Solid walls need to breath internally and externally if they are exposed to rain. If you can stop water penetration from outside then internal breathing will suffice. Treat the outside and then let the wall dry from inside, do not cover the wall with anything which will stop it drying out.
The wall can be plastered internally, I would not recommend the use of boards which encase the wall. With a solid external wall condensation will always be a problem when the room is damp but the wall should dry again when the humidity falls. Use a paint designed to allow the wall to dry through it.
I appreciate the reply stoneyboy,
I was thinking of painting the outside render of the external walls with breathable waterproof paint?
Then Internally I was going render the walls using a weak cement mix 6 sand to 1 cement with a waterproof additive with salt inhibiting properties? The reason I want it weak as the render does not bond to strongly to the soft brick and damage it and also to let the wall breath.
I did want to stud the wall out though to run my electrics and plumbing do you think there will still be a problem doing this?
Don't see much point in you rendering the wall internally if you are going to overboard it. If you overboard it you may end up with a condensation problem if the wall is north facing and it is a bathroom or kitchen where humidity tends to be higher.
Good idea to paint the outside render but seal any cracks with a flexible filler before you paint.
I was going to render the walls with a cement & sand waterproof additive to stop the damp then stud and board over which would contain my electrics and I could also pack the stud with insulation, this may help wiht the condensation issue?
I may just render the walls and chase my electrics in the render. So the walls will breath.
Also I've heard using a lime render rather then cement sand and additive to help the walls breath? Arggh so many approaches, confuses the hell out of me!!
Fit the electrics and then render/plaster. Lime plaster is ideal for your application but you will have to find horse hair - this will act as a binding agent in the lime plaster. And it is a devil to apply - good luck!