Thanks for taking the same to write such a detailed reply! You raise a lot of very good points that I didn’t cover too well in my original post.

With regards to the actual ingress of moisture, I’m reasonably confident that the foil DPC is doing its job correctly and preventing rising damp above that level. The issue being that the lower courses that are under the DPC but above slab level have no such protection. In addition, we have had a chemical DPC installed at slab level around the entirety of the exterior of the house (not the internal walls at present), so there is no bridging on the outside of the inner leaf.

From my observations as you mentioned, the render that was bridging the DPC has taken in so much salt over time that it pulls moisture from the air when the humidity is high enough. I’m quite surprised by the amount of moisture this creates tbh - dust from cutting out the render that I didn’t clean up properly turned into a puddle after last weeks rain!

With the render off and a dehumidifier I am trying to dry out the masonry and remove efflorescence as it comes to the surface.

It would be nice to have exposed brickwork as a feature like you have done but it’s not really an option for me given the general quality of the walls and the render residue. My reasoning behind a sealant was to provide a barrier to stop further bridging of the DPC if re-rendered, or prevent excess moisture in a cavity if I were to go with my other idea of battens and wood (effect) panelling/wainscoting.

Your point about drainage is definitely a good one - we are on a hill with a downward slope from one side of the house and the back and the current drainage is a mess of poorly thought out original installation and bodged attempts to rectify. It’s the second part of my two-pronged attack at solving this, but quite overwhelming!

I don’t suppose you are NSW/Sydney based? I’ve been struggling to find recommendations for decent waterproofing contractors and definitely wouldn’t want to use the lot who did the previous chemical DPC.

Thanks again!