Cement fiber board, commonly referred to by the tradename of Hardiplank, is becoming a popular siding alternative. As it’s name implies, it is a durable material made of a fiber unfused cementitious material formed under pressure. It can have many textures, from smooth to a faux wood textured appearance. Many factory colors are available and it is paint-able.
Cement fiber board will eventually become soiled by the usual suspects: airborne dirt, pollution, mold, mildew, algae, etc. It is cleaned in a manner similar to other common building siding materials. The cleaning process typically involves applying a cleaning solution to kill the microbes and soften the dirt and pollution, then rinse with a low to medium pressure fresh water rinse.