Surface Sampling (Tape, Swab, or Bulk)
To determine whether the suspected surface (visible stain, discoloration, etc.) sampled is indicative of mold growth on the sample location.
To determine and identify molds actually growing on the surface sampled, as opposed to the mere presence of mold spores.
To determine whether there is a skewing in the normal distribution of spore types present on the surface, and also note for "marker" genera, which may indicate indoor mold growth.
Note: A direct microscopic examination that directly identifies fungal growth (and doesn't just count the number of spores) is usually the best method of analysis for surface samples. While culturing a surface sample may help resolve a specific identification problem, used alone such a culture may result in an inaccurate characterization of the surface sampled.
Advantages and Disadvantages
Surface sampling is inexpensive and (for a direct examination) may be analyzed immediately.
A direct microscopic examination of a surface shows exactly what is there.
Surface sampling may also reveal indoor reservoirs of spores that have not yet become airborne.
The presence of biological materials on a particular surface is not a direct indication of what may be in the air.
Health problems related to indoor microbial growth are generally caused by the inhalation of substantial numbers of airborne spores, sometimes over a substantial period of time (exceptions being, for example, situations involving small children or immuno-compromised individuals).
Surface sampling for direct microscopic examinations usually requires no special equipment.
Use a piece of absolutely clear (not frosted) tape that is one or two inches in length. Handle it by the ends only.
Position the adhesive side of the tape over the suspect area and press firmly, do not rub the tape back and forth.
Remove the tape from the surface and place it onto a clean microscope slide, then place the microscope slides into a slide box or other protective container. If microscope slides aren't available, tape the tape sample directly onto a plastic bag adhesive side down.
Do not fold the tape onto itself.
Remove a one or two square inch piece of the suspect material and place it inside a clean plastic bag.
Swabs are a last choice for when the sampling area is difficult to reach, a bulk sample is not practical, or the surface is very wet and a tape sample will not adhere to the area of concern.
Tapes and bulk samples do not require special consideration.
Swabs should be sent via overnight courier with a cold pack to retard growth during shipping.