Betta Cemseal & Fix
This product can either be mixed to a slurry or a paste with water.
Once set, it provides a flexible coating that is completely waterproof, unlike other membrate products it dries to a concrete grey colour and is inconspicous for many slab applications.
I have used it to repair cracks in an undreground carpark, waterproofing a concrete spoon drain and many other applications where protection against water was needed.
It is another of those products that are certainly not the cheapest on the shelf at your local hardware but it works incredibly well.