Thinset is a mixture of sand, water, and cement that’s specifically designed for tile. It’s a type of mortar that adheres tiles to walls and floors, but it can be tricky to determine exactly how thick thinset should be under the tile.
You should mix thinset until it’s as thick as creamy peanut butter. When you apply it to your walls or floors for tiling, the thinset layer should be between 3/16ths of an inch and 1/4th of an inch (or between five and six mm) thick. Thinset that is too thick or too thin will not adhere properly to your tiles or cure correctly.
The table below highlights the thinset thickness for different tile sizes and trowels:
| Tile Size | Trowel Notch Size and Shape | Thinset Thickness |
|---|---|---|
| 2” x 2” and smaller | 3/16" x 5/32" V-notch | 1/9” |
| 4” x 4” and smaller | 1/4" x 3/16" V-notch | 1/9” |
| 8” x 8” and smaller | 1/4" x 1/4" square-notch OR 1/4" x 5/16" U-notch | 1/8” |
| 1/7” | ||
| 12” x 12” and smaller | 1/4" x 3/8" square-notch OR 1/4" x 3/8" U-notch | 1/5” |
| 1/5” | ||
| 12” x 12” and larger | 1/2" x 1/2" square-notch | 1/4” |
| 12” x 12” and larger | 1/4" x 1/2" U-notch | 1/4” |
| 12” x 12” and larger | 3/4" x 5/8" U-notch | 1/3” |
How Thick Should Thinset Be?
Thinset is a type of mortar made specifically to adhere to tiles. But there are several types of tiles, as well as different placements (like walls or floors) and different environments.
The general answer to this question is in the name – “thinset” should be applied “thinly.” This means between 3/16ths and 1/4th of an inch, except for medium bed mortar. You can apply medium bed mortar as thickly as half an inch.
What Happens If Thinset Is Too Thin Or Thick?
Proper thinset is a powder you mix yourself as needed rather than something you buy premixed. It dries by a chemical reaction between the cement and water instead of just a loss in moisture.
Most thinsets come in a dry form sold in a bag, which you can then mix with water according to the product’s instructions. You should mix your thinset until it’s as thick as creamy peanut butter.
Because the water kicks off the chemical curing process, you should only mix enough thinset for your current project. Thinset doesn’t store well and any excess you mix will harden before you can use it again.
When mixing thinset, consistency is important. Each commercial brand of thinset will come with its own specific instructions, but the general principle will be the same no matter the brand.
If you mix thinset too thinly, you won’t have a strong enough bond between your tiles and your floor. It will also be difficult to apply and it’s more likely to come out from the sides with any pressure.
If the mix is too thick, that means there’s not enough water. The thinset will be too dry to grip to your tiles, and it will harden too quickly without really adhering the tiles to your floor.
Tips For Mixing Thinset
Cement is a caustic material, and so the National Capital Poison Center recommends wearing protective gear whenever you work with it. This includes working with thinset, in which cement is a key ingredient.
Thinset lasts no longer than an hour, closer to 20-30 minutes. You should only mix an amount that you can apply within that time.
Always use cool water as warm or hot will speed up the curing process. Adding in more water after the initial mixing will not extend the life of your thinset. It can actually lessen thinset’s effectiveness.
In theory, it is possible to mix thinset by hand, but it’s very difficult, and you won’t get the best results. You should use a power drill and mixing attachment (also called a mixing paddle).
A cordless drill likely won’t have enough power to fully mix your thinset, and you might burn out the motor. Instead, use a corded power drill that plugs into an outlet.
Once you add the appropriate amount of water and mix into a bucket, let the thinset sit for ten minutes. This is known as letting it slake, and it allows the chemical reaction to begin.
Mix one more time and your thinset is ready to go. You can mix again as you work if you need to, but do not add more water.
Thinset is a very hard substance once dried, but it is possible to remove thinset from concrete or other surfaces with a little effort.
Recommended Thinset Thickness Under Tile
Standard thinset – modified or unmodified – should be between 3/16ths of an inch and 1/4th of an inch thick regardless of your project. This includes on shower walls, backsplash, glass tiles, porcelain tiles.
The size of your tiles can change the amount of thinset you need. Anything less than 15 inches on one side, such as a 12×12 tile, only requires a thin layer of 1/4-inch or less.
If you’re working with medium bed mortar or a special modified thinset, you can go slightly thicker, even to 1/2-inch. Always read the manufacturer’s label for further instructions.
Different Types of Thinset
There are several different types of thinset you can use for various projects. Some are good for vertical application, like replacing wall tiles in your bathroom, while others are better for large tiles.
If you choose the right thinset for the job, you should have no trouble tiling your home.
Unmodified Thinset
Unmodified thinset contains nothing but sand, cement, and water. Look for the A118.1 specification from The Tile Council of North America (TCNA) on the package to ensure your thinset is unmodified.
