How Long Does It Take for Mold to Grow? Posted on August 16, 2012 at 10:40 am.Written by Peter Kakoczky How Long Before Mold Starts Growing? Because mold is both damaging and dangerous to property and people, it’s important to pay attention to any evidence that it might be growing in your office or home. Too much water is the culprit: Water damage comes in many shapes and forms, from flooding to leaks in pipes to too much humidity in the air. It doesn’t take large amounts of moisture to cause water damage; accumulation of condensation on windows or an undetected drip from an under counter pipe is all that’s necessary.The perfect environment for mold growth has been created. Mold grows fast Once water damage has occurred, there is a small window of time, 24-48 hours, before mold will begin to grow, and once it begins it spreads quickly. As you can see from this brief time lapse video of a 2 week time span, mold grows rapidly once it begins.