The same rules apply for the positioning of movement joints externally – any pre existing joints in the subfloor must be continued through the tiled surface. Perimeter joints must be installed where applicable.
The most important difference for external movement protection is that the frequency of joint doubles or another view is that the protected area or field of tiling to be protected halves. This intention is to protect the installation from thermal shock where, for example, the tiled surface can be heated very quickly by the Sun even in Winter then be cooled rapidly by rain.
The choice of material for external joints is limited. Any aluminium based product will over time suffer corrosion at the exposed top edge. Brass based profiles will also suffer discolouration but will maintain their strength.
The natural material for use externally is stainless steel which will resist weathering and will retain its strength for many years.
See section on UV performance