Double concrete block skin?

Joined
15 Jan 2008
Messages
1,337
Reaction score
34
Location
Derbyshire
Country
United Kingdom
I've just got planning permission for my sister-in-law for a two storey rear extension to their house. They're just getting prices from builders and one builder who has been to look at the project has told them that he strongly advises that they build the walls with two adjacent skins of concrete block, then an insulated cavity and then the external skin of limestone. He's told them that as Limestone (the outer skin) is so pourus they'll get damp problems if they don't use a double skin of blockwork.

Firstly, does anyone know if using a double skin of blockwork would help prevent damp?

Has anyone ever built a cavity wall with a double blockwork skin on the inside so prevent damp?

Is the builder trying to increase his time he's on site while work is a bit slack?

Most of the work we are involved with is built from either Limestone or Gritstone and as far as i can recall we have only once specified an inner skin of more than 4inch block once when the client specifically wanted thick wall. I personally have never heard of any of our clients having damp problems from single blockwork skin walls, certainly where the walls have not been retaining walls anyway??
 
Sponsored Links
I've just got planning permission for my sister-in-law for a two storey rear extension to their house. They're just getting prices from builders and one builder who has been to look at the project has told them that he strongly advises that they build the walls with two adjacent skins of concrete block, then an insulated cavity and then the external skin of limestone. He's told them that as Limestone (the outer skin) is so pourus they'll get damp problems if they don't use a double skin of blockwork.

Firstly, does anyone know if using a double skin of blockwork would help prevent damp?

Has anyone ever built a cavity wall with a double blockwork skin on the inside so prevent damp?

Is the builder trying to increase his time he's on site while work is a bit slack?

Most of the work we are involved with is built from either Limestone or Gritstone and as far as i can recall we have only once specified an inner skin of more than 4inch block once when the client specifically wanted thick wall. I personally have never heard of any of our clients having damp problems from single blockwork skin walls, certainly where the walls have not been retaining walls anyway??
look at the plans you have ,THE ONES YOU SENT OFF TO GET PLANNING PERMISSION.there have all the details of what to use and the specs,:cool:
 
Are you sure that he didn't mean construct cavity blockwork and then face the outer leaf with the limestone?
 
I've just got planning permission for my sister-in-law for a two storey rear extension to their house. They're just getting prices from builders and one builder who has been to look at the project has told them that he strongly advises that they build the walls with two adjacent skins of concrete block, then an insulated cavity and then the external skin of limestone. He's told them that as Limestone (the outer skin) is so pourus they'll get damp problems if they don't use a double skin of blockwork.

Firstly, does anyone know if using a double skin of blockwork would help prevent damp?

Has anyone ever built a cavity wall with a double blockwork skin on the inside so prevent damp?

Is the builder trying to increase his time he's on site while work is a bit slack?

Most of the work we are involved with is built from either Limestone or Gritstone and as far as i can recall we have only once specified an inner skin of more than 4inch block once when the client specifically wanted thick wall. I personally have never heard of any of our clients having damp problems from single blockwork skin walls, certainly where the walls have not been retaining walls anyway??
look at the plans you have ,THE ONES YOU SENT OFF TO GET PLANNING PERMISSION.there have all the details of what to use and the specs,:cool:
ahhh ,after a double take on your question,i feel the builder is taking the p...,1 4inch inner skin is ample,was gdayuk the builder :)
 
Sponsored Links
look at the plans you have ,THE ONES YOU SENT OFF TO GET PLANNING PERMISSION.there have all the details of what to use and the specs,:cool:

They wont have the spec on, and i know that because i drew them!! Don't need to spec up and detail a drawing to get planning permission!!

Shytalkz - i see what you mean, yeah that would make more sense, i'm not sure if thats what he meant as i haven't actually spoken to the builder myself but i'll speak to the S-I-L and ask her. Is it necessary to build the walls like this to prevent damp in Limestone walls. Still can't say i've seen it before?
 
look at the plans you have ,THE ONES YOU SENT OFF TO GET PLANNING PERMISSION.there have all the details of what to use and the specs,:cool:

They wont have the spec on, and i know that because i drew them!! Don't need to spec up and detail a drawing to get planning permission!!

