Material Characterization and Fire Performance of Clay Boards

Abstract

Clay boards are emerging as a sustainable alternative to gypsum boards for fire protective linings in timber structures. However, their fire behaviour is still not well understood. Most existing studies focus on full scale systems, which show when a board fails but not why it fails. This thesis addresses this gap by investigating two commercial clay board variants with different compositions, densities, and thicknesses using a multi scale experimental approach.

First, the material-level behaviour was investigated, including microstructure, thermal properties, and thermal degradation. This knowledge was then used to interpret fire performance in small-scale cone calorimeter tests and intermediate-scale furnace tests. The results show that the performance of clay boards depends on both material composition and thickness. Under constant heat flux, both 22 mm clay board variants give comparable fire performance to a 13 mm Type F gypsum board. Organic components such as straw, wood, and miscanthus have little effect on thermal insulation.However, they play key role in maintaining structural integrity by binding the clay matrix together.Once these binders degrade, the clay board loses its strength and becomes prone to fall-off

Performance parameters obtained from cone calorimeter tests at 50 kW/m$^2$ showed good agreement with intermediate scale furnace tests conducted for 30 minutes. Comparison with the Eurocode 5 design model showed that current equations, which are valid for higher density boards, give similar but slightly conservative estimates of basic protection time when used for low density boards.

Overall, this study improves the understanding of clay boards at the material level. It helps relate material level knowledge of clay boards to their fire performance at small and intermediate scales. It also highlights the need for future full scale tests to better investigate board fall off, while considering the effects of orientation, material composition, jointing, and mechanical fixtures.

Popular Abstract

As construction moves toward more sustainable solutions, timber buildings are becoming increasingly popular. Timber stores carbon and can reduce the environmental impact of construction. However, timber burns, meaning buildings require fire protection systems that slow heat transfer and protect structural elements long enough for evacuation and firefighting.

Today, gypsum boards are widely used because they provide reliable fire protection. However, gypsum production and disposal create environmental challenges. Some gypsum products depend on industrial by-products that may become less available in the future, while gypsum waste disposal can create environmental concerns. Researchers and industry are therefore exploring alternatives that can provide similar protection with improved sustainability.

One possible alternative is clay boards. Clay-based materials have been used in buildings for centuries and are receiving renewed attention because they are natural materials with low environmental impact. Although clay boards are commercially available, surprisingly little is known about how they behave during fire exposure. Existing fire tests often show when a board fails, but not necessarily why it fails.

This thesis investigated two commercially available clay board products with different compositions and densities. Material characterization was combined with fire testing at multiple scales. Thermal properties, degradation behaviour, heat transfer, and fire performance were studied using heat flow measurements, thermal analysis, cone calorimeter testing, and furnace experiments.

The results showed that fire performance depends on both thickness and material composition. Organic fibres such as straw, wood fibres, and miscanthus had limited influence on thermal insulation but played an important role in maintaining mechanical integrity by helping bind the clay matrix together. Once these components degraded during heating, the boards became weaker and more prone to cracking or falling off.

The study also showed that two 22 mm clay board products provided thermal protection comparable to a conventional 13 mm fire-resistant gypsum board under constant heat exposure. Smaller laboratory-scale experiments also showed encouraging agreement with furnace tests, suggesting that reduced-scale methods may support future fire performance assessment.

These findings improve understanding of clay board behaviour during fire exposure and may support development of more sustainable fire protection solutions for timber construction. The work also highlights the importance of future large-scale testing to better understand real building performance, including effects of joints, fixings, orientation, and full structural assemblies.

• author: Shah, Muhammad Haris
• supervisor: Konrad Wilkens Flecknoe-Brown
• organization: Division of Fire Safety Engineering
• course: VBRM05 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Clay boards, Fire performance, Timber structures, Thermal insulation, Cone calorimeter, Furnace testing, Material characterization, Heat transfer, Fire protective linings, Sustainable construction
• publication/series: LUTVDG/TVBB
• report number: 5764
• other publication id: LUTVDG/TVBB—5764--SE
• language: English
• id: 9229105
• date added to LUP: 2026-06-02 08:28:12
• date last changed: 2026-06-02 08:28:12