On Mon, 23 May 2011 13:26:01 +0100, Martin Brown wrote:

For small repairs ordinary concrete will do provided you don't need it
to set under water.

Cement will set under water. Getting it stay in place while is sets
is a different problem. The "waterproofing" admixes don't help with
that, they only reduce the amount of water that will pass through the
set cement.

--
Cheers
Dave.