Tanking a cellar, sounds technical right? Well it is not rocket science however it must be applied correctly and used in the right situation. Merely tanking a cellar will not make it watertight where the water table is high – but let’s drill down into the why’s and wherefore’s.
In the images you see here, there is some surface mould, the concrete floor is darker than new concrete would be but there is no surface water or extreme moisture. This suggests that this cellar is above the water table but some moisture has seeped in from somewhere – this is usually rain water but could have been from a water leak up above at some point, it is extraneous really for now. We will go into depth in a different post and will cover the sources of damp in a house.
For now, we know there is damp, and it is manifesting as mould in a cellar on the walls, on the floor and the ceiling. Our remedy is tanking the cellar with a tanking slurry. You may sometimes see this referred to as cementitious tanking. Both names refer to the same product – a specially formulated mixture designed to be applied to cellar walls to stop water ingress. It either comes pre-mixed or as a powder to mixed on site with clean water.
Tanking slurries are a special blend of Portland cements, aggregates and chemical modifiers that work together to block the passage of water. Tanking slurry may contain an additional acrylic polymer to improve strength, bonding and abrasion resistance.
A bituminous coating may be recommended but this method is not suitable for tanking an entire cellar or basement. Bitumen coatings are more suitable for smaller above ground areas and external waterproofing. In cases of extreme damp you may want to consider a waterproofing membrane with a sump and pump system.