Ever notice a “wet dog” or “musky” smell after shampooing carpets? Adding moisture to carpet by shampooing might cause mold in carpet or make an existing mold problem worse.
People often think that shampooing carpets is a way to “deep clean” them and make the air inside better. But from a technical and microbiological point of view, shampooing can lead to carpet mold when water gets into the backing, padding, and the subfloor underneath the carpet. Mold simply needs a little bit of moisture to grow, and many carpet cleaning processes make the conditions perfect for mold to thrive.
The US EPA says “Mold can grow on or fill in the empty spaces and crevices of porous materials, so the mold may be difficult or impossible to remove completely“.
Knowing how moisture works in carpet systems helps explain why shampooing can sometimes let mold grow faster instead of getting rid of it.
Mold only needs water, organic matter, and air to grow.
Mold spores are constantly present indoors, even though they are very little. These spores stay inactive until they get some moisture. Mold can start to grow in 24 to 48 hours if the conditions are right and there is enough moisture.
Carpet is a great place to be because it has:
• Organic waste, like skin cells, dust, and fibers
• Limited airflow under the surface
• Several layers of porous material that hold moisture
• Shielding from light and drying
When you shampoo your carpet, the water awakens mold spores that are already deep inside the carpet system.
Carpet shampooing adds moisture to the surface and beyond. Even professional carpet cleaning tools can’t get rid of all the moisture that gets into the carpet while shampooing.
Scientific tests and observations in the field demonstrate that a lot of moisture stays trapped in the carpet fibers, backing, adhesive layers, padding, and the subfloor underneath the carpet.
These layers act like a sponge, soaking up and holding water.
The top of the carpet may dry out in a few hours, but the deeper layers may stay wet for 24 to 72 hours or longer, depending on the humidity, air flow, temperature, thickness of the carpet, and kind of padding. This wetness that lasts a long time is perfect for mold to thrive.
Carpet padding has a lot of holes in it and can soak up water. It is quite hard to dry padding all the way through once it becomes wet.
Padding is also full of organic matter, such as dirt, dust, skin cells, and microbes. Mold uses these things as food.
Because padding doesn’t let air circulate through it, moisture can stay trapped for long periods of time, letting mold colonies grow and spread without anyone noticing.
Moisture migration can move mold to places where it wasn’t before.
Moisture can move:
• Across the back of the carpet
• Down into the padding
• Into wooden floors
• Into construction materials that are next to it
This process can wake up mold spores that were dormant in places that didn’t show any signs of contamination before.
Because of this, shampooing can make the area of mold growth bigger by accident.
Mold often grows under the carpet surface.
One of the biggest dangers of carpet shampooing is that mold usually grows below the surface that you can see, like on the wooden flooring, along tack strips, and under baseboards. People who use the area may not know that mold is growing until they smell it or start to feel sick.
Cleaning the surface does not get rid of mold that is forming under the carpet.
If the humidity stays high inside after cleaning, mold is more likely to form.
This problem gets worse when there isn’t enough air flow, windows are closed, and the air doesn’t move about enough.
Leftover cleaning products can give mold more nutrients.
Some carpet cleaning products leave behind a film. These residues may have organic molecules in them that mold might use as extra sustenance. Cleaning residues, when mixed with moisture and dust that is already there, might actually speed up the growth of microbes instead of stopping it.
Carpet Mold Growth Often Goes Unnoticed
Contamination may not be obvious because mold grows underneath the surface.
Common signals of a problem are musty smells, complaints about the air quality inside that don’t go away, allergy or respiratory symptoms, smells that get worse when the humidity rises, and symptoms that get worse after cleaning the carpet.
If spores are stuck in the carpet fibers, air testing might not always find mold right away.
Conclusion
Shampooing can add moisture to the air, which can start and speed up mold growth.
When you shampoo your carpet, you add moisture to a layered, porous system that is hard to dry all the way through. This moisture wakes up latent mold spores and makes the carpet backing, padding, and underfloor materials perfect for microbial development.
Once mold has settled under carpet, regular cleaning procedures can’t get rid of it very well.
To keep mold from growing, you need to control the moisture correctly.
To stop mold from growing, you need to keep the carpet systems as dry as possible.
Cleaning the carpet may not be enough to get rid of mold if you think it is there.
Last Thoughts
Shampooing carpets might make them seem better on the surface, but it can also generate circumstances that are good for mold growth when moisture gets into deeper layers. Because carpet systems hold onto moisture and trap dirt, adding water without making sure it dries completely can make the air inside worse over time.
To stop mold from growing where it shouldn’t and keep indoor spaces safe, it’s important to know how moisture affects carpet materials.
In our practice, lab results show better results w dry vacuuming slowly several times in different directions than after carpet shampooing. We also see very high mold counts in carpet that is shampooed often.
If you’re not sure, we advise clients to get the carpet dust tested and find out what’s really lurking deep in those fibers. Find out more about what home furnishings can be tested here.
