Impact Testing of Terracotta Tiles in Rainscreen Systems

Terracotta tiles have gained popularity in architectural design, particularly in rainscreen systems, due to their aesthetic appeal and durability. Rainscreen systems provide a protective layer that enhances building performance by managing moisture and improving thermal insulation. However, the performance of terracotta tiles under various environmental and mechanical stresses is crucial for ensuring the longevity and safety of these structures. In the UK, impact testing plays a vital role in assessing the resilience of terracotta tiles used in such applications.

Impact testing evaluates the ability of materials to withstand sudden forces, which can occur due to environmental factors, human activity, or accidental impacts. For terracotta tiles, this testing is essential to ensure:

• Safety: Terracotta tiles can be exposed to various environmental stresses, and ensuring they can withstand impacts reduces the risk of tiles breaking and falling, which could endanger people and property below.
• Durability and performance: Impact testing helps assess how well the tiles will hold up over time under physical stress. Impact testing helps evaluate how terracotta tiles respond to different environmental factors and weather conditions, ensuring they remain intact and effective in protecting the building. Tiles that pass these tests are a safer product, leading to reduced maintenance and replacement costs.
• Compliance with Building Standards: The UK has strict building regulations that mandate certain safety and performance standards. However, Impact testing is not part of the specific requirements for facades but clients, architects and insurance bodies such as the NHBC are becoming more aware of the importance of ensuring that the performance of the terracotta tiles and all cladding products, meet the requirements of safety and serviceability that the developed CWCT (Curtain Wall & Cladding Technology) Technical Note 75 & 76 provides. This evaluation on impact provides confidence to the client team for the cladding to last for the design life anticipated. 

In the UK, impact testing of terracotta tiles typically follows the CWCT guidelines of TN 75 & 76 as there is no currently developed British Standard specific for impact performance of cladding although there are other documents and standards which have been used as referencing to develop these Technical Notes. The Standard for impacts of cladding used to be included in BS 8200:1985 – Design of non-load bearing external vertical enclosures of buildings but unfortunately, this standard was not developed and 95% of the document was irrelevant to current standards and applications and was withdrawn from publication on the 10^th Dec 2010.  The element of this document that was relevant, was the impact of facades section. The CWCT noted the importance of impacting of facades and through evaluation of the testing methods within BS8200, they streamlined the testing process to the evaluation noted in TN 75 & 76 today. TN75 outlines the requirements for impact testing the facades and gives guidance on specification and assessment of the impact performance. TN76 describes the methods of testing cladding panels for impact.

The common methodologies for impact include:

• Drop Weight Test: A standard weight is dropped from a predetermined height onto the surface. The height and weight are adjusted based on the desired impact level. This is a test not generally relevant to the façade cladding market and not part of the CWCT TN 75 & 76 impact performance of building envelopes. 
• Pendulum Test: A pendulum mechanism swings either a soft body or hard body element towards the tile or facade, simulating various impact energies. The soft body impacts are from a 400mm diameter coarse canvas bag of glass spheres marbles 3mm in diameter with various impacts ranging from 120Nm to 500Nm or Joules under serviceability and safety. The hard body impacts are from a 50mm diameter solid steel ball with a mass of 0.5kg and a 62.5mm diameter with a mass of 1kg. the impact energies are 3, 6 & 10Nm or Joules. Impact energies 3 & 6Nm are carried out by the 50mm diameter ball and the 10Nm carried out with the 62.5mm diameter ball. 

The results from these tests are analysed to determine whether the tiles meet the required impact resistance criteria set out by the client team. It is easy to review the document and specify your requirements to be class 1 for serviceability and Negligible risk for safety. However, terracotta is a brittle but robust material. Hard body impacts on profiled shaped tiles can crack the tiles but as long as they are safely maintained on the façade and it is possible to replace these elements, then the product is safe and fit for purpose. Understanding the scope of impact testing is important and we can help to guide you through this process if you require.  

Variations in the clay and glazing materials, tile thickness, geometry and size can often affect impact performance. This is why, often, bespoke tile designs are required to undergo a testing regime to establish their suitability. 

Impact testing of rainscreen systems is a critical component of building design and construction in the UK and ensures safety and performance. This is why as architects and builders continue to explore sustainable and aesthetically pleasing materials, the importance of rigorous testing cannot be overstated. 

Argeton terracotta is one of the most used terracotta cladding systems in the UK and the rest of the world. There are dozens of Argeton tile profiles available off the shelf with impact accreditations and at Telling Rainscreens we like to encourage design and innovation through continuously partnering with architects, designers and developers and investing in the impact testing of new tiles.