What is the permitted variation from the design thickness of layer for Item 300?

The permitted variation from the design thickness of a layer for Item 300 is established to accommodate the manufacturing and construction tolerances that are commonly encountered in materials engineering. The correct variation of +15 mm and -5 mm allows for a reasonable degree of fluctuation in the layer's thickness while ensuring that the final product meets the performance requirements and standards. Additionally, this range takes into account factors such as material shrinkage, settling, and installation practices that can affect the actual thickness during application.

This specific choice balances the need for a thicker application that may benefit the structural integrity or performance of the material while also ensuring that it does not fall below a critical minimum threshold, which could lead to reduced durability or functionality. Such tolerances are typical in engineering specifications to manage the real-world complexities of construction and material application effectively.