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Mold on concrete

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Concrete surfaces are typically not associated with mold growth.  However, if the conditions are right, significant mold growth and staining can occur.

Causes of concrete mold growth.

Mold growing on painted concrete wall
  • Mold growth requires both available moisture and a food source.  On it's own, concrete does not provide a sufficient food source for fungal growth. Unfortunately this is not especially helpful, because like almost anywhere in a building, dust quickly accumulates on the surface.  Within this layer of dust large quantities of food sources for mold are present.  Therefore, unless the concrete is kept extremely clean, mold growth can occur.
  • Of course, even if the concrete is covered in dust, mold will not grow without sufficient moisture.  In most situations, controlling the moisture, rather than the dust, is far more desirable.  This includes tackling both airborne moisture (lowering the humidity) and liquid moisture (flooding, vapor drive).

How is mold removed from concrete?

  • Thankfully, because of the extreme durability of concrete, removing mold growth is a relatively simple process.  The same setup procedures apply (containment, HEPA filtration, etc.) however, the concrete itself does not require removal and can be easily cleaned.  The removal process typically requires the use of both a fungicide and physical removal of the mold. The fungicide will deactivate and kill the mold spores, but staining and discoloration will likely remain.  This is often addressed with HEPA vacuuming, scrubbing, sandblasting, etc.  In large commercial settings, dry ice blasting is occasionally used to remove mold from concrete.  

What steps are necessary to prevent mold growth from reoccurring on concrete?

If the problem is related to liquid moisture:

If at all possible, resolve the exterior moisture issue.  This may be as simple as redirecting downspouts away from the affected area or sloping the ground away from the wall.  However, completely preventing moisture intrusion into the concrete often requires extensive projects such as excavating the adjacent soil and installing waterproofing and drainage.  This is quite expensive.  In an unfinished basement, the cost of such a project isn't typically worth the benefit.  The concrete can be kept dry from the inside with air movement and dehumidification.  However, you intend on furring out a concrete wall with a moisture problem, it must be permanently addressed. Otherwise, mold growth and rot will occur in the wall cavity. 

If the problem is due to airborne moisture:

Lower the relative humidity.  Concrete is a poor insulator and therefore can become quite cool during the winter months.  In a poorly ventilated basement, this can cause airborne moisture to condense on the surface and cause mold growth.  There are three ways to reduce the RH in the area. 

  1. Increase the temperature. The warmer the air in the room, the lower the RH.  Now remember, if the temperature of the room increases, but the temperature of the concrete wall remains the same, the problem will remain.  This is due to the dramatic increase in RH that occurs in the air immediately adjacent to the cold wall.  However, in a fairly mild climate, the increased temperature of the air will sufficiently increase the temperature of the wall to prevent condensation from occurring.  
  2. Improve the ventilation.  Assuming the condensation occurs during the winter months, bringing in fresh air from the outside will reduce the RH inside the building.  This is because warm air can hold much more moisture than warm air.  So if we bring wet cold air into the home through ventilation, and heat it up, the net level of humidity will drop.  It seems counter intuitive, but this can dramatically reduce the moisture load within the basement. 
  3. Dehumidify.  This isn't our first choice, but occasionally it is the only option. There are a couple of reasons I don't often recommend this technique.  First, dehumidification requires a significant amount of electricity.  Second, while it reduces the moisture in the air, it does nothing to improve the quality of the air.  Musty odors, chemical fumes, VOCs, etc. will all remain in place if dehumidification is used.  Alternatively, if the ventilation is improved, both the RH and the air quality will improve.


Recent Inspection Report regarding Mold on Concrete

Work #: 105031

Basement Flooding


  • RH: 80%  Temp: 56 deg F.  CO2 = 545 ppm   CO = 0 ppm
  • 15-18 inches of standing water was present throughout basement.
  • Virtually every surface (wood paneled walls, ceiling, subfloor joists, concrete etc…) was covered with mold growth.
  • All appliances were submerged and required removal.
  • Sump Pump was present but was not running due to the power being cut off to the home.
  • No ventilation to basement has trapped humidity and has allowed mold growth to occur on all surfaces.
  • Mold growth was observed behind all ceiling panels on car-decking subfloor and ceiling joists.


