How to Spot & Deal with Black Mold Caused By Water Damage in Your Home

Black mold is a common outcome of water damage to your home following a leak. If everything is not dried out completely, mold can thrive and spread rapidly.

Mold flourishes in moisture and needs it to survive and reproduce, so keeping your home dry and moisture free will ensure mold has the minimum opportunity to ruin your day.

Black mold on the wall
Black mold on the wall (photo: pixabay)

But worst of all, black mold can cause and aggravate health problems, especially in members of your family who already suffer from respiratory health issues.

So, what is the low-down on black toxic mold?

Please read on, and all will be revealed.

What Exactly Is Black Mold?

Molds are fungi. They produce millions of microscopic bacteria found everywhere, inside and outside your home, and are impossible, in normal circumstances, to prevent. It is when they come in contact with moisture, they can become destructive.

They will grow and spread rapidly, often out of sight, as they don’t need sunlight to survive.

Water Leaks & Black Toxic Mold

Black toxic mold is one of several different species of mold; the specific type will vary depending on the ambient moisture level, light levels, and temperature. They all have one thing in common – the need for moisture to survive and reproduce.

The microscopic spores will seek out moist places to make a home – damp carpets, walls, and ceilings. In fact, anything organic is ideal.

Mold feeds on organic materials like paper, wood, and foodstuffs, buries deep into the gaps in porous materials, and then does its worst. So, if you have had or have a water leak, it is important to dry it fully as quickly as possible to prevent mold.

Symptoms & Signs of Black Toxic Mold – How to Recognize It

The scientific name for black toxic mold is Stachybotrys chartarum, found in damp locations. You may have seen it on old bread in your refrigerator.

Although referred to as ‘black,’ it is not always so easy to recognize.

It often looks like a fuzzy coating, smudge, or stain, which can be green, orange, grey, or brown, but may change depending on the stage it’s at in its life cycle.

It often has a widespread ‘furry’ coating across its host and can be slimy to the touch but is always accompanied by an unpleasant musty, damp or stale smell.

It may be the smell you discover first if it’s hidden from sight. Don’t ignore it. You will find some examples here.

How Quickly Do Leaks in Your Home Take to Dry Out?

With small leaks, water clean-up should be done immediately, and any carpets or soft furnishings that have been affected should be cleaned and dried as soon as possible.

If you have a dry garage to locate the items, bring in a commercial dehumidifier to the area, which will remove moisture. If it’s a small leak, it should be dry enough for redecoration or tiling within a short time.

But don’t rush it. The more time you allow for drying out, the safer it will be.

If the flooding is extensive, clean-up and drying will take much longer– up to several weeks or even months in severe cases.

Your insurer will often bring in heavy-duty dryers and dehumidifiers to pull the water out of your home, and these will normally run day and night to be effective. If you have to air-condition, you can run that 24/7 too, as it also promotes dehumidification.

In severe cases, the drywall and insulation will have to be removed to allow the timber framing to fully dry out. There is no point in rebuilding with damp timber framing, which will later warp and cause further damage.

Your insurer will insist on signing off on major works before allowing you to proceed. If you start work too soon, your claim could be invalidated. This type of scenario can take months before your home is fully dry. You may have to relocate temporarily.

Once you have dealt with the source of the leak, clean up as quickly as possible. Any long delay in drying things out will promote mold growth and give you unwanted issues later on.

Ensure adequate ventilation during the drying-out period.

Also, remember the flood water may not be clean, so use disinfectant on everything that has come in contact with it.

Use Personal Protective Equipment (PPE), including boots, gloves, masks, and eye protection for safety. It’s a great idea to have these things available at home if you can.

Is Black Mold From a Leak Dangerous to Your Health?

Black toxic mold produces microscopic spores, which are common everywhere. If allowed to develop, areas of mold will shed millions of spores constantly into your home. It can be serious if anyone in your household has a compromised immune system, is aged, or is very young.

