thank you for your info ... so the magnesium makes it harder ? i made a polishable plaster that is so hard i cant even dig my finger in it or scratch it using the graymonts limeputty i guess theirs is high in magnesium even with one coat floated on it has mottling like stone or venetian plaster and it sticks to previously painted surfaces! i put a first coat to see how it bonded to the surface then plan to polish the 2nd while still wet . i did a sample already and it polishes like glass but u have to polish while wet. im extemely happy with the results. using lime/pozzolan component with 5 percent acrylic resins and dispersing agents. ROMAN CONCRETE! the virginia limeworks was had bits of sands or not ground up enough which scratched the surface. i think the mixture i made can be done on exteriors as well but only time and more experimentation will tell!