Tape Lifts, Swabs, and Bulk Samples: How to Choose the Right Surface Sampling Method

When collecting surface samples for mold testing, not all sampling methods are created equal. Each method has specific strengths and limitations, and you may choose differently depending on your priorities and the conditions on site.

The most common options for surface sampling are:

• Bulk sampling
• Tape lifts
• Wet swabs
• Dry swabs

Below is a practical guide to when Moldlab recommends each method—and when we recommend avoiding one altogether. The suggestions provided below correlate with our in lab operating procedures and may not be applicable to other laboratories. Please consult your own lab for guidance on best practices for surface sampling.

Quick Summary: Which Method Should You Use?

• Tape Lifts – Best for dry surfaces that are easy to reach
• Dry Swabs – Best for wet surfaces and tight or hard-to-reach areas
• Bulk Sampling – Best when you’re unsure which exact spot to test and destructive sampling is acceptable
• Wet Swabs – Not recommended for mold spore quantification

Bulk Sampling

What it is:
Bulk sampling involves collecting a piece of the suspect material (for example, a piece of drywall, carpet, or insulation) and submitting that piece to the lab for analysis.

Key considerations:

• Destructive method: Because you are removing part of the material, bulk sampling will damage the surface. It should only be used when the property owner or client is comfortable with destructive sampling.
• Suitable materials: Works well for most materials that can be cut, broken, or removed in small pieces.
• Good for quantitative analysis: Bulk samples preserve the amount of mold on the surface very well. Little material is lost in preparation, so they are appropriate for quantitative analysis (Test Code 9 or 10), where your report lists the exact number of spores identified under the microscope.

How the lab handles it:
When Moldlab prepares a bulk sample for analysis, our technician selects the most suspicious portion of the material to mount on the microscope slide. This:

• Can make bulk results more variable than some other methods, because the result depends on which part is chosen
• Also shifts the responsibility of selecting the “worst area” from you to the lab

Size limits:
Bulk samples cannot be larger than 6” x 6”.

Use bulk sampling when you:

• Are comfortable with minor damage to the material
• Want quantitative results
• Are not sure exactly which small spot to sample and prefer the lab to select the most suspicious area from the material you submit

Tape Lift Sampling

What it is:
Tape lift sampling involves gently pressing a piece of clear adhesive tape against a surface to collect visible or suspected mold growth.

Key considerations:

• Potential for minor damage: Tape lifts can sometimes pull off delicate finishes such as paint. While this damage is usually less significant than bulk sampling, it should still be considered, especially on sensitive surfaces.
• Excellent for quantitative analysis: Tape lifts reflect the amount of mold present on the surface very accurately, making them equally appropriate as bulk samples for quantitative analysis (Test Code 9 or 10).
• More consistent results: If you use a small piece of tape (about ¾” wide by 2.5” or less), the entire tape can be prepared and examined by the lab. This full-prep approach improves consistency between samples—though it does mean you must choose the most suspicious location to sample.

Limitations:

• Not ideal on wet surfaces: Tape does not transfer material well from wet surfaces.
• Challenging in tight spaces or long reaches: It can be difficult to use tape lifts in corners, behind obstacles, or when you need extended reach.
• Too much debris can obscure the sample: Sometimes tape lifts pick up large amounts of non-fungal debris, which can make it harder for analysts to see and identify mold.

Field tip:
After collection, you can visually confirm whether the tape has captured the right amount of material:

• The suspiciously colored area should be clearly visible on the tape
• There should not be thick clumps or heavy layers of surface material obscuring the tape

Use tape lifts when you:

• Are sampling dry, accessible surfaces
• Want quantitative results
• Can visually identify specific areas of concern and select the most suspicious spot

Wet Swab Sampling (Not Recommended)

What it is:
Wet swab sampling uses a synthetic-fiber swab moistened in a liquid, then run over a defined area (for example, a 10 cm x 10 cm square).

Theoretical advantages:

• The liquid can help collect material from both dry and wet surfaces
• Certain liquids can help inhibit bacterial growth between collection and analysis

Why we do not recommend wet swabs for mold quantification:

While wet swabs can collect material, the analysis method Moldlab uses cannot consistently and efficiently transfer all the collected material from the wet swab to the microscope slide. As a result:

• Significant amounts of fungal material are left behind on the swab
• The reported mold levels are consistently lower than expected

This means wet swabs tend to underestimate actual mold loading, making them unreliable for quantitative analysis.

In most surface sampling scenarios where you might consider a wet swab, a dry swab or tape lift will provide more reliable and interpretable results.

Dry Swab Sampling

What it is:
Dry swab sampling uses a synthetic-fiber swab (without added liquid), run over a defined suspicious area (for example, 10 cm²).

Key advantages:

• Non-destructive: Dry swabs do not damage the sampled surface.
• Excellent for tight or irregular areas: They are ideal for small, uneven, or hard-to-reach spaces where tape or bulk sampling is difficult or impossible.
• Works well on wet surfaces: Dry swabs can collect material effectively from wet areas where tape lifts struggle.

Field tip:
To confirm that you’ve collected material:

• Visually inspect the swab
• The suspiciously colored material should be visible on the swab tip

In the lab:
At Moldlab, we transfer material from the swab onto the microscope slide for analysis. Because of this:

• You do not need to worry about collecting “too much” material on the swab—excess can be managed during slide preparation
• However, some fungal material remains on the swab after transfer

This leftover material means:

• Dry swabs should not be used for quantitative analysis (Test Code 9 or 10)
• Results from dry swabs are slightly more variable than tape lifts when comparing exact quantities

Use dry swabs when you:

• Are sampling wet surfaces
• Need to reach tight, irregular, or delicate areas where tape or bulk sampling isn’t practical
• Do not require strict quantitative data, but rather qualitative confirmation of mold presence and identification

Putting It All Together

Choosing the right surface sampling method depends on:

• Surface condition: Dry vs. wet
• Accessibility: Open vs. tight or hard to reach
• Tolerance for damage: Whether destructive sampling is acceptable
• Reporting needs: Qualitative identification vs. quantitative analysis (Test Code 9 or 10)

In general:

• Choose tape lifts for dry, accessible surfaces when you need quantitative results.
• Choose dry swabs for wet surfaces and tight or complex areas, especially when you primarily need qualitative confirmation.
• Choose bulk samples when destructive sampling is acceptable and you want quantitative data but are unsure exactly which small spot to test.
• Avoid wet swabs when accurate mold quantification is important.

If you’re unsure which method is best for a particular site condition, you can always contact Moldlab for guidance. We’re happy to help you match the sampling method to your inspection goals so you get clear, defensible results from every sample.