Mold Control on a Budget



Here's a simple test to rule out the toxic black mold, Stachybotrys:

Toxic black mold requires water, not just elevated relative humidity, to grow. It also needs cellulosic material. "Cellulosic" refers to containing cellulose, i.e.,  wood or paper, such as the paper backing of drywall. So, if the black mold you see is neither in a wet area nor on cellulose, it's most likely not Stachybotrys.

Stachybotrys doesn't like these places:

  • bathroom grout
  • bathroom ceilings
  • windows with metal frames or window sills
  • foundation walls
  • ceiling joists of a basement or crawlspace
  • plaster walls
  • bread

Discussion: These places either aren't chronically wet enough or there is no cellulosic material for "toxic black mold" to grow on. Occasionally I've seen black mold on plaster, but the mold has been growing on the paint, not on the plaster. In these cases, just the paint needs to be cleaned off. Stachybotrys is different from common bread mold. Common bread mold is usually green Penicillium mold.

Stachybotrys does like places like these:


  • drywall in a flooded basement
  • drywall near a chronic washing machine leak
  • chronically wet piece of cardboard that is on the basement floor
  • wall cavity where there has been a chronic slow leak
  • bathtub access hole where there has been a chronic leak
  • behind a kitchen sink cabinet where there is a chronic leak

Discussion: Note the common themes of flooding and chronic water leakage.

Typical scenario for the growth of toxic black mold:

There's a plumbing leak in a wall cavity. You find

it and call the plumber. The plumbing leak is fixed, and you forget about the incident. However, water had leaked inside the wall cavity for a while before you found the leak. The paper backing of the drywall (also known as sheetrock or gypsum board) and the wood framing got wet. They didn't

dry out, and black mold grew.

Toxic black mold is common in flooded basements:

There's a flood in the finished basement. You take up the wet carpet but don't realize that water seeped under the base molding and into the wall cavity. Materials in the wall cavity remain wet, and  Stachybotrys grows on the paper backing of the drywall and on the back of wood paneling.

Question: I have what looks like black mold at the base of the foundation wall. Could that be Stachybotrys?

Response:  Apply the test: Is there chronic wetness and is there cellulosic material for Stachybotrys to grow on? "No" to both questions, so it's not Stachybotrys. There may be some black Cladosporium, which is the most common outdoor mold.

Black mold story:

Mr. and Mrs. Rosa saw black mold on their foundation wall. Fearing toxic black mold, they call in a mold remediation company. The company representative assured them it was Stachybotrys and sold them $14,000 of remediation services they didn't need, including a Humidex moisture-reduction device, which was improperly installed and sucked in fumes from an adjacent industrial complex. Mrs. Rosa was allergic to chemicals in the fumes and twice had to be taken to the emergency room with breathing problems.

Desperate for a solution, the Rosas called me in. When I saw the situation for what it was, I told them to disconnect the Humidex and suggested they speak with a lawyer. The lawyer brought action against the mold remediation company on the grounds that they sold the Rosas unneeded services.

The mold originally on the Rosas' foundation wall most likely was Cladosporium, which could have been scrubbed off with Borax and water.

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Updated 9-2011