Dry Lining a cavity block wall

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phester

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I am trying to dry line a very old cavity bock wall. They are 4 inch cavity block with no DPC so they are quiet damp. A structural engineer confirmed this. He recommended the injection chemical DMP to stop it coming through but I think that drylining would be a better option as the extension is also subsiding (nothing dangerous) so I dont think I will look beyond the 5year mark for waisting money in the extension.

My question is that with foam backed plasterboard the recommended thickness is 60mm. But I dont know if you can do a direct attach onto the block. I know that blobbing it on is not allowed with the damp. but to use battons I would loose another inch.

Could I use the foil backed bunji board and then use mushroom plugs I have heard them being called to do a direct attach to the damp wall?
 
yes you can use the mushroom fixings and blob the board. But also listen to your engineer. You can get the insulated boards pretty much any thickness you want.
Id also be interested as to how you reckon the subsidance is not dangerous
 
The single story extension is twisting away from the house. It is moving as a single unit and so the crack is uniform joining the extension to the house. I have removed the chiminy stack so there is nothing to fall in on the extension. The enginner advised me that in the short term there should be no major problem. I think that the subsidenance has been caused because of clayware drians to the back of the house that I have now replaced. It will take a few more months of monitoring to see what the effect of the soil drying up fully will be. I know that the foundations for this extenison are not up to regulation as my grandfather built it 60years ago.
 
Hi Phester

I would recommend a DPC, chemical can work but it is variable in success. This will prevent against rising damp going up the wall.

You will also need to consider ventilating the space between the wall and the drylining particularly if the wall is damp, and might want to consider a gyproc moisture resistant board (green coloured). It can be insulated with moisture resistant insulation.
 
is the foil backed foam board not a vapour barrier and so will act as a dpc. or should you still use a plastic membrane. when you say leave an air gap I assume that this then means to use lats and keep the board off the wall?
 
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