Crawl Space

Will Lime Kill Mold in a Crawl Space (9 Things to Know)

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If you have allergy issues or unpleasant smells in your home, it may result from mold in your crawl space. People use lime to kill mold and remove odors, so you might want to try it, but you are likely unsure how to proceed. 

You can use lime in a crawl space to treat mold and remove odors. Only use hydrated lime, also known as calcium hydroxide, as quick lime rapidly heats when mixed with water. Spread the lime over the mold and mildew in your crawl space and let it sit for about 10 minutes before sweeping it away.

If using lime to remove mold, there are several precautions you need to take to protect yourself and your home. You will also want to address the root issues that led to the mold in the first place. 

How Do You Know If Your Crawl Space Has Mold?

People will often suspect they have mold growth in their home when they notice a persistent musty smell. If your home smells like wet clothes, dirty socks, or rotten wood and you have already searched for the source unsuccessfully, it could be the crawlspace. 

While you may not think about it much, about 40% of the air in your home comes from your crawl space. So, if your crawl space is unhealthy, your home will also be. 

You can identify mold in your crawl space by looking for black, green, or white stains and blotches on the wood or concrete. You can also pick up a mold test kit from your local hardware store if you are unsure. 

In the worst cases, the mold in the crawl space will cause problems in your home. This can include:

  1. Health issues such as allergies, respiratory issues, and headaches
  2. Moldy baseboards inside the home
  3. Mold growth on floors and posts that border or sit above the crawl space

Why Is There Mold In Your Home’s Crawl Space?

The most likely cause of mold in your crawl space is high moisture and low ventilation. A crawl space should remain dry and have adequate ventilation to remove water that enters the area. 

Common reasons for too much moisture include:

  • Old or broken vapor barriers.
  • Leaks in plumbing.
  • Condensation from improperly insulated walls.
  • Rain infiltration.

If you have issues with mold, you will want to ensure that you fix these problems when you remove the mold. 

You should also ensure you have enough ventilation. It is best to have one square foot of screeded ventilation for every 150 square feet of space. Ensure that these vents are clear from obstructions, and consider adding more vents if you suspect this to be contributing to mold growth. 

Can You Safely Put Lime in Your Crawl Space?

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While many websites recommend vinegar or bleach, this is not always practical in crawl spaces with wood components or dirt floors. Also, inhaling chlorine bleach in the confined area of a crawl space can cause illness or injury to your lungs. 

While you also need to follow some health precautions when using lime, it generally does not lead to as many fumes as bleach and is more effective on wood posts and dirt floors. 

The other benefit of using lime is that it is a potent pesticide. Unlike chemical pesticides, it does not pose a danger to humans and will not leak fumes into your home. 

The remediation industry refers to lime mixed with water as ‘whitewash’ and encapsulates areas to remove mold and prevent its return. 

Whitewash has been used for hundreds of years to preserve wood, as in the case of barns and sheds. Even with the rise of acrylic and latex paints, some people still use hydrated lime mixed with water as it is cheap, simple, effective, and has no fumes. 

By coating wood surfaces in your crawlspace with lime whitewash, you kill mold and prevent it from regrowing. 

The Safety of Using Lime in a Crawl Space

Lime is safe to use to kill mold. It is an effective alternative to chemicals and provides more long-lasting protection than some ‘green solutions’ like vinegar. 

However, like using any chemical product, you do need to be cautious. Hydrated lime (calcium hydroxide) is safer than quicklime (calcium oxides) or chlorinated lime (CaOCl2) but is still highly caustic. 

When in contact with the body, it can cause skin burns, blindness, and lung irritation. So, you need to use it carefully and wear proper protective gear, including gloves, mask, long pants and shirt, and eye protection. 

While you need to handle it with care, it doesn’t leave behind any chemical residues and does not off-gas into your home as some other products would. 

Things to Know About Using Lime to Treat Crawl Space Mold

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If you are considering lime to remove mold from your crawl space and prevent it from returning, you need to know some things before beginning. We have created the following list to make it easy for you. 

1. Some Molds are Easier to Clear Than Others

Molds come in many forms. There are over 100,000 species of mold known to science. Some can be beneficial, as the antibiotic penicillin, while others like Stachybotrys can be deadly. 

White mold is one of the easier to remove and poses less of a health threat. Other molds are also not so dangerous to humans, but you should treat all as if they are hazardous to your health, and you should be careful to take proper precautions. 

Stachybotrys chartarum is one of the most dangerous mold species commonly found in homes and feeds on cellulose-rich materials like wood, drywall, and wallpaper. 

Stachybotrys is greenish-black in color and usually appears slimy. It can cause flu-like symptoms, skin irritations, and even death in infants

Determine what kinds of mold you have, and consider calling in the pros if it can be dangerous to your health. 

2. Only Use Hydrated Lime (Slack Lime)

Lime is a general word used to identify a variety of calcium-based compounds. It can refer to calcium carbonate (CaCO3) made of limestone and coral reefs.

