Do You Need A Moisture Barrier Under Ceramic Tiles?

Ceramic tile is a favorite flooring solution for many homeowners. Tile floors are durable, eco-friendly, and light on maintenance requirements. However, you can miss the benefits of tile floors if the installation is poor.

You need a moisture barrier under ceramic tiles if you want a durable floor and to avoid expensive future repairs. If water sits on a tile’s surface for a long time, it can seep down into the wood subfloor and damage it. Moisture seeping up from the concrete slab can also discolor the tiles.

Do You Need A Moisture Barrier Under Ceramic Tiles?

Skipping the moisture barrier may save money upfront or speed up the tiling project. In this article, I explain why vapor control is crucial in tiling even where it isn’t a building code requirement.

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Why You Need a Moisture Barrier Under Ceramic Tiles

Dealing with flooring moisture problems can be expensive and disruptive to normal life.

A moisture barrier under ceramic tiles during flooring installation can ensure peace of mind.

Also called a vapor retarder, a moisture barrier controls the movement of water vapor.

The goal is to ensure that moisture doesn’t reach areas where it shouldn’t.

Excess humidity can cause severe damage to wood subfloors, shortening the floor’s lifespan and requiring costly repairs.

Although many think ceramic tiles are waterproof, they’re only water-resistant.

You need a barrier between the tiles and the floor to reduce the risk of moisture leaks.

What Happens if Ceramic Tile Has Moisture Underneath?

If a ceramic tile has moisture underneath, the adhesive holding the piece in place can weaken and cause the tile to become loose. A loose tile can dislocate and leak more water down, resulting in mold growth and warping of the wooden subfloor.

Mold buildup underneath tiles can emit an unpleasant smell and affect your health. According to the CDC, mold exposure can cause asthma symptoms in people with allergies or worsen pre-existing asthma.

Moreover, mold growth in tile flooring installations that lack waterproofing can cause the wood subfloor to decay.

Some bugs that attack wood thrive in moist conditions.

As a result, excess moisture underneath tile flooring can increase wood pests and accelerate decay, putting the subfloor at risk of falling apart.

Excess moisture under tiles can also cause the pieces to expand, which may cause the tiles to lift or crack.

Can You Lay Tile Directly on Concrete?

You can lay ceramic tiles directly on a concrete floor, but you should consider installing a moisture barrier under the tiles. If you live in a humid area, vapor can seep up from the slab, penetrate the tiles, and cause problems on your floor surface.

You may want to test the moisture condition of the concrete slab to help you decide whether it requires waterproofing before tiling.

Lay a plastic sheet on the slab and seal the edges with tape to prevent air from getting under it.

Check the sheet after about three days. The slab requires waterproofing before installing the tiles if you find moisture under the sheet.

A concrete slab’s moisture condition can change over time.

For example, rain, snow, and plumbing leaks can increase moisture in a concrete slab.

Therefore, you should still consider installing a moisture management system on the slab, even if it looks dry now.

It’s better to err on the side of caution.

If you notice that the tiles discolor or see salt residue on the tile surface, these can be signs of moisture seeping up from the concrete slab.

Can You Tile Without Waterproofing?

You can tile floors without waterproofing, but plumbing codes require waterproofing in spaces such as showers.

Although codes are flexible on waterproofing tiles, you should consider installing vapor retarders in every space just in case something goes wrong.

Can You Seal Tile To Make It Waterproof?

You can apply a clear sealing product to the grout joints of already installed titles to make that area more water-resistant. Since putting a sealer on the joints doesn’t make them truly waterproof, proper care is essential. Don’t allow water to stay on the tiles for long.

Another tile care you may consider is applying fresh grout in the joints every few years.

Alternatively, you can remove the tiles, install a moisture barrier, and replace the tiles.

That will prevent vapor from leaking and damaging the floor.

Does Ceramic Tile Absorb Moisture?

