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Schluter DITRA Over Wood in a Bathroom

Cracked floor tiles are bad.

There’s a simple solution: Schluter DITRA

DITRA can be installed on wood or concrete subfloors.

Then, tile can be set on top of the DITRA.

Today, I’ll show you how to install DITRA on a wood subfloor.

Why Use Schluter DITRA 

Tile floors look beautiful.

But broken tiles don’t look great.

Broken Tile

Cracked tiles are an issue when the substrate isn’t prepared properly.

I check three things before setting a tile

  1. The joist span, e.g. 16″ on-center
  2. The subfloor thickness, e.g. 5/8″ or 3/4″ are good
  3. The DITRA Handbook

The DITRA Handbook has specific tips for subfloor thickness based on the joist span and tile species.

It’s an excellent source of information and should always be read prior to setting tiles.

The best part is anyone can read the DITRA Handbook and for the most part understand it.

The Benefits of DITRA

DITRA is way easier to install than cement board.

First, it’s light.

Second, it stops tile and grout from cracking.

Third, it can waterproof the wood subfloor.

How to Waterproof DITRA

DITRA can prevent mold and mildew from forming on wood subfloors.

I will show you how to install DITRA today and make it 100% waterproof.

Here are the supplies you need

  • Schluter DITRA
  • Trowel for Schluter DITRA
  • Schluter KERDI-BAND
  • Caulking Gun
  • Utility Knife
  • 1/2″ Drill
  • QEP Super Grout Mixer¬†
  • Rubber Grout Float
  • Five Gallon Bucket
  • Nitrile Gloves
  • Modified Thin-set (Ardex X5 or Mapei Kerabond/Keralastic)
  • Unmodified Thin-set (Mapei Kerabond)
  • These Amazon Links help support Home Repair Tutor, many thanks for using them

So what’s the first step when installing DITRA on a wood subfloor?

Know the Framing of Your Home

Schluter DITRA has the best technical support.

I constantly call my Schlute rep or the 800 tech support number.

They answer the phone every time!

Schluter also has the best installation directions.

Hey, they’re German and you know what that means…DETAILS my friend.


I always find the joist spacing before installing DITRA.

Here’s the basic rundown of how to use DITRA for ceramic or porcelain tile

  1. 16 inch on-center joist spacing with single-layer OSB or plywood subfloors
  2. 19.2 inch on-center joist spacing with single-layer OSB or plywood subfloors
  3. 24 inch on-center joist spacing with double-layer OSB or plywood subfloors
  4. 24 inch on-center joist spacing with single-layer OSB or plywood subfloors

Please read the DITRA Handbook to double-check these requirements. The Handbook can always change.

Each configuration has specific guidance for

  • subfloor requirements
  • substrate preparation
  • movement joints
  • thin-set, grout, and more.

DITRA can be installed over the following surfaces

  • plywood
  • existing vinyl floors
  • structural plank subfloors
  • concrete
  • and heated floors.

This tutorial is just for wood subfloors.

All the specifics for DITRA installation are in the handbook or on Schluter’s site.


I ensure subfloor panels are flat and properly fastened to the joists.

In addition, I Inspect the floor for protruding nails or screws and fix squeaks before moving forward.

Subfloors should have a 1/8″ gap between wood panels.

Tight subfloor seams don’t allow space for expansion and contraction.

If the subfloor lacks an expansion joint, it can tent. That tenting can cause tiles to crack.

Install Schluter DITRA Over Wood Subfloors

DITRA can be installed over plywood or OSB.

Schluter recommends using a modified thin-set over wood subfloors. Schluter ALL-SET is a modified thin-set and great option for setting DITRA

Schluter ALL-SET

I mix ALL-SET according to the membrane water ratio.

The ALL-SET should hold a notch but still be fairly fluid.

If I don’t use Schluter ALL-SET, I look on the bag for ANSI A118.1 and that’s an indicator that the thin-set is modified.

I measure the floor dimensions and cut my DITRA with a utility knife.

Then I dry fit the DITRA

And I clean and dampen the wood subfloor. This step is very important because it prevents the wood from sucking the moisture from the thin-set mortar.

This creates a solid bond between the thin-set and DITRA.

I use the KERDI trowel to apply thin-set to the subfloor for DITRA.

Here are the trowel sizes that can be used to set DITRA in thin-set

  • 1/4″ x 3/16″ V-notched or
  • 5/16″ x 5/16″ V-notched trowel or
  • DITRA trowel which features a 11/64″ x 11/64″ square-notched design

I apply the thin-set to the wood subfloor and make the trowel notches all run in the same direction.

How to apply thin-set for DITRA

Then I embed the fleece side of the DITRA in the thin-set, leave a 1/4″ gap between walls and membrane, and use a float to push the DITRA into the thin-set

How to install DITRA membrane

I lift up a corner of the DITRA to check for thin-set coverage.

The goal should be 100% coverage.

How to Make DITRA Waterproof 

I fill the cavities with unmodified thin-set mortar or Schluter ALL-SET

Then I comb additional thin-set over the joint using an approved trowel, e.g. the KERDI trowel.

Finally, I center the 5-inch wide KERDI-BAND over the joint and use the flat side of a joint compound knife to press the banding into the mortar.

How to waterproof DITRA

I use this method where DITRA meets drywall and other sheets of DITRA.

The gap between the bathtub and floor is notorious for water leaks.

I fill the 1/4 inch gap between the DITRA and tub with KERDI-FIX.

Then I fill in the cavities with ALL-SET and embed the 5-inch wide KERDI-BAND

Waterproofing against tubs is critical, and using KERDI-BAND makes this installation rock solid for years.

What’s Next

Knowing the right tile installation principles is critical and just one piece of any bathroom renovation.

If you’re remodeling a bathroom and need help join our Platinum Membership.

I promise the step-by-step tutorials and Personal Coaching will make your project much easier.

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DITRA Over Wood