Mold On Floor Joists – Removing from CrawlSpace & Basement

Is there a strong musty smell present in your crawlspace or basement?

Have you seen patches of mold on your floor joists that need to be removed?

In this guide you will learn:

  • How to recognize mold growing on a floor joists in a crawlspace or basement,
  • Identifying the Type of mold you have & Dangers of it,
  • Best ways to remove the mold from floor joists & Prevent it in the future.

How to Tell If you have Mold on your Floor joists

One of the first signs that will alert you that you may have mold on your floor joists in either the basement or crawlspace is a musty smell.

Due to the poor ventilation and cramped space in both of these areas, the smell will be apparent very quickly even if you cannot see any visible mold growth.

Mold growing on the floor joists may simply look discolored or damaged so make sure you look closely to be able to tell the difference.

You can quickly evaluate for mold by checking for moisture around the damaged area. If the wood is damp, it is probably mold.

If it is dry, it is more likely old damage or mold that has already been treated and left a stain.

Another early warning sign is visible water or moisture in either your basement or crawlspace.

This could be from a leak in a pipe, moisture and condensation from the ground in your crawlspace, or steam from a bathroom.

If there is visible moisture, always dry it out and check thoroughly for mold.

Most Common Causes of Mold On Floor Joists

The main cause for surface mold on floor joists in a crawl space is evaporation.

Moisture from the dirt evaporates and the moisture rises into the air, eventually reaching the floor joists above.

This moisture then penetrates the porous surface of the floor joists and, in time, can cause mold to grow.

This is especially common for crawl spaces located in humid climates that have constant moisture in the air. As well as in places that are prone to flooding or have heavy rains.

Mold can grow on floor joists in your basement for similar reasons.

Moisture from showers, washers, poor insulation, etc., can evaporate and soak into the wood of the floor joist.

If the moisture is constant, and the temperature remains cool, mold will usually start to form.

The main things to remember about mold growth are moisture, temperature, and food source.

Remove one or more of these factors and you can usually avoid a problem with mold, especially on your floor joists.

How To Remove Mold From Floor Joists

Tools to gather before you begin:

  • Disposable gloves
  • Face Mask / Respirator
  • Protective clothing
  • Spray Bottle
  • Putty Knife or Scraper
  • Protective Plastic Sheet
  • Vinegar, Bleach, Borax, or Baking soda
  • Water
  • Rags you can dispose of
  • Stiff Brush
  • Sealable plastic bag

Before removing any mold, remember that you should avoid touching the mold and breathing it in as much as possible.

The health risks from mold increase exponentially if you actually come in contact with the mold on the floor joist.

Removing mold as soon as it is found can help limit exposure to molds.

Wearing gloves or a face mask while removing and cleaning mold infected areas can also help avoid encountering the mold or breathing it in.

When working in a crawlspace, bring in as much ventilation as possible but make sure that you are not funneling it to another room inside your house.

Ventilation to the outside will be the best option.

Sealing off rooms and vents near the mold will also help stop the spread of spores throughout your house.

This can be done by opening a door or window or adding an air purifier.

1. Stop The Moisture

Any type of mold can only grow on your floor joists when there is moisture. Finding that source of water will help stop the spread of mold and hopefully prevent further issues.

Common culprits for mold on floor joists could be simple things like steam evaporation from showers in the basement to significant issues like flooding in and around the crawlspace.

Moisture can be stopped by fixing any leaks or flooding, making sure the area is well ventilated in order to dry, and ensuring proper insulation and protection on floor joists in the basement ceiling and crawlspace.

For mold found in crawlspaces, check around the outside of your home.

Make sure any water is draining away from the house.

Clean rain gutters or any other areas that can cause excess water frequently.

2. Put On Protective Gear And Seal Any Airways

Any type of mold is especially dangerous when breathed in.

Use a face mask or respirator before cleaning up mold to avoid breathing in any spores that get into the air.

Gloves, long sleeved shirts, and closed toed shoes will also help prevent coming in contact with the mold.

Sealing doorways and vents will prevent mold spores from spreading into other areas in your home.

Always open a window so there is ventilation while working.

If you are dealing with mold on a floor joist in a crawlspace, it is especially important to put plastic on the dirt below.

If the mold falls from the floor joists into the dirt, it will continue to spread quickly due to the excess organic material there.

Cover as much of the dirt or other organic materials as possible to truly stop the spread of the mold.

3. Scrape Off What You Can

Using a putty knife or any type of scraper, carefully scrape as much of the mold away from the floor joist as you can.

This is especially important for the center of the mold patch where it is the thickest.

Be careful to gently remove the mold and place it in a sealed bag quickly as to not spread the mold further.

Too much jostling or brushing at the mold can cause more damage by sending too many spores into the air.

4. Mix A Cleaning Solution

Cleaning solutions for molds can be done with simple household items.

Depending on how much mold you are looking at, will determine what you want to spray on mold on a floor joist.

Mix a cleaning solution of one of the following options:

  • 1 part vinegar and 1 part water. Vinegar has both antibacterial and anti-fungal properties that kill the mold well. It can also penetrate deep into the mold to kill the root of the problem.
  • 1 cup bleach to 1 cup water. Chlorine in bleach works well at killing surface mold but it will not kill mold that has grown deep into your drywall. Bleach should only be used if there is a small amount of mold, and you are sure it is only on the surface.
  • 1 part baking soda, 1 part vinegar, 1 part water. This solution will form a paste that can be spread on the surface of the wood. This is especially helpful for lessening staining and small patches of mold.

5. Spray The Mold With Your Cleaning Solution

Spray all visible mold thoroughly and let it sit for 10 to 15 minutes.

