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How to Test for Mold in Your House: A Complete Guide

mold growth

mold growth

There is no better detector of mold in a house than your own nose. Whether you can smell it yourself, or you or another house member begins to sneeze when they walk into a room, there may be a mold issue growing out of sight in a wall. Have no fear we’ll go over all the things you need to know about mold and your health, where to look for mold, how to help prevent mold, and of course, how to test for mold. Let’s dive right in.

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What Are the Hazards of Mold

According to the Centers for Disease Control and Prevention (CDC), the most common hazards for household molds affect those with allergies to the mold spores. The most common effects of mold are in the form of respiratory complications.

If you or a person in your household does not have a pre-existing respiratory condition such as asthma, then you should be fine with limited exposure. In fact, to some extent, we breathe in mold spores every day as we walk around outside. It is only when we are inside a confined area that their unique smell hits. That is not to say you should disregard the situation altogether. If left unchecked, the mold will continue to grow, and long term exposure can cause significant breathing issues.

Where to Look for Mold

Mold is a fungus that grows in dark, damp environments, so when looking around your house for potential mold hiding spots, begin in places like:

  • Behind the refrigerator
  • Under sinks
  • Under or behind the washer-machine
  • Around the baseboards, especially if heavy rains or recent water leaks have caused flooding
  • Attics or basements

These are places where mold will most commonly grow on the outside of the wall, making it visible and easy to locate and address. Keep in mind though, mold does not need light to germinate. So, any place with a moisture content (MC) over 20% is an area mold might grow.

Molds basement
Image Credit: Ken Mayer, Flickr

Some places in the house people often overlook are inside walls near:

  • An outside faucet
  • Water connections for a washer machine
  • The shower valve handles or showerhead

If no mold is visible and there is not yet a smell but you do have an allergic response to something, it might be wise to invest in a water content meter, also known as a moisture meter, from your local hardware or home improvement store. While they do not detect mold, they will detect wet spots inside the wall you may not see.

Something else you can do is to check your water meter to determine if you might have a leak. To do this, simply ensure all the water sources in your house are off, such as toilet water stops, faucets, and the water heater isn’t still filling from recent use. Then go out to your water meter, pull the cover, and look at your dial. There will be a large dial that keeps track of large quantity uses and a smaller dial off to one side. That smaller dial is what some plumbers call the leak detector. If it isn’t turning, you don’t have a leak; if it is, then you do, and a possible mold source.

How to Get Rid of Mold On Your Wall

If you do see mold on the outside of a wall, it is recommended to:

  • First, throw on some light personal protective equipment (PPE) such as some basic dishwashing rubber gloves, safety glasses, a mask covering your mouth and nose, and a long sleeve shirt and long pants.
  • Then, touch the wall; if it’s not soft to the touch, then the mold is superficial, and you can use a paint scraping tool to scrape some of the mold off.
  • Next, spray the molded area with a mixture of 1 part bleach to 2 parts water. Leave the windows open, so you don’t pass out from the fumes.
  • Let the area soak, then, using a bristle brush, scrub the area well until there is barely any sign of mold.
  • Next, using undiluted white vinegar, spray the area generously. This will kill any spores that might be deeper in the wall.
  • Lastly, let dry for a couple of hours at least, then touch up the paint as needed.
Removing Mold
Image Credit: Fevziie, Shutterstock

But what if it is soft to the touch? In that case, the drywall is saturated and needs to be replaced. To do this, put on the same PPE as mentioned above and:

  • Feel the wall, or use a water content meter, and determine where the drywall is completely dry in all directions. You should have a square or rectangular area.
  • Then, using a drywall saw, cut the area of the wall out. Be sure to cut all the way laterally to a stud on each side. Half of each stud should be free of drywall.
  • Now check the insulation on the inside of the wall; if it is wet, rip it out as well. You don’t want to be doing this again in 6 months.
  • With that done, measure your area and go buy enough insulation, drywall, drywall putty to cover, and drywall screws.
  • Fill the area between the studs with new insulation if necessary, then measure, and cut your drywall to fit. Using drywall screws and a drill, screw the drywall to the studs.
  • With the drywall putty, fill the gap between the new drywall and the old, let it dry for a few hours (or longer, depending on the instructions).
  • Finally, paint to match the existing wall.

How to Help Prevent Mold

Unfortunately, mold spores are pretty tough and resilient. After all, they have had several million years to evolve into an organism that survives where most other things die and are actually necessary to decomposition. That being said, we can mitigate them propagating inside our homes. The main thing to watch for is signs of wet spots; if you have a leak that saturates the drywall, be sure to remove all the wet or damp drywall around that area. Drywall patches generally come in 2′ x 2′ squares, so do not be shy about using a larger piece than you think is necessary.

If you have a severe storm that comes through, check your interior, outer perimeter walls, attic, and basements with a moisture meter a few days after the storm. Make sure you do not have a high moisture content lingering somewhere. Lastly, trust your senses — if you smell something odd or start sneezing in a room, check it out.

How to Test for Mold and What to Do When it’s Detected

Okay, now you have either smelled or seen mold in a room, had an allergic reaction, and/or found a spot holding moisture in the walls. Now what? Well, now it is time to test for mold spores themselves. The first thing you will want to do is either order or go to your local home improvement store and purchase a mold test kit. The ImmunoLytics DIY Mold Test Kit for Home is our favorite.

checking for molds
Image Credit: Andrey_Popov, Shutterstock

You’ll also want to grab:

  • Tape, electrical and painter’s
  • A marker/pen
  • At least 24 hours prior to testing, be sure to close all the doors and windows to the room. Drafts disturb mold spores, so doing this will allow the mold to consolidate.
  • Read the instructions in your kit; It should reference leaving a testing plate (like a Petri dish) open at about waist height in the room in question. The open end should be up to allow mold spores to settle on the inside of the plate, which has a unique “microbial culture” treated on the bottom. Normally the time frame is around 48 hours, but again, look at the instructions and follow the stated recommendations.
  • After the allotted time frame, place the cover back on the plate, seal it with electrical tape around the edge where the cover and plate meet.
  • Using the label provided in the test kit, or a piece of painter’s tape, write the day’s date and apply it to the plate’s underside.
  • Place your plate in a dark, cool place. Maybe a closet, a drawer, even a shoebox would work.
  • After about 48 hours, check your plate for mold. It will look like the mold you see growing on old bread or cheese that has been left in the refrigerator too long. If you do not see signs of mold, place it back in the dark spot and check it every 24 hours until it has been a week since the date you placed on the label. If there still is no mold, you’re clear!

If mold does appear, do not fret. You can place your sample in an envelope most test kits come with and send it to a lab recommended by the test kit. The lab will determine what type of mold it is and what the best course of action is for treatment. (There will be an additional charge for the lab work.)

It may take between 3-8 weeks in order for your tests to be returned. While you wait, you may want to repeat the process in other rooms in your house to determine the size of the contaminated area. This will also allow you to assess whether this will be a project you want to take on yourself or hire a company to do for you.

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Act Fast

Do not hesitate to act if you do find mold in your home. If allowed to go unchecked, it will continue to spread, seeking out new sources of moisture and darkness. We hope our guide has been useful in answering any questions that you may have had about household mold and how to test for it. Remember, it is not just a home but your castle; take care of it, and it will take care of you.


Featured Image: Fevziie, Shutterstock

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