Mold spreads as airborne spores travel from one location to another and begin to germinate. Within a home, mold can spread from walls to ceilings, from grout to tiles, and in some cases, it can even begin on the ground floor of a home and make its way upstairs.
Airborne mold spores can travel through air vents, beginning downstairs and making their way upstairs. This can especially prove problematic if your central heating system has dirty filters, which can create a breeding ground for mold. In order for mold to spread in a new location (such as upstairs), the second location must have a source of moisture. For instance, it may spread from a water-damaged pipe downstairs to a leaky shower upstairs.
High relative humidity puts your entire home at risk for mold contamination. For instance, if you have mold growing downstairs on a humidity-dampened carpet, you may track the spores upstairs with your shoes or bare feet and cause them to grow on a similarly humid surface on the upper floor. Mold can grow on almost any porous surface as long as it has moisture. Control your indoor humidity by circulating the air or running portable dehumidifiers.
Colonization occurs when mold spores have enough time to breed and multiply across large, difficult-to-manage spaces. Mold colonies require professional removal, because self-removal can easily cause the spores to spread. A mold colony can effect entire sections of a home. For example, a colony may penetrate ceiling tiles on the lower floor and ultimately impact the carpet on the upper floor, or it may slowly spread along the walls from the lower to the upper floor. Since mold colonies can deteriorate porous surfaces like wall boards and ceiling tiles, they need not remain confined to their initial surfaces, but can expand to new locations if left untreated.
Preventing the Spread
Contact a mold removal expert at the first signs of mold. If you have a very small area, like 1 or 2 square feet, you can attempt to kill it with diluted bleach (4 parts water, 1 part bleach), hydrogen peroxide (with equal parts water) or undiluted vinegar. If the mold shows rapid growth or deep penetration, do not attempt to remove it yourself. You can also stop spreading by drying out your home with a heater or dehumidifier.