Mold testing and inspection: when is it worth it?

Inspection and testing are different things

An inspection is a person looking: at surfaces, behind and under things, with a moisture meter and sometimes a thermal camera, to find where mold is growing and why. Most mold problems are solved at this stage.

Testing means taking samples, from the air or from a surface, and sending them to a laboratory to identify and count what is there.

An inspection answers “where is it and what caused it?” A test answers “what species, and how much is in the air?” The first question matters far more for deciding what to do.

When you do not need a test

Health Canada’s position is that any indoor mold should be removed and the moisture fixed, regardless of type, and that there is no exposure limit below which mold is considered safe. So if you can see it:

• Knowing the species does not change the plan
• A spore count does not change the plan
• The money is better spent on removal

When testing is useful

• A smell with no visible source. Air and cavity samples can help confirm hidden growth and narrow down where.
• After remediation. Clearance testing by an independent assessor confirms the work area is back to normal before walls are closed.
• Real estate. A buyer or seller may want documentation.
• Disputes. Between landlord and tenant, or with an insurer or builder.
• Health concerns. Where a doctor has asked for information about the home.

Types of test

Air sampling draws a measured volume of air through a cassette. Results are usually compared with an outdoor sample taken at the same time, because outdoor air always contains spores.

Surface sampling uses a swab or tape lift on visible growth to identify it.

Bulk sampling sends a piece of the material itself.

Home test kits that leave a dish open to the air are of little value. They will nearly always grow something, since spores are everywhere, and cannot tell you whether you have a problem.

The limits of air tests

An air sample is a snapshot. Results vary with the time of day, whether the furnace is running, and whether anyone has just walked through the room. A normal result does not prove there is no hidden mold, and a high one does not locate it. Results need interpreting by someone who has also inspected the building.

Why the tester should be independent

A company that both tests and remediates has an incentive to find a large problem and then to pass its own work. Using an assessor who does not do removal avoids that conflict. On larger jobs we recommend independent clearance for the same reason.

What a good inspection report contains

• Where moisture and mold were found, with photos and readings
• The likely cause
• The extent, including suspected hidden areas
• A recommended scope of work
• Any testing results, with interpretation

Questions to ask before you pay for testing

• What decision will the result change? If the answer is none, skip it.
• Will you inspect as well as sample? Samples without an inspection tell you little.
• How many samples, and why those locations? Each one should have a reason.
• Is an outdoor comparison sample included? Indoor air results mean little without one.
• Which laboratory analyses them? It should be an accredited lab, independent of the person selling the test.
• Will the report explain the results in plain language and say what to do next?
• Do you also do remediation? If so, consider whether you want the same company assessing the problem and profiting from the fix.

A sensible order of steps

1. Look and smell. Find where it is worst.
2. Check for moisture with a meter.
3. Fix any obvious leak or humidity problem.
4. Remove visible mold, yourself if it is small or professionally if not.
5. Test only if a question remains: a smell with no source, a dispute, or confirmation after a larger remediation.

More: mold removal and remediation.