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Mold Remediation: What's Involved

Updated: Jan 2, 2019


The three essential ingredients needed for Mold to grow are present in every home. Each ingredient has a remarkable shelf life, sometimes as old as the house itself, often in place years in advance. The common, conventional materials used to build homes have all the components needed to start incubating mold at a moments notice. With this in mind, mold growth is almost as common as the homes we live in. It only takes very small variations in the recipe to make a big difference in how the mold will manifest itself from being a small patch of benign Penicillium camemberti on your cheese, to something that could cost you thousands if it is wide spread Stachybotrys.

As long as the ingredients to prepare mold are kept dry, they will be stable practically forever. But, add water and maintain the right temperature for the proper length of time and the results may be harmful.

Recipe for Mold


The ingredients for mold are common to every home. The mixed cellulose is common in a wide variety of wood and paper products used to construct homes. The mold spore starter is floating in the air and supplied by nature. It will normally already be present at levels between 50 to 100 spores per square inch all over the home. No matter how clean the home is kept, there will be enough Mold Spore Starter present to result in a robust stew sufficient to take advantage of any damp area.

Variations in Mold

Once the water has been added there is a 24 to 48 hour lag period where the Mold Spore Starter and the materials in the home will absorb the water. If this isn't interrupted by drying, the molds will germinate and begin fermenting. Acids and enzymes are released. These begin to digest the cellulose materials. The incubating mixture will first begin to consume predigested cellulose such as paper and cardboard. This is followed by the deterioration of engineered wood such as particle board and oriented strand board. The water causes these manufactured materials to swell and begin to fall apart so the mold can access and grow on greater amounts of surface area. Solid woods take the longest amount of time to be adversely affected by mold. Materials like concrete, masonry, metal and glass or ceramic don't support growth at all (but can allow established mold growth to transfer onto them from adjacent materials.) At colder temperatures the spawning mixture takes longer to reach maturity. The warmer the temperature the greater the diversity and complexity of the organisms that develop. Each of the different types of mold spores that are present in homes have different types of ideal conditions that favor growth. Some molds develop best with minimal amounts of moisture such as would be present from high humidity. Other types of molds prefer long-term chronic moisture that requires weeks or months.

How to Limit Mold Growth

One of the strategies for limiting the amount of mold that grows after a hurricane or other catastrophic event is to quickly remove the nutrient rich building materials (gypsum wall board, insulation, carpet) to allow the less susceptible materials like wood, concrete, and masonry to have air circulation. Air movement can retard mold growth by cooling and drying the materials through evaporation. Depending on the humidity levels, this will have varying degrees of success.

A relative humidity of 40% or less, coupled with air movement, can make an ideal drying environment and keep mold from growing. Unfortunately, hurricanes occur in the warm humid months which leads to mold continuing to grow after the initial crisis has passed. At humidity levels over 60% materials dry very slowly, or not at all. Properly functioning air conditioners (check the condensation pan and drain line to be sure the water is being discharged outside the home) can help dehumidify and dry a building, but usually not quickly enough to remove the massive amount of excess moisture that is present in a hurricane damaged building.

Drying a building using outdoor air is a huge balancing act that at times of high humidity can be counter productive. If you bring in large amounts of air from the outside when it is wetter outside than inside then the drying slows or sometimes causes the building to get wetter. If you close up the building to prevent excess humidity from entering you may end up with the indoor humidity level climbing to a point where it is wetter inside than outside. This moving target is further complicated by the daily temperature difference between night and day.

If you have a certified professional drying company, they will attempt to create a balanced drying environment using dehumidification equipment and air movement to bring your home back into a controlled condition where the air conditioner can maintain the dry conditions inside the building so that it can be made ready for reconstruction.

Here are the general steps for mold remediation after a flood:

  1. It is important that you are adequately protected. Mold spore levels have been reported to reach 10 to 1000 times the normal levels during remediation. (See my post on respiratory protection). Also wear latex, polyethylene or nitrile disposable gloves with a second heavy duty glove on top. The thin inner glove protects the skin against contact with the mold and the heavy duty outer glove keeps the inner glove from being damaged. Disposable or washable coveralls with foot and head protection are also important.

  2. Evaluate first. Where are the areas of visible growth on materials in your home?

  3. Assuming that all the porous building materials that got wet with flood water have been removed, are there areas of mold growth that have been exposed on semi-porous or non-porous materials so that the growth is visible?

  4. Are there areas that got wet due to capillary action pulling moisture into hidden spaces? These areas should have also had the gypsum board and insulation removed.

  5. At a minimum the baseboard in areas that don't appear to have gotten wet should be removed to permit inspection behind them. If there is any evidence of silt, water or mold growth then the gypsum board behind the baseboard should be removed in logical increments. Some baseboards are now being made of recycled plastic. Since plastic is impermeable this increases the risk of moisture accumulating resulting in mold growth in areas outside of where the flood water flowed.

