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Removing Mold From Carpets

November 6, 2003
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Drying time is a crucial component


Q: Is carpet cleaning an appropriate method for removing mold from carpets?

A: It depends. If water in the carpet, especially carpet installed over pad, has resulted in actual mold growth, it is less likely that the carpet can be successfully cleaned. Mold growth usually results in staining and deterioration of the carpet fibers, backing and binding materials. When mold growth occurs because of standing water that permeates the carpet and the pad, it may simultaneously result in bacterial amplification, loss of structural integrity, discoloration and odor problems that cannot be corrected by surface cleaning. In these cases, the specialty restoration that might be successful in cleaning and restoring the carpet may exceed the carpet's value.

If carpet has been affected by settled spores with no indications of dampness or record of water damage, there is a much greater chance that carpet cleaning can be effective in removing the mold. When cleaning carpets by dry vacuuming with portable cleaners, the equipment must be true HEPA type (see "HEPA vs. High-Efficiency Vacuums" in the October 2003 issue). If the equipment exhausts directly to the outside, such as when a truckmount unit is used, spores will be exhausted to the outside where people passing by may be exposed. The Canadian Mortgage and Housing Corporation (CMHC) recommends removing mold spores from carpeting by vacuuming with HEPA equipment at a rate of up to 90 seconds per square yard.

The greater the number of spores that are present and the more they have been worked into the carpet, the harder it may be to remove them by cleaning. Dry methods of cleaning may not be effective in removing the water-insoluble binders that hold spores to the carpet surface. Bonnet cleaning or shampooing may be effective at detaching soils from fiber surfaces, but do not allow for their immediate removal. The delay in removal can allow for re-entrainment of spores into the air space.

Hot-water extraction provides for a more immediate and thorough removal of spores. According to studies conducted by Air Quality Sciences in Atlanta, hot-water extraction cleaning is the most effective method for removing mold contamination from carpet. The study was conducted by first predetermining the level of fungal contamination present. The carpet was pre-cleaned by HEPA vacuuming and cleaned using hot-water extraction methods. The reduction in fungal levels was reported to be better than 96 percent.

After cleaning, the carpet was divided in two. One half was maintained in a chamber simulating a dry environment, the other half kept at an elevated relative humidity (85 percent to 95 percent). Both sections of the carpet were re-tested after two weeks. Fungal levels in the dry portion of carpet remained low, but the carpet in the damp chamber showed a return to contamination levels similar to those present prior to cleaning.

The study shows that hot-water extraction cleaning that is dried quickly is an effective way of removing settled spores, if the carpet is kept in a dry condition. However, appropriate cleaning and drying will not prevent re-amplification if the carpet is left in a high humidity area. To prevent re-amplification, carpets cleaned with wet processes should be completely dry within six to12 hours.

It is also important that furnishings and items like plastic carpet mat protectors stay off the carpet until the carpet is thoroughly dry, to prevent trapping moisture and resultant mold and bacteria amplification.

There are several ways to promote rapid drying. First, if the carpet will tolerate it, use hot water in the cleaning process. It not only cleans more effectively, but it also results in a higher rate of evaporation. Second, increase the amount of extraction by using more dry extraction strokes of the wand to remove as much water as possible. Third, use the drying principles developed by the water-damage restoration industry to accelerate the drying of carpet. These include increasing the air movement across the carpet surface to move moisture into the air and then controlling humidity by dehumidification.

Air movers are a great way to speed drying by increasing the speed of air movement across the carpet. The property owner may also have ceiling fans or other types of fans that, with their permission, can be used. It is important that the property owner understand the necessity for rapid drying so they don't turn the equipment off too soon. Of course, the use of air movers assumes they are not being used in areas with mold growth or other contamination. Air movement can cause additional problems by spreading mold spores from areas of growth to other parts of the building.

Reducing the humidity can be accomplished by using outdoor air when the outdoor humidity is low. The outdoor air should be at least 15 grains lower than the inside air. Be aware that cold surfaces may result in problems with condensation. The decision to use outdoor air for drying requires the cleaner to have both a thermo-hygrometer and a psychrometric chart and know how to use them.

Outdoor air can be brought into the building using a variety of approaches. Kitchen, bathroom and whole-house fans can be used for setting up air circulation. However, care should be taken that the exhaust fans move air to the outside and not into an attic space or other internal part of the building where condensation might occur. On a windy day simply opening windows on both the upwind and downwind sides of the structure helps move the moisture-laden air to the outside.

If outdoor conditions are inappropriate for drying, mechanical dehumidification may be necessary. In order to be effective, this equipment will generally need to be left on-site and picked up the next day. The home air-conditioning system may also provide some dehumidification. However, inappropriately sized systems may just cool down the structure, cycle off and not remove much moisture. This cooling down and cycling off condition may actually slow down drying.

Increasing the heat in the structure may also speed carpet drying. As air temperature increases, its ability to hold moisture goes up so its relative humidity goes down. Warmer temperatures also directly encourage evaporation by adding the energy necessary for water molecules to evaporate. Turning up the thermostat is one obvious way to increase temperatures. The carpet will dry more rapidly by releasing its moisture into the air. The warm, moist air can then be exhausted to the outside. The cycle of warming up the air and then opening windows to exchange the warm moist air with cooler outside air can be repeated every hour or so until the carpet is dry. However, this can become rather labor intensive and economically impractical.

Many of these approaches require significant additional set up and/or handling time, and may create considerably more expense for the cleaner, but result in less chance of mold re-amplifying from remaining moisture after cleaning.

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