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Is Mold Lurking Under Your Tile?

Mold Under Tile


Mold and mildew living and thriving under your bathroom tiles should be an absolute no-no! Unless you actively take steps to prevent ideal growing conditions, mold under your tile will thrive in your bathroom!

Mold could be lurking under your tiles as it thrives in dark, damp, humid places. Tiled walls and floors in wet areas are the ideal breeding places for mold. Over time, mold can establish itself behind your tiles, posing a health risk and causing damage to the substrate and structure of your home.

Mold will very quickly grow in the places that you least expect. By being proactive and regularly checking your tiles, you can get rid of mold before it becomes an expensive-to-fix problem.


Can Mold Get Under My Tile?

A hand scrubbing bathroom tile with a cloth and vinegar

Mold lurking behind the tiles in your bathroom is a common but difficult problem to manage. All mold needs to thrive is:


  • Water and humidity
  • Temperatures between 35 – 120 degrees F  (1.6 C – 48.8C)
  • Darkness
  • Air
  • Food – any carbon-based, organic material


All it takes is a leak, crack, or damage to the tiles, grout, caulking, or even the tiles’ substrate around any tile in a wet room like the bathroom.

If the conditions are right, mold spores in the air can find their way through any tiny gap in the tiles or grout and will be drawn towards the moist, damp, humid, and hot areas behind the tiles.

Mold spores can even travel through drywall or plasterboards! 

Drywall is made from organic materials, making it a great food supply for mold spores. The softer materials used in drywall allow moisture to spread quickly, creating the ideal conditions for mold to grow.

Drywall and plasterboard are often used as a substrate underneath tiles.

Applying waterproofing to the substrate before you tile will help prevent the ideal growing conditions for mold to thrive in. How To Waterproof Shower Walls Before Tiling is a great resource for ensuring that your walls are waterproof before tiling!


How to Tell If Mold Under Your Tile

black mold on tile

Often the first sign of a mold problem is the moldy, musty smell that attacks your nose when you walk into the room. The damage has already probably occurred by this stage, and sorry to say, you are likely looking at a hefty repair bill.

Generally, if you can see mold growing on your tiles, it’s probably likely that mold is already thriving behind the same tiles! 

These are the signs to look for when you suspect that mold might be lurking behind your tiles:


  • Leaking water supply lines create damp spots for mold spores to grow. Bathroom pipes and plumbing fixtures should be checked regularly for leaks.


  • Visible mold on tiles can be a good indication of mold growth behind the tiles.


  • Peeling paint could indicate mold growth.


  • Nasty, musty smells are a good indication of mold!


  • Bulging walls generally indicate a problem behind your tiles.


  • A faulty HVAC system could cause mold to grow behind tiles in the drywall or substrate.


  • Cracked or broken tiles, caulking, and grout are generally signs that the waterproofing has been compromised, and mold could thrive behind the tiles!


Mold can be an unseen and unknown problem lurking behind your tiles for a while before you know about it or even realize that it’s there!


Can Floor Tiles Get Moldy?

Mop Color Tile Floors to Keep Clean


Floor tiles can get moldy, as can the substrate underneath, particularly if you have wooden floors. Look for these signs of mold growing on and under your floor tiles:


A muddy appearance can be a sure sign of moldSpongy tiles could indicate rotting, water-damaged floorboards
Cracks in the tiles, grout, and caulkingSoggy tiles
Stained tilesA sour or rotting smell


If you can see mold on your tiles, or it is recurring after you have taken measures to clean it, there is a good chance that mold could be causing hidden damage to any area behind the tiled area, most commonly to the backer board behind the tiles or to structure of your house.


How Mold Looks on Tile

What Mold Looks Like on Tile

If your tiles show any of the following signs, investigate quickly and deal with the problem immediately before it gets out of hand and causes expensive-to-repair damage to your home:

  • Red and orange streaks on the tiles

Red and Orange Mold on Bathroom Tile

  • Black-green slime around the tiles

Tile and Black Mold in Bathroom

Pink Mold on Bathroom Tile

The best way to confirm that the sludge on the tiles really is mold is by using a DIY mold testing kit, or you can simply dip an old clean rag in diluted bleach and dab it on the sludge. If the sludge lightens or changes color, it is most probably mold!