Make sure that you spray (or cover in paste) the entire surface of the floor joist that has mold spores.

6. Scrub The Remaining Mold With A Brush

Use a brush that has stiff bristles in order to remove the mold effectively.

Scrub the mold in a circular motion until it has all come off the surface of the floor joist.

Once all the mold has been removed, use either a wet rag or a disinfecting wipe to clean any residue off the wall.

If there are still spots of mold or anything concerning, repeat spraying it with cleaning solution and scrubbing as many times as necessary.

Dispose of all materials used for protection and cleaning in a sealed plastic bag.

7. Let It Dry

To prevent mold from coming back, floor joists in crawl spaces and basements must be completely dry.

Use a fan, a dehumidifier, or open a window to make sure there is plenty of ventilation to dry them out.

Mold on your Floor Joists?

Call 844-488-0570 for a Risk Free estimate from a Licensed Mold Remediation Specialist in your area.

We Can Help Remove the Mold & Prevent it from Returning.

Preventing Mold Growing On Your Floor Joists In Future

The biggest thing you can do to prevent mold is to prevent moisture. Mold cannot grow anywhere without sufficient, constant moisture.

Cleaning up spills, fixing leaks, properly draining water, venting bathrooms well, and insulating properly can all prevent the growth of mold.

Regular inspections and thorough cleaning can also be highly effective in preventing and stopping the spread of mold.

If mold or moisture is checked for regularly, you will be able to stop the problem quickly before it becomes an expensive risk to your health and property.

Avoid placing things with a lot of water in your basement and crawlspace.

This cannot always be avoided, as bathrooms and laundry rooms are commonly in the basement.

But where possible, avoid putting anything that could possibly leak water where there is less ventilation such as a basement or crawlspace.

Dangers & Problems With Mold Growing On Your Floor Joists

One of the most frequent danger to come from molds in the house is an allergic reaction.

Molds spread by sending off spores into the air.

These spores are hard to contain and so they are breathed in and can cause respiratory problems.

If a mold has been on a floor joist for an extended period, there will be a higher concentration of mold spores in the air.

Continual breathing of these spores can cause larger respiratory problems such as cough, trouble breathing, wheezing, etc. It can be especially harmful to those with a weaker immune system.

Molds can cause structural damage to floor joists if left untreated for too long.

This is especially dangerous in crawlspaces as they are inspected very infrequently.

Molds can eat away at the wood of the floor joist and weaken the structure.

It is particularly important to take mold seriously if found on a floor joist in a crawlspace or a basement as these are the foundations of the house.

Identifying The Type of Mold You Have on your Floor Joists.

There are four common types of molds that can be found on floor joists in both a crawlspace and in the basement.

Stachybotrys mold

Stachybotrys is one of the most common black molds on floor joists in a basement.

It is usually green to black in color and can be flat or fuzzy.

It is the most commonly identifiable black mold and grows very well when moisture is present.

This mold is also toxic when there is a lot of it on your floor joists.

A small amount will not do too much damage (although it should be taken care of quickly). But a large patch of this mold can cause health problems if left for too long.

Penicillium mold

Penicillium is a common mold found on floor joists in a crawlspace where soil is present. 

This type of mold grows best in soils and other organic materials which are commonly found in crawlspaces.

Penicillium is usually a white mold that can also be found on floor joists in basements.

It can vary from white to gray to black depending on how long it has been growing.

While a strand of Penicillium does contribute to antibiotics, breathing in or touching Penicillium mold on your floor joists can be harmful to your respiratory health so it is important to ensure proper removal.

Cladosporium mold

Cladosporium is another strand of mold that can be found on floor joists in basements and crawl spaces.

It can vary from green to black in color and grows in patches.

Cladosporium is generally an outside mold that spreads easily by sending spores into the wind.

These spores are generally not harmful to humans but can cause allergic reactions.

Aspergillus mold

Aspergillus mold is another common mold to find on your floor joists. It is the yellow or powder mold on floor joists.

It is very recognizable as it is the mold commonly found on certain foods, such as bread.

It can be anywhere from white to orange to a light brown color.

The texture of aspergillus mold differs slightly depending on how long it has been present on your floor joists.

It can begin as a fuzzy mold and develop into more powdery in nature, similar to what yellow pollen looks like.

How Much Does It Cost To Get Rid Of Mold On Floor Joists In A Crawlspace When Hiring A Pro

Depending on the size of the crawlspace, removal could cost anywhere from $500 to $6000.

Generally, you will pay between $13 and $30 per square foot.

Other factors to take into consideration are accessibility of the crawlspace or the location of the mold.

Mold that is in even harder to reach places could cost more.

The amount of mold is also a consideration.

Extensive mold that has spread to a majority of a crawlspace, is in the air throughout the house, and has caused damage to the floor joists is going to cost more than mold caught earlier on.

When To Call A Professional

Mold removal can become tricky when located in the crawlspace or basement of a house.

Small patches of mold that are in easy to reach locations can be a DIY project.

These are usually patches of mold that were caused by an obvious source of moisture and were caught before they spread or caused too much damage.

Mold that is in hard-to-reach areas, has multiple large patches, or has penetrated deep into the wood should be managed by a professional.

Professionals will be able to mitigate any mold that is growing as well as help eliminate the mold spores that are circulating in the air.

The best and easiest way to remove any type of mold from floor joists in the basement or crawl spaces is to call a professional.

They will be able to stop the source, remove the growth, and prevent further problems.


We have Mold Remediation Specialists that can help Remove the Mold & Prevent it from returning on your floor joists.

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