When it comes to cleaning your deck, some people might feel tempted to pull out some bleach from the garage and get started. Stop! Before you do this, you need to make sure that you are very careful. Chlorine bleach does an excellent job of killing bacteria and viruses but has not been proven effective in killing molds on porous surfaces. It also destroys the lignin in your wood deck, disrupting the way it is bonded together. The wood will become more prone to aging to an unattractive gray color and splintering along the surface. When it comes to chlorine bleach, think of it as a sanitizer, not a deck cleaner. It should stay in areas of the house such as the kitchen, on the counter, or in the bathroom cleaning surfaces there.
Chlorine bleach can cause deck stains or sealers applied to the wood to fail. It will remove any natural color as well leaving you with a bland, unattractive color. Bleach itself is 99% water. Water is one of the main contributors to the growth of harmful bacteria and mold. The ionic structure of bleach prevents chlorine from penetrating into porous materials such as wood—it just stays on the outside surface, whereas mold has enzyme roots growing inside the porous construction materials—however, the water content penetrates and actually FEEDS the mold. This is why a few days later you can notice darker, more concentrated mold growing (faster) on the bleached area.