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Odor & Mildew Control
Odor Control
Water damaged structures can develop odors that originate from chemicals released from wet building materials, wet contents, bacteria, urine from pets and other sources.
The musty, moldy odors in water-damaged indoor environments are compounds produced by metabolically active bacteria and fungi. While heath effects have not yet been attributed to MVOC (Microbial Volatile Organic Compounds) exposures, their presence is an indicator of microbial contamination, and the need for proper remediation practices and the use of appropriate personal protective equipment.
Treatments Include:
· Removal
· Cleaning
· Chemical Destruction of Source
What is Mildew?
The term "mildew" is a common term in the paint and coatings industry and is used to describe an unsightly discoloration of a paint film. Mildew is a general term for growth produced by mold fungi. This growth can occur on a variety of surfaces both of organic and inorganic origins. Surfaces can be inanimate, such as wood, vinyl, and aluminum; or living materials such as plants. Mildew can also grow on superficial surfaces such as dirt, grease, and other industrial pollutants, provided the appropriate nutrients are present to facilitate such growth. Moisture is the primary environmental component necessary for mildew growth, followed in lesser degree by temperature. Consequently, tropical areas that have high moisture (humidity) and high temperature profiles provide the greatest geographic challenges to mildew growth prevention. Hot, dry climates, as one would suspect, see much less mildew growth. Fungal spores are present in air at counts of 100 to over 1000 per m3 of air, depending on geographic location. Even freshly milled wood is immediately exposed to mildew regardless of location. Approximately 100,000 species of mildew exist, many of which affect the appearance and performance of finishes. Mildew can be transported from one surface to another by insects, animals, or air.
Effect on Appearance and Performance
Mildew affects finishes in both appearance and performance. Mildew generally appears in two forms, a spore type, which resembles caviar in appearance, or a mycelium or filament type. Mildew generally appears as an unsightly discoloration on a finish, thereby making the appearance unacceptable. The performance of a finish may be comprised either by mildew growth on the coating surface, or by the application of a coating to the mildewed surface. The presence of mildew can have a detrimental effect on dirt pickup, cracking, flaking, and adhesion properties of the finish. When an appropriate finish is applied to a mildewed surface, the adhesion of that finish to the substrate will be reduced to the physical interference of the mildew. When an infected finish is applied to a substrate, the above failures can occur even more rapidly.
Interference with Adhesion
Paints are designed to have excellent adhesion to a variety of surfaces. Depending on the paint manufacturer's intentions, a particular paint may be designed to adhere to wood, masonry, vinyl, aluminum, and/or other substrates. The presence of mildew or other foreign matters such as oil, grease, dirt, tree pollens, and/or other substances on a substrate interferes with the adhesion characteristics of the paint. It is in the homeowner's best interest to ensure that the substrate to be painted is properly cleaned and prepared prior to painting.
Intercoat Adhesion to Paints
When mildew has grown on a surface, a homeowner may think he can improve the appearance by applying a coat of finish directly over the mildewed surface. This approach is not a desirable cure. Instead, this new coat of finish provides protection for the existing mildew, preventing its removal, and can actually provide a nutrient source to facilitate new mildew growth. Because of the infestation below the newly finished surface, mildew will certainly appear again on the new surface. In addition to the poor appearance of the mildew, a greater problem now exists with the adhesion of the new finish to the old finish, a property commonly referred to as intercoat adhesion. By not following good surface preparation procedures, the homeowner has allowed the mildew to exist between the old and new coats of finish. Intuitively and quantitatively, we know that this mildew interferes with the new finish's ability to adhere to the old finish. Early failures such as cracking, flaking, blistering, can be expected. To insure the best intercoat adhesion, an appropriate method of surface preparation must be followed. This is described below.
Effect of Mildew on Wood
We have discussed some of the harmful effects that mildew can have on wood finishes. Mildew can also affect unfinished wood. In fact, it is often more of a problem with unfinished wood. The colored residue that mildew can deposit on a wood surface can cause severe discoloration; this discoloration can be a variety of colors but is most often gray or black. However, this mildew growth does not degrade the wood; mildew fungi are not capable of using lignin, cellulose, or hemicellulose for food. Therefore, mildew does not decrease the structural integrity of the wood. They can, however, use the nonpolymeric materials in wood, such as the extractives and natural oils for food. Wood species that are rich in natural extractives may be more prone to mildew growth than wood species with lower extractive content. Since mildew spores infect all surfaces, their growth can be limited only by controlling moisture, temperature, or using paint film mildewcides.
