Verified guide · Preparation

How to inspect and prepare a substrate before tiling

Do not start tiling until the substrate is stable, sound, clean, sufficiently flat and compatible with the selected system. Tiles and adhesive cannot repair an uncertain base.

Sources checked on 21 July 2026

Direct answer

Diagnose first; repair and prepare second.

Identify the substrate, check cracks and movement, remove weak or contaminated layers, measure flatness and verify moisture, age and site conditions. Choose primer, repair or waterproofing from the complete documented system, not by habit.

01

Checks before opening the adhesive

Record these conditions so the selected solution can be justified.

  • Substrate type and condition: concrete, screed, gypsum, board, existing tile or another material.
  • Stability and cohesion: no loose areas, unresolved deformation or active cracks.
  • Cleanliness: no dust, grease, wax, poorly bonded paint, laitance or release agent.
  • Flatness and geometry measured with the method and tolerance applicable to the system.
  • Moisture, age and curing within the project and manufacturer limits.
  • Compatibility between adhesive, primer, waterproofing, tile and substrate.

02

Which document decides each issue

01 · Regulation

Building requirements

The Spanish CTE may require moisture or safety performance where it applies. It does not prescribe every installation step.

02 · Technical standard

Installation rules

UNE 138002:2023 structures bonded installation in Spain; NF DTU 52.2 covers defined work in France. Their scope and the project determine use.

03 · Manufacturer

Product limits

The current data sheet defines permitted substrates, preparation, primers, thicknesses, times and conditions for that product.

04 · Good practice

Pre-installation control

Recording measurements, cracks and tests helps prevent an unresolved problem from being hidden under the finish.

03

Preparation sequence

This order reduces the risk of repairing twice or trapping moisture and movement.

  1. 01

    Identify the substrate, use, water exposure and the documents that apply in the project country.

  2. 02

    Inspect stability, cracks, existing joints and intermediate layers.

  3. 03

    Clean and remove anything that impairs bonding, then vacuum residual dust.

  4. 04

    Measure flatness and moisture with suitable methods and record the results.

  5. 05

    Repair or level with a compatible product and observe its curing time.

  6. 06

    Apply primer or waterproofing only when specified by the documented system.

04 · Stop point

Stop and obtain technical confirmation

Do not cover the substrate when any of these conditions remain unresolved.

  • Active cracks, movement, deformation or an unresolved structural joint.
  • Persistent moisture, leakage, salts or an unknown source of water.
  • A friable, hollow or contaminated substrate, or layers whose adhesion cannot be verified.
  • No documented compatibility between the substrate and the proposed system.
  • Flatness outside the permitted range with a proposal to compensate only with more adhesive.

05

Sources and scope

CalcuCeram summarises technical criteria in its own words. Check the complete document applicable in Spain or France, the project and the current system data sheets before work.

06

Frequently asked questions about substrates

Can I correct flatness by using more adhesive?

Do not assume so. Adhesive has a documented thickness and field of use. If the substrate is outside tolerance, use a compatible levelling solution and observe its curing time before tiling.

Does every substrate need a primer?

No. It depends on absorption, cohesion, substrate material and the selected product. Use only the primer specified by the data sheet or documented system.

Can I tile over existing tiles?

Only after checking stability, adhesion, cleanliness, flatness, joints and compatibility. Covering a hollow, loose or contaminated tile does not repair it.

07