Do-It-Yourself Mold Testing

Contact: EnviroHealth, 1009 Hemlock Circle, Manheim, PA 17545 – 888-735-9649, – May Dooley, MS, MA, CMC – Certified Microbial Consultant

What is Do-It-Yourself Mold Testing?

You do the investigations by using sticky tape sampling. You touch a 3″ piece of clear tape to the suspect surface and then mail it off to be looked at with a microscope. I can do that for a modest fee (see below), or you can contact a microbiological lab (for a not-so-modest fee).

The purpose of your sampling is to find the sources of mold growth (whether visible or invisible) that should be cleaned up in your home. Once you know where the sources are, you can determine what needs to be done to clean them up safely and effectively.

Question: What about the mold testing kits sold locally?

Response: I wouldn’t bother with them, for these reasons:

  • They are not known for their accuracy. You can get false negatives with them.
  • If it costs more to send them to a lab, hang on to them and see what develops. Don’t seal the cover, because the colonies need oxygen. Handle carefully. Put up high, away from children. Let grow a week or so. When finished with the plate, tape the cover on tightly and place in the regular trash.
  • They can be intimidating, with all the mold colonies that might grow. Ignore the black and white colonies. Count the green ones. If there are a lot of green ones, you may have a mold issue. If there are only a few green ones, who knows. Maybe more would be present with a better type of testing modality, or not.
  • The colonies that are black on both top and bottom typically are Cladosporium, the most common outdoor mold. Ignore them. They come in through doors, on shoes, etc. The white colonies typically are something called “sterile fungi.” They are little studied, do not produce spores, are ubiquitous, and may or may not be allergenic.
  • Even if lots of green colonies show up on the mold plate, you still have to find the sources of the mold growth, so you might as well start by looking for the sources and save your money on the home test kit.

TIP: Read through the remediation tabs before starting any removal, because mold can be dangerous to your health. You can make a bigger mess by improper remediation than you had when you started the project.

Do-it-yourself mold testing is ALWAYS a good first step, even if you plan to hire a local mold inspector.

Why? Because the local mold inspectors frequently miss sources of mold. The reason for this is simple: They don’t work with an on-site microscope. If you don’t fill in the gaps, it’s probable that no one else will. If you want a full mold inspection done at your home, you are going to have to step up to the plate. Period.

You and I, working together, can do a more in-depth job than most mold professionals. It will cost you a lot less, too. Why don’t mold professionals bring a microscope to the job? You’ll have to ask them that question. I’ve never been able to figure it out.

If they say that they aren’t “certified microbiological labs,” neither am I. That fact doesn’t stop me from using the best tool I have for a mold inspection. If mold is found, I show the homeowner on my computer monitor what it looks like. If independent third party confirmation is needed, a fresh sample is mailed off to a microbiological laboratory. You get the best of both worlds, the on-site workhorse microscope for immediate answers and the option for laboratory confirmation where needed.

This is not to detract from the talents and experience that many mold inspectors bring to the job…you just want a thorough job to be done. I understand that. You don’t want a satisfactory air sample report in the kitchen, only to have the inspector miss the active mold contamination inside the kitchen sink cabinet because the mold happens to be invisible to the naked eye and didn’t show up in the air sample. You get my drift?

No matter how good a local mold inspector is, the chances are high that he or she will miss mold growth if they don’t bring a microscope along to your home…either that or a crystal ball. Having a microscope isn’t a 100% guarantee of finding all sources of mold growth, but there’s a much better chance of identifying all sources than without a microscope.

Here are your choices for do-it-yourself mold testing:

  • Learn where mold might be hiding (see below). Take tape samples. Send the tape to me or to a certified microbiological laboratory to examine under a microscope and send you a report. With my service, you get pictures of your mold.
    • For legal purposes, you should have a lab report, though I do not know if my photo-documentation might be acceptable in a court. Check with an attorney. I think you’d be safer with a report from a certified lab, but then you’d probably have to have a local mold inspector also take the sample.
  • Or, procure your own microscope. I have posted instructions on using a microscope to check for mold. For a few dollars, I can send you some stain powder to use on the slides.

