Does one need liner padding to go underneath there liner when replacing a pool liner?
The answer is yes and no.
Today’s manufacturers are extending warranty coverage for those who purchase and install Armor Shield floor protection. Instead of a 1 year full 20 year pro rated warranty it gets bumped up to three years and 25 year pro rated. This is pretty good as most Armor Shield pads are relatively inexpensive.
If your old liner has lasted many years then you could forgo the padding and have a pretty good chance your new pool liner will last just as long as the old one. You wouldn’t get extended coverage warranty but you would have a good idea how long a new liner would last.
This Armor Shielding protects against anything sharp that may be lurking underneath your pools liner. It also helps with a common problem of bugs creating damage over time. The little bugs get underneath a liner (Ants for instance) and create thousands of tiny holes that not quite penetrate through the liner material. So having several thousand creates a soft spot in liner and can cause it to lose water quicker than evaporation.
The size you get is the diameter of your round or length and width size of an oval. If you have an in between size pool then getting the next size up is recommended. You can ether tuck it underneath itself or trim it with scissors to fit.
With an Armor Shield in place will guarantee your new pool liner will last for many years to come.