How to Interpret a Mold Lab Report
What Does a Mold Laboratory Report Look Like?
A professional laboratory report documents:
Samples submitted
Sampling locations
Sampling and analysis methods
Mold types identified
Airborne spore concentrations
Surface-sample findings
Laboratory determinations and comments
Certificate of Mold Analysis. Select the image to view the full-size page.
What are the different types of samples used and why use one over another?
Surface Samples
Surface samples collect material directly from a specific area so the laboratory can determine whether mold growth or mold structures are present.
Swab Sample
A mold swab looks like a long Q-tip, but it is sterile and designed specifically for laboratory sampling.
The inspector rubs the sterile tip across a stained or suspicious surface. The swab is sealed and sent to the laboratory for microscopic analysis.
Tape-Lift Sample
A tape-lift sampler looks similar to a microscope slide with a clear, sticky collection area in the center.
The sticky section is pressed lightly against a surface. It collects mold structures, spores, dust, and other particles for microscopic analysis.
Tape lifts work well on dry, flat surfaces where suspected growth or settled material can be collected without scraping the surface.
What a Surface Sample Tells Us
A surface sample answers a focused question:
Was mold growth or mold material present on the specific surface tested?
It does not determine conditions throughout the room, inside a wall cavity, or elsewhere in the building.
Indoor Air Samples
An indoor air sample collects microscopic mold spores floating in the air inside a particular room.
A calibrated pump pulls a measured amount of air through a collection cassette. Spores and particles become trapped inside the cassette and are examined by the laboratory.
The laboratory reports the mold types found and their calculated concentrations in spores per cubic meter of air.
What an Air Sample Tells Us
An air sample identifies the types and concentrations of mold spores present in the sampled air during a brief period.
It allows indoor areas to be compared with:
Other rooms
Unaffected areas
An outdoor control sample
Air sampling provides a snapshot of conditions during the sampling period. Results may change with ventilation, weather, humidity, occupant activity, cleaning, and operation of heating or cooling equipment.
Outdoor Control (Air) Samples
An outdoor air sample establishes a baseline for comparison.
Mold spores occur naturally outdoors and enter homes through doors, windows, ventilation systems, clothing, pets, and normal air exchange.
The outdoor sample helps determine whether indoor findings resemble normal outdoor conditions or suggest a possible indoor source.
How to Read the Analysis Tables
This is where things can get a little confusing. We will attempt to explain the entire process, but it is easier to do this part in person when possible.
Each vertical section of the laboratory table represents a different sample.
Before looking at the numbers, identify:
The sample number
The sample location
Whether it was an air or surface sample
The laboratory determination
The mold types identified
The concentration or surface finding
The laboratory comments
A number without its sample location and sample type has little practical meaning.
Surface Samples and Outdoor Control
This page shows the surface-sample and outdoor air-sample results. The laboratory identifies each sample, its location, and its determination.
Indoor Air-Sample Results
This page shows the raw counts and calculated concentrations for each indoor air sample.
What Do the Report Terms Mean?
Raw Count
The actual number of spores observed and counted by the laboratory analyst.
Spores per Cubic Meter
The calculated concentration of airborne spores based on the raw count and the volume of air collected.
This calculation allows air samples to be compared.
Percentage of Total
The percentage contributed by each mold type to the sample’s total spore count.
A high percentage does not automatically mean a high concentration. One mold type may represent most of a sample simply because the total count is low.
Present
Mold structures or growth were observed in the surface sample.
No Growth
The laboratory did not observe active or former mold growth above its reporting criteria in that surface sample.
Normal
The laboratory found no meaningful indication from that air sample of abnormal indoor mold amplification.
Control
The outdoor or comparison sample used as the baseline for evaluating indoor results.
There Is No Universal “Safe Spore Count”
No federal pass-or-fail limit has been established for airborne mold-spore concentrations in homes.
Interpretation considers:
Indoor and outdoor concentrations
Mold types identified
Differences between rooms
Moisture and water-damage history
Visible building conditions
Sample locations
Building construction
Occupant concerns
A lower count may still matter if an unusual mold is found indoors or the inspection suggests concealed growth.
A higher count may sometimes reflect normal outdoor conditions.
The numbers must be interpreted in context.
"Normal Air Results" Do Not Rule Out Hidden Mold
Normal air-sample results do not prove that hidden mold is absent.
Mold may be growing inside a sealed wall or ceiling cavity without releasing enough spores into the occupied area to produce elevated air-sample results.
Drywall, vapor barriers, insulation, paint, trim, and other materials may temporarily isolate the cavity from the room.
A concealed cavity may contain:
Condensation
Saturated insulation
Wet framing or sheathing
Deteriorated building materials
Extensive mold growth
If the cavity is sealed and air cannot carry spores into the occupied space, the hidden growth may not appear in the air-testing results.
Opening or demolishing the cavity can release previously contained spores and fragments. Appropriate containment may therefore be necessary before exploratory removal begins.
Normal testing describes the sampled air and surfaces at the time of testing. It does not certify that every concealed building cavity is free of moisture or mold.
Part Two: The Inspection Report and Recommendations
Using the results from a mold test battery is only one part of the investigation..
