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Help with Rendering

Chaps,

Quite a few jobs I've worked on have involved rendered walls, and we always used to get the pro's in to do it. But after watching them (and paying a lot for them!) I decided to give it a go myself, with pretty good results. However I went back to a job this week and the paint is seriously bubbling about half way up, needs stripping off and re painting. Now i realise this could be for a number of reasons so I'll explain a bit more...

The rendered walls were only 75cm high and made a stand-alone raised bed. Foundation at ground level (no DPC) I used 6 inch hollows filled with concrete. I put the scratch coat straight on to the blocks (didnt seal the blocks with anything) and then the finish coat with only plasticiser in the mix. Then the inside of the beds were lined with plastic (not perfectly i must admit, and the walls painted with 2 coats of Weatherseal is it? Or something similar exterior masonary paint. 

Can anyone give me any pointers where i may have gone wrong? Or if you have a more substantial way of doing it as I have only followed 1 plasterer's advise??? And do you guys try it yourself, or sub it out???

I'd really appreciate your thoughts as just had a job accepted with some more rendering

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Replies

  • How long between rendering and painting? The render needs to completely dry otherwise damp forms and paint bubbles. with indoor plastering i advise a minimum of 2 weeks before painting to be on the safe side, so i would say  longer for an outdoor wall.

  • Always useful to apply a coat of watered down external pva to seal wall prior to rendering (also if repairing render). Allow at least two/ three weeks to let render fully dry, then when painting apply a watered down first coat (50:50) to provide a key coat on all new render allow to dry. Then follow this with two/ three normal coats on top (this may be the trouble as the paint has not keyed to the render). As i do a bit of handyman work and have seen it before when the house holder paints new plaster with out painting on a watered down coat first then they call you in after there is a problem and the paint is loose and flaky.

  • ditto to all of the above, although I use a stabiliser on new rendered surfaces before painting

    Also, tack coat of SBR on the clockwork before applying scratch coat

    • Some house painters I know always apply a weak coat of normal undercoat first when painting new render.

      Tim Horner said:

      ditto to all of the above, although I use a stabiliser on new rendered surfaces before painting

      Also, tack coat of SBR on the clockwork before applying scratch coat

  • Thats really good helpful information - thanks everyone. A few more questions.....

    What kind of beading do you use? I have always used galvanised steel ( I think) and had no probs, but other people have told me to use stainless steel?? Also Tim, or anyone, what is SBR? 

    Thanks

    John

  • PRO Member

    SBR = Styreene Buttediene Rubber is for use in external conditions for example on the surface of block walls prior to applying the coats of render

  • Looks a great job be good to see more pictures when its finished and planted up

    Tim Horner said:

    ditto to all of the above, although I use a stabiliser on new rendered surfaces before painting

    Also, tack coat of SBR on the clockwork before applying scratch coat

  • Stainless steel the only way forward really. I have redone a few jobs where internal beading was used. The problem is that is the paintwork on the beading is ever compromised it will result in rust on the galvanised bead which will in time blow the render.

    SBR is a wonderful product, like Mick has said, its used in rendering as a primer before base coat but also as an additive in screeds, tanking.  ect.. Its like PVA but it also acts as a water proofer and inhibits the movement of salts through the wall. I also use it as a primer and bonding additive painted on the backs of paving slabs before they are laid.



    John Steiner said:

    Thats really good helpful information - thanks everyone. A few more questions.....

    What kind of beading do you use? I have always used galvanised steel ( I think) and had no probs, but other people have told me to use stainless steel?? Also Tim, or anyone, what is SBR? 

    Thanks

    John

  • thanks mate. Check out my Facebook page for updates on the progress of my current projects



    Austin Powell-Allen said:

    Looks a great job be good to see more pictures when its finished and planted up

    Tim Horner said:

    ditto to all of the above, although I use a stabiliser on new rendered surfaces before painting

    Also, tack coat of SBR on the clockwork before applying scratch coat

  • Great advise thanks everyone

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