Ready mix or premixed grouts should not be confused with cementitious grout mortar or sanded grout. What the former products offer is convenience, as the mixing has been done for you. The latter grouts come in powdered form and must be measured out according to package directions and mixed with water before the substances may be used to keep tile in place. In larger installations, mixing the grout just before application is well worth the extra effort. For small repair jobs, premixed grout may suffice.
Drying time for premixed grout is much longer than what is required for mix-it-yourself sanded grout. On a tiled floor, where the stress of heavy traffic is expected, you need a grout that will harden and cure quickly. Premixed grouts may not harden for days or sometimes weeks, making unwanted tile movement a real possibility. Sanded grout hardens completely in 24 hours and will fully cure in 30 days. In large installations, hardening time is crucial.
Project Scope and Joint Size
As a general rule, sanded grout is much less expensive than premixed products. Convenience can be costly if you are tiling a large area such as one you might find on a kitchen or bathroom floor, shower enclosure or backsplash. Sanded grout, sometimes called joint filler or floor grout, should absolutely be used in any tile installation where the joints measure 1/2 inch or wider. Using a premix in large joints could result in cracking as the grout dries and shrinks.
Traditional Sanded Grout
Years ago, sanded grout was formed by mixing fine white sand with portland cement in a 1:1 ratio and adding water until the mix reached a workable consistency. The result was a rough white grout that soon darkened with dirt because the abrasive texture of the mix made the hardened grout difficult to clean. Color choices were limited to white, gray or black and did not coordinate well with many colors of tile.
Today's Sanded Grouts
The sanded grouts available today come in a wide color spectrum designed to suit your chosen tile. Staining is less of an issue in modern sanded grouts, because many now contain latex or polymer additives designed to strengthen the grout and resist staining. Bags of sanded grout purchased today have a helpful chart printed on the bag that will help you to determine square foot coverage per pound. Tiling and home improvement store personnel can provide you with options and helpful advice.