We have a 35+/- year old inground gunnite pool. It has gotten to the point where it is so pitted and worn that it needs to be resurfaced. We plan on having it professionally sandblasted down to total bare concrete. I feel confident in my ability to trowel on a product but am not sure what to use. Would simple hydraulic cement troweled on do the job? I've researched other products too, but REALLY don't ever want to do this again! HELP??!!