I have an in ground 18' x 36' (approx 26K gallons). it's gunite/concrete. Don't know age of pool but house was built in 1976. I've owned it 11 years. I have some small cracks and several larger chunks missing from the top along the water line. I want to repair those missing chunks and cracks and re-plaster. Any advice on which products to buy? I planned on power washing before I begin to help get rid of all the algae I had last year.