When preparing to install tile, many homeowners and DIY enthusiasts ask the same question: What do you put down before tile? The answer to this question is critical, as the success of a tiling project depends largely on the groundwork performed beneath the surface. Tiling isn’t simply about placing tiles on a floor or wall — it’s a complex process that requires a firm understanding of materials, moisture barriers, leveling, and insulation.
In this article, we’ll explore the essential underlayments, substrates, and preparations needed before tile installation. Whether you’re tiling a bathroom floor, a kitchen backsplash, or a sunroom wall, understanding what to place beneath the tile ensures durability, safety, and a professional finish. We’ll break down each component step-by-step and provide actionable insights supported by best practices in the tile industry.
Understanding the Importance of Substrate Preparation
Before you ever place a single tile, the surface you’re tiling on must be properly prepared. This substrate — which can be concrete, drywall, cement board, plywood, or other materials — must be clean, dry, and structurally sound.
Clean and Debris-Free Surfaces
Start by clearing the area of dust, grease, oils, and loose particles. A clean surface promotes a strong bond between the tile adhesive and the substrate. Use a degreaser for greasy areas and a vacuum or damp cloth for dry surfaces. Make sure the area is fully dry before tile installation begins.
Dry Substrates are Essential
Moisture can compromise adhesives and cause mold growth beneath tiles. Always test the substrate for moisture. For concrete subfloors, a plastic sheet test can determine if moisture is rising through the slab.
Level and Structurally Sound
Bumps, dips, or uneven surfaces will translate through to the tile layer, creating issues with grout lines, lippage (uneven edges), and even tile cracking. Use self-leveling cement or patching compounds to create a smooth, even surface.
What Goes Under Tile? The Layers of Tile Installation
The preparation for tile typically involves multiple layers depending on the environment and the type of tile being installed. These include:
- Substrate (concrete, plywood, drywall)
- Waterproofing membrane (especially for wet areas)
- Cement backer board (for walls and wood subfloors)
- Tile adhesive (thinset or mastic)
- Expansion joints and movement accommodation systems
Choosing the Right Substrate
The underlying structure determines many of your material choices. For example:
Concrete Subfloors
These are ideal for tile installation, as they offer a solid, stable base. However, cracks and moisture movement must be addressed. If the slab contains excessive moisture, install a crack isolation and vapor barrier membrane before tile.
Wood Subfloors
Never tile directly over wood. Instead, install a cement-based backer board or other suitable underlayment such as Schluter Ditra. This adds rigidity and prevents flex, which can lead to cracked grout or broken tiles. Make sure the wood subfloor is free of squeaks and securely fastened.
Walls (Drywall or Plaster)
Tile isn’t ideal over drywall, especially in wet environments like bathrooms or showers. It’s best to remove the drywall and install cement board or glass-reinforced concrete (GRC) panels. This ensures proper support and moisture resistance.
Installing a Waterproofing Membrane
In areas exposed to water — like showers, baths, and kitchen backsplashes — installing a waterproofing membrane is critical.
Why a Waterproofing Membrane Matters Before Tile
Tile and grout are porous. Without proper moisture protection, water can seep into the substrate and cause:
- Mold and mildew growth
- Rot in wooden substrates
- Cracking and delamination of tiles
Products such as liquid membranes (e.g., RedGard), sheet membranes, and crack isolation membranes provide an ideal solution to this problem.
How to Apply Waterproofing Membrane
Start by preparing the substrate and covering all corners, seams, and drains with reinforcing mesh (like alkali-resistant fabric). Apply the membrane using a trowel or paint roller, ensuring full coverage, and allow it to cure thoroughly. Do not skip this layer if tiling in a bathroom or wet area.
Cement Backer Board Installations
Cement board (such as HardieBacker, Durock, or WonderBoard) is one of the most commonly used materials in tile preparation, especially for floors and walls.
Advantages of Cement Board Before Tile
- Highly resistant to moisture and does not swell like drywall.
- Provides a rigid surface that supports tile.
- Ideal for areas subjected to frequent water exposure.
Installation Tips for Cement Board
- Use corrosion-resistant fasteners to install cement board over plywood or wood subfloors.
- Leave a 1/8-inch gap between the boards to prevent cracking.
- Apply a layer of thinset under the boards before fastening to ensure they are bedded correctly.
- Tape and thinset the joints before tile to create a monolithic base.
Tiling on Expansion Joints and Movement Zones
All structures move slightly over time. Temperature changes, humidity, and settling of the building can cause cracking in tile surfaces unless movement accommodation systems are installed.
Use of Crack Isolation Membranes
Products like Schluter Ditra or Mapelastic help absorb stresses from the movement of the substrate. These membranes are particularly important when tiling over concrete slabs where cracks may develop.
Installing Ditra or Crack Isolation Membranes
The membrane is placed over a level substrate and secured with polymer-modified thinset. The tiles are then mortared directly onto the membrane. This layer goes down before tile to provide long-term protection against stress cracks.
Movement Joints in Tile Installations
Once the tile is installed, movement joints (often filled with silicone sealant) should be placed where the tile meets walls, fixtures, or where floor joists change direction. These joints prevent cracking by allowing slight movement throughout the structure.
