The image below shows a freshly installed bathroom tile bed using Efflock to repel water absorption and lock efflorescence. Efflock provides a primary water barrier over and above relying on a waterproofing membrane alone, and improves the general health and amenity of a bathroom by reducing humidity. For around $30 per bathroom, it's a cost effective insurance policy for both the builder and client.
Efflorescence does occur in bathrooms. With the growing trend of underfloor (under tile) heating, the potential for this problem is dramatically increased. The reason for this is that by heating an ordinary saturated tile bed, adhesive and grout, dissolved calcium hydroxide and other salts are driven back up through the grout through forced evaporation. The dissolved salts then react with carbon dioxide to form insoluble efflorescence deposits on the grout and tiles.
Thank you to Peter McCabe Builder in Pottsville NSW for sending the photo!