Cement and Sand Render to Internal Party Wall

[Rovernut]

I need to re-plaster a small area of wall behind some built-in wardrobes in an upper floor bedroom that suffers from damp. I would like to waterproof the wall before I plaster or alternatively use a waterproof plaster if there is such a thing.
I have investigated the cause of the damp and the usual suspects all check out ok.
Any help/ideas would be appreciated.

Thanks

 

[Frederick]

Have you completely discounted condensation? I have found that it is a very common form of dampness in built-in wardrobes. You have a combination of low airflow and clothes that still retain some moisture from the washing process - even if they are touch-dry. It is most commonly a problem where the wardrobe is built on a single-skin external wall, but I have seen it on internal walls.

 

[Tozzy]

Have you completely discounted condensation?

Do you think that Rovernut would have to fit an air brick/ vent louvre? Sounds good to me... if condensation is the cause.