how thick should tile adhesive be

How Thick Should Tile Adhesive Be? (DIY UK Guide)

How thick should tile adhesive be? It’s a great question, given that applying tile adhesive is mostly guesswork. Too little, the tile will fall off the wall; too much, and the tile surface will be uneven. 

In my experience, to understand tile adhesive thickness, we must get to grips with the trowel you’re using. After all, the trowel design determines the thickness of the adhesive. 

Different Types of Tile Adhesive

Before we dive into tile adhesive thickness, let’s discuss different types of tile adhesive. It’s a crucial part of understanding how thick the glue should be. And the more you learn, the more you save on hiring a professional tiler.

There are three main types of tile adhesive, and deciding which is the best for your project depends on how they perform in different settings.

Thinset Mortar

Thinset mortar is the most commonly used type of tile adhesive. It’s cement-based and comes in powder form, like this EverBuild Rapid Set Mortar, or premixed in large tubs, like this Bostik Rapid Setting Cement.

Pro Tip: As a rule of thumb, use five litres of water for every 22.5 kg bag of powder. Add the water slowly to ensure that you don’t make the mix too watery. 

The advantage of thinset mortar is it applies easily, making it easier to gauge the thickness. It’s also better in moisture-rich areas like bathrooms and kitchens. However, the downside is it’s prone to drying and cracking.

You’ll need to achieve 95% coverage when tiling in wet areas. Only 5% of the tile surface should be untouched by the tile adhesive.

Pro Tip: Add a PVA bonding agent to the thinset mortar to retain flexibility and stop cracking. 

Check out our bathroom tiling costs guide to get an idea of budgets.

Tile Mastic

Tile mastic comes in ready-mixed tubes and is a thick acrylic glue. It doesn’t have the same water resistance as thinset mortar, so it’s better in minimal moisture locations. 

When tiling in dry areas, you only need to achieve 80% adhesive coverage, leaving 20% of the tile dry. Because mastic is water-based, it cleans up quickly and is simple to apply. Mastic is better for making spot repairs like re-glueing fallen tiles than large-scale projects.

Epoxy Tile Adhesive

Epoxy tile adhesive is the most robust of all the glues as it withstands grease, moisture, heat, and anything else you can throw at it. The downside with epoxy tile adhesive is you need a well-ventilated room because it gives off a strong odour.

Wear a respirator if the room doesn’t have decent airflow or has no windows (e.g. cellars).

Epoxy tile adhesive is tricky, making it harder to get the right thickness on the tile surface. If you think it would be better to call in the pros, find your expert tiler on Rated People

Tile Adhesive Trowels

worker applying tile adhesive using tile trowel

Okay, so now we’ve covered adhesive, it’s time to get down to the nitty-gritty and discuss which tile trowel is the best. You can use square and U-notched trowels to spread the adhesive evenly. 

The shape and design of the trowel teeth are the key ingredients when determining the spread. However, each delivers a different adhesive depth. When you buy your new trowel, you’ll see that the teeth are measured in depth and width. 

The great news is you can purchase trowels in several sizes, from 4 mm to 20 mm. This Hogard Premium Trowel demonstrates the point perfectly, as it has an 8 mm depth and width, so the tile adhesive thickness stays the same. 

Square Trowel

When you apply the adhesive with a square trowel, you can expect it to compress to half the depth of the original application. So if the trowel lays down a 10 mm layer, the depth halves once the tile is pushed into place. 

Square trowels are ideal for heavier tiles because they deliver a thicker adhesive spread when using the largest gauge notches. It’s also better for distributing the weight of the tile while offering the maximum surface grip. 

Pro Tip: The trowel packaging states the depth and width measurement, but sometimes you’ll only see one measurement. So, if it says 10 mm, the width and depths are the same. 

Lays down more mortarUses more mortar
Wider notches for better gripNot suitable for mosaic tiles
Compresses deep into the mortar
Perfect for heavier or floor tiles
Ideal for any tile over 51 mm square

U-Notched Trowel 

U-notched trowels have a U-shaped edge, creating a crescent in the tile adhesive. When you press the tile onto the thinner ridges of the adhesive, they compact to hold the tile in place. 

Like this Vitrex Plastic model, U-notched trowels give an even spread of adhesive, but it’s worth noting that tile compression is two-thirds for U-shaped versions. So, if you have a 20 mm notch, once the tile is pressed into place, it reduces to 6.66 m㎡. 

When spreading the adhesive, u-notched trowels make it much easier to wiggle the tile into position. You’re more likely to use this type of trowel when tiling a wall, although that depends on the notch size. If you need to make adjustments, it’s great. 

Uses less mortarNot suitable for heavier tiles (depending on notch size)
Better for wall tiles
Ideal for mosaic tiles
Works with tiles under 51 mm square

Trowel Guide

Size MmTrowel TypeTile Size
4.78 notchSquare trowel114 mm wall tiles
6.35 notchSquare trowel122 to 203 mm tiles
6.35 to 9.5U or Square trowel203 to 406.5 mm tiles
12.7U or square trowel406.5 mm tiles +

The Correct Way to Apply Tile Adhesive

  1. Mix five litres of water into a bucket for every 22.5 kg adhesive powder. 
  2. Use a mixing paddle attached to a power drill to get a smooth consistency.
  3. Load the smooth edge of your tile trowel and start in the bottom left corner of the wall. Apply the adhesive in upward sweeping motions.
  4. Work in sections roughly two to three tiles wide and high.
  5. Flip the trowel and score the adhesive using the square notches to create thick ridges.
  6. Press the tile to the wall, starting in the bottom left corner.
  7. Use a rubber mallet to tap the tile down so the adhesive grips. Now, repeat until the wall is complete. 

Check out the video below for a comprehensive guide to applying tile adhesive:

YouTube player

FAQs – How Thick Should Tile Adhesive Be?

Can you use too much tile adhesive?

You can use too much tile adhesive. If you create large wet blobs under the tile, you weaken the bond between the cement and the tile. You’ll also extend the adhesive’s drying time, increasing the tile’s chances of moving in situ.

How much height does tile adhesive add?

It depends on how thick you apply it. Trowel sizes vary between 4 mm and 20 mm. If the trowel has a 10 mm square notch, you can expect an adhesive height of 5 mm. Once tile compression takes effect, you could reduce the depth thickness by half to two-thirds.

When should I use a V-shaped trowel?

V-notched trowels are perfect for installing mosaic tiles on a mesh backing or tiles smaller than 101 mm. Unless you work on intricate patterns, you’re unlikely to use a V-notch trowel for tiling walls and floors.

Final Thoughts – How Thick Should Tile Adhesive Be?

Tile adhesive thickness depends on the type (Thinset Mortar, Tile Mastic or Epoxy Tile Adhesive) you use and the trowel design.

Square trowels lay the cement in thicker lines, compressing it to cover more surface area.

U-shaped trowels create higher ridges, compressing to hold the tile. These trowels are better for wall tiles and mosaics.

Now you have the bit between your teeth, check out our guide on the best tile cutter in the UK to help you complete your project.