I am looking for a product or DIY approach to rendering a house extension that has no cavity wall. I have seen products but they are massivley expensive and can only be applied by approved contractors. Anyone done this to their property or know of any links or DIY advice?
They are massively expensive because it's a specialised job - you cannot buy the coating that goes over the top, it's not rendering, it's a type of polymer and it's only available to registered contractors.
You can dry line the internal walls and insulate underneath the p-boards and you can render the outside of the extension if you wish, but you can't insulate the ouside walls and render over them
What stops one fitting insulation, EML then rendering?
NT
rendering over expanded metal, over rockwool is an extremely bad idea, given that the render will crack up within months allowing water to soak the rockwool underneath, this will then freeze in winter, and then all the rendering will be blown off. wet insulation doesn't insulate.
The stuff they use is weird, it's like plastic, that is to say, if you try to chip a piece off with a hammer and chisel, it comes away like stringy nylon type stuff...it's hard to describe, exept that it's like plastic - this expands and contracts with the weather and is obviously completely waterproof
oh i see. Thanks. Presumably one could use wood or pvc cladding though over extra insulation, with an airgap provded between insulation and existing wall.
NT
Oh no, not another conspiracy ... "Registered" with who ?
No, no, you don't use rockwool, you use celotex, EML, and a latex modified render. A house near me had it done. You could see the boards on the wall before the render went up. Normal builders did the job, not registered spooks. Of course the whole thing may crack up and fail, buts it's been through a winter, looks OK.
If you used rockwool you would be silly, and with such a lack of stability, you may need some special render to survive. Rendering over celotax is not much different to rendering over a normal wall, maybe slightly less key I suppose.
Simon.
usually with the company who supplies the materials, and they don't supply them to anyone not registered with them.
and movement...unless the render is up to the job (IE it can expand and contract) then it's going to fall off, which is why they don't use rigid boards (celotex included) - it's a type of rockwool board with a foil face, this is affixed to the masonry with some kind of nail gun, the fixings have large washers (about 50mm) and then it's covered in mesh.
Also, from a DIY perspective, an extension is not do-able, at least not for less than many hundreds of pounds, making the whole exercise pointless IMV, hence my suggestion to dry line the interior.
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