Laying tile is more than just placing beautiful surfaces on floors or walls. Behind every lasting, professional-looking tile job lies careful preparation. Whether you’re tiling a kitchen backsplash, a bathroom floor, or an outdoor patio, the key to durability and aesthetics begins with what you put down before you lay tile.
In this guide, we’ll explore the essential materials, techniques, and considerations needed to prepare surfaces for tile installation. By the end, you’ll understand what lies beneath the surface and how each step contributes to the overall success of your project.
Understanding the Importance of Proper Preparation
Before diving into specific sublayers, it’s important to understand why preparation matters. Tiling without a proper base can lead to cracked tiles, moisture damage, poor adhesion, and costly repairs in the future. Here’s why preparation is crucial:
- A solid base ensures even weight distribution and long-term stability.
- Moisture-resistant layers prevent water damage, especially in wet areas like bathrooms and kitchens.
- Proper leveling and smoothing results in a uniform finish that enhances the visual appeal of the tile.
Now let’s break down the essential components you must install or apply before laying tile.
What to Put Down Before You Lay Tile: A Step-by-Step Approach
Each project, whether on walls or floors, indoors or outdoors, requires a slightly different set of preparations. However, several fundamental layers and steps are common across most tile installations. Let’s explore them in detail.
1. Subfloor or Wall Surface Preparation
The first layer you need to address is the base material—the subfloor or wall surface. The type of surface determines the next steps in your preparation.
For Concrete Subfloors:
Concrete is a solid foundation, but it must be clean, dry, and free of cracks. Clean it thoroughly and patch any cracks with a cement-based patching compound.
For Wood Subfloors:
Wood, whether plywood or OSB (oriented strand board), should be sturdy and level. Install a cement backer board over the wood surface to prevent moisture damage and provide a stable substrate.
For Wall Surfaces (in bathrooms or kitchens):
Drywall or plaster can be used, but for durable, moisture-resistant installations, cement board or non-paper-faced drywall is recommended.
2. Cement Backer Board Installation
Cement backer board, sometimes known as cement board, is one of the most important underlayment materials, especially in wet areas such as bathrooms, showers, and kitchens.
Why Use Cement Backer Board?
Cement board provides a stable, water-resistant base that won’t warp, rot, or mold. Unlike traditional drywall, it can withstand moisture, making it ideal for areas where water exposure is frequent.
Cement Board Installation Steps:
- Cut the board to size using a utility knife or saw.
- Secure it with galvanized screws spaced about 8 inches apart.
- Use thinset mortar to fill seams and screw heads.
- Apply fiberglass mesh tape over seams to prevent cracking.
Once installed, the cement board provides a rock-solid, alkali-resistant surface for tile adhesion.
3. Waterproof Membrane or Uncoupling Layer
For areas exposed to water, like bathrooms, showers, or pool surrounds, installing a waterproofing membrane is not optional—it’s essential.
Waterproof Membranes:
There are two primary types of waterproof membranes used before tiling:
| Type | Description |
|---|---|
| Sheet Membrane | Pre-formed sheets made of polyethylene or PVC. They’re durable and provide excellent water resistance. |
| Coating Membrane | Applied using a trowel or brush, usually made of modified urethane or acrylic. It dries into a flexible layer that seals out moisture. |
Uncoupling Membranes:
Even in dry areas, uncoupling membranes can be used to protect against cracks transferring from the substrate to the tile. Schluter®-DITRA and DITRA-XL are popular examples. These membranes:
- Act as crack isolation materials.
- Allow for minor movement between tile and substrate.
- Provide a flat, even base for tile installation.
4. Thinset Mortar Application
Mortar is the bonding agent that holds your tile to the prepared sublayer and is usually the last step before the actual tile is placed. The kind of mortar used depends on your application and tile type.