It can cause nasal congestion, sneezing, coughing, and wheezing, but more seriously, it can inflame existing conditions like asthma. Mold prevention and removal is a top priority.

In the event of a serious outbreak of black toxic mold, anyone at risk should be relocated until the risk is dealt with to avoid further medical problems.

How Do I Prevent Black Mold Growth After Water Damage?

Rapid clean-up and water removal following a leak or a flood are essential to prevent mold from getting a toehold in your home.

The only way to prevent black mold is to avoid areas of moisture and high humidity levels in your home. This is common in bathrooms, shower rooms, and kitchens, so adequate ventilation is critical to move the moisture-laden air from the area quickly and effectively. Mold will not grow in dry, moisture-free conditions.

How Fast Does Mold Grow & How Do I Stop It?

Mold starts growing when its spores settle on damp wood, fabric, or drywall, and it can spread around your home within 48 hours. It is established between one and 12 days and grows at around 1 square inch per day.

The priority is to stop any water leak or collection of moisture, giving life to the mold. Dry everything out thoroughly using dehumidifiers and/or cranking up your air-con. Open windows and doors, if possible, to increase airflow, which will speed drying.

Can I Remove Black Mold Myself?

Once discovered, cleaning and removing all the black mold deposits you find is a good idea.

The first thing to do to prevent the spores from spreading is to gently vacuum up loose materials using a HEPA Filtered vacuum cleaner. The filter traps harmful particles. If the infestation is widespread, then seek professional assessment and removal. Check the CDC recommendations on mold removal.

If the mold area is small and accessible, you could remove it yourself using some of the suggested materials below in the next section.

What Kills Black Mold? Are There Natural Materials I Can Use?

If black mold is growing on scrap material like old timber or drywall, remove these and dispose of them properly.

Clean the area thoroughly, ensuring any source of moisture is removed and all leaks are sealed.

Ventilation is important ongoing, so check for blocked vents to maintain good airflow.

Everything in the area affected by mold can be cleaned using standard household cleaning materials*, or natural remedies like:

  • Borax
  • Laundry Detergent
  • Ammonia**
  • Hydrogen Peroxide
  • Tea Tree Oil
  • Household Vinegar
  • Baking Soda
  • Bleach**

* Always exercise extreme care when using all cleaning materials, read and follow the instructions carefully. Use PPE, protective gloves, glasses, and masks, and make sure the area you are working in is well-ventilated. Check out the useful instructions here.

** NEVER MIX AMMONIA with BLEACH; it gives off toxic gas, which can kill you.

How to Reduce the Risk of Black Mold

Reducing the risk of black mold in your home is as simple as avoiding leaks and high humidity and ensuring effective ventilation in areas with high moisture levels.

If you have a leak, clean it up fast and remove any damaged items for disposal or remedial drying; the faster, the better. It has to be thorough; if you leave moisture, black mold will return.

Ensure good ventilation in bath and shower rooms, kitchens, and laundry rooms to eliminate humidity. Fans linked to light switches will help clear moisture quickly.

Keep underfloor areas well-ventilated by ensuring vents are free of obstructions. Remove scrap timber, drywall, or other waste materials on which mold could make a home.

If deprived of moisture, black mold cannot reproduce full stop, so the solution is in your own hands.


Leaks and flooding in your home can be dramatic, stressful, and often completely avoidable. Pay a little attention to what’s happening around you inside and outside your home. Everyone in the family should keep an eye (and a nose) out for odd things or smells and let someone know. The faster a water leak is dealt with, the better, and the less chance of mold getting a grip.

(Check out this excellent resource here (in pdf) – FEMA Mold Resource. In Canada, FEMA can be found here.)

Mold is almost always completely avoidable, but if you are unfortunate enough to experience an outbreak, like water leaks, the faster you deal with it, the better the outcome will be for your home and family.

As the EPA says, ‘if you deal with the mold but don’t deal with the leak, the mold will return.

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