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[Dodger2303]

Hey awesome people.

We have two exterior walls in our flat that are non cavity. We are on a 2nd and third floor and have never had damp issues previously.

We have recently been doing renovation works and found that these two walls had plaster and cement so flakey that we have removed it. We now have bare brick. The outside of the building f has a render over the brick.

I am now in a worry cycle of what to do now.

I want to avoid battening and adding thermal insulation as we really dont have the space to lose and so would like to Refinish it instead.

If we sbr the wall first and then apply a sand and cement layer with a waterproof add mix in it, is that likely to be ok.

If so would I use something like this

https://eroofing.co.uk/shop/sika-1-wate ... 3IEALw_wcB

Someone may come and do this for us but I want to sanity check the method.

Really desperate for advice so thank you all.

[stoneyboy]

Hi dodger2303,
There is no definitive answer to your question.
Solid walls were intended to be breathable both inwards and outwards and certainly not to be combined with central heating which presumably you have in one form or another.
You say the outside is rendered but is this permeable? If it's painted are you sure there are no defects which would allow water ingress?
Are the walls in an exposed location and not exposed to direct sunlight to dry them out? If yes damp is very likely to move to the inside surface.
Possibly your suggestion of inside sand/cement rendering is the best solution but whether you should try to make this impermeable is unanswerable. If you were able to guarantee no defects to an impermeable layer where would any damp end up? It would probably appear in the walls on the ground floor.
The final issue to consider is what will happen to condensation - the seriousness of the effects of this will depend on how you live and how you deal with it.
Regards S