I have some defects in the concrete floor of my pool that I need to resolve before putting in the new liner. I'd put them in these categories.
Large dips (2 inches)
Loose concrete (thin top layer only)
Three 1 inch holes in deep end constantly bubbling water into the pool
I have the vinyl patching cement and sidewalk cement (without rocks). I guess I've always thought that if you are patching with cement it is important to give the new concrete some way to grip the old concrete. In this case, however, I don't think the new concrete will have anywhere to go (I've read that some people use sand) so perhaps it doesn't matter. Please take a look at the pics and tell me what you think.