Where to Look for Mold Near Bathroom Tile

A hand with a rubber glove scrubs mold from the corner of a window

Mold is categorized into two categories in your tiled areas:


1. Surface mold 

2. Mold behind the surround, aka “hidden mold”


Mold reproduces very quickly by releasing spores into the air. Moisture, heat, and organic matter – like dust or human skin! – provide the best environment for mold to grow. 

So every time you use warm water in the bathroom, either by taking a bath or a shower or simply washing your hands and face, you contribute to the habitat that mold loves! The mold fungus will appear within 48 hours of the spore being released from the existing organism if the temperature is right!

Most of the time, surface mold is visible to the naked eye in the bathroom and can be dealt with by washing it away with good cleaning products and a good hard scrub, but the unseen spores hiding away cause the most damage.


Is Hidden Mold Dangerous?

scrubbing bathroom mold from tile with hard brush

There are many different types of molds, with around 100 000 classes that can reproduce via spores. According to the Centers For Disease Control And Prevention (CDC), the most typical molds that you will find in and around your wet areas are:


  • Aspergillus
  • Cladosporium
  • Penicillium
  • Stachybotrys – Black mold


Although visible mold can cause health issues to people susceptible to respiratory problems and people with autoimmune diseases, mold growth behind the tiles and inside the wall cavity usually doesn’t cause health issues. 

The tiles act as a barrier preventing the spores from entering the indoor environment. However, when you do open up the area during the repair process, take steps to protect the indoor environment so that it doesn’t become contaminated by the spores.

While most mold is unhealthy to breathe, certain molds are toxigenic (producing poison) and produce mycotoxins which pose a serious threat to humans. 


How To Check For Mold Under Tile


If you do suspect that mold is growing behind your tiles, there are various checks that you can do to confirm your suspicions before calling a professional mold inspector (yes, they really do exist!).

You could remove the tiles to check for mold, but that’s a costly proposition if you plan to replace them. So instead, try one of these methods:


1. A Digital Moisture Meter

A Digital Moisture Meter 

The General Tools MMD4E digital moisture meter is an all in one tool with multiple functions:


  • Mold tester
  • Moisture reader
  • Water leak detector
  • Humidity sensor


This battery-powered, super safe to use 9-volt moisture meter is a great tool to detect any hidden leaks throughout your home, not only behind your tiles. It provides accurate moisture readings and, with its on-screen icons, is super easy to use!

See it on Amazon


2. A Fiber Optic Camera

A Fiber Optic Camera 

Our high-tech world has many tools to make our lives easier, so why not use them? The Depstech 1080P digital borescope camera is the perfect tool to see what is happening behind your tiles! Simply drill a small hole through the substrate, insert the camera cable, and voila! Instant access to the world behind your tiles!

This camera has some impressive features:

  • Completely waterproof
  • Dual lens, wide-angle color split-screen allowing you to see from different angles
  • The high-quality semi-rigid cable can be bent to access narrow spaces
  • The front camera has a focal range of 1.2 – 3.1 inches (3 – 8 cm), and the side range has a range of 0.8 – 2.4 inches (2 – 6 cm)

See it on Amazon


3. DIY Home Mold Test Kit

DIY Home Mold Test Kit

A home mold test kit is quite simple to use and should indicate that you do indeed have mold thriving behind your tiles! A good test kit will determine the type of mold too!

The Healthful Home 5-minute mold test kit is an affordable home testing kit for those who need answers in a hurry! Simply cover the edge of a screwdriver with a swab from the kit and probe through the drywall or substrate into the suspected infected area. 

This kit was designed in an EPA-licensed and AIHA-accredited lab and is proudly made in the USA.

The easy-to-use 3 step kit includes:


  • Antibody-based tests against 32 mold types
  • All materials necessary for testing
  • Instructions for use

See it on Amazon


The Best Way To Fix Mold Damage Under Tiles

A contractor measures the dampness in the walls with a moisture meter

If you do suspect mold behind tiles and a tool or test confirms it, then you’re going to have to remove the tiles, fix the damaged areas, and replace the tiles. Sorry! 

This could be time-consuming and expensive, so call in the professionals to do a proper job and remove the mold completely.

Find a reputable contractor in your area with good contactable references before you begin. You might be able to supply the materials for the job and only pay the contractor for labor.


