EN 16306 Determination of Resistance of Marble to Thermal and Humidity Cycles

The European standard "EN 16306 Natural stone test methods - Determination of the resistance of marble to thermal and moisture cycles" describes a laboratory method for determining the resistance of marble intended for exterior cladding of building facades to thermal and moisture cycles. Some marbles are known to experience warping and rapid strength loss when used as exterior cladding.

For the purposes of this standard, the following terms and definitions apply:

• Bending refers to the transformation of a flat, planar shape into a curved or bowl-shaped shape in a convex or concave direction. Other common terms for the same phenomenon are cupping and bending. Convex bending is measured in positive values, while concave bending is measured in negative values.
• Convex bending refers to the upward bending of the middle portion of the sample away from the moist substrate.
• Concave bending refers to the downward bending of the middle portion of the sample away from the applied heat.
• Marble is a metamorphic rock containing more than 50 percent carbonate (calcite, aragonite, or dolomite) by volume, formed by the metamorphic recrystallization of carbonate rock. Only geologically defined marble is applicable to this standard. Stones that are solely commercially defined as marble (e.g., polishable limestone) do not need to be tested.

In principle, bending is measured on test specimens placed in a test chamber and subjected to heat cycles on one side and humidity on the other. The temperature range is from 20°C to 80°C, with each cycle lasting 24 hours. The temperature is measured on a black reference plate placed on the surface of one specimen to control the climate within the test chamber. Strength loss should be measured on the reference and exposed specimens according to EN 12372, and the results compared.

Sampling is not the responsibility of the testing laboratory unless specifically requested. At least six samples should be thermally cycled within the test chamber, and a similar number of samples from the same batch should be used as references for measuring the flexural strength of the untreated material. Samples should be selected to be representative of the material to be tested. For identification testing, any foliation should be considered. Six samples with faces perpendicular to the foliation and six samples parallel to the foliation should then be selected. For technological testing, it is sufficient to select samples with a single, common orientation based on the sample's intended use. Doubling the number of test samples has proven valuable for very heterogeneous marble types.

Test specimens shall be slabs measuring 400 mm plus or minus 5 mm in length, 100 mm plus or minus 5 mm in width, and 30 mm plus or minus 2 mm in thickness. It is crucial that no other dimensions be used. Changing the thickness affects the humidity and temperature gradient, so the recommended limits no longer apply. The specimen surfaces shall be cut or honed (not polished). In the case of honed surfaces, these should always be placed facing up. Specimens shall not be chemically treated in any way.

To ensure that consecutive bending measurements are made at the same measurement point, on the same surface, and on similarly oriented samples, indelible marks are placed on the samples. The samples are numbered in consecutive order.

Samples are dried in a ventilated oven at 40°C for one week or until the change in weight between two consecutive readings, 24 hours apart, is less than 0,1 percent and then cooled to ambient temperature (20°C plus/minus 3°C) before exposure.

After drying and cooling, a reference height measurement is made at the bending measurement point. Only one sample should be removed from the test chamber at a time for measurement. All other samples should remain in the test chamber until the measured sample is returned and repositioned. Each sample is gently placed on three support points that touch each of the three guide rollers. The sample should be positioned exactly the same way for each measurement. The gauge pin is gently lowered onto the surface of the sample, and the reading is taken. It is essential for the measurement that the samples, supports, guides, and gauge pin are clean. Before measuring each test sample, water and dust should be removed from the contact points.

In short, the EN 16306 standard outlines a procedure for assessing how marble withstands cycles of temperature and humidity changes when used as an external cladding on building facades. These conditions can lead to issues such as warping and rapid strength loss in certain marbles, making this test crucial for ensuring durability and safety in construction applications.

Each heat and humidity cycle includes:

• Wetting phase (e.g., immersion or moisture exposure)
• Heating stage (e.g. 60 degrees to 80 degrees in a controlled oven)
• Cooling phase (return to ambient or controlled low temperature)

The number of cycles typically ranges from 20 to 100, depending on the intended exposure simulation. The following parameters are typically checked during and after each cycle:

• Warpage: Measured using measuring instruments or laser displacement tools.
• Visual inspection: Check for surface deterioration, cracking, or discoloration.
• Mass change: Samples are reweighed to assess material loss.

Flexural strength is often tested before and after cycling using standards such as EN 12372.

The purpose of the test is to evaluate the durability and suitability of marble for outdoor use (especially facades), as some marbles warp or buckle due to moisture and thermal expansion, or lose strength or suffer surface damage from repeated exposure.

Our organization, which has been supporting businesses across all sectors for years through a wide range of testing, measurement, analysis, and evaluation activities, boasts a strong team of employees who closely follow global developments in science and technology and are constantly improving themselves. In this context, we also provide testing services in accordance with the standard "EN 16306 Natural stone testing methods - Determination of the resistance of marble to thermal and moisture cycles."