The Value of Control Samples For Mold Testing and Sampling

Thursday, January 15, 2009 by Steven-Canter

You think there may be Black Mold or some other type of mold in your home? You have musty odors or a visual mold inspection has verified this concern. What’s next? The next step is to verify if in fact is it really mold and whether it is affecting the living area of your home. Are there mold spores in the occupied areas of the home? This will be verified by performing sampling of the air in the home as well as the exterior of home. The most common method is non-viable microbial samples collected in a cassette sampling device that are sent to an accredited laboratory for analysis. The samples gathered on the interior of homes--“suspect areas” and “non-suspect areas”--rely on a relative comparable mold sample of what is “normal air”. The most common “normal air” is likely around the exterior of the home, this is called the “Control Sample”. It will be compared to the interior occupied air sample(s) to see just how much more elevated conditions may be compared to our “Control Sample”, or our fresh air.

The “Control Samples” are the most valuable samples that are taken during the sampling process; as we make opinions based on the outcome of our fresh air relative to interior conditions.

How many of these Mold Samples should be taken? Conditions are very different around most homes and neighborhoods and between neighbors from side to side. They all have different things going on that may have adverse affects. There is great debate as to how many outdoor control samples should be taken.  Is one (1) sample enough? Answer = NO, it is not. One (1) sample only gives very limited source date with which to compare to.

Remember this sample is the one (1) the Laboratory and the IAQ Industry professionals us to form their opinions about indoor mold contamination.  Based on the findings for this one (1) sample it may or may not drastically affect the correction of your home as well as the cost to remedy it.

Finally, what do I recommend? With the many years of sampling homes and seeing the cost for having the complete information to make opinions from, I have to say the number of Exterior Control Samples is;

4--one from each side of the home is best,

2 is good or OK (This is as few as I will take during a project of mine)

1 is a waste of your money and everyone’s time.

The mold sampling needs to be performed by certified and trained professional at they will be able to properly perform the gathering of this sampling of air and direct you toward the correct remedial process required to bring you home back pre-loss condition.