Commercial calcium carbonate is usually referred to as agricultural lime and is milled limestone. This is used to amend soils and can also be a source for other types of lime. 

If you heat limestone (CaCO3), carbon dioxide (CO₂) is released to leave behind CaO, also known as quicklime. 

People use quicklime in many manufacturing and food manufacturing processes. It is a mixture of calcium oxides (CaO) that is highly reactive with water. When it contacts with water, a strongly exothermic reaction occurs. 

The reaction between quicklime and water can reach temperatures up to 572 degrees Fahrenheit. This can cause deep burns on the skin and melt the container it is mixed in. 

You should never use quicklime as a cleaner or to remove mold as it is the high alkalinity can burn your skin and damage surfaces. Instead, you want lime that has already reacted with water, calcium hydroxide (Ca(OH)₂). This is also called slaked lime or canning lime. 

3. Wear Protective Clothing and Gear

You want to wear protective gear because of the lime solution and the mold spores in the crawl space. 

It is best to wear a respirator and a protective suit when dealing with abundant mold growth areas. 

While hydrated lime is safer than quicklime, you should still take precautions. Getting a small amount on your skin is not a major cause for alarm, but getting the powder in your eyes or lungs can cause painful and sometimes permanent injury.  

If you plan to make whitewash by mixing hydrated lime with water, mix outside in a ventilated environment rather than in the crawl space. 

Once you’ve made the whitewash mixture, there is less chance of creating dust that you breathe in, but be sure to wear eye protection. Wear long clothes and gloves to protect your skin. If you get the mixture on your skin, wash it off with soap and plenty of water. 

4. You Can Make a Simple Mixture of Lime, Water, and Salt

To make the whitewash mixture, use 1 part water to 2 parts salt and eight parts hydrated lime. You don’t need to be exact with the proportions but should try to get a thick final product like pancake batter. 

After mixing, let it sit for about an hour to react fully and firm up. 

5. You Can Paint on Lime Whitewash Just Like Paint

Use the whitewash to kill mold and treat porous surfaces. 

  • For concrete, apply and let sit for at least 10 minutes and then wipe away or wash off. The lime solution will not penetrate the concrete and may become dust that reduces air quality in your home
  • For metal surfaces, apply and remove as with concrete.
  • For wood, apply with a brush as you would paint and allow it to penetrate. There is no need to wipe off, as it will continue to prevent mold growth. 

6. You can Spread Powdered Lime on Dirt Floors.

If your crawl space has an unfinished floor, you can sprinkle lime on it to kill mold spores and insects. 

Apply a thin layer of hydrated lime over the dirt and leave it. There is no need to remove the lime as with concrete or steel surfaces. 

7. You Need to Fix Sources of Moisture

Help to prevent mold from coming back by removing any sources of water. Moisture can penetrate through dirt floors of some crawls spaces or cracks in the concrete foundation. 

Most larger crawl spaces have a moisture barrier made of thick plastic sheeting. If the crawlspace is covered entirely by sheeting, it is called encapsulation

Ensure that the sheeting is not compromised and let water in. If so, you will need to patch or replace it. 

Another source of moisture is condensation from poorly insulated walls. In this case, adding insulation and a moisture barrier should fix the issue. 

Lastly, check for any leaking pipes or appliances such as water heaters that can introduce water to the space. 

8. You Need to Ensure Good Ventilation 

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Even if some water seeps into your crawl space, good ventilation will prevent mold growth. Adequate ventilation (1 square foot of screeded ventilation for every 150 square feet of space) will ensure that air circulates and removes moisture. 

Check that you have enough vents, that a screen or expanded steel covers them, and that debris or storage items are not blocking them. 

In cooler climates, ventilation reduces the efficiency of HVAC systems and leads to heat loss and increased energy bills. In this case, you can either close the vents in the winter or opt for a non-vented encapsulated crawl space. 

If you have an encapsulated crawl space, then you will need to find another way to remove moisture and move air around, such as:

  • Redirecting some air from the HVAC system into the space
  • Installing a blower fan that vents outside
  • Install a dehumidifier or air intake system

9. You Don’t Need to Risk Your Health

If your mold problem is severe, it may be better to call in the pros rather than fix it yourself. Exposing yourself to mold can lead to allergies and cause respiratory illness. 

When assessing your mold problem, consider these three factors:

  1. Is the mold causing the wood to rot and deteriorate, compromising its strength?
  2. Are the mold stands larger than about 3 square feet in area?
  3. Do you have family members with asthma, compromised immune systems, or respiratory issues?

Final Thoughts

Professional teams can better assess the risk and make recommendations to clear the existing mold and mitigate future mold growth. 

There are many ways to clean mold with household cleaners, targeted chemicals, and green solutions like vinegar. Lime is also a valuable tool against mold, especially when used as a whitewash on porous surfaces such as wood. 

Hopefully, this article has helped you understand how to use it safely and take precautions. No matter how you decide to clean away the mold, you need to take steps to ensure the mold doesn’t return to cause more problems later down the road. 



Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.