Plaster typically costs less than pebble and is (or should be) a very smooth cementitious material. Quartz plasters are better than marble plasters. Plasters can be colored but only inorganic pigments should be used as organic pigments can degrade quickly over time. Darker colored plasters (blues and grey) are often subject to mottling and variations in color.
Aggregate (or "pebble") finishes are just plaster finishes with aggregate material exposed. They are often a bit more forgiving in terms of their strength (aggregate strengthens cement) and you can get a much wider variety of colors and patterns to them. Aggregate can be round and smooth or very fine and some finishes can be polished to achieve an aggregate look but with a plaster-like smoothness. Aggregate plaster can be colored as well and the same rules apply.
The major plaster/aggregate manufacturers are PebbleTec, SGM Inc., and CL Industries. There are smaller plaster manufacturers as well and many shady, fly-by-night operations. If you do choose to go with one of the big named brands, you should get a list of their licensed and trained applicators in your area. There are many mom & pop type pool plastering businesses that swear they are licensed applicators for a particular brand even though they aren't or their licensing/training has lapse. Only the plaster manufacturer can tell you who their trained applicators are and, if you want the warranty on materials and workmanship, you need to go with a licensed outfit.
I suggest you look at the websites of those companies I mentioned and start there. Then get names of approved applicators and start working quotes. Be prepared from some seriously eye-watering price quotes.....
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And do not accept a scope of work that is simply a cleaning of your current plaster and skim-coat of new material. Skim-coats are cheap fixes that don't last. If you are getting the pool remodeled, then the old plaster needs to be chipped out down to the gunite shell and redone. Many outfits will swear that skim-coating is fine but its a band-aid at best.