Tiling on Heated Subfloors: The Role of Insulation and Matting
When installing radiant floor heating systems, the materials used under the tile play an even more critical role.
Thermal Insulation Under Tile?
Unlike in colder environments where insulation is necessary, tile conducts heat efficiently. However, in areas with high subfloor heat loss (e.g., a basement), insulating mats or high-density panels can be used under the heating mat to improve efficiency.
Types of Insulation for Tiling
– Insulated underlayment (for above-grade floors)
– Reflective insulation (to enhance heat retention)
– Plywood and insulation barrier layers
These layers should be placed according to manufacturer guidelines **before tile** and the radiant system is applied.
Floor Leveling and the Use of Self-Leveling Compounds
No matter how hard you try, some subfloors won’t offer the required flatness for tile. This is where self-leveling underlayments (SLUs) come in.
What is a Self-Leveling Compound?
A fluid mixture of cement, polymers, and other additives that flows and hardens into a level surface. It’s particularly useful for concrete and wood substrates that are uneven or cracked.
Applying Self-Leveling Compound Before Tile
Prep the subfloor with cleaning, degreasing, and priming. Use a gauge rod or screed rod to spread the compound evenly and guide the height. After curing (usually 24 to 48 hours), you’re ready to set your tile.
Adhesives and Thinset: The Final Layer Before Tile
Once the substrate is ready, the final layer before tile is the bonding agent — typically thinset mortar or mastic.
Thinset vs. Mastic: Choosing the Right Option
– **Thinset cement** is a Portland cement-based product with polymers. It is used for most tile installations and is ideal for areas with moisture.
– **Mastic** is an organic adhesive suitable for dry areas and typically used with wall tiles.
The type of tile also affects your choice. For porcelain or natural stone, always use a polymer-modified thinset for optimal adhesion.
How to Apply Thinset Before Tile Installation
Using a notched trowel appropriate to the tile size, spread thinset in manageable sections. Work in small areas and comb the thinset to ensure even ridges. Press each tile firmly into the thinset — never slide tiles — to create a solid bond.
Special Considerations for Different Tile Types
The preparation required **before tile** varies slightly depending on the type of tile being used.
Ceramic vs. Porcelain Tiles
Both are common and durable, but because porcelain is denser, it requires a stronger adhesive and may need a modified thinset.
Natural Stone Tiles
Natural stone such as marble, limestone, or travertine requires a more stable subfloor, often with a crack isolation membrane. It also requires a slightly different trowel size to accommodate the tile’s weight and irregularities.
Large Format and Porcelain Panels
Very large tiles or ultra-thin porcelain panels require flat surfaces and special large-format thinset. They also often require back-buttering to ensure complete contact with the subfloor.
Final Tips for a Successful Tile Installation
Before diving into any tiling project, consider these expert tips:
Plan Before You Measure
Lay out the tile pattern dry to ensure even cuts and minimal waste. Start from the center of the room and work outward.
Use Proper Tools
From laser levels to wet saws, the tools you use significantly impact the final look and durability of the tile installation.
Let It Cure
Just as important as what you put down before tile is giving the tile and adhesive time to cure properly — typically 24 to 72 hours before grouting.
Grout with Care
Use sanded grout for joints wider than 1/8 inch and unsanded for smaller joints. Clean excess grout promptly using a damp sponge and water.
Maintenance Matters
After installing, protect your tile investment with proper sealing (for natural stone and grout joints) and regular cleaning using pH-neutral cleaners.
Conclusion: A Seamless Surface Starts Beneath the Tile
The question of **“What do you put down before tile?”** might seem simple, but the answer reveals the complexity of tile installation. The right preparatory steps — from waterproofing to backer board, self-leveling compounds to crack isolation membranes — ensure a tile job that stands the test of time.
Remember: tile is only as good as the surface beneath it. Taking time to properly prepare the substrate not only prevents expensive mistakes but also enhances the final aesthetic and performance of your tiled space.
Whether you’re renovating a small bathroom or designing a large commercial kitchen, understanding the materials and methods needed **before tile** will guarantee a professional, lasting finish. So next time you’re ready to place those first tiles, make sure what’s under them is just as carefully considered as what’s on top.
What materials are typically used as a base before tiling?
Before installing tile, it’s essential to prepare the right base or substrate to ensure a long-lasting, durable installation. The most common materials used as a base include concrete slabs, cement backer board, and plywood subfloors. Each offers different advantages, depending on the tiling location and the environment. For wet areas like bathrooms or showers, cement backer boards are preferred because they are water-resistant and provide a solid base that won’t warp or degrade over time.
In addition to the substrate, a bonding agent like thinset mortar is applied between the base and the tile. This helps create a strong, secure adhesion and also compensates for minor surface imperfections. In some cases, an uncoupling membrane or waterproofing layer may be added to the base to prevent cracks from transferring from the substrate to the tile surface. The goal is always to create a clean, level, solid, and moisture-resistant surface that supports the tile without moving or flexing.
