Alex Underwood, head of marketing (tiling), ARDEX Group, details everything you need to know about adhesive classifications
Tile adhesive classifications are standardised codes used to define how an adhesive performs under certain conditions.
For fixers and contractors, they are often considered an essential guide when deciding whether a product is suitable for a specific installation, substrate or environment.
However, while these classifications are widely recognised and have benefit, they can often be misunderstood or oversimplified. When selecting your tile adhesive – you need to consider more than just classification.
In the UK, formal adhesive standards were not introduced until 1980. Before this, tilers relied on manufacturer recommendations and practical experience to select suitable products.
The first real attempt to standardise testing came with BS 5980 in 1980, which outlined performance criteria for tile adhesives.
Today, tile adhesives are classified under BS EN 12004, introduced in the UK in 2001. This system uses a combination of letters and numbers to describe performance. For example, C refers to cementitious adhesives, D to dispersion adhesives, and numbers like 1 or 2 indicate normal or improved performance.
Additional letters highlight specific properties, such as T for reduced slip, E for extended open time, and F for fast setting. This coding provides a clearer, more detailed understanding of how an adhesive will perform under laboratory conditions.
Another important factor is deformability, classified as S1 or S2. These ratings indicate how much an adhesive can deform under stress. S1 adhesives are considered deformable, while S2 adhesives offer higher deformability. It is crucial to remember that deformability doesn’t equal flexibility.
This deformability is typically achieved through polymer modification and is especially important when tiling areas subject to movement or temperature changes. However, higher deformability does not automatically mean better performance in every situation.
Choosing the right adhesive goes beyond simply reading the classification. Each project must be assessed individually, taking into account the substrate condition, environmental factors, tile type, and expected load.
Factors such as ease of application, setting time, and site conditions also play a significant role, noting that classifications test results are based on laboratory testing with fixed room temperatures and materials.
Real world conditions can vary dramatically, so products need performance that is consistent on-site. It is important to also remember that not all product categories have standardised classification for performance – such as uncoupling – and that product innovations can also develop ahead of existing testing.
Innovations such as BAL AF Max, which is an uncoupling and adhesive system in one, has classifications for an adhesive, but its performance as an anti-fracture system are not within these classification limits.
Ultimately therefore, understanding these classifications ensures an aid to appropriate product selection, but ensuring you refer to the manufacturer guidance and product technical data will confirm what installations the product is suitable for and if this is guaranteed by a manufacturer warranty.