Here’s how to work with me:

  • At your home, look for damp areas and areas around plumbing. Mold needs food and water. Mold’s food is cellulose, i.e., wood and wood products (ceiling joists, subflooring, and sill plates), natural materials (such as wicker, upholstery fabric, unfinished wood surfaces of furniture, and the bottoms of recliners and box springs). See below for more details on where to test.
  • Get clear 3/4″ tape – store-brand Walgreen’s or Walmart transparent tape…not packing tape, Invisible Tape, Magic Tape, or Satin Tape.
  • Take a 3″ piece of tape. Hold the tape by the thumb and first finger of one hand. Press the middle of the tape to the surface you want to test. As long as there isn’t too much debris on the tape, touch several more spots on the same surface. Light from the microscope has to be able to penetrate through the debris, or all I will see under the microscope is a dark blob on the tape.
  • Fold one end of the tape back 1/4″ to make a small tab.
  • Place the tape sticky-side down onto a piece of plastic, such as a zip-lock bag – flat-out, like you were putting a band-aid on the bag. Do not fold the tape back on itself or make a loop of the tape. Do not use a baggie because sometimes the tape won’t separate from the thin plastic.
  • If there are multiple tapes, line them up one after the other on the bag. Number them and provide a key to their locations on a separate paper.
  • Put the bag and paper in an envelope and send regular mail to EnviroHealth, 1009 Hemlock Circle, Manheim, PA 17545. If sending overnight, please do not require a signature.
  • The fee is $15 for 1 sample, $25/3, $50/8, $100/20. Make your check out to “EnviroHealth.”
  • Turn-around time is typically a few days, depending on my schedule. If you are pressured time-wise, please call ahead, 888-735-9649.
  • Feedback will be in the form of emailed photos of your mold, so be sure to include an email address, plus your phone number.

Story: “Ida” learns how to take tape samples, but misses the part about where to test.

Ida saw spots of what look like black mold on her bathroom ceiling and on the diffuser (vent cover) of an air-conditioning duct. She was concerned whether mold might have spread throughout her home. With two small children, her concerns were heightened.

She found her way to my website,, and clicked on the drop-down tabs under the mold tab. Seeing “how to test,” she read the instructions and sent off her samples. She didn’t pay attention to the “where to test” tab, because she figured she knew where she wanted to test. After all, what she was looking at looked like mold.

According to the instructions, Ida got her tape from Walgreen’s. She was able to get their store-brand transparent tape, ¾” wide. When she got home, she gathered a piece of paper, pen, a small Ziploc bag, a step-stool, and her tape. The instructions said to take a 3-inch piece of tape, hold it by the two ends, and touch only the middle section to the surface she wanted to test.

The first-place she stopped was in the bathroom. She got up on the step-stool to reach the black discolorations on the ceiling. With one hand she held onto the step-stool, and with the other hand she held a 3 inch piece of tape with one hand, with one end of the tape on her thumb and the other end of the tape on her next finger. She pressed the tape firmly against one of the black spots.

When she held the tape up to the light, she could see some sort of black material on the tape. She suspected, probably correctly, that this black material was mold. Carefully she got down from the step-stool, bent back one end of the tape to make a little tab, and placed the tape on the outside of the small Ziploc bag. With her pen, she placed a #1 on the tape, and on her paper, she wrote in “1. Bathroom ceiling, black spots.”

Next, she proceeded to the air conditioning diffuser. She repeated this process with the tape, and again, upon holding the tape up to the light, she could see black material on it. This became sample #2. After making a small tap on one end of the tape, she carefully placed the tape sticky-side-down on the small Ziploc bag under tape #1 and marked on her paper, “2. AC diffuser.”

