After educating myself about the mold issue, I realized that there were really two problems…getting rid of the mold, and keeping it away.

I’m used to using household bleach to eliminate pesky mold collecting on the tiles of the bathroom walls. It works well for that. But it doesn’t work so well on mold growing on wooden or other porous surfaces, such as the lower press-board shelves inside my shed. The bleach kills the surface mold – no problem. But the bleach may not penetrate the wooden surface. Further, the bleach evaporates, leaving no residue. This is basically a good thing, but it does nothing to prevent the mold from returning.

Another product that reportedly works well for mold control/destruction is Borax, available locally as “20 Mule Team Borax”. A solution of Borax kills plenty of mold, penetrates wood to some extent, but most importantly, leaves a thin film of Borax behind after the water dries. This is helpful in preventing recurrence of the mold.

The other solution to preventing recurrence was leaving the overhead fan running at all times.

The reason this is helpful has to do with why the mold formed in the first place.

During the hot, humid, southern Illinois summers, outside air is drawn in through the vents underneath the eaves. The hot air continues up and out the roof ridge vents. But some of the humid air mixes with the rest of the air inside the shed, and as it cools, it falls towards the floor. The floor is cooler than the rest of the shed, in part because the insulation keeps the shed interior cooler in general (radiant heat is reflected away by the white steel skin, and the underlying reflective mylar insulation).

The other reason for the floor being cool is that the floor consists of a large slab of concrete, which retains its night-time cooling for a long time before warming to the heat of the day.

When the humid summer air hits the cooler concrete slab and shelving within a few feet of the floor, condensation occurs, which powerfully enables mold to grow on those surfaces. That is why my lower shelves had mold, but not the upper shelves.

Leaving the fan on circulates the air within the shed, evening the temperatures, and the humidity within the shed. This, combined with the thin film of Borax left on the vulnerable surfaces, has eliminated the mold.

Provlem solved.