Spring showers not only bring grass and flowers but mildew. Spring is the "dampness" season and when the heat is reduced, higher humidity will be the result; if the heating unit is not equipped with a fan there will be less circulation of air. (Both conditions are ideal for producing mildew.)

Mildew, a fungus, gets its food from another source because it does not contain chlorophyl that is needed to convert water and carbon dioxide into food. Mildew grows on a number of things; those associated with the carpet industry are protein and cellulosic fibers. The cycle starts when a spore from the air settles on a fiber and under proper conditions begins to grow by sending a root system inside of the fiber to obtain food. As it grows runners will shoot off along the outside of the fiber and, in turn, develop roots. If the growing conditions are good, so much material will be removed from the fiber that it becomes a skeleton. The fiber will not only be very weak and easily broken but will make a noise when compressed. Mildew plants produce spores that are transferred by the air to other locations-the spores and plants can remain dormant for long periods of time if proper growing conditions are not present.

Growing conditions for the many kinds of mildew are not the same; most of those associated with textiles grow better in temperatures ranging from 75' to 851 F. (Below these, growth may be retarded or stopped. As a rule, mildew will not grow as well in high temperatures-very high temperatures will kill it. Moisture is needed and the amount present will affect the growth.) Mildew may not be noticed until after a carpet has been flooded; however, it could have been growing slowly on the fibers-the growth had been slow because of the small amount of moisture present-humidities above 70% will cause rapid growth but if the mildew is kept under water it will not grow. Poor circulation of air will contribute to good growing conditions as it is not as apt to remove the moisture from the fibers-sunlight has a drying effect. The colors of mildew range from an almost colorless white to black, and in shades of red and green. Food for the various types of mildew is obtained (usually) from protein or cellulosic fiber. Mildew, found growing on both the face and the back of a wool carpet, is probably two different types.

The characteristic musty odor associated with mildew is due to bacteria feeding upon its waste. As true with most odors, it is more noticeable during periods of higher humidity which will not only speed up the mildew growth, therefore the amount of waste, but the moist air will carry the odor quicker than dry air will.

When a musty odor is detected, action should be taken to prevent permanent damage to the material. The affected area can be weakened, completely destroyed, or stained.

Mildew is not always easy to remove, especially when it grows on the back of wall-to-wall carpet. A loose rug can be taken to a cleaning plant for a thorough cleaning which will usually kill the mildew. Additional precautions can be taken by letting the rug hang in a dryroom for a period of time after it has dried. Most mildew cannot withstand temperatures above 115' F. Painting the back of the carpet or the face (if the face dyes will withstand it) with a 1/2% of hydrogen peroxide (then exposing it to the sun for several hours) will definitely kill any remaining mildew. This may not remove stain as discoloration may be inside the fibers, so very destructive bleaching or stripping may be required. Locating a mildewed area on the back of wall-to-wall carpet may be almost impossible if part of the carpet cannot be lifted-the entire area may smell and even close to the exact location of the odor may not be detected, but if it can be found. Chlorine bleach treatment will kill the mildew. The bleach can be applied with a syringe; however, care should be taken not to allow it to spill on the face yarns; only small quantities of the bleach are required as an excess may wick to the surface or destroy the fibers. If some of the carpet can be lifted in order to locate the mildew, it should be cleaned with a detergent solution followed by a light application of 1% solution of hydrogen peroxide. If possible, dry the area before relaying the carpet. This can be done with heat lamps, heaters, fans, exhaust from the vacuums, etc.

The same type of problem can happen on upholstery if mildew is in the padding. Care has to be taken not to have damage from dye bleeding, water rings, or color from bleaches.

If the mildewed area has been cleaned and treated with a little bleach, all of the fungus should have been killed. However, this will not prevent new growth in the same or adjacent areas if the article is returned to the same conditions in which the mildew grew-there are spores in the air at all times, and only proper growing conditions a food source are necessary spread the mildew-the way to pre- vent this growth is to eliminate any growing condition. The easiest one is to control moisture in the air; dehumidifiers will remove enough moisture to prevent or retard growth. It is better to prevent mildew growth than to try to treat it afterwards.

Author: Hopper, R.N.
Date/Pages: May 1973, 6

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Article provided by the Association of Specialists in Cleaning and Restoration (ASCR).