13 Dec What about mold?
Three conditions must be met to have mold:
- A food source
- Fungal spores
- Moisture
Food for mold is everywhere- plants, plant debris, wood, fabric, paint, paper- anything with carbon and hydrogen. Mold spores are part of the dust that settles on everything. Because of this, the key growth condition for getting mold is moisture. Some molds can grow when the air moisture or humidity near their place of residence reaches 70%. Other molds require up to 90% local humidity and this takes actual liquid water.
This liquid water can be provided by:
- Condensation
- Water Leaks
- Rising Damp
Condensation
The percentage relative humidity or RH is the ratio of the amount of moisture in the air to the amount of moisture the air can hold at its current temperature. If the air temperature decreases the relative humidity increases. Water vapor from the air condenses on a surface when the surface temperature has decreased to the dew point air temperature (DP). This is what happens on the inside of a windowpane when it’s cold outside. This why we see dew on the grass some mornings. The heavier the dew, the lower the surface temperature of the blades of grass.
The DP air temperature is the temperature at which the relative humidity of the air reaches 100% and no more water vapor can be held by the air. When that happens the water begins to condense on the cold surface. Note that the DP temperature is a function of the air moisture content. The more moisture the air holds, the higher the DP air temperature.
Sources of moisture in indoor air are:
- Human Activity
- Leaks
- Rising Damp
- High Outside Humidity
Leaking Water
Leaks can be from outside water entering through structural defects such as roof problems, flashing defects and siding gaps. Flashing is used around windows and doors and where the roof meets vertical walls. The purpose of flashing is to guide outdoor water harmlessly away from the structure. Leaks can be from the inside of the house from waste water lines, pressurized water supply lines or from water consuming appliances. The most insidious leaks are slow leaks that wet materials inside walls, but are not active enough to be seen inside the house.
Rising Damp
Rising damp describes water movement through porous materials via capillary action. Capillary action occurs when the space the water passes through is small enough that the normal surface tension of water propels the water through the space even vertically against the force of gravity. The tendency of water to move via capillary action can be seen by looking closely at the surface of water in a glass. Where the water meets the glass, the water is beginning to creep up the side of the glass forming an area called the meniscus, the curved upper surface of a column of liquid.
The concrete slab upon which many homes are built is the most common source of rising damp. Slabs should be poured on material that provides a capillary break like crushed rock. When that is not done correctly, ground water moves up through the soil into the concrete slab and up into the house. This increases air moisture content and increases the temperature at which condensation occurs.
Even in situations where the capillary break is present, excessive watering, poor grading and lack of rain gutters can so wet the earth near the edges of the slab that rising damp still becomes a problem around the outside perimeter of the house. Floor areas with rising damp have elevated moisture levels in the air which increases the dew point temperature to a point that condensation is a frequent occurrence. Moldy carpeting in perimeter areas of a slab on grade house indicates a rising damp problem.
Mold Spores are Everywhere
Even if your house has no mold growth, indoor air and all surface dusts contain mold spores because spores come from outside. Outside mold grows naturally prevents the surface from being permanent covered by leaf litter. The levels and types of fungi inside a home depends on what’s outdoors. If a home has moisture problems causing fungal growth, the indoor quantity and species of fungi will be different than the outside and will show fungi found on water-damaged materials. In order to make this comparison air samples are taken inside and outside in order to provide enough information to help confirm or deny active inside mold growth.
Testing for Presence of Mold
Testing to determine if active mold growth is occurring in a building can be done in numerous way.
The most prevalent testing methods are:
- Air samples are collected and the spores are visually identified to the Genus level, one level short of species. This is quick and inexpensiv.e
- Air samples are collected and the spores are grown. Resultant growth is used to identify mold species. This is time consuming and expensive.
- Dust sample are collected and evaluated by ERMI, the EPA developed Environmental Relative Moldiness Index. This method checks for 36 selected mold species using Polymerase Chain Reaction which identifies the presence of the mold species by its DNA. No variability, more accurate the 1 0r 2.
