insulating external rendering

[kd]

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?

 

[Phil L]

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

 

[meow2222]

kd wrote:

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

 

[Phil L]

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

 

[meow2222]

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

 

[sm_jamieson]

Oh no, not another conspiracy ... "Registered" with who ?

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.

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.

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

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.

 

[Phil L]

Oh no, not another conspiracy ... "Registered" with who ?

usually with the company who supplies the materials, and they don't supply
them to anyone not registered with them.

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.

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.