When installing tile there are two basic options for grout: sanded or unsanded, which may also be referred to as non-sanded. The main difference between these two types of grout is in what they contain, which largely impacts how they're used. The best type of grout to use depends on the type of tile you're grouting and how it is to be installed.
Sanded grout is made up of one part Portland cement to two parts fine sand. Unsanded grout contains one part Portland cement to two parts calcium carbonate. Cellulose is added to both types of grout to hold the water when it is mixed, and defoamers are added to prevent bubbles forming. Polymers are also added to give strength and flexibility to both grout types.
The obvious difference between sanded and unsanded grout is that sanded contains sand and unsanded does not, but their usage is the most important difference. Unsanded grout is used for joints (the spaces between the tiles) that are less than 1/8 inch apart. Sanded grout is used when joints are more than 1/8 inch apart. In smaller joints, the sand cannot fill the joints and won't fill all of the cracks and crevices as it needs to. Limestone, marble and other types of natural stones typically require the use of unsanded grout. These surfaces are soft and may scratch, so a grout with fine particles is required to avoid ruining the finished surface. Granite tiles are the exception because they're hard enough in most cases that sanded grout won't scratch, but the joints must be adequately spaced to use sanded grout instead of unsanded. Sanded grout is ideal for ceramic and porcelain tiles, which have a hard surface that will not scratch. Ceramic and porcelain require a more durable grout because they're often used in high traffic applications such as bathrooms and floors.
Strength and Durability
Sand reinforces the cement in sanded grout, making it less likely to crack. Essentially, sanded grout is very similar to sand and cement with colour added to it. Unsanded grout is basically coloured cement. It is not as durable as sanded and will crack if used in joints that are too wide. This is why when natural stone like marble is used in flooring applications, the joints are less than 1/8 inch because there is less chance of the required unsanded grout cracking with a narrower joint.
Cleaning and Maintenance
Sanded grout is more porous than unsanded, so cleaning products are able to get into pores and remove dirt and debris that may be inside. Colourants are also available to restore sanded grout to its original appearance. These colourants aren't available for unsanded grouts. Acidic cleaners are necessary to clean stains from unsanded grout, but these cleaners can only be used on ceramic and porcelain tiles, not natural stone. Oftentimes regrouting is required to eliminate stains on unsanded grout.