Coefficient of Linear Thermal Dilatation

As solid natural materials, stones respectively expand and compress respectively due to the increase and reduction of temperature.

In tropical and subtropical climates, as of Brazil, the minimum temperatures seldom reach the degree of freezing water, therefore bigger problems with loss of physical and mechanical resistance almost not existing, resulting from the tension of emptiness caused by the presence of ice in the interstices of the stones.

However the maximum temperatures being quite high, a sensible expansion process in the stones is noticed, especially for the coverings applied on floors and façades, when submitted to insolation.

The coefficient of thermal expansion assessed for the different lithological types, allows the defining of the minimum recommendable spacing between the plates of a covering, in order to prevent its contact, lateral compression or imbrication.

As for fixed vertical coverings with metallic inserts, without mortar, the space between the plates is empty and allows the dilatation to accommodate. In coverings of floors and façades fixed using mortar, the joint of the plates with fastening materials fills in these empty spaces that would accommodate the dilatation; the problem in this condition, is still aggravated by the stone coefficient of differential dilatation, the mortar and the joining material, which may cause the detachment of plates and their fall from the façades.

In Brazil, the tests for characterization of the coefficient of linear thermal dilatation are performed with two test cylinder-like bodies, warmed from 0° to 50°C water and again cooled until 0°C, according to ABNT-NBR 12756 norms. The results from these tests are expressed in (mm/mx°C)x 10-3.

It should be pointed out that, dark materials absorb the solar rays with more intensity, wasting less heat, reaching a higher thermal degree, therefore developing higher dilatation indices. These dark materials are therefore advisable for construction coverings in tempered and cold climates, for in regions of hot climate there will be as much the technical problem already quoted, as a larger spent of energy for the air-conditioning.