Mold in homes can pose a persistent and even dangerous problem. Ultimately, professional testing needs to be undertaken to ascertain the presence of mold that might not be visually noticeable. In addition, professional testing is necessary to definitively identify the type or types of mold that might be present in a residence. This comprehensive overview of the mold collecting and sampling process aids you in understanding how the presence and type of mold are undertaken. You need to understand the type of mold present in your residence as a prelude to obtaining professional mold eradication services.

Preliminary Notes and Directives

Before diving into a comprehensive review of mold collection and sampling, a number of preliminary considerations need to be borne in mind. These begin with an understanding that the wheel is not reinvented every time mold collection and sampling occurs. The process itself begins with the utilization of the IAC2 Mold Sampling Decision Chart and the IAC2 Standards of Practice to ascertain precisely when as well as where samples need to be taken inside a residential building.

A sampling of the air needs to occur both inside and outside a residence. This is undertaken for comparison purposes. Two important factors must be borne in mind with regard to air samples:

  1. There should not be any mold found inside a residence that is not present outside the home.
  2. The recorded concentration of mold inside a residence should not be greater than the concentration outside the home.

Mold spores in sampled air can vary significantly in regard to a number of factors, including:

  • The life cycle of mold spores
  • Atmospheric conditions
  • Environmental conditions

Bear in mind that air sampling potentially becomes necessary if the presence of mold is suspected but cannot be visually identified. For example, mold may be present if there is a musty odor. The ultimate objective is to identify the location of mold contamination and the extent of that contamination.

The outdoor air sample is what science is known as the control sample. It is used to compare and contrast with indoor air. Thus, the outdoor (control) and indoor air samples need to be collected as close in time as possible as well as under similar prevailing circumstances. Examples of maintaining collection commonality include:

  • Samples collected at the same air-flow rate
  • Samples collected for the same time duration
  • Samples collected at the same level above the floor
  • Samples collected utilizing the same collection device

Three types of sampling will be utilized to make reliable determinations about mold contamination. These are:

  • Surface sampling
  • Indoor air sampling
  • Outdoor air sampling

Each of these sampling methodologies is discussed and analyzed in turn.

As mentioned a moment ago, maintaining a consistent air flow rate is crucial to sampling for mold contamination. There is an assortment of different measurement meters, air pumps, and spore collectors available for use in the mold inspection process. In using an air pump, the device needs to be adjusted to collect air at the specific flow rate recommended by the manufacturer.

Proper flow rate is crucial. If the air flow rate is too fast, the spores bounce off the collector plate and do not stick. If the air flow rate is too slow, the spores float around the collector place and do not stick.

The result obtained via an air pump sample is recorded in a calculation of spores per meter cubed or spores/m3.

Rotameters are defined as air flow meters designed to provide accuracy through an easy to read instrument. The operation of a rotameter is rather simple:

  • Air passes through a vertical, tapered tube
  • In doing so, the air pushes a float or small ball
  • The ball rises, increasing the clearance between the tube wall and the ball
  • The ball becomes stationary at the juncture when the diameter of the tube is large enough to allow total air flow past the ball
  • The flow rate can then be determined by reading the number on the tube at the middle position of the ball that has become stabilized    

Surface Sampling

Surface sampling is designed to achieve three objectives in regard to what appears to visible mold:

  • Confirms whether what appears to be mold is, in fact, the actual microbial growth
  • Measures the relative extent or degree of mold contamination
  • Confirms whether the microbial growth is producing airborne mold spores

Area of Concern

When an area of concern is identified, one surface sample is to be taken. Examples of what constitute areas of concern are:

  • Apparent mold growth
  • Moisture intrusion
  • Water damage
  • Musty Odors
  • General conditions conducive to mold contamination

•    Additional surface samples may be performed at the discretion of the inspector.

No Area of Concern

If no area of concern (as enumerated a moment ago) is identified, no sample need be taken.