Why is it important to install a backer board before tiling?
Installing a backer board before tiling, especially in high-moisture areas like bathrooms and kitchens, is crucial for long-term durability and performance. Backer boards, such as cement board, provide a stable surface that is resistant to water damage, mold, and mildew. Unlike drywall or plywood, they do not swell or deteriorate when exposed to moisture, making them ideal for wet environments and helping preserve the structural integrity of the tile installation.
Moreover, using a backer board allows for better adhesion when applying thinset and tile. It also helps prevent flexing, which can cause tile cracks or grout failure over time. Backer boards must be secured properly using appropriate fasteners and the seams must be taped with alkali-resistant tape and thinset to create a monolithic surface. Proper installation ensures that any future movement in the structure beneath won’t compromise the tile finish, giving homeowners peace of mind and saving costly repairs.
Can you tile directly over drywall or plywood?
In some applications, it is possible to tile directly over drywall or plywood, but several conditions must be met to ensure a successful installation. Drywall is generally not suitable for wet areas, such as behind a shower or tub, because it can absorb moisture, swell, or support mold growth. However, in dry areas like kitchen backsplashes or living areas, tiling over properly prepared drywall may be acceptable as long as the surface is clean, dry, flat, and free of any loose material.
Plywood, on the other hand, can work as a base for tiling if additional preparation is completed. The plywood should be at least 5/8 inch thick and must be covered with a cement backer board or a suitable tile underlayment system. Tiling directly on plywood without reinforcement can lead to flexing and cracking, especially in flooring applications. Therefore, it’s recommended to install a secondary layer such as cement board or a decoupling membrane to create a more stable and rigid substrate for tiling.
What is thinset mortar and why is it important before tiling?
Thinset mortar is a cement-based adhesive that is crucial in bonding tiles to the substrate. It is mixed with water and sometimes with latex or polymer additives to enhance its flexibility and bonding strength. Thinset serves dual purposes: it adheres the tile to the base material and fills gaps to ensure even, level tile placement. It is an essential element in any tile installation because it provides a durable, long-lasting bond that can withstand temperature changes and moisture exposure.
The correct application of thinset is just as important as choosing the right type. A notched trowel is used to spread thinset evenly, creating ridges that collapse under the weight of the tile to ensure full coverage and a strong mechanical bond. Proper thinset coverage prevents hollow spots that can lead to tile cracks or detachment over time. In wet areas, modified thinset with polymer additives is recommended for best results. Overall, thinset mortar acts as the foundation between the substrate and the tiles and is a pivotal component for a successful install.
What is an uncoupling membrane and should I use it before tiling?
An uncoupling membrane is a thin, often plastic-based layer installed between the tile and the substrate that allows for slight movement and stress without cracking the tile surface. It works to absorb any differential movement (or “coupling”) between the subfloor and the tile, making it a useful addition in floor installations where structural movement is possible. Uncoupling membranes also often provide a waterproofing layer and help protect the tile job from cracks developing in the underlying surface.
Using an uncoupling membrane can significantly extend the life of a tile installation. It’s especially important in environments where thermal or structural movement is common, such as over concrete slabs or in areas with high foot traffic. These membranes can also reduce the risk of cracks caused by subfloor imperfections. While adding a membrane increases both time and cost, it offers added insurance against expensive repairs later. For high-quality or large-scale tile installations, it is often recommended to include this layer as part of best practice.
What role does leveling compound play in preparing a surface before tiling?
Leveling compound is a cement-based product that is used to fill in uneven areas and create a smooth, flat surface prior to tile installation. It is critical in ensuring tiles lie flat without lippage (uneven tile edges) and that weight is evenly distributed across the surface. If the substrate has dips, humps, or other inconsistencies, applying a floor leveling compound can correct these issues and create an ideal base for successful tiling.
The compound is typically mixed with water to form a pourable liquid that is spread across the substrate using a trowel or gauge roller. It self-levels to an extent but may require some manual smoothing. Once dried, it provides a stable, even surface that’s suitable for tile bonding. It should be used only on structurally sound substrates and must be fully cured before tiling begins. Leveling the surface before tiling not only enhances appearance but also prevents stress fractures, making it an essential step in any precise tile layout.
What should I do after applying the base materials but before setting the tile?
After installing base materials, such as cement backer board or a plywood subfloor with underlayment, the next step is to ensure the surface is completely clean, dry, and flat. Dust, grease, and debris should be removed using a vacuum and a damp cloth, as even small particles can affect the bond between thinset and the tile. Any cracks or irregularities remaining after installation should be patched with a suitable patching compound or modified thinset in order to create a seamless tile base.
Additionally, if you’re tiling in a wet area like a bathroom floor or shower pan, it’s advisable to install a waterproofing membrane or apply a liquid waterproofing coating after securing and taping the seams of the backer board. This step helps prevent water from seeping into the subfloor and causing damage over time. Once all preparations are complete and materials are fully cured, a dry layout of the tiles is often recommended to plan spacing and cuts effectively. Only after confirming that the surface is ready should you proceed with applying thinset and setting the tile in place.