Grinning or Ghosting, in Building Surveying, us a phenomenon where the outline of the external brick or blockwork is visible through a render finish on a property. This is a resulting combination of thermal bridging and penetrating dampness.
It often appears following rainfall at the start of the drying process, as the outline of the block or brick shows the differing levels of absorbency and/ or evaporations of the masonry compared to its bedding mortar.
Many things need to be taken into consideration in order the prevent grinning or ghosting, such as:
- The make-up and thickness of the render finish
- The vapour permeability of the render and substrate behind it
- The insulation and thermal transmittance of the wall
- The location and orientation of the wall
- Environmental factors such as wind-driven rain and wind exposure