Swab Sampling

A swab is one of two of the methods used to collect a surface sample to ascertain the presence of mold. A swab utilized in obtaining a surface sample comes protected in a container in the form of a plastic tube. The swab (made from cellulose) is moistened with a liquid preservative which is stored in an ampoule at the end of the storage tube.

The swab is used to take a surface sample from an area of concern. Once the area of concerned is swabbed, the swab itself is returned to the tube, which is immediately sealed. The tube containing the swab is then sent directly for analysis at a designated laboratory.

A unique sample number should be noted on the tube and in a register. The number should be written directly on the rube itself. There needs to an associated chain of custody documents that contain the following information:

  • Sample number
  • Location of swabbing
  • Date and time of sampling
  • Name of the person who took the sample

A swab establishes the presence of spores and delineates the specific types of fungi that are present in an area of concern if any.

Tape Sampling

Utilizing a tape system provides a rapid method to sample what appears to be a visible mold. Indeed, a tape system is the most common way of conducting a surface sample. The tape system allows for the efficient collection of samples in a short period of time.

The intent of this presentation is not to endorse a specific product. Nonetheless, noting the most widely used tape system is appropriate. The Bio-Tape system is the most widely used by inspectors. The Bio-Tape system tops the list for a number of reasons, including:

  • Individual tapes are easier to handle
  • Tapes are individually numbered
  • Slides are flexible and do not break

Tape sampling cannot make a quantitative analysis. Rather, it provides information about:

  • The presence of fungi
  • Identification of the mold genera
  • A possible rough estimation of the percentage of each individual genus

The methodology for using the tape system is relatively simple:

  • Remove the slide from the mailer
  • Record the sample number from the slide, together with any other identification information Prior to taking the sample
  • Peel the protective liner off the slide to expose the adhesive
  • Place the slide, sticky side down, onto the contaminated area
  • Press down gently
  • Lift the slide from the surface
  • Place back into the slide mailer
  • Do not replace the protective liner 
  • Record all information on the chain of custody document
  • Mail the sample to the laboratory

Carpet Sampling

The sampling of carpet for the presence of mold requires its own, unique process. Carpet has the potential for containing the history of any mold that has been present in the residence of a period of time. A carpet sampling may also reveal mold that was not detected elsewhere in the residence because it previously had been covered up or cleaned.

In doing a carpet sample select an area in a residence that has had little foot traffic. With that said, do not conduct the test on an area under furniture. The sample area should be 6 x 3”.

What is known as a carpet sampling cartridge is what is utilized together with a vacuum to collect a sample from an area of the carpet. The cartridge is inserted as deeply as possible into the pile of the carpet.

Personal Protective Equipment

When sampling for mold, the use of personal protective equipment is highly recommended. This is necessary because the sampling process can involve direct contact with mold. The recommended personal protective equipment, or PPE, is:

  • Gloves
  • Respirator (rated N-95 or higher)
  • Goggles or other protective eyewear
  • Smock, apron, uniform, or other clothing covering

Outdoor Air Sampling

Outdoor air sampling is an integral element of a comprehensive inspection and analysis for the presence of mold. An overview of the outdoor air sampling process provides insight into what is involved in this element of the mold inspection process.

Upon Arrival at the Inspection Site

The outdoor sampling should occur directly after arriving at the residence. It should precede the interior testing because weather conditions can change, even dramatically so, in a short period of time.

Prevailing Weather Conditions

Outdoor air sampling should not be conducted during severe weather conditions. High winds increase that variability of mold spore concentration, which throws off the test results. Rapid fluctuations in barometric pressure will also alter the spore count in a manner that impacts the accuracy of the final mold test results at a residence. In most cases, weather predictions provided by the National Service or even the local news prove adequate for determining whether conditions will be suitable for outdoor sampling.

Other weather conditions to bear in mind when it comes to performing an accurate outdoor air sampling are:

  • No rain
  • Above freezing
  • No snow covering

Outdoor Testing Process

The outdoor testing process should include taking two samples. These samples ultimately are used as the control samples for comparison with the samples that will be taken indoors.