Mold on Basement Wall
  • CAUTION:  Power must NOT be restored to the home unless all water has been pumped out of the basement and a certified electrician has given approval to reconnect the power.  Client may need to perform a significant number of repairs prior to approval from electrician. 
  • All water must be pumped from basement prior to any remediation work commencing. 
  • Any persons entering into basement MUST be wearing full personal protective equipment including: a fit-tested half-mask with a minimum of P-100 filtration, eye protection, gloves, disposable coveralls, rubber boots with non-skid soles.
  • Recommend sealing entry door to basement from main level of home to establish a containment zone.  Ensure all in-floor penetrations are also sealed.  Client may use spray foam insulation to perform the air sealing.
  • Recommend sealing all air ducts to the upstairs to prevent cross contamiation.
  • All remediation must be conducted under negative pressure, HEPA air filtration to capture all airborne mold generated during the remediation process.
  • All furniture, appliances, wood paneling, ceiling tiles and any other non-structural item must be torn out and removed from basement.
  • Recommend removal of all three-dimensional mold growth from surfaces via HEPA vacuum, wire brush and/or hand sanding.
  • Some locations may be better suited to treatment using a two-stage chemical treatment.  (see below for details)
  • It is also highly recommended that all mold remediation also be carried out in accordance with Lead Safe practices due to the likelihood of lead based paints being present.
  • All remaining surfaces are to be dried completely before any rebuild work is considered.
  • Environix highly recommends the installation of a battery back-up system for the sump pump to ensure this type of flooding does not happen during power failures.
  • Recommend a final wet-mop and a thorough HEPA vacuuming of all surfaces after remediation has been completed to ensure that all mold spores have been removed from surfaces.
  • Once all remediation has been completed, it is highly recommended that indoor air quality clearance testing be conducted prior to the home being re-occupied.
  • Please refer to the New York City Department of Health Guidelines for additional information regarding mold removal protocols and techniques.
  • Recommend installing a Panasonic Whisper Green® ventilation fan in basement to assist in evacuating the relative humidity from inside the building.  Whisper Green ventilation fans operate consistently at a low volume (30 cfm) and automatically ramp up to a higher volume (80 cfm) when a motion sensor is activated. An integrated timer will maintain the higher volume for a set period of time and then return the fan to the lower operating level until activated again.  

 Hall Bath 

Extent of Basment Flooding
  • Significant visible mold growth was noted on the ceiling of the bathroom.
  • Bathroom had a suspended ceiling which appears to have trapped water vapor and caused condensation to form.  This appears to be the source of the mold growth.
  • No ventilation fan was observed in bathroom.
  • Bottom of bathroom door was flaking paint and is likely a lead based paint hazard.


  • Recommend removal of visible mold growth under full containment and utilizing a negative pressure, HEPA air filtration system.
  • Personal protective equipment must be worn during any remediation work.
  • All mold remediation must be conducted using Lead Safe practices.
  •  Recommend removal of all three-dimensional mold growth from bathroom ceiling via HEPA vacuum.
  • Recommend a two stage, chemical treatment to bathroom ceiling to kill and encapsulate any remaining mold and/or staining.
  • Recommend installing a Panasonic Whisper Green® ventilation fan in bathroom to assist in evacuating the relative humidity from inside the building.  Whisper Green ventilation fans operate consistently at a low volume (30 cfm) and automatically ramp up to a higher volume (80 cfm) when a motion sensor is activated. An integrated timer will maintain the higher volume for a set period of time and then return the fan to the lower operating level until activated again.


Main Floor

  • Several locations were observed where paint was peeling from surfaces. 
  • Linoleum flooring in bedroom may be asbestos and should be tested.


  • Recommend having a full lead based paint and asbestos survey done prior to any remodel work being conducted.
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