Cementos Molins

Fixing ceramic tiles on uneven substrates

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On many occasions, when the substrate is uneven, ceramic tiles cannot be fixed in a thin layer and it is necessary to use other fixing materials called thick layer adhesive mortars, which can provide good adherence when the required fixing thicknesses are about 15 mm.

When the support is uneven, it is not advisable to use the “touching” or “spot” fixing technique, because otherwise it limits the adherence of the adhesive mortar, and this may cause the tiles to work loose or fall.

The “false Floating and buttering ” method, which consists in spreading the adhesive mortar over the support and using the “touching” or “spot” fixing technique, produces the same effect as the “touching” fixing method, but also requires an excessive amount of adhesive mortar.

Check the smoothness of the support with a 2 m long ruler; if differences are greater than 5 mm, a thick layer adhesive mortar is to be used as the fixing material.

In order to level the support surface, when working with thicknesses up to 15 mm, while also guaranteeing adequate adherence without any absorption, it is necessary to use VAT® FLEX RAPID.

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Check that the support is well set, strong and stable (its curing period has finished).

Clean the surface of any waste that may hinder the adhesive mortar’s adherence, like dust, paint, oil, etc.

Recommended period for support curing
HorizontalConcrete flooringsConcrete slabs2-6 months2-4 months
VerticalConcrete wallsBlock wallsBrickwork6 months2-3 months2 months
Intermediate layersLoad distributionRegulatingLevelling28 days28 days28 days


Mix with a slow electric mixer (500 rpm) and spread VAT® FLEX RAPID onto the support using the semicircular notched trowel, preferably with semicircular teeth.

For fixing tiles larger than 900 cm2 using the Floating and buttering method.

Press the tiles firmly so that the grooves of tile cement are flattened.

Leave a minimum grouting joint width of 2 mm indoors, and 5 mm outdoors; regrout after 24 hours using the grouting range BORADA® by PROPAMSA.


  • Do not apply in wet weather, or with temperatures of <5ºC or >30ºC.
  • With poor absorbency supports, open the pore with water and hydrochloric acid at 50%.
  • You can use VAT® FLEX RAPID on outdoor base plate renders on a brick support, up to a maximum height of 2 m.
  • Do not apply more than 15 mm thick, or less than 5 mm.



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