There are different methods you can use to make your mosaics. The following is a description of the most popular methods. All have pros and cons depending on the type and size of your mosaic you are about to create.
Direct Method
The first method is the direct method. The direct method involves directly placing the individual pieces of tile, called tesserae, directly onto the surface where your mosaic will be. This method is nice when doing small projects such as flower pots, or for surfaces having a three-dimensional look, such as walls. You will have a dimensional look if your pieces of tesserae are not all the same thickness.
Another nice thing about this method is that you see your mosaic take life, and as it takes life you can make little adjustments. However this method is not suited for large projects and for mosaics needing an even surface such as a floor mosaic.
Indirect Method
The next possible method you can use is the indirect method. This method involves gluing your tesserae face down on a paper backing. Once it is completed you can then transfer the mosaic sheets into your mortar where it will permanently reside. Once the mortar has dried you then wash away the paper to reveal your art work.
This method is used for large projects because it allows you to work away from the site and gives you more time. You can also divide your mosaic into smaller sheets of one or two square feet. This method will also give your mosaic an even surface since it is the face of your tesserae that is glued to the paper.
The only disadvantage of this method is that you do not see your mosaic come to life since you are gluing all your pieces face down onto an opaque paper. Your mosaic will become visible only when you wash away the paper.
Double Direct Method
The double direct method is a modern version of the direct method. It is sort of a combination of the indirect and direct methods. This method involves gluing your individual pieces of tile onto a fibreglass mesh.
You can use this method for large projects, and it is a very good method when you are making mosaic borders. You also have the leisure of working where you want, like you would with the indirect method, and seeing your mosaic evolve as you are adding pieces, like you would with the direct method.
This is the method I prefer, I really cannot see any big disadvantage using this method, it is a bit longer to create your mosaic but you can really see your mosaic come to life and make little adjustments along the way.
So the method you decide to use to make your mosaic might depend on your project but you have the final word, use the method you think will work for you. As a beginner I recommend you make small projects using the direct method. As you become experienced and want to make larger mosaics go towards the double direct method. Once you are at ease with this try your hand at the indirect method.