Too Much Mortar Under Tile: Causes, Effects & How to Avoid It

Too much mortar or too little mortar under tiles can negatively impact the entire flooring experience. The key to having the right mortar height is to calculate the ideal thickness needed for your floor.

A layer of mortar when tiling is key because it allows you to even the surface, and it is also an ideal avenue for the tiles to bond.

The trouble with too much mortar under the tiles is a lot for you to ignore proper planning. If you have no idea on the right thickness, get help from a professional on the right thinset for your floor. Below, we look at how you should calculate the right thin-set, the effects of too much mortar under your tiles, and how to tackle it.

Measuring Mortar Thickness

How Thick Should Thinset Be?

Depending on how high you wish your tiles to be, apply between 3/16 inches and ⅜”  thickness of thinset.  Anything above that will be setting you up for disaster since the tiles won’t bond properly, and the mortar can come up to the grout level while creating lippage.

If you’re tiling your bathroom wall, it could be dangerous using the wrong thickness if thinset since the tiles could fall off and hurt the bathroom users.

How to Calculate Thinset Thickness

Considering your floor terrain, you need to have the right trowel to have the right thickness. This is the tool you will use to calculate the size of the thinset you want.

Different trowels have a varied surface area that distinguishes the amount of mortar you scoop and apply.

Using the trowel as your guiding tool here is how to calculate thinset thickness: 

  • Using a square trowel whose teeth are evenly spread will get you a  ½” depth.
  • If you use a square trowel that measures ¼”x ¼” expect to get a thinset that is ⅛” thick.
  • Assuming you have a ⅜”x ⅜”  you will get a 3/16” thinset. Get the drill?

The spacing between the teeth of your trowel and their size determines the thickness of your thinset.

What if the teeth are U-shaped? Good question. In that case, the thinset will be ⅓” of the size of the tooth. 

You can also improvise cardboard and use it to get the right thinset size.

Using a Cardboard to Get the Right Thinset Thickness

In tiling, time and again, you are called to be creative. Using cardboard to determine the thickness of the thinset is one such moment.

Here is how to do it:

  1. Get cardboard. Most tiles are shipped in cardboard.
  2. Place tiles on the cardboard as most boxes have a 3/16” thickness, which is also the common thinset thickness.
  3. Align the tiles with cardboard. It should give you the correct thickness to pursue.

Using cardboard is an easy task that consumes minimal time than other tricks.

Too Much Mortar Under Tile and the Effects

How much mortar you have under your tiles matters. Different types of floor material require different sizes of thinset. The effects of too much mortar under the tiles can be devastating.

Below, we look at how much thinset is required for different types of floor material and how the thinset size affects the flooring exercise. 

1. Glass Mosaics

The glass mosaic floor setting is thin. For this reason, you should have the right size of thinset. Experts in tiling recommend using a notched trowel measuring ⅜” x ⅜” to get the ideal thinset size of 3/16 inches.  It’s expected that the trowel will evenly spread the thinset for the best results.

Although the glass mosaics demand a thicker thinset than ceramic and porcelain, anything above 3/16 inches is too much.

The effects of having too much thinset on glass mosaic floors include:

  • Uneven surfaces
  • Grout oozing onto the surface
  • Unappealing disconnected tiles

2. Ceramic and porcelain

Ceramic and porcelain tiles are the most preferred for areas constantly exposed to water, such as the kitchen and bathroom. The reason is they are highly waterproof.

However, even with this quality, you need to properly fix the tiles with the proper thinset size for them to hold. Ideally, you should have between ¼” thinset to ⅜” at most. Anything beyond that will be problematic.

The effects of having too much mortar under ceramic and porcelain tiles include:

  • Disjointed tiles
  • Weak points that can’t stand heavy impact resulting in broken tiles
  • Uneven floor finishing
  • Grout surfacing on top of the tiles through the cracks
  • A weak bond between the tiles

3. Spanish pavers

Spanish pavers are among the strongest flooring you can have on your outdoor. It’s imperative to have the right size of thinset to allow the pavers to hold heavy weights.

A ⅜” trowel is perfect for Spanish pavers since the maximum thinset size you can get is the recommended 3/16 inches.

Too much mortar under the Spanish pavers will discolor the surface through the mortar bleeding into the surface. And there will be uneven floors given the disentangled bonds on the edges of the pavers.

4. Natural Stone

Natural stone is primarily uneven. Therefore, to ensure uniformity while working with any type of natural stone, you need to have a thick, uniform thinset.

A deeply notched trowel that’s U-shaped works best on natural stones. The thickness of the stone determines the size of the trowel. For instance, thin stones can work perfectly having a  ¼” inch thinset. 

Too much mortar under natural stones destroys your chances of striking a balance and having even surfaces. In general, poorly-done tiles will easily come off in steam showers thus reducing the benefits of steam showers.

What Happens if Thinset Is Too Thick?

Expect to experience the following when the thinset is too thick:

  1. Grout will be oozing onto the top of the tiles giving them a bad look. In addition, the grout takes up your time and energy to clean.
  2. There will be uneven surfaces that can lead to your loved ones tripping over. 
  3. The disjointed tile bonds give your floor poor finishing. 
  4. Too much thinset will easily stain your floor. 
  5. A thick thinset is susceptible to air bubbles that can rigger a bigger tragedy as they create weak points, especially for heavy loads.
  6. You will need to buy more mortar to cover the entire section, which will cost you more.
  7. You will have to remodel in the future to create the evenness expected on floors.

Any floor is expected to be properly bound, given that itʼs expected to support your household foot traffic. The pavers should also be strongly structured if vehicles pass through.

Too much mortar under your tile is not only a waste of resources but also takes up a lot of time to correct. Involve a professional in case you doubt how thick the thinset should measure.
Besides tiles, these principles also apply to other parts of the bathroom and home in general. The right and thinset for a shower pan are important in keeping your shower leak-proof.


Whether you choose to have a professional tile setter to do the job or do it yourself, it’s good to learn early enough the right size thinset.

The size of your thinset will determine the stability of your tiles. Too much thinset, and your tiles can’t hold the pressure. Expect to witness uneven floor surfaces from the underlying thick mortar.

Different tiles and wall types require a different thickness of the thinset.  The goal is to have unstained floors that are evenly set out.

Calculate the expected thinset size using either the trowel size or cardboard. Take time to properly plan the exercise to avoid unnecessary delays that could lead to the mortar drying up before being utilized. 

Laticrete. Direct Adhered Ceramic Tile, Stone, Masonry Veneer, and Thin Brick Facades – Technical Manual.

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