If the surface is infected with mildew, it can be removed using a mildew cleaner, but it will return if the growth conditions remain the same. If wood is to be painted, it is beneficial to remove mildew before painting. This increases effectiveness of the paint film mildewcide.
Common Species
There are a variety of common mold species know to effect coatings performance. A list of 19 of the most common species appears below:
Alternaria sp., Aspergillus flavum, Aspergillus niger, Aureobasidium pullulans, Botryodiplodia sp., Cephalosporium sp., Cladosporium sp., Fusarium sp., Helminthsporium sp., Monilia sp., Mucor sp., Pacacilomyces sp., Penicilium sp., Pestalotia sp., Phoma sp., Pleospora sp., Rhizopus sp., Stemphylium sp., Trichoderma sp.
Of these species, Aureobasidium pullulans and Aspergillus Niger are the most common mold species encountered.
Necessary Contributing Factors
Substrate & Environment
Regardless of specific species, all mildew require oxygen, water, a food source, and a narrow temperature range to metabolize and reproduce. Typically, mildew causes problems with the finish after it has been applied and dried, and does not affect the product in the can as there is usually insufficient oxygen present for metabolism. Mildew needs water to grow. Consequently, as the humidity of the environment continues to rise, the mildew flourishes. For food, mildew generally metabolize organic food sources like starches, sugars, proteins, and some oils found in paint systems. Specifically, mildew can also feed on pollens, bacteria, or many other organic contaminants on the finished surface. Temperatures from 70 to 90 Fahrenheit to 20 to 30 Celsius are ideal for mildew growth. Below freezing, mildew fungi become dormant, however, they do not die.
Paint film
Other factors that can also contribute to mildew growth include the type of finish and its surface characteristics. Generally, top quality paints offer the best protection from mildew. As the quality of the paint decreases, the chance for mildew growth typically increases (a further discussion will follow under Mildew Control). Generally, latex finishes are more mildew resistant than alkyd paints.
Geographically Prone Areas
Mildew growth can occur anywhere in the world. Climates that supply more of the contributing factors discussed above will promote greater mildew growth. For example, hot, tropical regions often have the greatest mildew growth. Coastal regions generally grow more mildew than dry inland areas. However, inland areas near lakes, rivers, or heavy vegetation can experience heavy mildew growth.
Odor Control
Water damaged structures can develop odors that originate from chemicals released from wet building materials, wet contents, bacteria, urine from pets and other sources.
The musty, moldy odors in water-damaged indoor environments are compounds produced by metabolically active bacteria and fungi. While heath effects have not yet been attributed to MVOC (Microbial Volatile Organic Compounds) exposures, their presence is an indicator of microbial contamination, and the need for proper remediation practices and the use of appropriate personal protective equipment.
Treatments Include:
· Removal
· Cleaning
· Chemical Destruction of Source
What is Mildew?
The term "mildew" is a common term in the paint and coatings industry and is used to describe an unsightly discoloration of a paint film. Mildew is a general term for growth produced by mold fungi. This growth can occur on a variety of surfaces both of organic and inorganic origins. Surfaces can be inanimate, such as wood, vinyl, and aluminum; or living materials such as plants. Mildew can also grow on superficial surfaces such as dirt, grease, and other industrial pollutants, provided the appropriate nutrients are present to facilitate such growth. Moisture is the primary environmental component necessary for mildew growth, followed in lesser degree by temperature. Consequently, tropical areas that have high moisture (humidity) and high temperature profiles provide the greatest geographic challenges to mildew growth prevention. Hot, dry climates, as one would suspect, see much less mildew growth. Fungal spores are present in air at counts of 100 to over 1000 per m3 of air, depending on geographic location. Even freshly milled wood is immediately exposed to mildew regardless of location. Approximately 100,000 species of mildew exist, many of which affect the appearance and performance of finishes. Mildew can be transported from one surface to another by insects, animals, or air.
Effect on Appearance and Performance
Mildew affects finishes in both appearance and performance. Mildew generally appears in two forms, a spore type, which resembles caviar in appearance, or a mycelium or filament type. Mildew generally appears as an unsightly discoloration on a finish, thereby making the appearance unacceptable. The performance of a finish may be comprised either by mildew growth on the coating surface, or by the application of a coating to the mildewed surface. The presence of mildew can have a detrimental effect on dirt pickup, cracking, flaking, and adhesion properties of the finish. When an appropriate finish is applied to a mildewed surface, the adhesion of that finish to the substrate will be reduced to the physical interference of the mildew. When an infected finish is applied to a substrate, the above failures can occur even more rapidly.
