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In its natural setting gypsum is deposited in thick, compressed layers and is thus highly adept at assimilating pressure. The cardboard facing endows the boards with great tensile strength (see surfacing
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The combination of pressure resistant core and tension resistant cardboard liner therefore gives gypsum products great stability and flexibility.
Thanks to their good performance properties, even thin boards can span relatively large distances. Similarly, the good performance properties allow large parts of the surface to be drilled or sawn out for light fittings.
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The deflection and the load capacity of the ceiling systems are tested in accordance with the principles set by the EN 13964 standard, 2004. The humidity and temperature conditions present during the tests are described in Appendix F of the standard. The load and deflection values in question can be found in the section about Moisture.
Loads exceeding those rated should be transferred to the suspension system or to an independent overlying structure. In case of lightweight fixtures suspended directly from the ceiling elements, a special fixture plug which expands on the back of the ceiling element should be used.
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The deflection is categorised under 3 classes:
| Class
| Maximum deflection in mm
| | 1 | L/500 and not more than 4 mm | | 2 | L/300 | | 3 | no limitations | | L is the shortest distance between the furring battens. |
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The deflection is tested under the below mentioned conditions which are categorised under 4 classes:
Class
| Conditions
| | A | Building structures exposed to a maximum relative humidity of 70% and a maximum temperature of 25°C. | | B | Building structures exposed to a maximum relative humidity of 90% and a maximum temperature of 30°C. | | C | Building structures exposed to a relative humidity degree higher than 90% and to the risk of condensation. | | D | Load is heavier than in the above classes. |
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The load capacity is stated as a combination of the abovementioned, the net weight and the built-in weight.
| Deflection class
| Humidity class
| Type of load
| | 1 | A | No load (–)
| 2
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B
| Point load (N)
| 3
| C
| Linear load (N/m1)
| —
| D
| Area load (N/m2)
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