Types of Thinset Mortar:
| Type | Best For |
|---|---|
| Unmodified Thinset | Use with standard applications, especially in dry areas and alongside latex or polymer additives. |
| Modified Thinset | Ideal for wet areas or large-format tiles, as it includes polymers for increased flexibility and adhesion. |
| Large Format Tile (LFT) Thinset | Specifically designed for tiles larger than 15 by 15 inches, offering extended open times and better coverage. |
How to Apply Thinset Mortar:
1. Mix thinset mortar with water according to the manufacturer’s instructions.
2. Apply using a notched trowel, adjusting notch size based on tile dimensions.
3. Work in small sections to prevent the mortar from skinning over before tile placement.
4. Allow the thinset to set for 24–48 hours before grouting.
5. Optional but Recommended Layers
Depending on your project’s scope and environment, there are additional layers you might find useful.
Plywood or Underlayment Boards (for Floating Homes or Older Floors):
In homes with uneven or older wood subfloors, adding a layer of exterior-grade plywood (⅝ or ¾ inch) can significantly improve the surface quality.
Self-Leveling Underlayment:
For uneven concrete floors, self-leveling compounds create a flat, even surface. This step ensures your tiles sit flush and flat, preventing lippage and uneven wear.
Crack Isolation Membranes:
Even on a stable subfloor, especially in dry areas, an isolation membrane helps absorb stress and movement, offering an extra defense against tile cracking.
6. Vapor Barrier Installation (In Critical Wet Areas)
In showers, steam rooms, and pool areas, a vapor barrier may be needed behind the cement board or drywall to prevent moisture from escaping into the wall cavity. Typically made of polyethylene sheeting, vapor barriers ensure long-term structural integrity and mold prevention.
Tiling Over Existing Surfaces: Is It Possible?
In some cases, you can lay new tile over an old tiled surface—but only if it’s done correctly.
When Can You Tile Over Existing Tile?
- The existing surface is clean, dry, and structurally sound.
- The tiles are firmly attached without any cracking or lifting.
- There is no moisture issue beneath the old tiles.
What You Need to Do:
1. Sand or roughen the existing tile to promote adhesion.
2. Apply a primer or bonding agent if thinset or adhesives are being used.
3. Install new tile using modified thinset mortar.
4. Note that tiling over existing tile increases floor height, which may affect neighboring transitions.
In most cases, for the best result and longevity, it’s better to remove old tile and start with a fresh, clean base.
Do You Need to Use Mortar Beds or Sand-Cement Mix for Floors?
In professional tile setting, a mortar bed or sand-cement mix might be used as a base before cement board or tile is applied—especially for exterior applications like patios.
Mortar Beds:
A mortar bed is a layer of cement, sand, and water applied at a proper slope, especially in shower floors for proper drainage. It is often used when installing a waterproof membrane such as a liquid or sheet liner.
Sand-Cement Mix:
For outdoor tiling, particularly around pools or porches, a sand-cement base can provide drainage and a strong bonding surface. However, it must cure thoroughly before tiling.
Different Areas, Different Materials: A Breakdown
The materials and layers you select before laying tile often depend on where you’re installing the tiles.
Kitchen Floors and Walls
– **Substrate:** Plywood or concrete.
– **Underlayment:** Cement board recommended for backsplashes.
– **Mortar:** Modified thinset for durability and resistance to spills.
Bathroom Floors and Showers
– **Substrate:** Concrete or installed plywood with backer board.
– **Waterproofing:** Sheet or liquid membranes over all shower and tub areas.
– **Membrane Type:** Uncoupling membranes or crack isolation systems are ideal.
– **Vapor Barrier:** Recommended behind stud walls.
Outdoor and Balcony Areas
– **Substrate:** Concrete, pavers, or properly supported decking.
– **Drainage Layer:** Sloped mortar bed or drainage mat.
– **Waterproofing:** Essential if the area is above a living space.
– **Adhesive/Mortar:** Use frost and freeze-resistant thinset for cold climates.
Tile Adhesion Layers
Beyond traditional thinset and mortar, some tile projects can use organic, polymer-based adhesives—especially for lightweight tiles.
