How we mentioned in previous article, a good tile and wood flooring adhesion depends on a correct diagnosis and proper preparation of the substrate beforehand. The following description explains how this should be done. The substrate must be flat, hard, stable, well adhered, clean, dry and have normal absorption.
5. Adhesion. How to check the adhesion of the existing coverage?
The substrate must be cohesive and resistant in order to ensure the cement-based adhesive bonds properly.
5.1 Check the adhesion of existing tiles or rigid floor tiles by gently tapping with a hammer.
5.2 Any hollow sounding tiles or tiles with poor adhesion must be removed and replaced or repaired.
5.3 To check the adhesion of existing paint, carry out a cross-hatch test using a suitable knife or cutter. Emulsion paint is not suitable for tiling over.
5.4 Score the paint in small 2 x 2mm squares over a total area of 10 x 10cm. The paint is considered suitable for tiling if 80% of the area of the small squares remain bonded. If not, the paint must be removed mechanically.
6. Cleanliness. How to clean the substrate?
The substrate must be clean in order to ensure the adhesive bonds properly.
6.1 Eliminate any traces of contaminant with a scraper. Carefully vacuum any dust and then apply the primer.
6.2 If the existing floor covering has been removed, eliminate any traces of adhesive so that no film residues remain, only residual coloration of the substrate. Apply the primer.
6.3 If the existing covering is retained, remove any traces of varnish or wax with an emulsifying pad and sugar soap. Wash existing paints, vinyl or ceramic tiles.
6.4 On concrete, remove any residues that may affect the adhesion, such as superficial free lime or traces of oil, using high pressure cleaning, sanding, abrasive cleaning, etc.
7. Humidity. How to check if the substrate is dry?
The substrate must not leach moisture.
Plaster substrates must not have more than 5% residual moisture during application. A minimum of 4 weeks drying time must be allowed prior to tiling.
Anhydrite screeds must not have more than 0.5% residual moisture before being covered.
Cement/sand renders and screeds must be left for 2 weeks and 3 weeks respectively prior to tiling unless special fixing methods are employed.
Gypsum plaster should normally be primed before applying a tile adhesive. If the adhesive is cement-based, it must be sealed with the primer.
Remove any laitance from anhydrite screeds and seal with the primer before applying any cement-based product, levelling compound or tile adhesive.