Mildew is a variety of fungus that feeds on organic matter and is attracted to areas with excess moisture. Slight mildew growth will not cause a problem, but if it is left to grow unchecked, it will eventually decay wood, textiles, paper products or any materials made of organic matter. This can be a problem if you are using a storage unit that you aren’t able to check for mildew growth very often. If this is the case, put items in your storage unit to help prevent excess water.
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Moisture barriers prevent water from seeping up through the ground and in through the walls and ceilings. High-quality storage units should already have moisture barriers built into the unit, but not all units have this. Purchase moisture barriers from a hardware or home improvement store and lay them over the floor, walls and ceiling. Use a staple gun to secure into place.
Silica gel, a chemical that absorbs moisture from the air, will help keep your storage unit dry and lower water vapor in the air. Purchase silica gel from a chemical supply store or online outlet, as it is tough to find at a hardware store. Place an open container of silica gel in the center of the storage unit. Silica gel is blue when dry but will turn pink as it absorbs water vapor. Replace the silica gel when it turns pink.
Anhydrous Calcium Chloride
Anhydrous calcium chloride is another chemical that will absorb water as it sits in your storage unit. Unlike silica gel, which keeps its shape as it absorbs water, anhydrous calcium chloride liquefies. Place the granules in a rust-resistant metal container or old water jug. Cut holes in the container and hang it over an enamel pot to catch the liquid and leave the rest of the granules dry. This will last up to two months, depending on humidity levels. Anhydrous calcium chloride is more commonly used to melt snow on highways, so you may be able to find it more easily at a hardware store.
Activated alumina, another powder solution, absorbs excess water vapor to keep your storage unit dry and prevent mildew. Unlike anhydrous calcium chloride, activated alumina does not liquefy or even soften as it absorbs water. You can also regenerate it--after it has absorbed as much water as possible--by heating it to 600 degrees Fahrenheit.