When it comes to long-lasting tile installations, what’s underneath your tile is just as important as the tile itself. Schluter Systems offers a variety of underlayment membranes designed to address different installation challenges, from crack isolation to waterproofing and even uncoupling. But how do you know which one is right for your project?

In this guide, we’ll break down the key types of Schluter underlayment membranes, their primary functions, and how to use them effectively.

What Are Underlayment Membranes?

Underlayment membranes are materials installed between the subfloor and the tile to:

• Prevent cracking caused by substrate movement

• Provide waterproofing in wet areas

• Allow vapor management in moisture-prone spaces

• Improve tile durability and lifespan

Schluter Systems is one of the industry leaders in this space, offering a full line of membranes tailored to different tile installation needs.

1. Schluter-DITRA

Primary Use: Uncoupling membrane

Best For: General tile installations over concrete or plywood

Key Features:

• Uncouples the tile from the substrate to prevent cracks in the tile/grout

• Waterproof and vapor management capabilities

• Load distribution to protect tile and stone

• Lightweight and easy to cut and install

Recommended Use Cases:

• Standard bathrooms, kitchens, and living areas

• Substrates prone to minor movement or cracks

• Over wood or concrete subfloors

How to Use:

1. Apply thin-set mortar to the substrate.

2. Embed the DITRA membrane fleece-side down using a float or roller.

3. Use unmodified thin-set mortar to install tile over the membrane.

Pro Tip: Use Schluter-KERDI-BAND on seams and edges for added waterproofing.

2. Schluter-DITRA-HEAT

Primary Use: Uncoupling membrane with integrated heating cable channels

Best For: Heated tile floor installations

Key Features:

• Same uncoupling and waterproofing benefits as DITRA

• Specially designed to hold STRATA_HEAT or DITRA-HEAT heating cables

• No need for a second layer or self-leveling compound

Recommended Use Cases:

• Bathrooms, basements, or anywhere heated floors are desired

• Retrofits or new construction

How to Use:

1. Embed DITRA-HEAT in thin-set mortar.

2. Press heating cables into the membrane grooves as desired.

3. Tile directly over the membrane with unmodified thin-set mortar.

Pro Tip: Use with the Schluter DITRA-HEAT thermostat for full system compatibility.

DITRA-HEAT vs. DITRA-HEAT-DUO: What’s the Difference?

When it comes to installing heated tile floors, Schluter offers several versions of its DITRA-HEAT membrane to suit different needs and subfloor conditions. Here’s how they compare:

DITRA-HEAT

The Standard Heated Floor Membrane

• Thickness: ~1/4" (5.5 mm)

• Bottom Surface: Fleece-backed (requires thin-set mortar for installation)

• Primary Use: Standard heated floor installations with uncoupling and waterproofing benefits

• Sound Insulation: Not included

• Installation Surface: Plywood, OSB, concrete

Best For: General residential heated floor installations where subfloor prep is already complete.

DITRA-HEAT-DUO

Heated Floor Membrane with Integrated Sound Control & Thermal Break

• Thickness: ~5/16" (7 mm)

• Bottom Surface: Bonded fleece + compressible layer

• Primary Use: Adds impact sound reduction and a thermal break, allowing the floor to heat faster

• Sound Ratings: IIC and STC ratings for multi-floor buildings

• Installation Surface: Concrete or wood substrates

Best For: Multi-story homes, condos, or basements where noise reduction and faster heat-up time are desirable.

DITRA-HEAT-PS & DITRA-HEAT-DUO-PS (Peel & Stick Variants)

Faster, Adhesive-Backed Installation – No Mortar Needed Underneath

• Installation Method: Peel-and-stick backing – no thin-set mortar required beneath the membrane

• Time Savings: Speeds up installation by eliminating drying time of thin-set below membrane

• Application Surface: Must be clean, smooth, and suitable for adhesive bonding (concrete, plywood, etc.)

• Available Versions:

  • DITRA-HEAT-PS: Same as standard DITRA-HEAT, but with pressure-sensitive adhesive

  • DITRA-HEAT-DUO-PS: Same features as DUO, but with peel-and-stick backing

Best For:

• Fast-track projects

• Installers working on tight timelines

• Jobs where traditional thin-set installation isn't ideal

⚠️ Note: Peel & Stick versions are not recommended over dusty, uneven, or porous subfloors. Surface prep is key!

Quick Comparison Table

3. Schluter-KERDI

Primary Use: Waterproofing membrane

Best For: Shower walls, steam rooms, and wet areas

Key Features:

• 100% waterproof and vapor-retardant

• Ideal for direct application over drywall or cement board

• Works with Schluter shower trays and niches

Recommended Use Cases:

• Shower walls and floors

• Steam showers and tub surrounds

• Waterproofing over drywall (not just cement board!)

How to Use:

1. Spread thin-set mortar on the substrate.

2. Embed KERDI using a drywall knife or trowel.

3. Overlap seams by 2 inches or use KERDI-BAND to seal.

Pro Tip: Pair with KERDI-DRAIN or KERDI-LINE for a complete waterproof shower system.

4. Schluter-KERDI-DS

Primary Use: Vapor-retardant waterproofing membrane

Best For: High-moisture environments like steam rooms

Key Features:

• Thicker than standard KERDI

• Greater vapor control (perm rating of ≤ 0.75)

• Designed to meet ASTM standards for steam showers

Recommended Use Cases:

• Commercial or residential steam rooms

• Saunas and spa installations

• High-performance wet environments

How to Use:

• Same installation method as regular KERDI

• Be sure to use proper seam overlaps or KERDI-BAND

Pro Tip: Ensure proper slope and ceiling insulation in steam rooms before installing.

5. Schluter-DITRA-XL

Primary Use: Uncoupling membrane for large-format tile

Best For: Large tiles or when floor height needs to match adjacent floors

Key Features:

• Thicker than standard DITRA (5/16" vs 1/8")

• Ideal for tiles 15" or larger on one side

• Adds height to match with hardwood or carpeted floors

Recommended Use Cases:

• Living rooms, hallways, or large open areas

• Over radiant heating systems

• Where floor height needs to be raised

How to Use:

• Identical to DITRA, but consider extra care with large tiles to ensure levelness

Pro Tip: Combine with large-format tile leveling systems for best results.

Final Recommendations: Which Membrane Should You Use?

Installation Tips:

• Always use the right mortar type (modified or unmodified) depending on the membrane and tile.

• Use Schluter accessories like KERDI-BAND, corners, and drains for system compatibility.

• Ensure subfloor is flat, clean, and dry before installation.

Choosing the right Schluter underlayment membrane is essential for a durable and problem-free tile installation. Whether you need uncoupling, waterproofing, or floor heating, there’s a Schluter solution tailored to your project. With proper planning and installation, your tile system will not only look amazing—it will last for decades.