The visual inspection, moisture meter readings, infrared scans and other inspection tools are used to provide additional information that is used to summarize your current situation by understanding what types of mold spores are in the house where they are located and how much there is to deal with.
All information collected from mold testing as well as a thorough site inspection is brought together in one final recommendation that will detail what the site conditions are, what the recommendations are for occupancy, and what the recommendations are to read the column if there is one.
Here's a fictitious example home which is being used to show you what you can expect from your mold inspection and testing survey.
Property Background
This sample property is a two-level home with a finished basement.
The homeowner reported:
Previous water entry around basement windows
A plumbing leak above the kitchen ceiling
Concern about possible concealed moisture and mold
The inspection focused on:
Kitchen ceiling below the former leak
Basement laundry-room window
Basement bedroom window
Attic near the access panel
The inspector documented visible conditions, checked accessible materials for moisture, prepared a property sketch, and selected sample locations based on the water-damage history.
Property Sketch
The sketch identifies the rooms, sample locations, and areas of concern.
Additional Inspection Photographs
Kitchen Ceiling
The ceiling had been opened following a plumbing leak. Temporary containment remained around the opening.
The accessible cavity was inspected for remaining moisture, staining, deterioration, and visible fungal growth.
Basement Laundry-Room Window
Minor water staining was visible around the laundry-room window near the washer.
These photographs document visible conditions. Photographs alone cannot determine whether a material contains mold.
Samples Collected at This Property
Sample location | Sample type | Laboratory determination |
Center kitchen ceiling behind containment | Swab | No growth |
Basement window near washer | Swab | No growth |
Basement bedroom window | Swab | No growth |
Basement bedroom | Air | Normal |
Attic near access panel | Air | Normal |
Kitchen | Air | Normal |
Outside | Air | Control |
Air-Sample Findings
Sample location | Total spores/m³ | Determination |
Basement bedroom | 420 | Normal |
Attic near access panel | 1,000 | Normal |
Kitchen | 640 | Normal |
Outdoor control | 5,600 | Control |
All three indoor samples were substantially lower than the outdoor control and were classified by the laboratory as normal.
The indoor samples were primarily composed of molds also present outdoors. The results did not show a strong pattern of airborne indoor mold amplification.
The three surface samples showed no mold growth on the exact materials sampled.
Inspection Findings
The testing results were reassuring, but the inspection still identified conditions requiring attention:
Moisture-related staining around the basement windows
Deterioration of materials below the windows
Evidence of previous water intrusion
An unfinished ceiling opening below the former plumbing leak
The possibility of concealed moisture around inaccessible window and wall assemblies
The normal laboratory findings do not eliminate the possibility of mold inside sealed cavities.
Possible Concealed Conditions Around the Windows
Water-damaged drywall or trim may need to be removed during repairs.
Once the wall is opened, the contractor could discover:
Condensation behind a polyethylene vapor barrier
Saturated insulation
Wet framing or sheathing
Mold growth inside the wall cavity
Materials requiring additional removal
A sealed wall cavity could contain substantial mold growth without producing elevated spore counts in the room.
If concealed moisture or mold is discovered, work should stop long enough to evaluate the newly exposed conditions. Containment, additional removal, cleaning, drying, or further testing may be needed before repairs continue.
Inspection Conclusions and Recommendations
The laboratory found normal indoor air results and no mold growth in the three surface samples. No evidence of widespread airborne mold amplification was identified.
However, the inspection found moisture-related conditions that should be corrected.
Kitchen Ceiling
Confirm that the plumbing leak has been permanently repaired.
Verify that the cavity and framing are dry.
Remove remaining debris.
Complete the ceiling repair after dry conditions are confirmed.
Reevaluate the area if concealed mold or wet materials are discovered.
Basement Windows
Correct drainage, flashing, caulking, or window-well defects contributing to water entry.
Carefully remove deteriorated porous materials where necessary.
Inspect the wall cavities as materials are removed.
Replace wet or damaged insulation.
Clean and dry sound remaining materials.
Use appropriate containment if concealed mold is discovered.
Monitor the windows during heavy rain and seasonal condensation.
Attic
Maintain adequate ventilation.
Monitor for roof leaks and condensation.
Correct future moisture sources promptly.
Improving Indoor Air Quality
Based on this inspection, the homeowner should focus on moisture control and building maintenance:
Repair water-entry points.
Keep indoor humidity controlled.
Use bathroom and kitchen exhaust fans.
Maintain the heating and cooling system.
Replace HVAC filters regularly.
Keep basement materials dry.
Correct leaks promptly.
Avoid closing wall or ceiling cavities until materials are dry.
Monitor repaired areas for recurring staining, odors, or deterioration.
The findings do not support broad mold demolition or whole-house remediation.
Additional investigation is recommended if new water intrusion, musty odors, visible growth, or concealed damage is discovered.
Master Certified Services provides independent mold inspection, testing, consultation, and laboratory-report interpretation. We do not perform mold remediation.
Kevin Buck, Master Certified Services of MN, LLC
Call or text: 218-464-8315
Information furnished by Master Certified Services of MN, LLC. Mold testing evaluates environmental conditions; it does not diagnose illness or guarantee that a building is safe for every individual.
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