Render over roughcast

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c9656750

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Hi all

this is my first time here, so apologies for any mistakes...

I have just had an extension built on the side of my (painted, sound, roughcasted) house - its built from medium density type concrete blocks (not thermalite type)

I now would like to render both this and the house to match, so if someone could offer some advice on:


(I shall be using sand and cement..)
  • Can i render over existing painted roughcast, as its sound (weel hard as diamond actually, it would be virtually impossible to get off without most of the bricks)?
  • If so, do i need to use SBR or similar
  • Should I use reinforcing mesh, firbreglass or eml - on the extension or the house?
  • can i render straight onto the extension, or does that need a primer of some kind?
  • edge beads - good idea or not?
  • If so, how do i stick them to the walls?
  • what depth should i render to - both on the house and the extension - the levels dont "match" anywhere, the joins are all right angles between house > extension.
  • i would like a semi textured finish, something like hi-build, can this be achived with sand and cement?
thanks in advance - all comments appreciated.
 
might be best with a thin coat system mate one of the others will explain later there is quite a few ways of doing it there are a few primers out ther now that go over paint
 
You cant render over paint it doesnt matter how sound the render is the new render sticks to the paint, you need to either eml or get the paint off
 
Tend to agree with you all re rendering over painted roughcast but I remember when me dad used to take me to work with him when I was a kid and rendering over painted 'slopdash' and 35 yrs later when I go back to Ireland its still on there, and NO CRACKS!!!!. I think that if the paint is well adhered, it's the 'mechanical' bond for want of a better word that holds it on. Mind you, the sand is a lot sharper in Ireland
 
no manufacturere will ever back anything that is going over paint - even if the product has been designed to be used over painted surfaces, it will only ever be as good as the adhesion of the paint itself to the old render and how long that will last. that said there are renders and prep products for use on painted backgrounds
 
plasterjfe said:
no manufacturere will ever back anything that is going over paint - even if the product has been designed to be used over painted surfaces, it will only ever be as good as the adhesion of the paint itself to the old render and how long that will last. that said there are renders and prep products for use on painted backgrounds
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True. But if the paint is well bonded its the massive mechanical 'key' of roughcast (similar to eml/riblath over painted render etc) which holds it on


Oh and I believe he was saying it was roughcast not render
 
surely the paint will come back to an extent with a good effort, the roughcast will be uneven so at least the tops of the piant will come off easy if you try.

Just get stuck in and get your hands dirty man, everyone always tries to miss out the nasty bit - the prep is the key to any good job, dont cut corners IMO:RpS_thumbup::RpS_thumbup:
 
Ok, thanks for all that everyone - so if i get some of the paint off, and use mesh (was thinking fibreglass?) we should be ok?

couple more -

how do i get the paint off - cant exactly use stripper can i?
could i use a grinder or similar to cut some grooves in the roughcast as a key?
 
NEEDLE SCALER needle gun is what you want get it from a hire shop m8
or use a steam jet wash and mold cleaner then use hp12
maybe even a refina power prep i think thats what there called ???
 
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