Quote:
Originally Posted by
kent wallace 
One problem with any sealer that hardens solid without any flexability is that concrete cracks. When it cracks the hard sealing surface will crack with it. The more structural integrity in your shell the longer it will take to crack. This is the advantage of flexible coatings and the leader in that is Polyurea.
Polyurea and other flexible coatings also can be installed properly or improperly resulting in a failed system. Mechanical clampiing at all penetrations is the most commonly overlooked item in any coating aplication.
Any courtyard or indoor aplication with a coating that hardens will eventually leak and undermine the foundation of the surrounding structure. It's only a matter of when.
Polyurea applied correctly will last a lifetime. All other coatings that I know of will at some point need to be done again so double the cost or triple if the structure is really poor over the lifetime of the pond. Polyurea on the other hand can flex and stay intact even when the structure cracks and moves.