Mastic:
Tile mastic is a premixed adhesive suitable for ceramic tiles in dry areas like kitchen backsplashes. However, it’s not waterproof and must never be used in wet areas or with porcelain or natural stone tiles.
Epoxy Mortar:
For high-temperature or chemical-prone environments such as commercial kitchens, epoxy adhesives are often used. Though more costly and harder to work with, they offer maximum durability and resistance.
Double Bonding Technique (for Lightweight Tiles):
For very small or lightweight tiles, especially mosaics, applying thinset not just to the substrate but also the back of the tile improves adhesion. This is known as back-buttering.
The DIY vs. Professional Debate
Whether you’re doing the job yourself or hiring a contractor affects the preparation steps.
DIY Considerations:
– **Cost-effective prep materials** are readily available at home-improvement stores.
– Time and skill are needed for proper surface leveling, cement board installation, and waterproofing.
– Beginners may struggle with vapor barriers, mortar beds, or liquid membranes.
Professional Considerations:
– A licensed contractor offers peace of mind and possibly a warranty.
– They ensure all waterproofing standards (such as ASTM and ANSI) are met.
– Professionals are familiar with local building codes that may affect installation methods.
The Bottom Line: Build Your Base with Confidence
Before you lay tile, understanding and preparing the layers underneath is essential for long-lasting beauty and performance. Always invest in high-quality materials—from backer boards to moisture barriers—and do the prep work right. While corners can be cut in some DIY projects, tile installation is not the place to do it. The success of your tile job depends directly on what you put down beneath it.
So, next time you’re about to start tiling, take a moment to assess your surface, identify the necessary substrates, and choose the correct underlayment and bonding agents. With this preparation strategy in place, your tiling project will stand on—and over—a foundation built for beauty and resilience.
Start Your Tiling Project Today with the Right Foundation
Regardless of whether you’re working on a kitchen wall or a full bathroom renovation, the first steps—preparing the base, waterproofing, installing backer boards, and proper thinset application—dictate how well the job will hold up. By taking the time to get these foundational elements right, you’re not just making your home look great. You’re investing in its future.
From moisture resistance to crack prevention, each step plays a role in ensuring your tiles remain beautiful, sturdy, and damage-free for years to come. Begin your next tiling project with confidence—because when it comes to tile installation, the secret to success really is in what you put down before you lay tile.
What materials should be applied before laying tile?
Before laying tile, it’s important to apply the right foundational materials to ensure a durable and stable installation. In most cases, a cementitious backer board is installed over a plywood or concrete subfloor to provide a solid, moisture-resistant surface. This is especially crucial in wet areas such as bathrooms and kitchens. Additionally, a waterproofing membrane, like a liquid membrane or sheet liner, may be applied over the backer board in areas exposed to water to prevent moisture damage.
The actual layer that goes directly under the tile is usually thinset mortar, which acts as the bonding agent between the tile and the substrate. Thinset is mixed with water and applied using a notched trowel to ensure even coverage and proper adhesion. The type of thinset used—modified or unmodified—depends on the tile type and installation conditions. These preliminary steps create a strong bond and prevent future issues like cracking, warping, or mold growth.
Why is preparing the substrate important before tile installation?
Proper substrate preparation is crucial because it provides the foundation that supports the tile and helps prevent future failures. An uneven, weak, or improperly prepared substrate can lead to cracks in the tile or grout, water infiltration, and uneven surfaces that compromise aesthetics and safety. For example, a subfloor that flexes underfoot can cause ceramic or stone tiles to break over time if not properly supported by a stable underlayment.
Additionally, ensuring the substrate is clean, dry, and free of debris such as dust, oil, or old adhesives allows the mortar or bonding agent to adhere correctly. If the substrate is not adequately prepared, the tiles may not bond properly and could loosen or shift after installation. This preparation step may also involve repairing any damaged areas or applying a leveler to create a flat surface, which is essential for achieving a professional and durable tile installation.
