Is Underlayment Necessary for Tile on Concrete?

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Underlayment for tiling works can make all the difference in the project. Basically, it is an essential process if you do not want to redo your tiles in the near future. Lack of underlayment of tiles can lead to the development of unexpected cracks in your concrete slab. In simple terms, “underlayment is like an insurance policy.” To give you a clear picture of the entire topic of tile underlayment, here is a complete guide with relevant answers to all your queries.

Can you Lay Tile Directly on Concrete?

Yes! It is okay to put tiles directly on concrete with some caveats. This is because as the house contracts and expands, so does the flooring. That is the reason why you require a solid base for installing tiles.

Ceramic tiles cannot shift, bend, or flex. The product used to fill tile seams, tile grout, cannot shift and bend either, even more reason to use concrete. However, concrete does not respond well to foundation shifts. The groundwater that is pushing from below can crack it. It is better to assume that your concrete, at some point in its lifespan, may crack. If you want to install tile directly on the concrete floor, ensure that the floor is in good condition.

How do you prepare a Concrete Floor for Tile?

Follow the steps below to get your concrete floor in good condition for tiling;

1. Gather your Supplies.

Before you commence your work, please take the time to gather the necessary tools and equipment. Here are the things you will need:

  • Broom
  • Concrete sealer
  • Dustpan
  • A five-gallon bucket
  • Concrete patching compound
  • Trowel
  • Scrub brush
  • Roller with extended handle
  • Towels or cloths

2. Sweep the Floor.

It does not matter if your concrete looks clean or dirty; you should start the process by sweeping the floor.

 To give the floor a thorough sweep, use the broom and dustpan. Also, ensure that you have removed all the dust, dirt, and debris that accumulates once you are done.

3. Scrub the Floor.

After you are done sweeping the floor, give the floor a good scrubbing to remove any stubborn and persistent dirt and stains.

4. Rinse the Floor.

After you have scrubbed the floor, use warm water to rinse it off. If you cannot get access to warm water, cold water will still do.

Since you will need the floor to be fully dry before the next step, it is recommended you wait for about a day to allow the floor to dry completely. If you live in an area where there is high humidity, use a box fan to hasten the drying process.

5. Patch any Cracks

You will need to patch cracks in the concrete floor after you have cleaned it. This is because the concrete can expand and cause the tiles which are above it to break or shift.

In as much as you should fill the cracks, you must also make sure that no other compound remains on the floor’s surface. You should know that uneven surfaces and bumps on the concrete floor can make the tiles break after installation.

During patching, most people usually wonder if they would need a moisture barrier under tiles. Well, yes. A moisture barrier should be installed to protect the flooring against moisture or moisture vapor. Trust me; you do not want moisture problems after installing your tiles as they can ruin the entire project. Therefore, to prevent this from happening, install a moisture barrier under tiles, and this also includes ceramic tiles.

6. Fill any Depressions.

If by any chance, the floor has any damage, you will have to repair them. You will use the concrete patching compound for this step. Also, make sure that the floor is completely dry before proceeding to the next step.

Some people usually ask themselves if porcelain tiles need underlayment, well yes, they do. For your porcelain tile to last for long, you need an underlayment. Both porcelain and ceramic tiles are rigid, so if they are installed on surfaces that are not flat, they can crack easily.

7. Apply the Sealer.

After you have cleaned, patched, and repaired the concrete floor, you can now seal it. The process of sealing creates a protective layer that can prevent moisture from seeping through the concrete and into the tile floor.

Use the roller with the extended handle to apply the sealer. Ensure that you have covered the entire floor to create an effective protective layer. Be keen on avoiding uneven layers of the sealer. Once you are done, let the sealer dry up completely.

How Do You Waterproof a Concrete Floor before Tiling?

When you waterproof the concrete, a barrier is created that repels water and permits the water vapors that are trapped to escape. It also removes stains from mildew and mold. You can waterproof your concrete using concrete sealers.

There are mainly two types of sealers; penetrating sealers and film-forming sealers. The film-forming sealer will protect your flooring with a layer of epoxy or acrylic.  

One thing to note about this type of sealer is that it is readily accessible. However, the main problem with the film-forming sealer is that it wears off quickly. This then makes users apply it a lot of times just to get the best results.

The penetrating sealer uses substances such as siloxanes and silicates, which then permeates the concrete. It does not change the appearance of the concrete, and it also lasts longer. The main disadvantage of this is that it is too expensive.

NOTE: You should not apply a sealer to fresh or new concrete. It would be best if you waited for at least a month before you seal it. This is because for the new concrete to cure completely, it needs some time.

Does Tile Need Underlayment?

Yes! It does. The primary purpose of the tile underlayment is to smooth out spots that are uneven in the subfloor. It also creates an unbending layer that inhibits the floor from flexing. Without an underlayment, even a slight movement of the subfloor can make the grout lines to crumble and tiles to crack.


Putting in place an underlayment goes a long way in preventing the common problems that occur when tiling. To get the best results, make sure that you conduct proper research to know which product is best for your house. All in all, there are many advantages that come with installing underlayment, and there is no reason why you should not install one.

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Joe McGuinty
I’ve been working with floors for over 12 years. I started as a flooring contractor, primarily in materials selection. Then, I switched careers into accounting, so my wife and I began buying, renovating, and re-selling homes on the side. You’d be surprised how much value you can add to a home simply by adding new floors.

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