- Air samples are collected which are evaluated for presence of microbial volatile organic compounds (MVOC) indicating active mold growth.
- Surface samples are collected on sticky tape and evaluated by a lab as to identity, number and sometimes growth fragments.
- Dust samples are collected and evaluated for mycotoxins sometimes made by about 200 out of 200,000 species.
Testing Cost and Handling Built-in Variation in Sampling
Everything in our world has built in random variation. The supply of mold spores varies with air current, time of day and even season. The collection rate of sampling equipment has variation. The lab that studies the sample has slight variations in measurement techniques. The science of statistics deals with the estimating what’s occurring in the real world despite the variations in what’s being measured.
What does this mean so far as determining if an inside space is free of active mold growth? So far as methods 1 and 2 are concerned, it means that more than one sample must be taken at each location. Being conscious of cost to the client, yet desiring somewhat reliable data, the minimum number of samples is three per location- inside and outside. With this minimum number of samples, the level of spores inside has to be at least five times the level outside to state with some assurance that there is active inside mold growth. As more samples are taken per location, the multiplier drops below five, but the cost to the client increases. On the other hand, use of ERMI requires only one composite sample of the entire house to determine the level of risk that there is inside mold growth. But use of a composite does not allow pinpointing the areas in the house where mold is growing. So if there is a problem, additional testing using method 1 is required.
Testing is Secondary
Sampling for mold is often talked about, but is really a secondary consideration. Often testing is not even needed to determine is mold growth is a problem and where the moisture is coming from that is causing the problem. Building history, client observations and expert inspection and measurement of moisture in materials should be the combined if needed with sampling and lab testing to determine if there is active mold growth in the building. In this field experience counts for a lot. Anyone can collect samples, but few have the experience and persistence needed to see what needs to be seen and integrate all the information gathered to draw an informed conclusion.
Toxic Mold
“Toxic mold” is a meaningless term, used by the poorly informed. It is probable that virtually all mold spores have the potential for causing allergic response depending on the individual and the level of exposure. Additionally, a limited number of molds make mycotoxins. Most mycotoxins are poisonous, however, some like Penicillin and Cyclosporin are medically beneficial. Mycotoxin is not always produced and production occurs under poorly understood conditions. Sensitivities to mycotoxins probably vary widely.
Individual Response Varies
Individual allergic response to mold spores has been scientifically demonstrated. Individual trigger points are variable. The amount of an allergen needed to elicit a serious response in a sensitive individual could be thousands of times lower than that needed to invoke so much as a sniffle in an equally healthy, but non-sensitized person.
Exposure Standards
Because of the differences in individual susceptibility, no mold exposure standards exist. There is little understanding of why people in an obviously mold infested house suffer health problem, whereas, most people outdoors in relatively humid climates with very high spore counts do not have similar health problems.
There is controversy over the role mold plays in indoor problems. Because of a lack of research, evidence against mold is primarily based on observation. Unfortunately, for some people years of scientific observation is not proof enough. It seem reasonable, but it is not proven that indoor health problems are probably caused by the accumulation of spores, microbial volatile organic compounds (MVOC) and sometime mycotoxins.
The Best Defense is a Good Offense
Since spores are everywhere, the best defense against mold growth is a dry house. Find and stop causes of condensation, leaks and rising damp. Dry out wet materials within 36 hours before spores sprout and rapid mold growth begins. Discard anything that can’t be dried out in this time. This usually means that wet drywall, carpet pad and upholstered furniture must go. Do this and you only have to deal with a water problem, not a mold problem.
Who to rely on?
It is best to get an expert, independent inspector to determine if there is a mold problem, the extent of the problem, and how the problem should be remediated. The person doing this should not be connected to the company that will do the remediation. Since there are many over night wonders in the mold business, look for length of experience and recognized certification. Check references.
Worthwhile certifications are from: