[Cob] waterproof interior plaster?

[Tys Sniffen]

Anybody heard of this?

http://www.bmi-products.com/special/special_shower_finish.php 

 

think it might work over cob for a shower?  Maybe do an exterior (lime)
plaster, then this stuff over it? 

 

Or maybe it's just another industrial product.

Tys