ADVICE & SOLUTIONS

FIXING TILES ON CALCIUM SULPHATE – ANHYDRITE SCREEDS

 
ADVICES PREPARATION APPLICATION FINISHING

What needs done with this substrate which requires particular precautions before fixing the tiling?

 

It should not be confused with a cement mortar screed.

 

Recommendations :

• In all cases, refer to the AT technical authorisation and contact the manufacturer of the screed for specific application instructions.

• An additional protection against humidity as specified in the AT technical authorisations of the screeds is necessary. (Work in accordance with the AT technical authorisaton of the screed and the CPT specification).


SUITABLE SUBSTRATES:

Calcium sulphate based screeds should conform to the appropirate CSTB technical authorisations. Their common parts are described in the CPT specification n° 3578.

 

Maximum thicknesses covered by the CPT specification n° 3578:

• 6 cm max without heating system

• 7 cm max with low temperature water heating system. BEFORE

 

FIXING THE TILES IMPORTANT:

Follow the instructions given in the relevant AT technical authorisations in force.

 

SUBSTRATE PREPARATION

The condition of the substrate should always be checked before fixing the tiles. The surface of the screed must be sound, dust free and not have any signs of laitance. Completely eliminate the surface skin as per the instructions in the AT technical authorisation of the screed. The use of CERMIFILM primer improves the surface condition.

 

Floors with concealed underfloor heating:

A heating cycle must be carried out (DTU 65.14) before fixing the tiling as per the procedure described in the AT technical authorisation of the screed. Switch off the heating 48 h before fixing the tiles, during the work and at least 48 h after fixing the tiling.

 

Evenness of the screed: after sanding and the treatment of any fissures (as per the AT), the maximum unevenness must be less than +/- 5mm under a 2 m rule and +/- 1mm under a 20 cm ruler.

 

Residual moisture:

should be measured with a carbide spray and be less than or equal to: 

- 0.5% in humid areas classified E2 (maximum) (kitchens, bathrooms, WCs, etc.) 

- 1% in areas classified E1 (living rooms, lounges, bedrooms, etc.).

 

Complying with the indicative drying times does not preclude the need for a residual moisture test.


FIXING THE TILING:

This should be done as per the CPTspecification n° 3527. Direct bonding of tiles on calcium sulphate based screeds, in other words:

 

With CERMIFILM primer:

- Double spreading with CERMITEX, CERMIPLUS, CERMIPLUS RAPID, CERMIPLUS XL FLEX, CERMIFLEX ALG ;

- Single spreading CERFLOOR RAPID, CERMIFLEX ALG.

 

Without primer:

- Single spreading with CERMIDRITE

 

• Since these are quick setting adhesive mortars, only small quantities should be mixed at any one time.

 

• Work on areas of around 2m² and regularly check the adhesive is being properly transferred onto the back of the tiles.

 

• Maximum adhesive thickness: 5 mm.

 

- When fixing the tiles, allow for suitable inter-tile joints, for example around 5 to 6 mm for 30 x 30 tiles, and allow for the necessary technical joints such as peripheral and expansion joints.

 

- For finishing, use for example CERMIJOINT SOUPLE, CERMIJOINT TX + CERMILATEX on floors without underfloor heating or CERMIJOINT Souple on floors with underfloor heating.

 

• Direct bonding with CERMIFACE bond breaking system - See Technical Data Sheet n° 820.

 

NB: For private humid rooms.

 

E2 rooms maximum: bathrooms, WCs, domestic kitchens.

 

An additional protection against humidity as specified in the AT technical authorisations of the screeds is necessary. (Work according to the CPT specification and the AT technical authorisation of the screed).

 

Example of solution: water proofing a floor/wall angle over 10 cm: after having applied CERMIFILM on the floor and skirting board areas, allow to dry before sticking down AR 12 reninforcement strip with 2 coats of CERMICRYL water proofing in the angles (See Technical Data Sheets n° 101 and 300).


In routine areas, finish with CERMIJOINT SOUPLE or CERMIJOINT TX + CERMILATEX for enhanced water proofing.

 

CLEANING OF JOINTS

• Use KITAJOINT.


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