What is the purpose of using backer board before tiling?
Backer board serves as a strong, stable, and moisture-resistant foundation that supports the tiles and helps prevent long-term damage. Commonly made of cement, fiberglass, and other durable materials, it provides a better surface for tile adhesion than standard drywall or plywood. This is particularly important in areas exposed to moisture, where a regular wall or floor surface would be prone to warping or mold growth.
Using backer board also ensures a consistent surface that resists shrinking, swelling, or moving with humidity changes. This stability helps prevent cracks in both the tile and grout lines. The board must be properly fastened with screws, and all seams should be taped with alkali-resistant mesh tape and coated with thinset to reinforce the joints before tiling begins. This process helps create a long-lasting and robust installation.
Can I tile directly onto drywall or plywood?
Tiling directly onto drywall or plywood is generally not recommended, especially in moisture-prone areas such as bathrooms, kitchens, or exterior walls. Drywall is porous and susceptible to water damage, which can lead to mold growth and deterioration over time. Plywood, although stronger than drywall, is still vulnerable to warping or swelling when exposed to moisture, which can compromise the structural integrity of the tile installation.
However, for certain low-moisture interior areas, such as a living room or bedroom wall, you can tile over drywall if it is in good condition and properly prepared. The surface must be clean, dry, and primed to provide better adhesion for the thinset. Even in such cases, applying a cement backer board over the drywall or plywood is a more durable and safe option. This provides a more reliable surface, ensures longevity, and aligns with best practices for tile installation.
How do I apply thinset mortar correctly before laying tile?
Applying thinset mortar correctly is a critical step in tile installation. First, choose the appropriate type of thinset—modified (latex-additive) or unmodified (powder-only) based on your project. Mix the thinset with water according to the manufacturer’s instructions until it reaches a smooth, pancake-batter consistency. Allow the mixture to slake (rest) for a few minutes and then remix it to ensure uniformity.
Use a notched trowel to apply the thinset to the substrate in an area you can comfortably tile within 15–20 minutes. Spread the thinset in a 1:1 ratio so that it creates full contact with both the substrate and the back of the tile. Apply it consistently by holding the trowel at a 45-degree angle and combing it evenly across the surface. Press the tile firmly into the thinset using a slight twisting motion to ensure proper bonding and eliminate air pockets, which could weaken adhesion over time.
What is the role of a waterproof membrane in tiling?
A waterproof membrane plays a vital role in tile installations, particularly in areas exposed to water such as showers, tub surrounds, and outdoor surfaces. Its primary function is to prevent moisture from seeping through the tile and grout layers and into the substrate, which can cause mold growth, water damage, and structural issues. By creating a protective barrier, the membrane ensures long-lasting durability and prevents costly repairs.
Waterproof membranes can be either liquid-applied coatings that cure to form a continuous barrier or sheet membranes that are adhered directly to the substrate. These membranes should be applied after installing the backer board and before laying tile. Seams, corners, and around plumbing penetrations must be reinforced with fabric or mesh to prevent cracking and leakage. Always follow the manufacturer’s instructions and local building codes to ensure your installation meets all necessary standards for performance and safety.
Should I let the thinset dry before tiling?
It’s not recommended to let the thinset dry completely before placing tiles into it. Thinset has a limited open time—usually between 20 to 30 minutes—depending on factors like temperature, humidity, and air circulation. If the thinset starts to skin over or dry out before placing the tiles, it should be scraped off and replaced with fresh material to ensure adequate adhesion.
After applying the thinset, tiles should be set firmly into place within the open time. Delaying the process can compromise the bond, leading to weak spots, hollow spots, or future tile loosening. If you’re working in a hot or dry environment, it’s wise to mix smaller batches of thinset and work quickly. Once all the tiles have been placed, they must be allowed to cure for 24 to 48 hours before grouting to ensure the bond fully develops and any residual moisture is released.