Frequently Asked Questions (FAQ)

/Frequently Asked Questions (FAQ)
Frequently Asked Questions (FAQ) 2017-09-17T16:44:26+00:00
What are the optional deformability classifications; S1 & S2? 2017-07-26T18:35:16+00:00

S1 and S2 are defined in BS EN 12002:2002 as additional classifications for adhesives. Effectively, they describe how much an adhesive will deform to accommodate a limited amount of movement after tile fixing. These are optional standards and no adhesive must meet either classification​, nor does the deformability test, take into account flexural strength as part of the test.

S1 – Deformable adhesives (for cementitious adhesives only)

S2 – Highly deformable adhesives

What are the adhesive classifications C, D, R & F, T, E? 2017-09-18T12:37:33+00:00

The Classification and designation of tile adhesives as outlined in BS EN 12004:

C = Cementitious

D = Dispersion  (Ready mixed)

R = Reaction Resin

Tile Adhesive Classes:

1 = Normal adhesive

2 = Improved adhesive (meets the requirements for additional characteristics)

F = Fast setting adhesive (cementitious only) achieves 0.5 N/mm² within 6 hrs.)

T = Non slip (walls)

E = Extended open time i.e. > 30 minutes (for cementitious and dispersion adhesives only)

Tilers Common Terms 2017-07-24T13:26:13+00:00

Additive: More often refers to a liquid polymer that can be added to a grout or adhesive to improve its adhesion and flexibility.

Adjusting time: The length of time after fixing a tile that it can still be adjusted without detriment to the adhesive bond strength.

Brew: What the tiler must have before any work begins. This can be at any time of the day.

Buttering: The process of spreading a thin layer of adhesive on the underside of textured tiles directly before bedding. This is to ensure a full bed adhesive is achieved.

Calibrated / Un-calibrated: Calibrated tiles indicate a product submitted to specific mechanical finishing to obtain more precise dimensions.

Efflorescence: The appearance of light deposits of salts on cementitious materials, occasionally visible in grout lines. It’s a result of moisture bringing salts to the surface that when dry leave a white powdery deposit showing light and dark variations within the grout. This can due to migrating moisture from the background substrate, by watering or premature cleaning of the grout. It is not detrimental to grout performance.

Frost Resistant: The ability of a tile, adhesive or grout to perform even when the external conditions can result in frost formation. The tiles usually have very low water absorption to ensure cracking does not occur.

Internal / external: Products that are suitable for both internal and external use without affecting their performance.

Is your kettle broken?: What the tiler says when he hasn’t had a brew.

Knocked: A written off invoice.

Laitance: A term used to describe a fine particle material deposit (often referred to as ‘fines’ or ‘fat’) found on the surface of cementitious or calcium sulphate subfloors. The deposit is a weak interface and should be removed to ensure the tile adhesive has a sound, strong surface to bond to. Laitance should be mechanically removed and hoovered up. It is caused by too much water when installing a screed. It can also be found when a levelling compound has been mixed with too much liquid.

Movement joints: Gaps left in tiled floor and sealed with a flexible material to minimise the development of stresses within the tiling system, between different substrates, where tiles abut uprights, at corners and where expansion joints are present in the existing background.

Mould resistant: The ability of a product, usually a grout, to resist the growth of mould.

Muck: General term for the required adhesive. e.g. the muck is mixed in the bucket.

Open time: The time, usually in minutes, after application of an adhesive within which it will still bond and secure the tile. This can be influenced by the nature of the substrate (with absorbent substrates reducing open time) also the ambient conditions where warm, dry conditions reduce the open time.

Polymer modified: This term refers to adhesive and grout formulations that include added polymer for increased adhesion and flexibility. Polymer modified products are common due to the increased use of vitrified and porcelain tiles, which have a low absorbency and require a ‘better’ adhesive to adhere them.

Pot life: The length of time after mixing a grout or adhesive to use it. After the pot life has been reached, the mixing product should be discarded. Water should not be added to try and regain its characteristics.

Primer: A liquid applied to a substrate prior to tiling. Used either to enhance adhesion or to reduce porosity providing a longer open time for the adhesive.

Rapid setting: An adhesive modified so it sets rapidly, by utilising different cements and technologies. Enables tiling and grouting to be carried out in a shorter time frame.

Ready mixed: Adhesives that are supplied ready for use, without the requirement to add any water or liquid polymer. Usually acrylic based and generally only used for wall tile installations where set time is not so critical.

Set time or ‘Foot traffic’: The time, usually in hours, after which a bonded tile can be grouted and/or walked upon without affecting the bond. The set time for ready mixed adhesives is largely dependent on the type of tiles and substrate.

Slaking: Allowing time for the mixed adhesive to absorb water.

Slump or slip: The vertical movement of a wall tile after it has been bedded into an adhesive. Modern adhesives are modified with anti-slump or anti-slip characteristics.

Solid bed fixing: Bedding under the tiles which, as far as is practicable, is free of voids, so that the tiles are solidly supported.

