block built shed water ingress

Hi all I have a damp issue with my block built shed

in a space at the bottom of my garden I have a block retaining wall 1m high. it is 1 block longways wide built on concrete footings with a purforated drain pipe in behind.

I decided to build a block shed building of the retaining wall for 2 sides of the shed.

So I:

• had the floor concreted (4inch thick)
• built the walls of the shed using blocks on there edge
  
• fitted a fiber glass roof, clad walls with larch, fit doors, insulated the roof etc.
• tanked interior walls using kb to 1m (following the instructions).
• there was a considerable ammount of condensation but I was happy the wall was water. tight so I rendered using waterproofer in the render.

after a week and happy it was dry I started to paint the interior then this morning I woke to find water penetration in multiple locations.

So it appears the tanking has failed.

can anybody suggest any ways I could fix this without removeing all of the render and re tanking.

Not sure how tanking works on the inside of a wall, presumably the drainage is supposed to keep the water at bay? but how about building a drained cavity and then having a dry inside leaf? Then there won't be any water pressure on your internal wall coverings.

I'm struggling to visualise the tanking and the rendering, with the new and retaining walls and where the failure is. It might not have been a good idea to tank and render.

Hi woody, so the block walls make up the 1st metre of 2 of the walls then using wall ties I built the other 2 walls from the base of the concrete pad, it is at this height where the issue is (although I have built another 1m on all 4 sides).

I then preped and tanked the interior on all 4 sides, and then rendered ontop of the tanking.

the failures are in a few places in that 0-1m section