The air pump sampling should run for a period of 10 minutes. One of the two samples should be taken on the windward side of a residence (the side of a house from which the wind blows). The second sample should be taken from the leeward side of a residence (the side of a house shielded from the wind). There should be nothing overhead the location at which a sample is taken.

A 10-feet rule should be followed for outdoor air sampling:

  • The sampling should be conducted 10 feet away from any ventilation intake equipment at a residence
  • The sampling should be conducted 10 feet away from any other types of air intakes, registers, vent pipes, exhaust fans, ventilation fans, other openings of any type
  • The sampling should be conducted 10 feet away from the most commonly utilized entrance into a residence

Indoor Air Sampling

Indoor air sampling is to be conducted under what is known as closed building conditions. In other words, a residence should be closed to outdoor air in advance of the sampling occurs. This is necessary to stabilize the air that might contain mold spores. Closed building conditions increase the reliability of the final test results.

The following conditions need to be considered when it comes to residential closed building conditions for the purposes of indoor sampling as part of testing for mold:

  • Windows and external doors should be kept closed during the sampling period. External doors can be opened very briefly for entry and exit into a residence.
  • External-internal air exchange systems should be turned off.

Location of Indoor Air Sampling

The air pump sampling should run for 10 minutes at all sampling locations in a residence. At least one air sample should be taken at a register to the HVAC system. At least one air sample should be conducted at an area of concern. This is an area in a residence that presents:

  • Moisture intrusion
  • Water damage
  • Musty Odors
  • Visible apparent mold growth
  • Other conditions conducive to mold growth

At least one air sample should be taken from an area in a residence for which there is no concern for the presence of mold.

Indoor Testing Process

The indoor testing process begins with the calibration of the air pump flow. The air pump flow is measured using the rotameter (a device which was discussed previously). Calibration should be undertaken at least once daily on an air pump.

Once calibrated, tubing is attached securely to the air pump, connecting it to the sampling device. Activate the air pump, paying attention to airflow consistency.

All air samples must be taken at the same volume. The sampling devices manufacturer provides guidance about sampling time and volume.

When the sampling process is completed and the air pump is stopped, a unique sampling number is assigned to the sampling device. In addition, necessary information is recorded on the chain of custody form.

The slides containing the collected sample is placed in a protective case. If a cassette collector is used, the collector is closed.

The calculation utilized regarding a sample is the volume multiplied by the liters of air pumped by the number of minutes. A sample calculation is illustrative:

Based on 20 liters of air pump multiplied by 10 minutes equals 20 liters per minute or 200 liters total. 20L x 10 minutes = 200L. 

Review of Limitations and Exclusions

There are specific limitations and exclusions that are associated with a professional mold inspection. A homeowner desiring professional mold inspection needs to understand these limitations and exclusions:

  • Mold inspection is not a guarantee, warranty, or insurance policy of any type
  • Mold inspection is not exhaustive from a technical standpoint
  • Mold inspection is not designed to identify latent or concealed defects or conditions
  • A mold inspection will not always identify growth that is not readily visible at the time of inspection
  • The scope of inspection does not encompass future mold growth

In addition, a mold inspector is not required to report certain elements, factors, findings:

  • The condition of a system that is not readily accessible
  • The condition of a system that is not in the IAC2 Standards of Practice
  • The service life expectancy of a system
  • The capacity, size, BTU, performance, or efficiency of a system
  • Code compliance
  • Compliance with installation guidelines
  • Presence of rodents or other animals, insects, or other pests


Professional mold inspection is not a foolproof process. Nonetheless, it is the best course to take to ascertain whether mold exists in your residence as well to identify the type of mold present in your home. When mold is identified in your home, immediate attention should be given to eradicate the growth to protect the residence itself and the health and wellbeing of those who reside in or visit a residence.