Almost all well-structured concrete floors can be sanded, old and new. There are some exceptions.
For new floors, no special mixing design is required to get good results. However, the floor should be in place at least 28 days before the start of polishing to ensure adequate curing. Some retail and warehouse facilities that plan to polish the floor after placement may specify installation of the floor as smooth as possible to minimize the polishing steps required.
Existing floors often require some surface treatment before polishing to remove dust, grease, coatings or stains. However, wavy floors that require a lot of repair or very porous floors may not be ideal for polishing. An experienced contractor can usually determine the suitability of the floor.
To help solidify and densify polished concrete surfaces, some contractors typically use permeable hardeners on the concrete after the first step of the grinding process. These products can be applied to new or existing floors and they work by chemically reacting with concrete to form a hard crystalline structure. They also prevent concrete dust and provide additional protection against water penetration and soiling.