In This Spring 2006 Issue...
A Mold and Mildew Primer
Questions & Answers
Mold and mildew refer to the visual appearance of various fungi, typically pigmented fungal hyphae, on the surface of organic material such as textiles.
What is the difference between mildew and mold?
The term mold can be used interchangeably with mildew or can be used to describe the process of becoming mildewed.
What are Fungi?
Fungi are spore-bearing organisms that contain no chlorophyll. They obtain their nutrients from their surroundings and give off a musty odor.
What does mildew look like?
Mildew color ranges from black or gray to orange and red in addition to white. It can look like a white powder on the surface of a fabric. The appearance often takes on an irregularly shaped stain or small splatter-like spots. If permitted to grow it may produce a symmetric cross or star shape as it propagates along the fibers in both the warp and fill directions of the fabric.
How does it smell?
Mildew has a musty odor like a damp basement.
What causes mildew?
Mildew is a fungus that grows on moist textiles when left for a prolonged length of time in a damp, warm condition with little or no air circulation or sun light.
What promotes the growth of mildew?
Temperature, moisture, sunlight, ultraviolet rays, contamination and air circulation all affect microbial growth. The ideal conditions for mildew advancement are as follows: A temperature between 68° and 86°F, relative humidity being 70% or greater, textiles contaminated with unsanitary soils or water, a dark environment absent of sunlight with little or no air circulation.
What conditions restrain the growth of mildew?
Temperatures above 115°F will kill most mildew, but not all microorganisms. Since moisture is necessary for fungi to grow, a dry environment will prevent mildew growth. Ultraviolet radiation associated with sunlight will also kill mildew.
Will freezing kill the mildew microorganisms?
Mildew fungi are not killed by freezing. They can survive long periods of storage at temperatures below 32°F.
What effect does mildew have on fabrics?
At first mildew grows on the surface of fabrics, staining or discoloring it. An unpleasant odor usually accompanies this growth. Eventually mildew may grow into the fiber and rot or degrade it.
Can anything else cause damage similar to mildew?
Bacteria can also cause fiber discoloration and fiber degradation when fabric is subjected to damp, warm conditions. Water-damaged textiles contaminated by bacteria will have a sour odor in the initial stage of damage. Later, such fabrics will develop a musty odor similar to mildew.
What are bacteria?
Bacteria are small, single cell, microscopic organisms. Under proper growth conditions, bacteria reproduce rapidly.
Are some fabrics more susceptible than others to mildew or bacteria growth?
The most susceptible fabrics are comprised of cellulose fibers such as cotton, linen, ramie, and rayon. Leather, suede and natural rubber are also excellent mediums for the growth of microorganisms. Mildew becomes ingrained in the pores of the leather where it can permanently stain the leather and affect the dyes. Such unconstrained mildew growth can cause thin areas and holes to appear.
Which fabrics are less susceptible to mildew?
Synthetic fabrics such as polyester, acetate, nylon and acrylic are generally resistant to mildew. But under the right conditions, they can also be subject to mildew growth and stains will result. Silk is highly resistant to mildew and will not be damaged except under extreme conditions. Mildew will not form in wool unless the fabric is stored under damp conditions and for an extended period of time.
Can the effects of mildew be reversed?
Depending on the length of time mildew has been allowed to grow and the damaged it has caused, complete restoration of mildewed fabrics may not be possible. Even if the stains can be completely removed, the fabric may be weakened and could even fall apart during cleaning or use. Ozone treatment before cleaning is the only method to permanently remove the musty smell of mildew. This treatment chemically breaks down and eliminates all organic odors. Once the surface fungus is removed, always perform the ozone treatment before any attempt is made to remove the mildew and its stain.
How can mildew be removed?
Wear gloves when handling items contaminated with mildew or flood water. When handling extremely contaminated items you should not only wear gloves, but also goggles and an organic respirator in order to avoid absorbing fungal hyphae through the skin, mucous membranes or lungs.
Mildew is insoluble and cannot always be removed from fabrics. In an attempt to remove mildew the following procedures may be of assistance:
Ozoning is an effective method for destroying odor through oxidation.
If mildew stains remain or sun exposure was not possible, use wet cleaning procedures for launderable items.
Colorfastness testing is accomplished by first clipping a small piece of the fabric from an unexposed seam. Apply the bleach that will be utilized to the clipping. Rinse then dry the clipping and compare the color of the clipping to the original garment. If there was no color change the garment is colorfast to the bleach that it was tested for.
Chlorine bleach (Sodium hypochlorite) is the preferred bleaching agent if the item is colorfast to this aggressive bleach.
If chlorine bleach is not appropriate, use another agent like sodium perborate. Sodium perborate is safe to use on most silk, wool or nylon items. However, it may not be safe on white fabrics made of silk or wool as it may affect the optical brighteners used to make the fabric white. Again, be sure to test for color fastness.
For the few items that may not be colorfast to sodium perborate, hydrogen peroxide is safe on most fibers and colors. Hydrogen peroxide may be used on white silk and wool. Again, test for color fastness using only the 3 percent solution to test (or dilute a 30 percent solution by 10).
For dyed fabrics that cannot withstand the use of oxidizing bleaches, wet-clean with a neutral synthetic detergent and ammonia. This will help remove the odor and stain but will not kill the mildew.
To kill bacteria associated with flood damaged articles, wet-clean in water between 140° and 158°F with normal bleach concentrations. Tumble dry then expose to the sun if permissible.
For non-washable items take them to the drycleaner. Drying at 158°F and stem finishing at 356°F under 80 PSI will kill the bacteria. However, dry cleaning may not remove water soluble impurities and items may require full restoration. A discussion on restoration is beyond our attempt here.
Painted Leather Items
For painted leather items try the following after testing in a discrete area. Wipe the surface clean with a damp cloth. Clean with a diluted alcohol (1 cup denatured or rubbing alcohol to 1 cup water). Dry in air with a fan. If the mildew remains, wash with saddle soap or soap with a fungicide. Again, testing in a discrete area.
Dyed Leather Items
For dyed leather items we recommend taking them to a dry cleaner that specializes in leather cleaning. An ozone treatment will be beneficial for removing the odor associated with mildew.
How to Prevent Mold & Mildew
The key to preventing mildew is to avoid storing soiled articles in damp conditions.
How to Reduce the Humidity of the House
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