Module 1: Surface Preparation 

Proper surface preparation is the foundation of a successful tiling project. A poorly prepared substrate can lead to cracked tiles, adhesive failure, and moisture problems. This module covers the key steps in ensuring a stable, clean, and level surface before tile installation.

1. Assessing Substrate Conditions

Before tiling, the substrate (the surface receiving the tiles) must be evaluated for stability, flatness, and cleanliness.

• Structural Integrity: The substrate must be rigid and free from movement. Wooden floors should be checked for excessive flexing, and concrete slabs must be fully cured (typically 28 days for new pours).

• Cleanliness: Remove dust, grease, paint, or old adhesive residues. A contaminated surface prevents proper adhesion.

• Flatness: Use a straightedge or level to check for dips, bumps, or unevenness. Deviations greater than 3mm over 1m require correction.

• Compatibility: Ensure the substrate material (concrete, plywood, cement board) is suitable for the chosen tile type.

2. Moisture Testing Methods

Excess moisture can ruin tile installations by causing adhesive failure, mold growth, or efflorescence.

• Concrete Moisture Test:

• Plastic Sheet Test: Tape a plastic sheet (1m²) to the floor for 24–48 hours. Condensation underneath indicates high moisture.

• Calcium Chloride Test (ASTM F1869): Measures moisture vapor emission rate (MVER). Acceptable levels are typically ≤5 lbs/1000 sq ft/24 hrs for most tile adhesives.

• Relative Humidity (RH) Probe (ASTM F2170): Drills a hole and inserts a sensor for accurate moisture readings.

• Wood Subfloor Moisture Check:

• Use a moisture meter—acceptable levels are usually ≤12% for wood subfloors.

3. Leveling Techniques

An uneven surface leads to lippage (uneven tile edges) and poor adhesion.

• Self-Leveling Compounds (SLC):

• Ideal for concrete floors with minor imperfections.

• Requires priming and proper mixing for a smooth, flat surface.

• Patching Compounds:

• Used for localized repairs (cracks, holes).

• Plywood Overlays:

• For wooden subfloors, additional layers (e.g., cement backer board or 1/4" plywood) may be needed to stabilize and level the surface.

4. Priming and Sealing Surfaces

Primers improve adhesion and prevent excessive moisture absorption.

• Primer Selection:

• Acrylic Primers: For porous surfaces (concrete, masonry).

• Epoxy Primers: For non-porous or slick surfaces.

• Application:

• Apply evenly with a roller or brush; allow proper drying time (as per manufacturer’s instructions).

• Sealing:

• Some substrates (e.g., gypsum-based boards) may require sealing to prevent water damage.

5. Solving Common Substrate Issues

• Cracks in Concrete:

• Fill with a flexible patching compound or use an anti-fracture membrane.

• Uneven Wood Subfloors:

• Sand high spots or add underlayment (e.g., cement backer board).

• Efflorescence (White Salt Deposits):

• Clean with a mild acid wash (e.g., vinegar solution) and seal the surface.

• Loose or Delaminated Old Tiles:

• Remove completely or apply a decoupling membrane over a stable base.

Conclusion

Proper surface preparation ensures long-lasting tile installations. Skipping this step can lead to costly failures. Always follow manufacturer guidelines for substrates, primers, and leveling methods.