In order to choose the best grout float for your project, you should consider what types of grout and tile you are using, what kind of area you are working in and a few personal preferences. Many projects will use a standard rubber grout float, but the characteristics of non-standard floats can make a big difference when you do need them for certain materials. Also, grout floats made for working in specific areas can be invaluable when trying to get good coverage in hard-to-reach places. Once you have the basic choices made, there are just a few more options to consider that mainly depend on personal preference.
Standard grout floats are usually made of rubber, have a rectangular shape and can be used for most basic projects. When you start using more specialized material, however, a different kind of grout float might be necessary. One such float is a stone grout float, which is used when tiling with natural stone. The natural stone can be damaged more easily than tile, and you will need to make sure you have a stone float with a softer surface to prevent scratches and marks.
Another tiling material that warrants its own kind of grout float is epoxy grout. This type of grout is generally much stickier than regular cement grout and can be difficult to work with. When using epoxy grout, you will want to have an epoxy grout float to make spreading easier. This is usually achieved by having beveled edges on the sides of the float so that it resists sticking to the grout.
Besides materials, you should also consider what kind of area you are working in. Bathrooms and kitchens often have small spaces under cabinets or other fixtures that are hard to cover effectively with a standard grout float. For these areas, an offset float will be very helpful. Offset floats have the handle set back to one end as opposed to centered. This gives you a longer tip that you can get under a cabinet edge without your hand or the handle being in the way. These floats are often a little narrower than standard floats which also helps for getting into small areas.
A margin grout float is similar to an offset float in that it can be invaluable for reaching small or obstructed areas. This type of float is also narrower, but the handle is attached to the the back instead of the top of the float. This design would be very difficult to use if you needed to apply even pressure and cover a large area, but it is perfect when trying to fit into a small, defined space. This type of float can fit into otherwise obstructed areas and is also good for repairs when you need to target a very specific space in the grout.
The other main choices in grout floats have less to do with function and more to do with your own personal preference. For instance, the traditional design of floats has a D-shaped handle centered on the top of the float. There are also versions available where the handle is open on one side and designed to be more ergonomically helpful. The backs and handles themselves can be made out of different materials such as plastic, aluminum, and wood. These options may make a difference in comfort and durability, but they basically all work the same way when it comes to effectively completing your project.