When specifying materials for kitchens, worktops and other surfaces that may be exposed to heat, it is important to understand how they perform in practice. For architects, designers and other decision-makers, material selection is not only about aesthetics, but also about documented performance.

SINTEF tested several natural stones from Lundhs Real Stone® to assess how the surfaces respond to both dry and wet heat.

The results demonstrate a high level of resistance: all tested varieties of Larvikite and Anorthosite achieved the highest score of 5, corresponding to “no change”, at every test temperature up to 300 °C.

What was tested?

SINTEF carried out laboratory testing of eight different natural stone varieties intended for use as worktops. Six of the varieties were Larvikite, one was Anorthosite and one was Granite.

The Lundhs Real Stone® materials included in the testing were Lundhs Emerald®, Lundhs Blue® and Lundhs Royal® in Larvikite, as well as Lundhs Antique® in Anorthosite.

The stones tested included both polished and silk/leather finishes, as well as slabs with thicknesses of 22 and 32 mm. The testing therefore covered several of the finishes and dimensions commonly used for worktops and other interior applications.

Two types of heat exposure were investigated: dry heat in accordance with NS-EN 12722 and wet heat in accordance with NS-EN 12721.

Dry heat: direct contact with a hot object

For the dry heat test, a heated aluminium element was placed directly on the stone surface. The heating element had a diameter of 100 mm and remained in contact with the surface for exactly 20 minutes.

The tests were carried out at 125, 150, 200, 250 and 300 °C. Three parallel tests were conducted at each temperature level. The samples were then left undisturbed for 16 to 24 hours before the surfaces were visually assessed.

The result was the same for all tested varieties of larvikite and anorthosite: no visible changes in gloss, colour or surface texture were recorded at any of the temperatures, including 300 °C.

Wet heat: heat combined with moisture

In use, a surface may be exposed to both heat and moisture at the same time. SINTEF therefore also carried out a separate wet heat test, in which a heated element was placed on a damp cloth on the stone surface.

Again, the contact time was 20 minutes, and the tests were carried out at temperatures ranging from 125 to 300 °C. After cooling and a resting period of 16 to 24 hours, the surfaces were visually assessed.

The result was again consistent: the tested varieties of both larvikite and anorthosite achieved a score of 5 at all temperatures. This means that SINTEF recorded no changes in gloss, colour or surface texture following the testing.

For Lundhs Antique®, which is Anorthosite, SINTEF also noted that the sample slab had some faintly visible, mineral-filled fissures prior to testing. No opening or increased visibility of these fissures was observed as a result of the heat exposure.

Tested beyond the standard temperature levels

An important point in SINTEF’s report is that the temperatures used in this test were significantly higher than those normally specified in the relevant test standards.

SINTEF states that the standard test temperature for dry heat is 200 °C, while wet heat is tested at 100 °C. In the test programme for Lundhs, both methods were carried out progressively at temperatures of up to 300 °C.

The results therefore provide an indication of how the tested surfaces performed under considerable heat exposure within the conditions of the relevant test methods.

What do the results mean for material specification?

For architects and designers, the test results provide documented performance data when considering Larvikite or Anorthosite from Lundhs Real Stone® for worktops and other surfaces where contact with hot objects may occur.

At the same time, it is important to distinguish between what the test documents and other forms of temperature exposure.

The test assesses resistance to short-term heat exposure on the surface. It does not assess the materials’ fire resistance, prolonged exposure to high temperatures, or performance in specific constructions and installations.

For specification purposes, the results should therefore be understood for what they document: very good resistance to surface heat exposure under the described test conditions.

Larvikite and Anorthosite as functional natural materials

Natural stone is often selected for its appearance, materiality and ability to give a project a distinct identity. For materials used in functional areas, however, technical performance must also be documented.

SINTEF’s testing shows that the tested varieties of Larvikite and Anorthosite from Lundhs Real Stone® combine the distinctive character of natural stone with documented resistance to both dry and wet heat exposure.

For specification, this provides a clearer basis for decision-making – and greater freedom to use natural stone on surfaces where aesthetics, functionality and durability are all important.

The test was carried out by SINTEF in 2019. The test results apply to the specific samples examined by SINTEF. Testing was conducted on natural stone worktops, and the results should be considered in relation to the test method, product, surface finish and the specific application.