

    angellonewolf Member

    Messages:
    4,202
    Location:
    bristol england
    not pva what you need is sbr to seal it
     
    Westfield-builder and Parm like this.
  6. julianf

    julianf Member

    Messages:
    3,988
    Location:
    devon, uk

    By chance I got a dumpy bag of sand from a different supplier. They charged me a fortune for it (£56 plus vat or somthing) but it seems to handle very nicely, so maybe it's something special. Was hoping to just use that. It's yellow, well graded, and seems quite clean.
     
  7. Parm

    Parm I have fun doing stuff

    Messages:
    9,034
    Location:
    Towcester
    I’ve always seen it done in two coats. First up a scratch coat then finish coat.

    It’s more forgiving than gypsum. Once you’ve got it floated flat you can use some of the drier stuff that falls off to fill in dips etc.

    I’v had a go few years ago and it came out ok, I’d never earn a living from it though
     
  8. dholdi New Member

    Messages:
    12
    Location:
    Preston - England
    As wolf said above, absolutely not pva, sbr is a bit more expensive but what you should be using before anything else.
     
  9. tommy dunlop Member

    Messages:
    119
    uk south east
    dont face it up to wet then finish with nice soft sponge
     
  10. tommy dunlop Member

    Messages:
    119
    uk south east
    start bottom left corner,cover 1mtr high and move across to the right,then go back to the left corner then do top half and move right,if your left handed start from right corner, if it was easy every man and his dog would be doing it lol
     
    slim_boy_fat likes this.
  11. eddie49 Member

    Maybe it is plastering sand? That provides a very easily workable mix.
     
    eLuSiVeMiTe and brightspark like this.
  12. mm289 Member

    Messages:
    447
    Dover, Kent
    Seems to be lots of different opinions on render when I was doing it on the pizza oven.

    Basic rules I found were top coat weaker than base coat, its about suction into the substrate so i wouldn't PVA.

    For my 1st mix I did 4:1 sand:cement with the sand a 50:50 sharp and plastering and some plasticiser.

    Second coat was 5:1 same sand mix but waterproofer instead of plasticiser. Was put on wet on dry but I scratched the 1st coat.

    Top coat can be floated when nearly dry with a wooden float then brushed smooth with a damp sponge.

    Worked for me:thumbup:

    Cheers,

    MM
     
  13. tommy dunlop Member

    Messages:
    119
    uk south east
    its a bit like tig welding ally (practice)
     
  14. angellonewolf

    angellonewolf Member

    Messages:
    4,202
    Location:
    bristol england
    ive only done a few small amounts of render quite heavy compaired to plastering but as said 2 coats same as plastering dont play to much or you will pull it off
     
  15. TechnicAl

    TechnicAl Member

    Messages:
    6,353
    Location:
    Rotherham
    I once Tyroleaned (is that a word) a whole Bungalow (big bungalow) for my brother........Mix stuff and pour it in a tray that straps in front of you, turn the handle and flick it at the wall......I reckon it was about half and half, that is, half on the wall and half on me...It took me ages but I needed the money (I was 17)....I walked past the bungalow the other day and it still looks good (Im now 65)....
     
    dobbslc, Stingray, jenki and 3 others like this.
  16. brightspark

    brightspark Member

    Messages:
    26,609
    Location:
    yarm
    I once did my 2 walls 1st a scratch coat then the second coat with washed plastering sand then tyroleaned it .looked real nice
     
  17. Kayos

    Kayos Member

    Messages:
    4,664
    Location:
    Yorkshire
    I've seen it done with sbr and whatever render was needed

    I've also seen an acrylic type system used, a mesh is attached with pins, this is rendered then an acrylic top coat is applied. This looks good when done right but I've also seen it rushed, the top coat basically slipped off in a big sheet
     
  18. jimbo84 Member

    Messages:
    508
    Location:
    Up North
    Gave my mate a lift rendering the small extension on the back of our old house, he knows what he's doing, I don't :D. Straight onto the bricks with a render (plastering) sand, cement and lime mix. Think the mix was 5:1:1, some plastersiser in both and a waterproofer in the base coat. Applied in two coats, a scratch coat one day, top coat the next, pebble dashed to finish. Hasn't fallen off....yet.

    There's a whole different view on rendering from every different plasterer/renderer when you start looking round, different methods different views, think once one of them has what works for them they stick to it and don't entertain what works for somebody else.
     
  19. mtt.tr

    mtt.tr Member

    Messages:
    704
    Essex England
    Personally id go thinset.
     
  20. jenki Member

    Messages:
    184
    Location:
    Carmarthen, S Wales
    +1 for waterproofer in the first coat.
     
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