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Rendering over masonry paint

Discussion in 'Plastering and Rendering' started by 88v8, 10 Oct 2021.

  1. 88v8

    88v8

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    Block wall, 60s. Sound cement render then old masonry paint.
    Got a lot of the paint off, but can't get rid of all the mist coat.

    Need to render over the render, to add 3/4" of thickness.
    4:1:1 cement lime sand then 5:1:1

    I think I should start with a bonding agent. SBR seems to be a favourite.
    Which one would you use?

    V8
     
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  3. tell80

    tell80

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  4. 88v8

    88v8

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    Hehe, OK, any particular brand or are they all the same?

    V8
     
  5. 88v8

    88v8

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    I should take my specs when I go shopping... the small print, or considering the space taken up by the H&S crap, the tiny print.... when I got the SBR home, it says 'Do not use over painted surfaces'.
    So I hired a needle scabbler and removed the rest of the paint. Not a job I'd want to do again.
    Anyway, it leaves a good surface, no further prep.
    Scratch looks OK.
     
  6. Godwasaplasterer

    Godwasaplasterer

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    you could have used rendabond
     
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  7. 88v8

    88v8

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    Thankyou.
    I checked the data sheet of Bostik PVA (used to be Rendabond) and it says for outside work to use Bostik SBR, so I just bought some.
    The first job went OK, but I have more to do with the same paint problem and I really don't want more days with the scabbler, so thankyou.
     
  8. Godwasaplasterer

    Godwasaplasterer

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  10. 88v8

    88v8

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    Ahh yes, even better. I checked the data sheet and there is no problem over paint.
    And I can wait until it's dried.
    Bit cheaper at Sealants & Tools Direct https://www.sealantsandtoolsdirect....ip-extra-grip-render-bonding-coating-rendgp10
    I'll still strip as much of the paint as I can, but this will make the job easier for an amateur like me :)
    Thanks again.
     
  11. 88v8

    88v8

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    Rendagrip yesterday, left a day to dry.
    Scratch coat on this morning.
    Very little suction.
    Slow drying.
    Waited two hours to scratch it.
    Not sure how much grip it's got on the wall really. Feels strange with so little suction.
    Will leave it until day after tomorrow to put the top coat on.
     
  12. Godwasaplasterer

    Godwasaplasterer

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    It will be slow in this weather. and there wont be much suction given the rendagrip, paint ,and the wall will be damp to start with.
    from my experience the stuff gives a good mechanical key so you should be fine.
    the longer it takes to cure the better really as long as it don’t wash off overnight.
     
  13. 88v8

    88v8

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    It will be OK if there's rain, it's under the overhang of the thatch.
    Do you think two days is too soon for the top coat? Don't want to pull it off the wall when the top coat dries.
     
  14. Godwasaplasterer

    Godwasaplasterer

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    i’d leave it longer . a week this time of year. but that’s just me.
    2 days should be good.
     
    Last edited: 26 Oct 2021
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  15. 88v8

    88v8

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    I left it a week to do the second coat. No hollow spots when I tap it. Seems OK.
    Second coat 5:1 as I said, but 4:1 for lime.
     
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