Ceramic tile installation on irregularly shaped substrates

On many occasions, when the substrate has an uneven surface, standard EN 138002 indicates that it should be regularised until, using a two-metre ruler, the differences in flatness are less than 5 mm. Occasionally, other materials or adhesives may be used which, owing to their characteristics, allow thick layers to be applied, capable of providing good adhesion when the required tile-to-tile thicknesses are of the order of 10-15 mm.

When there are deficiencies of planimetry in the substrate, it is not advisable to use the “tapping” or “sticking” tile installation technique, because this limits the adhesion of the adhesive mortar, which can lead to detachments.

The “false double gluing”, which consists of spreading the adhesive mortar on the substrate and applying “dabs” or “dabs” on the piece, produces the same effect as “tapping” tile installation, as well as excessive consumption of adhesive mortar.

Check the flatness of the substrate with a ruler 2 metres long; if the differences are greater than 5 mm, a thick-bed adhesive mortar can be used as a bonding material at specific points (low areas).

VAT® FLEX RAPID/ PAM® ECOGEL FLEX/ PAM® ECOGEL SUPERFLEX must be used to even out the substrate surface up to a thickness of 15 mm and to ensure proper adhesion to non-absorbing parts.

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Solution: Laying ceramics on irregularly-shaped substrates


Check that the substrate is perfectly set, resistant and stable (has completed its maturing period).

Clean the surface of any residues that may hinder the adhesion of the adhesive mortar, such as dust, paint, oil, etc.

Recommended period for the maturation of carriers
HorizontalsConcrete floors
Concrete floors
2-6 months
2-4 months
VerticalsConcrete walls
Block walls
6 months
2-3 months
2 months
Intermediate layersBurden sharing
28 days
28 days
28 days


Knead with a slow electric mixer (500 rpm) and spread VAT® FLEX RAPID/ PAM® ECOGEL FLEX / PAM® ECOGELSUPERFLEX on the substrate with a notched trowel, preferably with semi-circular teeth.

For the application of tiles larger than 900 cm², double bonding must be carried out.

Apply good pressure on the tile until the grooves of the tile adhesive are flattened.

Leave a minimum joint width of 2 mm in interiors and 5 mm in exteriors; grout after 24 hours with the BORADA® range of joint mortars by Molins.


  • Do not apply in rainy conditions, or at temperatures < 5ºC or >30ºC.
  • On poorly absorbent substrates, open the pore with water and 50% hydrochloric acid (salfuman).
  • VAT® FLEX RAPID/PAM® ECOGEL FLEX/ PAM® ECOGEL SUPERFLEXcan be used for external skirting boards on brickwork with a maximum height of no more than 2m.
  • Do not apply in thicknesses greater than 15 mm or less than 5 mm.

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