Because it’s less reliant on air to cure than modified thinset, unmodified is good for floors that already have a moisture barrier. This includes radiant floor heating or a waterproof membrane.
In most other situations, modified thinset is the better option due to its increased durability.
Modified Thinset
This type of thinset includes additives like latex to increase its adhesive strength and increase moisture retention for the curing process. It’s currently the most popular form of thinset because of these high-performance factors.
Modified thinset does have its limitations, however. Because of the additives, modified thinset needs air to cure properly.
If you’re installing tile over an impervious material, you’re sandwiching the thinset between two surfaces that block out that required air.
This means modified thinset has a longer cure time and you shouldn’t use it for heated flooring or Ditra membranes. Otherwise, modified thinset is a smart choice that will last for a long time.
Look for both the TCNA A118.4 and the A118.11 specifications on your product packaging to determine if it’s modified.
Glass Tile Thinset
Glass is nonporous, so most thinsets have a difficult time getting a good “grip” on the surface. This type of mortar is made especially for glass tiles.
It’s often white due to the transparency of the glass. Since you can see the color of the thinset behind the glass, white offers a good neutral base.
Epoxy Thinset
This is a heavy-duty thinset, great for commercial areas or garages. It’s extraordinarily adhesive and it’s better at resisting damage from chemical spills or fumes.
Epoxy thinset is also good for resin-backed tiles, with which other mortars don’t bond very well.
Its quality does come at a price. Epoxy thinset is much more expensive than regular thinset, so you should reserve it for difficult flooring projects or ones that need greater chemical resistance.
Not All Mortar Is Thinset
Thinset is a type of mortar, but there are other mortars that do not fit the description of thinset.
No-Slump Mortar
Also known as no-sag mortar, this is great for wall tiles. Because mortar takes several hours to cure, the weight of tiles can cause them to slip down vertical surfaces.
With a mortar designed to prevent sagging, your tiles will stay in place as they cure. It’s also good for larger tiles since it’s less likely to budge under the extra weight.
Medium Bed or Large Format Tile Mortars
This mortar is made with coarse sand, and you can apply it in a thicker layer than other mortars like thinset. Usually, you can apply it about half an inch thick.
This extra thickness does increase the hardening time, but that has its benefits. A longer curing time reduces how much the mortar shrinks, which makes for a stronger bond.
This is especially important for larger tiles with more surface area that needs adhering, such as a 12×24 tile. “Large format” tiles are larger than 15 inches on any one side.
Mastic
Mastic (also just called tile adhesive) is not quite the same as traditional thinset. It’s more of an adhesive that dries from exposure to air rather than the chemical process of mortar.
This means that you can buy mastic premixed, since there’s little to no chemical reaction between the water and other materials. However, this also means that it’s not as durable as other mortars and thinsets, and it doesn’t offer the same pressure support.
Mastic is meant for ceramic tiles and has a tackier texture than true thinset. Because it’s more glue-like, it’s less likely to slide down a wall. This means it’s also good for backsplashes.
Unlike traditional thinset, mastic is not good for large tiles; the organic-based material just can’t support the weight well enough. It’s also no good for showers and any other high-moisture environments.
Difference Between Thinset And Grout
Thinset and grout are both tiling materials, and they both contain a mixture of sand, cement, and water. Thinset, however, goes beneath the tiles and uses its stronger bonding qualities to “glue” the tiles directly to the background.
Grout goes in between the tiles and is more for protecting the edges of each tile and bonding them all together into one large surface, filling in any gaps the thinset couldn’t reach.
Grout also contains additives like polymer and isn’t meant for large surface areas. It dries to a somewhat flexible, almost rubbery finish, while thinset mortar dries hard and solid.
Related Questions
How thick should thinset be under Ditra?
Your thinset should be about 1/8th of an inch thick between your Ditra membrane and your substrate. When using thinset between Ditra and your tiles, it should be between 3/16ths of an inch and 1/4th of an inch thick.
How do you apply thinset to cement board?
Thinset is great for cement board because of the slow cure time; you can adjust as needed before the thinset hardens under the cement board completely.
You will need a 1/4th-inch notched trowel to evenly spread the thinset across the board. Aim for a layer that’s 1/4th of an inch thick or less. If you’re applying the thinset on top of cement board to lay down tile, adjust your layer of thinset for the type of tile you’re using and the environment.
Pull the notched side of the trowel across your thinset to create ridges. Lay down your cement backer board while the thinset is still wet.
In Conclusion
When it comes to the thickness of thinset, there’s two different meanings to consider: the consistency and the application thickness.
A properly mixed thinset should have a consistency as thick as creamy peanut butter. In terms of applying thinset in between your tiles and your wall or floor, you should apply most thinsets in a layer that’s between 3/16ths of an inch and 1/4th of an inch thick.
The precise measurements will vary based on the type of thinset and the type and size of the tile, but anything in this range will give you the right thickness for most projects
