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Concrete Floor Moisture Control: Essential for Durable Tile

Checking the moisture in the subfloor helps prevent big damage to tile floors and reaches a successful, durable tile setup. You might think checking the subfloor for moisture isn’t necessary before installing tile floors, since tiles usually resist moisture well. But ignoring this step might end up with bigger problems.

Even if tiles don’t get damaged by moisture immediately, moisture can still cause serious issues with your floor setup. Your attractive tile floor might become a mess.

To prevent such messes, let’s discuss this.


Table of Contents

Effects of Moisture on Tile Floors

High moisture levels in the subfloor can cause issues like tile cracking, mold, and damage to the structure. Here’s why:

Tile Cracking

Moisture can make wood subfloors expand and shrink, putting much pressure on the tile floors. If moisture changes too much, the tiles can face much stress that may cause cracks.

Such cracks might be thin lines or big splits across the tile – neither is good! More importantly, they can weaken the floor’s overall strength.

For such reasons, the current ANSI standards for installing tiles clearly do not recommend using oriented strand board (OSB). However, if you’re going to lay ceramic or other tiles directly to plywood, always use some anti-crack or uncoupling layer. This layer can absorb some of the movement in the wood caused by moisture.

Cracked tile repair

Growth of Mold

Moisture under the floor can cause mold. Tiles do not let air pass as other floors like wood do, so moisture can easily start mold or mildew under the tile.

The problem goes beyond just how it looks. It can harm health, especially for those with allergies, breathing issues, or weak immune systems.

Damage to the Structure

If you do not keep checking moisture, it can cause big problems for wooden flooring. The problems can include the floor bending, swelling, or rotting. Any of them might also harm the tiles, causing cracks, and uneven edges that might end up with trips, or other expensive repairs.

By taking steps to control moisture before installing the tile floor, you can help prevent these moisture-related issues.

Source of Moisture

Most materials used for subfloors absorb or release moisture based on the air around them. So, places with high humidity can cause a lot of moisture in the subfloor.

Leaks from pipes or appliances can also cause a large amount of moisture. Poor drainage around the building, water from the ground, and insufficient slope next to the building (which creates problems with water from rain, snow, or sprinklers) can all increase moisture levels under the floor.

tile moisture 01

Interestingly, concrete subfloors always contain a lot of moisture, regardless of outside conditions. This is because water is one of the three main components needed to make concrete (the others being cement and aggregate).

Even if a concrete floor seems completely dry and hard, it still holds considerable moisture. It can take months after the initial concrete pour for the floor to dry out enough for a successful installation, whether dealing with tiles, wood, or other flooring.

How to Test Moisture in Concrete Subfloors

If you have a concrete subfloor, you’d better test its moisture. The best way is to do an in-situ relative humidity (RH) testing. The method is accurate and reliable. Although there are other methods, they might not be as stable and could lead to incorrect conclusions.

The RH test gives you results in about 24 hours. It involves putting a few RH sensors at a certain depth into the concrete (40% of the slab’s thickness if it’s drying from one side).

For tile laying, an RH level under 75% is usually seen as safe. Yet, checking the tile or adhesive maker’s advice is essential.

RH sensors

Sometimes, people use a moisture meter for concrete, which is better than not checking at all. However, the meters might not give accurate readings more than about 1 inch deep into the concrete and can be quite off. Since a bare slab often holds more moisture deeper inside, a concrete meter is probably not a good idea for the slab’s overall moisture.

How to Handle Too Much Moisture

Finding out that the moisture levels in a concrete floor are too high for laying tiles might be annoying. Yet, you should feel relieved because finding this out early saves you from more serious and expensive troubles later.

What can you do about too much moisture?

Luckily, there are several ways to deal with it. Letting the concrete dry naturally is often the best choice, especially if you’re not in a hurry. With good ventilation and airflow, the concrete can dry faster.

Here are our suggested methods:

Improve Ventilation

To improve air quality and reduce sweating, you can regulate indoor airflow and temperature. One simple method is to open a window, which promotes cross-ventilation after laundering clothes or showering.

Install exhaust fans at high points within the bathroom and kitchen to capture moisture effectively. Additionally, fans and vents in the attic prevent the air from becoming stagnant, thereby enhancing circulation throughout the dwelling.

Get a Dehumidifier

Buy a dehumidifier, an affordable device that removes moisture from the air, to prevent condensation and boost overall comfort. It also removes musty smells and stops mildew and mold from growing. Before you buy one, measure your space to choose a suitable model.

Repair Leaks and Cracks

Look carefully at every part of your house, both inside and outside, for any leaks or cracks. They could let extra moisture into your home and make your tiles sweat. If you find any, call a professional repairer or plumber to repair them immediately.

Use Preventive Steps

Stop sweat and mold built-up with these steps:

  • Cover aquariums.
  • Put lids on pots while cooking.
  • After showering, let air out directly to the outside – open a window to let out heat, not just a door to another room in your home, which could cause humidity to increase inside.
  • If you can, dry clothes outside, letting the water evaporate into the air rather than gathering inside your house.
moisture mark stains on granite floors

Get an Epoxy-Based Moisture Control System

If it fits what you need and your money plan, add an epoxy-based moisture mitigation system to keep moisture down. It puts a special coating, called epoxy or resinous, on the top of a concrete slab. This coating works with the slab to stop too much moisture vapor from coming through the top. It is a good choice for building work that needs to go without problems.


Which methods are most effective for measuring moisture levels in tile floors?

Tools such as moisture meters for tile and masonry, calcium chloride tests for vapor emission rates, and infrared cameras that detect temperature changes due to moisture, are the top methods for measuring moisture levels in tile floors.

What long-term effects does excess moisture have on the integrity of tile flooring?

Long-term moisture can lead to tile delamination, efflorescence (salt deposits), mold and mildew growth beneath the tiles, and deterioration of the adhesive and grout. Such issues damage both the strength and look of the tile flooring.

tile moisture 02

What are the most effective techniques for expeditiously drying a moisture-compromised tile floor?

Use industrial-grade dehumidifiers and air movers to circulate air and reduce humidity, along with heat drying in severe cases. For subfloor moisture, professional remediation may be necessary.

What indicators should be monitored for early detection of moisture damage in tile flooring?

Indicators include discoloration or darkening of the tile or grout, a musty odor, visible mold or mildew, loosening of tiles, and efflorescence. Regular inspections can help in early detection and mitigation of moisture damage.

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