Firstly, heaviest grinding of an old and heavily damaged concrete floors requires the use the hardest grinding tools, such as metal-bonded diamond tools. Metal tools are the toughest grinding accessories. Such tools are perfect on any concrete surface, as they are made in low gradations ranging from 6 to less than 120. Diamond grinding tools also come in different sizes of the abrasive surface. This allows the pressure to match with the size of the grinding machine. Metal tools are also classified due to the hardness of concrete thery are used for. Hard concrete requires a softer metal binder and soft concrete requires a harder metal binder.