Cementious tanking or membrane for damp wall treatment??

[Deluks]

Your current standard board has let internal vapour through which may have condensed on the cold external wall.
Using the foil backed board would prevent this. In which case there is no need for membrane.

Kingspan K18 (or similar) fixed to timber battens on the wall would be a good option here, the thickest you can get, which I believe is 62mm (50mm insulation + 12.5mm plasterboard all in one) The insulation itself already has a foil back on both sides.

 

[totallymedicine]

hi i just went to the garage and it is MUCH drier since teh plaster board came off. still wet at teh bottom but i presume this is where the condensation has dripped down as opposed to rising damp.

if there any thing lost by adding teh membrane anyway even if it is largely due to condensation.

i will go for teh k18 boards as advised but thought as extra back up

 

[Deluks]

As long as each edge of the insulation board rests on a batten you'll be ok without any other membrane. Putting it against the wall before the insulation will cause problems.