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You are here: Home / Prep / Floor Prep / Use These 7 Schluter Ditra Installation Tips and Avoid Problems

Use These 7 Schluter Ditra Installation Tips and Avoid Problems

April 30, 2023 by James Upton 6 Comments

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This post contains 7 real-world tips for installing Ditra. I’m a 25+ year tile installer and I use all of these tips when I install uncoupling membranes.

First, let’s clear up a couple of things:

  1. Yes, these tips work for all uncoupling membranes. So, they’re relevant even if you’ve bought an alternative to Ditra. This includes installing Ditra-Heat, Ditra-Heat-Duo, and other heated uncoupling membranes.
  2. This post does not cover why Ditra is a great product or if it’s a good choice for your project. Instead, I’ve written another post on what Ditra is and how it works.
  3. Down in the FAQ at the bottom of this post, I’ve listed some common problems Ditra installers have and how to fix them.

Estimated reading time: 9 minutes

7 schluter ditra installation tips
Table of Contents (Click to Expand)

Table of contents

  • Ditra Installation Tip 1: Mix Your Thinset Loose Enough
    • Which Thinset to Use
  • Ditra Installation Tip 2: Water Thy Floor
  • Ditra Installation Tip 3: Dry-lay the Pieces Before Installing
  • Ditra Installation Tip 4: Use the Proper Sized Notch Trowel
  • Ditra Installation Tip 5: Trowel the Notches in the Short Direction
  • Ditra Installation Tip 6: Install Small Sections at a Time
    • Don’t Let Thinset Mortar Skin Over
    • Turn Off the AC and Block Heat Registers
  • Ditra Installation Tip 7: Apply Good Pressure to Embed the Membrane
  • Frequently Asked Questions When Installing Schluter Ditra Uncoupling Membrane

Here are the 7 installation tips:

Ditra Installation Tip 1: Mix Your Thinset Loose

This might be the most common mistake: Not adding enough water. Remember, the mortar needs to be thinner than it would be if you were installing tiles.

How thin is thin?

If you are using Schluter mortar, then they tell you right on the bag to add another 1-2 quarts of water per bag. [1]

But what if you don’t need to mix a full batch or thinset? The,n you can take a look at my post on how to mix a small batch of mortar.

You want the mortar to be thin enough to bond to the fleece on the backside of Ditra. Additionally, loose thinset mortar won’t dry out as quickly when it’s spread over a large section of floor.

Which Thinset to Use

I recommend that you use Schluter’s All-Set for anything Schluter-related. This includes:

  • Installing Ditra over wood subfloors
  • Installing Ditra over concrete
  • Installing tile over Ditra
  • Installing Kerdi to create a waterproof shower
  • Installing tile over Kerdi or Kerdi-Board
  • Installing Schluter’s Shower pans

Schluter All-Set meets ANSI 118.4, 118.11, 118.15. Additionally, you can use it for small tiles, subway tiles, and LFT tiles like 12x24s.

Plus, Schluter offers an extended warranty with this product. Plus, it’s just a really nice mortar to use (when mixed properly).

Yes, we could get into modified vs unmodified mortars, but… why? Just use All-Set if you can get your hands on it. It can be used for 90% of your installations.

making the substrate damp. Saturated surface dry
Saturating the substrate with water before installing Ditra

Ditra Installation Tip 2: Water Thy Floor

Here’s what you want to avoid: spreading mortar over the floor and having it skin over before you have a chance to lay Ditra over it.

One of the ways that you can help your cause is by dampening the substrate (your floor) before spreading the mortar.

However, you don’t want standing pools of water on the floor. Rather, you want the substrate to be damp while the surface is dry.

There’s a technical term for this, which is saturated surface dry (SSD). [2]

So, “give your floor a drink,” as they say. Dampen the surface to receive the membrane immediately before spreading mortar over the floor.

Ditra Installation Tip 3: Dry-lay the Pieces Before Installing

Another technique to speed up installation is to have your piece cut and in place before you trowel the mortar.

