Moisture in the Home
Microscopic mold spores exist in nearly every indoor and outdoor environment, and they harmlessly land on many surfaces in the home without creating problems. But when mold spores land on a moist surface, they can quickly create a mold colony.
For this reason, experts always stress that removing mold colonies in your home is only half the battle; removing the excess moisture that created the ideal growth conditions for the mold is the key to preventing future colonies.
A desiccant is any material designed to control moisture. If you have ever seen a silica gel packet inside a pair of shoes or a bag of beef jerky, you have seen desiccants in action.
Other desiccant materials include activated alumina, anhydrous calcium sulfate, calcium chloride and a line of products sold as "molecular sieves" Calcium chloride is generally sold as small, white granules that are placed in rooms with especially high humidity. Calcium chloride can hold twice its weight in water, so under optimum conditions, it can greatly reduce the amount of moisture in a room.
Place the calcium chloride granules in a container made from non-rusting screen or waxed cardboard perforated with small holes. Calcium chloride liquefies as it absorbs moisture and liquid calcium chloride can burn holes in some materials, so you will need to place the cup inside a larger enameled pot.
Place in a small area like a closet or cupboard and replace when the granules have all turned to liquid. One pound of calcium chloride will last anywhere from two weeks to two months, depending on the amount of humidity in the area in which it was placed.
The University of Florida's IFAS Extension guide to controlling indoor moisture warns that calcium chloride and other desiccants may not be particularly effective in small areas such as closets. If a closet is humid, it is typically because the entire house is humid.
Small containers of calcium chloride can absorb moisture from a small, enclosed area, but will obviously be unable to absorb moisture from the entire home. As long as the rest of the home continues to supply moisture and humidity to the closet, the closet will remain overly moist until homeowners carry out a larger scale operation to lower the humidity in the entire home.