Heat Variation of Substrates

When different substrates are subjected to heat, the majority of these substrates experience some degree of thermal expansion. However, how much thermal expansion they experience is dependant on a number of factors and some substrates are more susceptible to thermal expansion than others.

Thermal expansion of substrates is when a substrate changes in shape, area and/or volume due to a change in temperature. For example, when in the sun, a substrate may expand slightly due to an increase in heat. Some substrates are subject to a greater impact of thermal expansion than other substrates.

The impacts of thermal expansion need to be taken into consideration during the design and construction phases, as well as during renovations, as there are several effects that it can have on the building. These effects include, cracking of finishes, breaking of joins in construction, increased internal impact of varying external temperatures.

ROCKCOTE coating systems for differing and adjoining substrates take into account the potential thermal expansion of these substrates when specified on a project. This is one reason why different base renders are required on different substrates. However, there are some common substrates on which we recommend lighter colours to be used. This is to reduce the heat variance and thus the thermal expansion of these susceptible substrates. Therefore, due to the likely increase in thermal expansion and potential impact that thermal expansion has on building occupants, ROCKCOTE has LRV limitations on some substrates and will not warrant coating systems over these specified substrates with LRV percentages lower than specified in the table below.

Substrate LRV Limitation? LRV Minimum*
AAC Panel No
Core Filled Fibre Cement Sheet Yes 25%
Core Filled PVC Yes 40%
Blueboard Yes 40%
Brick and Block No
Expanded Polystyrene (EPS) Yes 40%
Extruded Polystyrene (XPS) Yes 40%
Magnesium Board Yes 40%
Off-form Concrete No
Tilt-Up Precast Panel No

*ROCKCOTE will not warrant the use of colours with a LRV (Light Reflectance Value) of less than this percentage over the specified substrate.