My basement was tanked about 20 years ago. I think the method was using slurry but I’m not sure. A damp patch started to appear about 5 years ago and has slowly got worse. I think it was caused by a blocked gutter but can’t be sure it’s not coming upwards. I hacked of the plaster (see photo) and found this area had not been tanked which wasn’t a surprise as it’s 4 feet from the ground and an internal wall. The tanking stops exactly to the right and below the area I’ve revealed (see photo). It’s only a small area but needs to be fixed. As you can see there’s some rather big holes that need filling. I’d usually get someone in to do the whole job but thought I’d have a go myself (wife seems to think I can’t escape because of self isolating). I’ve bought tanking slurry, SBR, sharp sand, cement and was thinking of buying some additive like Renderguard Gold or Sika 1 (expensive stuff). I’ve read lots of advice but I’m still not sure how to proceed with filling the gaps/holes and tanking this small area. The window in the photo is not an outside window but is to another room.