Shytalkz - i see what you mean, yeah that would make more sense, i'm not sure if thats what he meant as i haven't actually spoken to the builder myself but i'll speak to the S-I-L and ask her. Is it necessary to build the walls like this to prevent damp in Limestone walls. Still can't say i've seen it before?
Derby ,right :LOL:
 
one builder who has been to look at the project has told them that he strongly advises that they build the walls with two adjacent skins of concrete block, then an insulated cavity and then the external skin of limestone.

Probably not two skins of block then cavity then limestone but two skins of block work with an insulated cavity faced with limestone.
Fastneattrowel has tried to read the question twice but his finger obviously got tired from touching the words on the screen so he still hasn't got the gist of it.
 
gday2uk - thanks for your reply. Yes i agree with you and the previous poster that he must have meant a cavity wall with two skins of blockwork with the external blockwork skin faced with Limestone.

I've spoken to someone else today who thinks that building it like this would make it easier to build the external skin, rather than building the external skin out of just limestone but that the builder's insistance that he recommends this to prevent damp may be just his way of saying ' I don't fancy building the outer skin of just Limestone as its a bit tricky'??

Can anyone say whether the additional blockwork skin will help prevent dampness and is there likely to be damp problems if the wall is built with a purely limestone outer skin??
 
As long as there are two skins there should be no problem with damp from outside. Also with a cavity you can obviously insulate it. Can you not get limestone faced blocks to use for the outer skin? I would have thought a purely limestone outer wall would be expensive? Also the porosity will vary depending on the type of limestone used so if a dense un-porous type is used there will also be no problems building it single skin.
 
It used to be the normal way to build with stone in the West country, stonework with a 4 inch block backing wall. The main reason is that if you have stones of different widths it is much easier and more stable to build and also to get the correct sized cavity.
However by putting up the inside skin first and then using a full fill insulation as the backing, a 4 inch backing is not required. This is now the most popular method. Damp won't be a problem with a cavity wall, as bricks are also porous.
 
It’s been my experience that most builders prefer to build a traditional blockwork cavity wall with insulation and then stick the stone to the outside that acts purely as an aesthetic cladding.

Like this:

This takes away any worries he may have that the stone wall he’s building will not be very stable etc. I have done one job though where the stone wall alone was used as the outer leaf and it hasn’t fallen down yet AFAIK. If the builder is happy to do it and can get hold of a decent stone waller then it’s down to them and your engineer. I have also found structural engineers have similar views ie some prefer it as a pure cladding and others are happy to use it as part of the cavity wall structure.

Ps A really good stone waller is the key to getting your extension to look good so I’d get a m2 sample panel done first.
 
one builder who has been to look at the project has told them that he strongly advises that they build the walls with two adjacent skins of concrete block, then an insulated cavity and then the external skin of limestone.

Probably not two skins of block then cavity then limestone but two skins of block work with an insulated cavity faced with limestone.
Fastneattrowel has tried to read the question twice but his finger obviously got tired from touching the words on the screen so he still hasn't got the gist of it.
whats the big problem gday , skin of limestone +cavity+ insulation+inner blockwork,why you making a mountain of a mole hill,only time your get damp through a cavity if its bridged ie muck on a wall tie or all your droppings filling the bottom of cavity up. leave it to the experts gday and try ya luck in the plumbing department :LOL:
 
Thanks for all the replies - from the consensus i think it seems that the two blockwork skins are not REQUIRED but may make building it easier and will make the outer skin more structurally stable - however, the builder's (who my S-I-L has been talking to) claim that without it they'll have damp problems, appears to be unfounded unless the cavity is bridged with 'muck' (which i assume could still happen with the blockwork cavity anyway).

I get the feeling that gday2uk and fastneattrowel have forum history??
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top