This way, you’re not monkeying around with cutting Ditra while mortar is spread and the top is drying and skinning over.

Have the piece cut and put it in place prior to picking it up and spreading the thinset.

Ditra Installation Tip 4: Use the Proper-Sized Notch Trowel

This tip is pretty self-explanatory. Too small of notches and the membrane won’t bond.

If the notches are too big, you’ll get a lumpy installation, and you’ll end up squeezing the mortar out when you work to embed it in the thinset mortar.

You can use a 1/4 x 3/16 V-notch trowel or get one of the 11/64-inch square-notch trowels made especially for Ditra (aka the Ditra Trowel).

Tip: If using a product other than Ditra, make sure to read the manufacturer’s instructions for which trowel size to use.

Some products like Ditra-Heat, Ditra-Heat-Duo, Ditra XL, and alternative uncoupling membranes such as Redgard want you to use a larger trowel size.

Tile Notch Trowel sizes. Which trowel size do you need for ....? [Full vid]
Watch this video on YouTube.
This video is set to start with the trowel you would use for uncoupling membranes like Ditra

Ditra Installation Tip 5: Trowel the Notches in the Short Direction

If you watch the video above, you will also see that I am troweling the mortar notches all in the same direction.

This is called directional troweling and is important to do, especially when installing uncoupling membranes.

It’s a good idea to trowel the notches in the short direction of the membrane.

Think about this: Air will be in the low channels of the notched mortar. You want that air to take the shortest route possible to escape.

So, if you unroll the membrane, then you want the trowel lines to be perpendicular to the way that you unroll it. This is just a good fundamental practice when troweling mortar.

notch troweling thinset mortar in the same direction
You want to trowel your mortar all in the same direction. Ideally, your trowel lines will be more consistent in one direction than this photo shows

Ditra Installation Tip 6: Install Small Sections at a Time

Along with tip number 2 about wetting the surface, you want to work with small sections at a time rather than taking the time to try to trowel mortar over a large section.

If you have a large section of Ditra that you’ve unrolled and cut into place, you can fold half of the membrane over and install it in two different steps.

Fold the Ditra in half (don’t crease it). Then, wet the surface of the exposed half, trowel the mortar, and embed half of the section.

Then, peel the other half back and repeat.

This is a good technique to use when you have your pieces already cut in place and you don’t want to move them out of place excessively.

Turn Off the AC and Block Heat Registers

It’s not a bad idea to turn the thermostat off and block any heat registers so that air doesn’t blow across your exposed thinset notches before the membrane is installed.

By the way, you are putting in sleek-looking, tile-in heat registers, aren’t you?

Ditra Installation Tip 7: Apply Good Pressure to Embed the Membrane

Finally, you want to make sure Ditra gets embedded really well into the fresh mortar. You can do this with a roller, a wood float, or even a chunk of 2×4.

Additionally, Schluter makes a roller for this purpose. [6]

The best technique is to start in the middle and work your way to the edges.

You want to collapse the thinset ridges and push the air out of those short air channels that we talked about in tip 5.

Lastly, walk around and step over every bit of the Ditra surface to ensure it’s properly embedded.

Regularly pull the corner of the membrane back from time to time and inspect how well the thinset transfers to the membrane.

Review

Remember, the 7 steps are as follows:

  1. Mix your thinset loosely
  2. Give the floor a drink
  3. Dry fit the pieces in place first
  4. Use the right trowel
  5. Trowel the notches all in the same direction, and hopefully, air can escape
  6. Install small sections at a time
  7. Press down really well and embed Ditra into the mortar

Below are some answers to some common Ditra installation problems and questions:

Frequently Asked Questions When Installing Schluter Ditra Uncoupling Membrane

Why is my Ditra not sticking to the floor?

There are a variety of reasons that Ditra may not stick to the floor.

