Brownstone is a soft sandstone from Connecticut which is famously in use throughout Manhattan and Brooklyn for building stone and has, ever since installation, rapidly deteriorated from the freeze thaw cycle. It is probable that it was an unwise material choice to begin with, driven by expediency and the iconic beauty of the stone. Regardless, your brownstone restoration choices are (1.) to replace it, with fabricated stone, (2.) to replace it with artificial stone cast out of a more durable synthetic or (3.) to mold a solution in place. Riya Contracting Corp employs all of these methods. Shown is an example of the latter.
Check it’s chemistry. If you find what is bothering the stone treat it the way so you can save it. Analysis will show you is the problem sulphate, nitrate or carbonate. According to that choose best chemical reaction to make meltable salts into non meltable in water(usualy those chemical formulas are sttonger than the stones). Voila, jou have just saved a piece of valuable sandstone.
Fantastic! Very helpful blog especially to a clueless guy like me!