Concrete is not food. Mold needs a carbon source and a wet surface, and a bare slab supplies the water but almost none of the food, so growth on concrete is living on the dust, the paper facing, the paint film or the glue sitting on it. That matters because it changes the fix: the surface can usually be cleaned rather than removed, and the job that decides whether it comes back is the water behind it.
Can mold grow on concrete, and what is it eating
It grows on concrete rather than in it. What feeds it is the organic layer on the surface, meaning settled dust and skin, the paper face of plasterboard fixed against it, carpet glue, or a coating that holds moisture against the slab. The authority's own framing is that mold needs moisture and a nutrient source, so the useful question in a basement or a garage is which of the two you can take away, and on concrete the answer is almost always the moisture.
What does mold on concrete look like on a floor or a wall
Usually a flat, patchy bloom rather than the raised fuzz you see on timber, because there is so little for it to build on. Black speckling in the pits of a trowelled slab, white or grey powdery patches along the foot of a block wall, and a tide line where the wall meets the floor are the common shapes. Efflorescence, the white crystalline salt water carries out of the concrete, looks similar and is not growth at all: it crushes to powder between your fingers and returns after rain.
Is black mold on concrete dangerous, and what changes the answer
What decides the risk is the area affected and whether anybody is breathing it, not the colour. The health guidance does not separate species by danger, because the reaction people have is to exposure rather than to a name, and testing to identify a species rarely changes what has to be done. What does change the answer is scale: a patch on a garage floor is a cleaning job, and a whole basement wall is a containment job because the disturbance puts spores in the air.
Black mold on concrete floor and the water underneath it
A slab on ground that reads wet is usually taking water up rather than taking it in from the room, and paint or vinyl laid over it holds that water at the surface where growth can use it. Cleaning the top of a slab that is still wicking is the reason so many basements are cleaned twice. The order that works is find the water, deal with it, then clean, and only then put a covering back that can tolerate a slab breathing through it.
Cleaning it, and when the material has to leave instead
The concrete itself is almost always cleanable, and what has to go is the porous material against it: the plasterboard, the timber batten, the carpet and the pad. Mechanical removal followed by a registered disinfectant held for its stated contact time does the work on the masonry, and a coating goes on afterwards only if the moisture has been dealt with, because sealing a wet wall moves the problem rather than ending it.
Questions people ask about mold on concrete
Can mold grow on concrete if nothing else is there?
Barely. It needs a carbon source, and a genuinely clean slab gives it almost nothing, which is why growth appears where dust, paper, glue or paint has been sitting on the surface with water behind it.
Is mold on concrete dangerous to live above?
The area and the exposure decide it rather than the colour. A patch you can wipe is a cleaning job; a wall of it is a containment job, because disturbing it is what puts spores into the air people are breathing.
What does black mold look like on concrete?
Flat, patchy and in the surface texture rather than raised, often as speckling in a trowelled floor or a dark band at the foot of a wall. White crystalline patches that crush to powder are efflorescence, not growth.
Does the concrete have to be removed?
Almost never. Concrete cleans; the porous material fixed to it does not, so what leaves the building is the plasterboard, the batten, the carpet and the pad rather than the slab.