Sodium chloride, which is commonly known as rock salt, has long been a cheap and easy way to remove the ice from sidewalks, driveways, and other surfaces. But rock salt does have its drawbacks. It's corrosive. That means it gradually destroys certain surfaces. Rock salt can damage many surfaces including metal and concrete. It also kills vegetation. It cannot be used on brick, flagstone or any material that has mortar joints, according to Mortonsalt.com. It can make flagstone, in particular, flake off. Since rock salt cannot be used on flagstone, you'll need to use calcium magnesium acetate (CMA) instead. This product is essentially made from limestone and vinegar–it is the safest ice melter to use on flagstone.
Buy a bag of calcium magnesium acetate at a local hardware or home supply store. This ice melter is much more costly than rock salt. However, you'll save in the long run because it's not corrosive like rock salt. It won't harm driveways, walkways and vegetation.
Remove the lid from an old coffee can. Poke several holes all around the lid with a screwdriver. Make sure the holes are big enough for the calcium magnesium acetate granules to pass through.
Fill the coffee can with the ice melter and replace the lid. Read and follow the manufacturer's directions on the bag of calcium magnesium acetate. Basically, you'll sprinkle it in a light, even layer over ice.
Wait 5 to 10 minutes for the ice on the flagstone to melt. Remove the slush with a snow shovel.