These include improper mortar, improper mixing of mortar, improper substrate to install Ditra over, troweling that wasn’t directional, thinset skinned over, improper trowel size, or perhaps Ditra has too much ‘memory’ [see question below]

How do I keep the edges from curling up with Ditra?

The edges curling up are caused by Ditra having too much ‘memory’. This refers to roll memory. It is still used to being rolled up.

This can be relieved by getting Ditra out of the cold and unrolling it in the room. It can be relieved by bending the membrane the opposite way of the roll before it’s installed.

You can also weigh the corners and edges down until the mortar has completely dried. Tile boxes work great for this.

How long do you wait to tile after installing Ditra?

While Schluter says that you can install tile immediately after installing Ditra, it’s not something that DIYTileGuy recommends.

I’d rather see you wait overnight, at a minimum, and let the mortar dry completely.

If you install a tile and then have to pull it back up, you risk pulling the membrane up and debonding it from the subfloor.

Can you walk on Ditra immediately after installing it?

You can walk on Ditra immediately after installing it, and this is a good way to continue to embed the membrane into the fresh mortar underneath.

You’ll want to avoid twisting your feet and, instead, apply pressure as straight up and down as can be reasonably expected.

How flat should a floor be before installing Ditra?

As a rule of thumb, you want to do any leveling or flattening of the floor prior to Ditra being installed.

Your floor flatness requirements depend on what type of tile is being installed on top of it. I cover floor flatness requirements in my post on self-leveling.

Do you need underlayment with Ditra?

Ditra is a tile underlayment. It adheres directly to the substrate. No additional underlayment is needed as long as your substrate meets the minimum requirements for tile installation.

You can go to the Schluter website and download their Ditra Handbook which will tell you what the minimum requirements your substrate needs to meet. [3]

Can I install Kerdi on a floor?

Wood or concrete subfloors are not approved substrates for Kerdi membrane. [4,5]

References

  1. Schluter All-Set product page [download link from page]
  2. Wikipedia: Saturated Surface Dry
  3. Schluter Ditra product page
  4. Schluter Shower System Installation Handbook [download link from page]
  5. Schluter Kerdi, Kerdi DS technical data sheet [download link from page]
  6. Schluter Ditra Roller web page

Filed Under: Floor Prep Tagged With: featured

Reader Interactions

Comments

  1. Blair Grossman says

    August 10, 2023 at 8:53 pm

    Hi James.

    I screwed up and used the wrong trowel for Ditra XL. I didn’t realize the xl needed a 1/4 X 1/4 instead of the 11/64.

    Other than. that I seemed to go well and adhered. Am I okay or not?

    Thanks,

    Blair

  2. James Upton says

    August 13, 2023 at 9:31 am

    As long as it’s adhered well it doesn’t really matter which trowel you use but it’s difficult for me to imagine that it can be stuck well with the smaller Ditra trowel. I would go over it and check for spots that may have loosened and reapply those.

  3. arkesh mehta says

    March 20, 2024 at 6:56 am

    how many 50 lb. bags of all-set required for installing ditra and tile botha 200 sq. ft room??

  4. James Upton says

    March 21, 2024 at 11:00 pm

    Hard to say exactly especially without knowing the tile size but maybe 6?

  5. Joe Serratore says

    July 15, 2025 at 11:46 am

    Hi James, Once Ditra membrane is installed and allowed to dry overnight, can I apply a “smooth coat” finish of thinset over the membrane to completely fill in all the squares and then allow that to again dry overnight before actually installing any tiles? Or do you have to install the tiles right away, at the same time, after filling in the squares? Just curious and wondering if that would cause any issues by doing it in multiple steps like that?

  6. James Upton says

    July 17, 2025 at 3:54 am

    They want you to wait. But when I installed my uncoupling membranes, I applied the mortar coat before setting tile. Also, I did it the day I installed and didn’t wait over night. You can walk on the membrane once it’s installed and it’s a good way to use up extra mortar.

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Hi! I'm James!

I own a bathroom remodeling company in the Seattle area and blog about tile installation in my spare time.

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