Ceramic tiles absorb moisture through tiny pores on the surface. The moisture absorption rate varies by tile type. Impervious tiles have the lowest moisture absorption rate of less than 0.5%. Non-vitreous tiles have the highest moisture retention rate of more than 7%.

Vitreous tiles have a moisture absorption rate of 0.5% to 3%. Semi-vitreous tiles have a moisture retention rate of 3% to 7%.

Impervious and vitreous tiles are suitable for covering typically damp spaces such as bathrooms, kitchens, and basements.

They’re also ideal for outdoor flooring environments.

How To Prepare a Floor for Tiling

Proper preparation is crucial to a successful tile installation project.

Here’re a few steps you can take to make your floor ready for tiling:

1. Repair the Floor

You should install tiles on a firm, level surface.

If you plan to tile an existing floor, the surface may require some repairs.

For concrete floors, seal the cracks and level depressions.

For wood floors, check the structure’s stability.

You may need to replace worn-out materials so you can have a solid surface to work on.

Fill the gaps and sink protruding nails and screws.

Clean the floor to remove dust, dirt, and debris that could interfere with the tile’s bonding.

2. Ready the Waterproofing Material

A plastic sheet is the commonly used type of vapor barrier in floor tiling.

The sheet is available in various thicknesses, ranging from 6 millimeters to 20 millimeters (0.24 in to 0.79 in). The wetter the area, the thicker the sheet you’d require for moisture control.

The moisture management material should be large enough to cover the floor.

If you use multiple pieces of the vapor control material across a floor, ensure that the seams are taped to prevent moisture leaks.

Some moisture control materials are available in the form of flexible membranes.

In addition to controlling vapor movements, these membranes prevent tiles from cracking when the floor expands or contracts.

If you’re looking for the best tiling membrane that controls both moisture and cracking, I recommend the Schluter Ditra Membrane Tile Underlayment Amazon. This tile underlayment is available in various lengths, allowing you to choose your size. Moreover, the membrane is easy to install.

3 Common Floor Tiling Mistakes and How To Avoid Them

1. Skipping Moisture Barrier Installation

Installing a moisture management system is an extra but necessary step in a tiling project.

Laying tiles over a flexible waterproofing membrane can protect your floor from moisture problems, prevent cracks, and ensure a long-lasting floor.

While skipping the vapor barrier in a tiling project may save you money now, you may have expensive repairs to deal with down the road.

If you use multiple pieces of a vapor barrier, ensure the joints are sealed or overlapped to prevent moisture leaks.

2. Cracking Tiles and Causing Wastage

Ceramic tiles can crack easily. Flooring tiles mostly crack during cutting.

You may have many cracked tiles if you use the wrong cutting tool.

Consider the Leegol Electric Wet Tile Saw on Amazon to cut tiles accurately and reduce wastage due to cracks.

This machine is flexible to accommodate different cut types.

3. Wrong Grouting

Grout fills tile joints. Beautiful grout lines are a result of skillful tiling work.

Grout can come as a prepared mixture or powder you need to mix yourself.

Poor grouting can cause many problems on tiled floors.

Mix the grout according to the manufacturer’s instructions.

In many cases, self-mixed grout should be allowed to rest for several minutes before applying to tile joints.

Press the grout into the joints and let it sit for about 30 minutes.

Wipe out excess grout with a damp sponge for clean grout lines. Work in small sections at a time.

I recommend QEP Tile Tools Grouting Sponge (available on for grout line cleaning.

This premium-density sponge has rounded edges to reduce grout digging.


You should lay a vapor barrier under ceramic tiles to control moisture movements.

The wood subfloor can rot and fall apart if exposed to excess moisture.

Moisture seeping up from the concrete floor can discolor the tiles and make them ugly.

Cheers, tools owners!

Hi there! My name is Jack and I write for ToolsOwner. I have a passion for everything related to tools and DIY projects around the house. You often find me in my workshop working on new projects.