Replacing Your Tile Surround

a construction worker sits in the tub in a bathroom under construction

When it’s time to replace the tile around your tub, you may opt to DIY. To see what’s involved, read my post How to Replace Tile Around a Bathtub (in 12 Steps).

Pro Tip: Any bathroom tile project requires a great bathroom tile calculator to help you figure out how many tiles to order and what it will cost. Fill out the form below, and I’ll send my free tile calculator straight to your inbox.



Can Water Leak through Bathroom Tiles?

Are Bathroom Tiles Waterproof

Although many tiles are used for aesthetic purposes in the bathroom, some materials are not conducive to use in wet areas unless they are properly treated and sealed.

Not all tiles are waterproof, so apply a waterproofing membrane to the substrate first before you tile any area. Check out my post Are My Bathroom Tiles Waterproof. (Spoiler alert: The answer is probably not!)

Water can leak through untreated tiles into the substrate, providing a nice moist area for mold spores to thrive.  Simply using the correct grout and caulking will not prevent water from seeping through and mold growth. 


Seal Tiles and Grout

installing ceramic tiles

It is important to regularly seal certain tile materials to prevent moisture from penetrating the tile. If this problem is unaddressed, mold growing inside your tiles can create ideal growing conditions for the mold spore.

Another common problem is mold growing within the tile itself. Porous tiles like Travertine tiles should be sealed regularly to prevent moisture from penetrating the tile and creating a good home for mold!

To find out more about sealing tiles, read my article for some great tips on tile sealers and the correct grout to use with any tile!


8 Steps to Control Mold Growth Under Your Tile

Bathroom mold on the ledge with rubber ducky

The best way to keep your tiles squeaky clean and free from mold is to control the ideal conditions it thrives in. Keep bathroom tiles clean and fix any moisture problems!


1. Improve Circulation

Make sure that fresh air circulates through the room. Open the windows during and after your bathtub time and switch on the bathroom fan. My comprehensive guide on the right bathroom fan will help you choose the correct fan for your space!


2. Remove Mold Quickly

If you notice any mold in your home, no matter the type, get rid of it as quickly as possible! Remove mold from household surfaces using soap and water, a bleach solution, or mold-killing products – always follow the manufacturer’s instructions and use PPE when using chemicals. Wear a face mask and eye protection when working to remove mold or call a professional.


3. Use a Dehumidifier

Install a good dehumidifier to reduce the moisture levels in the bathroom to around 30% – 50%


4. Use a Smart Bathroom Fan

Check the humidity levels after you bathe. Turn on the fan, leave the room and close the door behind you. Check the room after 10 minutes. If the air is still damp and humid, it could mean that the fan is not moving the air enough. This compact, energy-efficient bathroom fan includes a humidity sensor so it will automatically turn on whenever the moisture level gets too high. (Note: Make sure that the fan you buy can cover the square footage of the area.)


5. Squeegee

After you bathe, remove excess water from the walls and tiles – a squeegee is a great water-removing tool!


6. Use a Backsplash  

Protect the wall areas that are wet often. See my post Does a Bathroom Vanity Need a Backsplash for great ideas on what materials to use as a backsplash in your area! 


7. Seal Tile and Grout

Maintain your tiles and grout regularly. At least once per year treat porous tiles, all caulking, and grout should with a sealer. Fix any and all leaks in your home’s wall, roof, or plumbing. Mold needs moisture to grow!


8. Replace Damaged Substrate

If mold is living in your drywall or other materials under your wall or floor tiles, replace the damaged panels with new ones.


So, Can Mold Lurk Under Your Tiles?

Mold Behind Tile in Bathroom

Mold lurking under the tiles in your home is a very real possibility. The bottom line is that the only way to prevent mold from lurking behind your tiles is to manage the conditions that could cause the ideal environment for the fungus to grow and thrive.

Once you spot any mold in or around your home, get rid of it as soon as possible. Mold spores can and will grow anywhere in your home if the conditions are right.

For more on how to prevent and eradicate bathroom mold, read my post Bathroom Mold: A Battle Plan to Destroy It.

And be sure to check out my ultimate guide to bathroom tile, which includes resources about bathroom tile materials, bathroom tile colors, tile finishes,  waterproofing bathroom walls and tile, grouts, sealants and more. 


Tags: bathroom mold, hidden mold, how to get rid of bathroom mold, mold behind tiles, mold under tile, what is bathroom mold

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