After doing that, she decided to check the bedrooms. Tape #3 was used to sample dust in her daughter’s room. Tape #4 was used to sample the walls in her son’s room. Tape #5 was used for the walls in the master bedroom. Tape #6 was used on the carpeting in her son’s room. Tape #7 was used on the carpeting in the basement playroom. And the last tape (8/$50) was used on her daughter’s favorite stuffed animal, a teddy bear.

Now she was ready to mail off the eight samples to me at EnviroHealth Consulting, Inc. She put the small Ziploc bag in an envelope, along with the key (list of sampled locations), and a check for $50 made out to EnviroHealth.

When I received the samples, I looked at them one by one under the microscope. A 3” piece of tape just about fits on a microscope slide. I put a drop of pink fuchsin stain on the microscope slide and smoothed out the tape over the liquid. The stain was absorbed by mold, making it easier to distinguish mold from debris.

I looked at the first slide from the bathroom, and as I expected, there was the black mold, Cladosporium. Cladosporium likes to grow in areas of condensation. In my experience, it is a fairly well behaved mold in these locations, i.e., it doesn’t become airborne that readily. Thus, cleaning it up is just a homeowner’s maintenance job. Just wipe it off with Borax or BonAmi sprinkled on a damp sponge. A dark stain may remain, which is the melanin that protects the mold from UV C. Spray with Concrobium Mold Stain Remover and then re-paint.

When Cladosporium grows on a bathroom ceiling, ventilation needs to be improved. If there is an exhaust fan, it needs to be used during or after showering.

Tip: Some exhaust fans are pretty ineffective. To check yours out, take two squares of toilet tissue and, standing on a step-stool, hold the squares right up to the exhaust fan. If the exhaust fan is so weak that it can’t even suck up two squares of toilet tissue, maybe it’s time for an upgrade of the exhaust fan.

Next I looked at the second tape from the air conditioning diffuser. Again as I suspected, the AC diffuser also had Cladosporium on it. Because of the mix of warm and cold air at the diffuser, condensation is common, and Cladosporium is common. Again, this is a homeowner’s maintenance job just to wipe off the diffuser. This localized mold has nothing to do with whether a system is or isn’t contaminated. That’s a separate issue in most cases.

Next, I examined the remaining six tapes, and all were negative. However, I was not comfortable with these negative readings. Ida had sampled six areas that would be far down my list for where to check. I questioned whether her remaining samples would deliver any useful information.

If you are taking of sending me samples to examine, first read through the “Where to Sample” tab. Be clear on what the first objective of sampling is: to find the sources of mold growth. Without knowing where the sources are, you won’t know where to clean. Finding the sources is really pretty much common sense. Again, mold grows around leak areas and in damp areas, so you look for areas with water, leakage, or higher relative humidity than other areas (such as basements and crawlspaces).

If I were sending in eight samples, here is where I would sample:

1. inside kitchen sink cabinet, lower rear where back meets base and in plumbing access holes
2, inside master bathroom sink cabinet, as above
3. inside bathroom sink cabinet, as above
4. Inside half-bath sink cabinet, as above
5. Deep inside an AC vent (after taking off the vent cover)
6. Ceiling joists and subflooring (the support for the first floor) in basement or crawlspace
7. Underside of bottom wood step in basement
8. Assorted contents in basement, such as unfinished wood surfaces of furniture, upholstered furniture, etc.

(Check the attic, too, for signs of discoloration or mold. Just pro-rate the amount for additional tapes.)

