We've just signed off on remedial works addressing failed external tanking in a series of houses where the homeowners were initially (and understandably), very resistant to the concept of cavity drainage waterproofing.
For the uninitiated, cavity drainage involves the use of internal drainage channels linked to a suitable point of discharge (sump pump system or 100% reliable gravity drain), in association with cavity drainage membrane vapour barriers (yes the egg-carton membrane), typically installed to all walls and floors. Water penetrates, flows down-hill through the channels, out, and is totally isolated from the interior.
It is a strange concept to many, because surely the ideal is simply to block water out, no?
Well, this is often easier said than done in a remedial situation. It is often trialled, and often fails, only for cavity drainage to successfully remedy.
We have some poignant examples of this, from situations in which external tanking has failed, they've excavated externally, attempted repair, filled the hole back in again, and yes it leaks once more, only for cavity drainage to remedy.
We dealt with another, which was a newbuild house, where external bitumen sheet membrane was applied to protect the basement, only for this to leak during construction, so internal cementitious tanking was specified as a remedial, this was installed and they finished the basement, which then flooded, had to be stripped out, sucessfully treated with cavity drainage (by Trace), then being fit out again i.e. purchase of three waterproofing systems, two fit-outs and one strip-out... ouch. See pic below.
Internal polymer modified cementitious tanking slurry. This installation was inspected by the supplier during installation, but it still leaked.
Look at the approach taken by each and every one of the structural warrantee providers (NHBC etc.), who employ cavity drainage time after time to successfully remedy failings in other forms of waterproofing systems. These organisations have to resolve such issues, because if they don't, the liability remains theirs, and so it is in their best interest to fix problems right first time.
I think it is only a matter of time before the wider industry and public come to understand that cavity drainage must be employed in new construction (I'm referring to residential space) to design out such failures in the first instance.
Anyway, in every case that an independent individual questions the approach, if you provide them with enough information, they ultimately understand why suitably designed and installed cavity drainage is the right approach, providing lowest risk.
They always come around in the end.
