Note:at the bottom of this page is a link to a pool painting product called Ultra Guard Pool Coating,which is guaranteed not too blister,peel,or chalk. I have not tried this product myself yet,but I have heard from others it is an outstanding product!
Pool painting is something I know a little something about - I have painted about 6 or 7 seven pools or spas over the years. I have used water based acrylic, chlorinated rubber, and epoxy based paints.
Water based acrylic paint - this paint is a good choice when you are selling your house and want to spiff up the pool good and cheap and let the sucker that buys your house deal with it later. I have used it twice according to instructions....the pool looked great but a few weeks later when I came back to service pool, the surface of pool would cloud when I brushed it....it even came off on my hand when I rubbed it. Its been a few years since I have used this product, perhaps its improved now.
Chlorinated rubber paint - I believe this is superior to water based paint and "gives" a little more than epoxy based paints so its less likely to chip than epoxy. However it is no longer available in California due to environmental considerations, and other states may soon follow suit. A synthetic rubber based paint is available but I have no experience with it...it is available through Leslie's Swimming Pool Supplies.
Epoxy paint - this paint is probably the most durable but also the most likely to bubble if the plaster underneath is not rock solid....if the plaster has any weak spots the epoxy will pull the plaster from the surface as it dries.
So...given a choice between pool replastering and pool painting, I would choose pool replastering every time. However if you are on a budget, and you are painting the pool for your own enjoyment and not just to sell your home, I would say going with epoxy is the most durable choice...IF the surface has been prepared correctly. If you have rock solid plaster that is just discolored, then simply acid washing and cleaning the surface before painting will probably be fine. I have not tried the synthetic rubber paint,but IF it has the same properties as the chlorinated rubber paint,then it would probably be more forgiving in regards surface preparation.
If your plaster is flaking or crumbling, ALL loose spots MUST be removed or your paint will flake off....there is no need to worry if the process of removing the loose plaster leads to a rough surface - there is epoxy paint available with high amounts of solid material to fill in these areas. Sometimes, sandblasting the pool can be a great way to prep the surface and makes an acid wash unnecessary. However, if you decide to hire someone to prep and paint your pool for you, ESPECIALLY if you have weak plaster that needs to be attended to, figure it will cost one half to two thirds the price of replastering if its done right. If you have solid plaster, then it may be less.
Be careful when painting a pool previously painted as not all coatings are compatible - for example,if pool was previously painted with acrylic,you may repaint using chlorinated rubber or water based epoxy but not solvent based epoxy.For more help,you can call your local Leslie's Swimming Pool Supplies or Nelsonite Pool Coating 800-544-1998