Here’s what to note about this list:

  • I’m checking for areas of plumbing leakage in sink cabinets.
  • If mold growth is found deep inside an AC vent, this would be a clue that there may be contamination in the ductwork. That’s what I’m looking for, not for Cladosporium on the diffuser.
  • I’m not checking walls. Most paint contains a mildewcide (pesticide) which protects against mold growth, except when wet for a prolonged time.
  • I’m not checking carpeting. Tape sampling isn’t that useful for routinely checking carpeting, although there are times when it can be. For example, low pile carpeting in a damp basement may reveal mold growth, or carpeting that had been wet at one time may reveal mold growth. But most carpeting is better checked by sending a vacuum cleaner dust sample to a microbiological lab.
  • I’m spending more than half my time checking in the basement, because below-grade areas are typically damper than upstairs. I want to find out if Aspergillus and/or Penicillium are growing under the basement steps and if they are growing on the ceiling joists and subflooring. The results from these samples will help me to gauge the risk for mold growth in the basement.
  • I also want to do a preliminary test on contents and storage in the basement.

I’ve reached my limit of eight tapes, but doing a few more could be helpful, such as testing more stored items, and doing more sampling at finished walls in the basement. Sometimes I can reach behind a finished wall from an unfinished area, and then I try to tape sample at the bottom of drywall and on lower studs and sill plate. Another approach is to wrap a 3 inch piece of tape around a blunt kitchen knife, and to try to slide the tape under base molding. If there is mold in the wall cavity, it will often show up under the base molding as well.

Tip: if I’m sampling ceiling joists and subflooring, I typically do one tape for each. I’ll touch that tape to multiple areas on ceiling joists, and the second tape to multiple areas on subflooring. This broadens my database of investigation. Again, I’m careful not to get too much debris on any one tape, because the light from the microscope won’t go through a lot of debris. If I’m sampling furniture, such as the underside of box springs, I could touch the tape to 10 spots. I’m not so much interested in quantifying the results. I can gain a sense of the amount of mold by noting whether there’s a little or a lot. A little or a lot – that’s what we need to know.

Also, if I am told that there had been previous leakage here or there, I will put more attention to those areas. If there was water leaking in a wall cavity, I’ll slide a kitchen knife with tape wrapped around it under the base molding, if there is room. If not, if I were onsite, I’d typically drill a 1/4″ hole and take an air sample in the wall cavity.

The microscope is my most important tool at an inspection, because the microscope helps me to find the sources of mold growth. High levels of mold can be present that are invisible to the naked eye. Once you know where the sources are, then you can figure out what to do to clean them up. If you don’t know where the sources are, you don’t know where to remediate.

Question: My house is in a damp location, and it smells musty inside.

Response: In that case, mold could be growing on vulnerable materials. In addition to the above suggestions, I would also do some tape sampling on upholstered furniture upstairs, the bottoms and backs of wood furniture (more accessible to mold growth than shiny, finished surfaces), the underside of box springs, under base molding at various locations, the underside of kitchen cabinet drawers, on clothing in a closet, etc.

Summary of where to test:

  • When tape-testing, concentrate on looking for sources of mold growth.
  • Sources of mold growth are more likely to be around plumbing, former leak areas, and below grade spaces (basements, crawlspaces, and lower levels of bi-level or split-level homes).
  • Touch the tape to multiple areas of the same, or similar, surfaces.
  • If you find black Cladosporium mold on bathroom ceilings, AC diffusers, windowsills, shower curtains, bathroom grout, just clean it up. It’s a homeowner’s maintenance task. The mold is most likely Cladosporium. If you feel more comfortable sending me the tape sample, send it. Peace of mind is worth something, too.

Question: What’s the difference between black Cladosporium mold and the “toxic black mold”?

Response: Cladosporium is the most common type of outdoor mold. It is also common indoors, especially in areas of condensation. Because its spores are not so readily released, it can be cleaned up easily by a homeowner. Stachybotrys is the so-called “toxic black mold.” It is a toxigenic mold, that is, it can produce virulent toxins that have even been used in germ warfare. Stachybotrys loves drywall that has been wet for a week or more, such as from a hidden plumbing leak. Stachybotrys should be remediated, which is a higher level of cleaning than you would do with Cladosporium on your refrigerator door gasket.

Now that you have an example of do-it-yourself mold testing and some guidance about how you can do your own tape-samples and send them off to me, let’s take a look at some of the issues with testing by a professional mold inspector.