Last week I got a couple of estimates to replaster my pool. One contractor stated, "You pool is 17 years old and has never been replastered. To maintain the integrity of your original pool shell, we would sandblast the old plaster, then apply a bonding agent, then apply a new plaster coat to the bonding agent." He simply refused to chip it out by saying a chip out is for a pool that has been sandblasted a couple of times first and is 20 years or older. The next day another contractor stated: "The only way to get proper bonding on a new plaster coat is to chip it out down to the gunite shell. Whatever you do, DO NOT SANDBLAST THE ORIGINAL OLD PLASTER AND APPLY A NEW PLASTER COAT TO ANY BONDING COAT. IT WILL NOT ADHERE PROPERLY AND YOU WILL BE WASTING YOUR MONEY." Which one of these contractors is telling me the truth?