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Understanding tile adhesive classifications and what they mean

Everyone knows what tile adhesive classifications mean don’t they? Or do they? Here, David Rowley, ARDEX Group UK training and technical support manager, clears up some of the confusion

Did you know that before 1980, tile adhesives didn’t have British Standard classifications and fixers were referred purely to a suitable BAL tile adhesive for the application in hand? This was because Building Adhesives Ltd (BAL) was set-up specifically by the British Ceramic Tile Council (BCTC) in the 1960s.

The current system of classification as we know it was first introduced to the UK in 2001 as BS EN 12004:2001, after which the BS 5980:1980 standard was withdrawn and replaced. This was a candidate harmonised European Standard, including Annex ZA provisions for CE marking of adhesives for tiles.

This introduced a classification with various numbers and letters to help describe tile adhesive characteristics.

These are:
C = Cementitious
D = Dispersion
1 = Normal characteristics
2 = Improved characterises
T = Reduced slip
E = Extended open time
F = Fast setting

In 1998, a European standard for the determination of transverse deformation for cementitious based adhesive and grouts was first published (BS EN 12002). In 2002 this standard was revised where ‘classes’ of transverse deformation were introduced with cementitious adhesives classifications for S1 or S2 when tested in accordance with BS EN12002:2008.

S1 adhesives are described as “Deformable (in conjunction with all the above features, this adhesive also has a deformability of between 2.5mm & 5mm)” while S2 adhesives have deformability of above 5mm.

In simple terms deformability means how much a solid, for example a cementitious tile adhesive, can change shape when a force is applied. S1 and S2 categories are normally achieved with additional polymer modification of cementitious tile adhesives and are associated with the tile adhesive being “flexible”.

BS 5384: Part 4:2015 advises that: “S2 classified adhesive and unbonded screeds are not suitable in heavily trafficked areas”.

Choose on a case-by-case basis
Think about where the adhesive is to be applied. Are the particular tile adhesive’s characteristics suitable for the particular application and site environment and conditions?

It’s a simple fact of tiling that you should treat each project on a case-by-case basis – each background must be properly assessed and prepared i.e. free from contamination, clean, dry, rigid, stable and capable of taking the types of expected loads imposed upon it without excessive movement or vertical deflection.

There are additional application properties which may also be considered –– is it easy to mix? Is it easy to trowel out? Would a pourable tile adhesive be a better choice in the case of large format tiles?

Maybe you need to build out the adhesives bed thickness (where suitable) in places such as window reveals, or isolated areas on the floor.

Does your adhesive need to set quickly for a fast-track application, or are there temperature/humidity considerations on site where you might benefit from the use of a normal setting adhesive? Alternatively, you may need to allow additional time for the tile adhesive to set in colder temperature of a minimum of 5°C and rising.

Using an S2 with an uncoupling mat
Another interesting question we often get asked is: “Can I just use an S2 with an uncoupling mat to get over difficult floors?” For the reasons stated above, the use of an uncoupling matting or a highly deformable S2 adhesive will not compensate for a poorly constructed or poorly prepared floor substrate.

The same would be true if tiles were applied to the uncoupling matting using an S2 adhesive. The uncoupling membrane is designed to neutralise lateral stresses that occur between the floor substrate and the tile covering.
BAL is hosting a webinar on Understanding Adhesives and Grouts at 6pm on 24 July on its Facebook page

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