Mold is a variety of fungus that will grow in areas of your home that have excess moisture. Mold can grow on any organic matter in your home such as wood floors, furniture or even on joists. Mold will grow in joists in areas of the home that don't receive a lot of ventilation or that have a lot of moisture. This makes mould on floor joists in attics and basements quite common. Clean mould from your home's joists as soon as possible to prevent damage to the joists and your home.
Mix 3 qt. water with 1 qt. bleach.
Add ¼ cup liquid dishwasher detergent to the liquid solution. Mix until the dishwasher detergent dissolves completely.
Pour the solution into a pump sprayer.
Spray the solution over the mould growth on the joists. Spray several feet from the visible mould growth to ensure that you clean all of the mould spores from the joists. Not all mould growth is visible; microscopic mould growth will be around the perimeter of the visible mould growth.
Let the solution sit there for 15 minutes. This will give the bleach time to loosen the mould spores' hold on the unfinished wood.
Scrub the unfinished wood with a scrubbing brush to loosen all of the mould growth.
Rinse off the mould with a clean cloth soaked in clear water.