Substrates made of gypsum, plaster, anhydrite, etc.

Traditionally, we can find sulphur-based substrates (gypsum, plaster, anhydrite, perlite plaster, etc.).

In relation to the adherence of a ceramic tile to these types of substrates, the interaction between the sulfates and the cement of the adhesive products must be taken into account, causing expansion of the substrate and, consequently, detachment of the cladding.

Another detail that cannot be overlooked in these types of operations is the difference in resistance between the substrate (gypsum, plaster, anhydrite, etc.) and the adhesive (cementitious), which could cause detachment thereof.

Preliminary analysis

The described substrates (gypsum, plaster, anhydrite, perlite plaster, etc.) may react with the cement, giving rise to cement-gypsum incompatibility. Therefore, adhesives with special additives are required in order to:

  • Inhibit the formation of expansive compounds (calcium sulfoaluminates) that break the adherence plane.
  • Ensure a perfect bond between the adhesive and the substrate.
  • Ensure homogeneous setting.
  • Avoid using adherence primers.

Technical considerations

The first consideration to be taken into account is the state of the substrate on which the cladding will be installed:

  1. Remove any surface patina; surfaces must be resistant, clean and perfectly set.
  2. Avoid dead gypsum plasters or weak rendering.
  3. Residual humidity of less than 3%.
  4. Greater attention must be paid to prefabricated gypsum or plaster, performing the following preliminary operations:
  • Removal of the assembly paste.

The substrate must have the adequate flatness and be clean of dust generated during the execution of grooves.

  • As a result of the manufacturing process of this type of substrate, we find less porous and very smooth sheets, preventing adherence of the adhesives, due to which the surface of the prefabricated gypsum must be prepared by applying GECOL Primer-TP adherence primer diluted with water in the ratio 1:3.

 

A second consideration to be taken into account is the design of the joints, making sure to:

  • Leave at least 2 mm joint spacing between tiles.
  • Execute perimeter movement joints in corners and changes in plane, height or material.
  • Execute expansion joints between door and structural cavities of the building.

All expansion joints should be filled with elastic mastics such as GECOL Elastic-MS.

 

Likewise, the use of mechanical anchorages is obligatory whenever tiles with dimensions greater than 60 x 40 cm or 40 kg / m2 are installed.

Jointing mortar must be applied in accordance with the times marked in the Technical Data Sheet of the adhesive.

Commissioning will take place 48 hours after executing the joint.

Recommended products

Adhesives

Conventional ceramics gypsum supports

Anhydrite supports

Joint mortars

From 0 to 20 mm quick setting

Up to 6 mm

From 3 to 15 mm

Flexible mastic

Elastomeric mastic

Additive

Warnings: The data provided by this Constructive Solution were prepared based on standard onsite installation processes. However, we recommend that you consult our Technical Department in the event of any specific circumstance info@gecol.com