Mold may or may not be visible. When it is, it appears as a surface stain or discoloration, or as a dark growth. At times, a musty smell is present Modern building materials and methods, such as well-insulated homes where outside air does not easily come into the house, allow for mold growth. Put your trust in A&A Mold and Allergy Investigations for San Diego Mold Testing. You can count on our commitment to the highest quality customer service and nearly two decades years of experience. For more information, visit our website.