Tanking: Applying waterproof membrane, usually incorporating a mesh, in areas such as showers to protect moisture sensitive background substrates from water impregnation.

Technical issue: This can be anything that has gone wrong, as it’s not the tilers fault.

Tensile adhesion strength: A standard test used to determine adhesion strength of tiles and adhesive. Usually quoted in N/mm² and the higher the number the greater the bond between the materials.

Tile backer boards: These boards can be constructed from a variety of materials including cement, or resin based compounds and may be reinforced to give added strength. These boards are sometimes suitable for use in wet areas, e.g. showers, or for their insulation properties.

Underfloor heating: There are two basic underfloor heating systems used with tiling installations. The first is warm water pipes within a screed. This does not generally require any special products to be used. The other is electrical mats placed on the screed surface. These often need to be covered in adhesive (polymer modified) or in a suitable smoothing compound.

Water repellent: Used usually when referring to grout, it’s the ability of the product to repel water from its surface. Note; Does not imply a waterproof grout.

Water resistant: The ability of an adhesive or grout to still retain its performance even when subject to full immersion in water.

Water staining: A situation where moisture gets into natural stone, or some porous body ceramic tiles, resulting in discolouration, usually of the edges, but sometimes the faces of the tile.

Working time or ‘Workability’: The time, usually in minutes, after mixing an adhesive or grout that will still retain its characteristics to enable it to be applied, bedded onto and finished. With a rapid setting adhesive the working time will be reduced the longer the material is left in the mixing container. Also, warmer temperatures will reduce the working time.

Can I tile to Timber floors? 2017-07-24T13:20:15+00:00


Many adhesive manufacturers produce specific groups of products for tiling to suspended wooden floors.

Generally, the floor needs to be stable with normal humidity levels and be physically capable of bearing the extra weight. The floor is then overlaid with a proprietary intermediate substrate to separate the tiles from the floor, eliminating cracking and crazing caused by movement and differential rates of expansion and contraction due to temperature changes. Specific types of product used for the overlay are relevant to different situations.

The overlay is then followed by the application of a sealant where necessary and adhesives and grouts designed to be suitable for this purpose.

Is there a weight limit when tiling a wall? 2017-07-24T13:19:58+00:00


The maximum weight of tiling which can be supported by a dry, well-adhered plaster background is 20kg/m². Equivalent to ceramic tiles with a maximum thickness of 8mm plus tile adhesive or natural stone tiles with a maximum thickness of 7mm plus tile adhesive.

The weight of tiling to a plasterboard background direct (without plaster skim) should not exceed 32kg/m². This is equivalent to a ceramic tile and adhesive with a maximum thickness of 12.5mm and natural stone and adhesive with a maximum thickness of 10mm.

Weights quoted include the tile and adhesive. Further advice should be sought either from the manufacturer, regarding the suitability of the adhesives and grouts. In addition guidance must be sought from board manufacturer regarding additional information on recommended methods for the installation of boards.The following table is a general guide to common types of building board and the maximum recommended weights for tiling.

Wall Substrates Maximum Weight of Tiling per m²

Gypsum Plaster 20Kg/m²

Gypsum Plasterboard Direct (without a plaster skim) 32Kg/m²

Wood-based sheets 30Kg/m²

Foam-cored tile-backing boards 60Kg/m²

Fibre-cement boards 60Kg/m²

Gypsum Fibre boards 35-40Kg/m²

*In this context tiling is defined as a tile plus its bedding and grouting material.

Are there minimum quality standards for tile adhesives? 2017-07-24T13:17:27+00:00


BS EN 12004 is the standard which sets out the minimum performance requirements for ceramic tile adhesives in Europe, setting out the designation and classification system for the different types of adhesives based on performance in the various tests.
For any manufacturer to conform to the Standard, the product must possess the mandatory, fundamental characteristics outlined for each type of adhesive. Where a manufacturer classifies a product to a category within the Standard, e.g. CIT, this automatically confirms conformance.
Where a product is CE marked, this does not automatically mean that its performance complies to all the mandatory requirements in BS EN 12004, but implies that the adhesive satisfies the mandated part of the Standard.

Essentially, this means that a cementitious adhesive failing to meet the performance requirements in the heat ageing and freeze/thaw tests, i.e. the fundamental characteristics, can still carry the CE mark because neither of these requirements form part of the Construction Products Directive Mandate for Durability.

Before specifying cementitious adhesives, the Technical Data sheets should be checked. The description may reference BS EN 12004 and may carry a CE Mark but it is important to examine the rest of the text. If the adhesive fails to meet the requirements for heat ageing and freeze/thaw the text should say either NPD (no performance determined) or should state a value in N/mm2, which will certainly be less than 0.5N/mm2.

Therefore, good quality products will carry a classification rating such as C1TE, a CE Mark and a reference to BS EN 12004, with substantiated data on the label. Low performance adhesives will have omissions to this data, especially for classification rating.