Interference with Adhesion
Paints are designed to have excellent adhesion to a variety of surfaces. Depending on the paint manufacturer's intentions, a particular paint may be designed to adhere to wood, masonry, vinyl, aluminum, and/or other substrates. The presence of mildew or other foreign matters such as oil, grease, dirt, tree pollens, and/or other substances on a substrate interferes with the adhesion characteristics of the paint. It is in the homeowner's best interest to ensure that the substrate to be painted is properly cleaned and prepared prior to painting.
Intercoat Adhesion to Paints
When mildew has grown on a surface, a homeowner may think he can improve the appearance by applying a coat of finish directly over the mildewed surface. This approach is not a desirable cure. Instead, this new coat of finish provides protection for the existing mildew, preventing its removal, and can actually provide a nutrient source to facilitate new mildew growth. Because of the infestation below the newly finished surface, mildew will certainly appear again on the new surface. In addition to the poor appearance of the mildew, a greater problem now exists with the adhesion of the new finish to the old finish, a property commonly referred to as intercoat adhesion. By not following good surface preparation procedures, the homeowner has allowed the mildew to exist between the old and new coats of finish. Intuitively and quantitatively, we know that this mildew interferes with the new finish's ability to adhere to the old finish. Early failures such as cracking, flaking, blistering, can be expected. To insure the best intercoat adhesion, an appropriate method of surface preparation must be followed. This is described below.
Effect of Mildew on Wood
We have discussed some of the harmful effects that mildew can have on wood finishes. Mildew can also affect unfinished wood. In fact, it is often more of a problem with unfinished wood. The colored residue that mildew can deposit on a wood surface can cause severe discoloration; this discoloration can be a variety of colors but is most often gray or black. However, this mildew growth does not degrade the wood; mildew fungi are not capable of using lignin, cellulose, or hemicellulose for food. Therefore, mildew does not decrease the structural integrity of the wood. They can, however, use the nonpolymeric materials in wood, such as the extractives and natural oils for food. Wood species that are rich in natural extractives may be more prone to mildew growth than wood species with lower extractive content. Since mildew spores infect all surfaces, their growth can be limited only by controlling moisture, temperature, or using paint film mildewcides.
If the surface is infected with mildew, it can be removed using a mildew cleaner, but it will return if the growth conditions remain the same. If wood is to be painted, it is beneficial to remove mildew before painting. This increases effectiveness of the paint film mildewcide.
Common Species
There are a variety of common mold species know to effect coatings performance. A list of 19 of the most common species appears below:
Alternaria sp., Aspergillus flavum, Aspergillus niger, Aureobasidium pullulans, Botryodiplodia sp., Cephalosporium sp., Cladosporium sp., Fusarium sp., Helminthsporium sp., Monilia sp., Mucor sp., Pacacilomyces sp., Penicilium sp., Pestalotia sp., Phoma sp., Pleospora sp., Rhizopus sp., Stemphylium sp., Trichoderma sp.
Of these species, Aureobasidium pullulans and Aspergillus Niger are the most common mold species encountered.
Necessary Contributing Factors
Substrate & Environment
Regardless of specific species, all mildew require oxygen, water, a food source, and a narrow temperature range to metabolize and reproduce. Typically, mildew causes problems with the finish after it has been applied and dried, and does not affect the product in the can as there is usually insufficient oxygen present for metabolism. Mildew needs water to grow. Consequently, as the humidity of the environment continues to rise, the mildew flourishes. For food, mildew generally metabolize organic food sources like starches, sugars, proteins, and some oils found in paint systems. Specifically, mildew can also feed on pollens, bacteria, or many other organic contaminants on the finished surface. Temperatures from 70 to 90 Fahrenheit to 20 to 30 Celsius are ideal for mildew growth. Below freezing, mildew fungi become dormant, however, they do not die.
Paint film
Other factors that can also contribute to mildew growth include the type of finish and its surface characteristics. Generally, top quality paints offer the best protection from mildew. As the quality of the paint decreases, the chance for mildew growth typically increases (a further discussion will follow under Mildew Control). Generally, latex finishes are more mildew resistant than alkyd paints.
Geographically Prone Areas
Mildew growth can occur anywhere in the world. Climates that supply more of the contributing factors discussed above will promote greater mildew growth. For example, hot, tropical regions often have the greatest mildew growth. Coastal regions generally grow more mildew than dry inland areas. However, inland areas near lakes, rivers, or heavy vegetation can experience heavy mildew growth.
