Tanking a basement externally!

[handyman77]

I have been asked to tank a basement of a school. Problem is they dont want the inside done. (it has been done and is currently letting in water when theres torrential rain). They have all the childrens lockers that they dont want to be removed. There could be a problem with cracked drain pipes due to huge trees and as these need to be dug out and replaced They are considering tanking the outside is this a viable option ( im not to sure about it)
Any ideas? And how would be the best way to do it?
Thanks

 

[handyman77]

Thinking about using a french drain and tanking!

 

[Norcon]

How big an area is it? How big is the excavation?

http://www.sdg.ie/waterproofing/tanking-membranes/

We used that bitusheet recently. Though didn't use their protection board. We just used hardboard instead from a builders merchant.
Surface needs to be dry though.

Also seen that dual seal used on another job. Which can be applied on damp surfaces.
Both were applied to poured concrete reatining walls.

There's no end of products out there for this type of job.
The french drain will be a big help.
Then you have all the liquid painting sealers also to choose from.