  6. A logical height for removing gypsum would generally be a minimum of two feet up although it is generally quicker and easier to remove at the joint between the sheets of horizontally installed gypsum which will generally be at 4 feet up. These heights or distances help insure you go far enough and don't leave mold that has not yet reached a density where it is visible. It also makes re-installation of new gypsum board easier since you won't have to do extensive trimming of the new pieces to fit. Make sure the home is dry so you don't put the new materials in too soon!

  7. Remove all built-in cabinets and other surface covers from any area that may have primary or secondary moisture accumulation. Leaving these in place prevents a thorough inspection behind the fixture. Lower cabinets that were flooded will almost always have silt, mold and bacteria contamination behind them. Upper cabinets will depend on how high the water rose from the flood and from capillary action as well as how long they stayed wet. If there is more than minor evidence of secondary damage or visible mold growth they should be removed for disposal to allow the damaged wall board and insulation behind them to be removed and discarded. Even if there is no apparent damage to the cabinet - it should still be detail cleaned - (which will be a topic of a future post in the next few days)

  8. Based on the locations with visible growth are there areas built of similar materials that got wet or damp where mold is likely to be present?

  9. In some cases you may discover areas of pre-existing mold growth from a leaky pipe or other damage that occurred prior to the flooding. This growth should also be removed.

  10. After catastrophic flooding where the entire home is involved, using containment is generally not helpful or necessary. If there is an upstairs or other area that stayed dry, it may make sense to isolate those areas with a separation of polyethylene plastic. It is important that this containment barrier not be installed over wet materials, which will trap moisture and slow or stop them from drying. Also keep the air circulation and drying going in the areas that didn't get wet to prevent water vapor from migrating into those materials.

  11. If you have a box fan, you can seal it to a window so it is exhausting to the outside. This will help exhaust excess mold spores that are released to the outside instead of having them move into less contaminated parts of your home. Professional mold remediation companies will use a HEPA filtered air filtration device to exhaust the air to the outside. In an emergency where you don't have the professionals and their equipment available, the use of a box fan will help, but try to exhaust it in a direction where the air won't be sucked back into your home or into a neighbors home. Outdoor air does a great job of diluting the contaminated air. Ideally the contaminated air would be exhausted through duct-work up above the roof line of your home where it will disipate and be diluted. You may be able to use duct tape and disposable flex duct to construct a make shift exhaust vent. If you don't have new duct you may be able to scavenge used duct-work that is being discarded from a damaged HVAC system to create a make shift exhaust.

  12. In order for there to be a flow of contaminated air to the outside through the fan, you will need "make up air". This is clean fresh air that is allowed to come into the contaminated area to create cross ventilation. The amount of air coming in should be just a little less than the amount of air being blown out through the box fan. This will maintain a negative pressure inside the work area but allow enough fresh outdoor air to come it to help control the contaminants and continue the drying.

  13. Once all the mold growth has been discarded by removing the mold contaminated porous materials, the framing and other materials that have visible growth remaining should have an aggressive cleaning to remove that mold. This is generally done by wire brushing or sanding while HEPA vacuuming. You don't have to remove all the water staining, just the surface growth. There are some that suggest using biocides to kill the mold for this step. It is my opinion that biocides don't help. You are just adding more water to the home. Even if the mold is killed the EPA tells us that dead mold is still allergenic and some dead molds are toxic. Use biocides for the final disinfection of surfaces where flood caused bacterial contamination, but not for mold.

  14. If you don't have a HEPA vacuum cleaner, the vacuuming can be done by placing a shop vacuum cleaner outside or running an exhaust duct from the vacuum cleaner to the outside. This way the mold that gets through the bag will be exhausted to the outside.

  15. The aggressive cleaning can be done while the materials are slightly damp, but the final cleaning needs to wait until everything is completely dry.

The information in this post is for catastrophic flooding situations. Homes that have had lesser water intrusion events that result in mold growth generally require greater amounts of containment and controls to keep the contaminants isolated to the area where the growth has occurred. In catastrophic flooding when virtually everything is involved, the entire home can generally be treated as one giant work area.

Just three simple ingredients are all it takes. Sadly, growing mold in homes that have been built using current construction methods is quite easy. Unfortunately, some homes may have developed multiple pre-existing problems over many years. After a catastrophe is a difficult time to have to recover from the flooding and hurricane damage, but fortunately a little extra time and work now can avoid extra headaches later. If care isn't taken while the wall cavities are opened up and accessible you won't have the option of easily addressing them later once everything is reconstructed.

The next post will provide more information about monitoring the temperature and humidity in the air to make drying decisions. Please make sure to check back for this information.

Edit: Checklist for Drying your Home is posted.

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