What is Osmotic Blistering?
Osmotic blistering is a defect in a wall covering such as a paint finish – typically seen on exposed external walls.
An osmotic blister founds when salt, often containing dissolved salts or other contaminants penetrates through the paint film and creates pressure beneath, leading to the formation of blisters.
Osmosis
Osmosis is simply the movement of water molecules from an area of high water concentration to an area of low water concentration across a permeable membrane. It could also be described as the diffusion of water of solvents to balance the solute concentrations across two divided areas.
Causes of Osmotic Blistering
This phenomenon is driven by osmotic pressure, which can be exacerbated by factors like poor substrate preparation, contamination, or overcoating too soon.
Contamination
Water-soluble salts on the surface of the substrate can draw moisture into the paint through osmosis.
Moisture Entrapment
Water or solvents trapped within the wall finish, such as paints, especially when overcoating too soon, can create pressure and lead to blistering.
Permeation
Moisture can permeate through the paint, even when the surface is seemingly dry, and can cause blistering.
Poor Surface Preparation
Inadequate cleaning or preparation of the substrate can leave contaminants behind, which can trigger osmotic blistering.
Temperature Changes
Rapid temperature fluctuations can cause moisture to condense on cold surfaces, which can later trigger osmotic blistering.
High Humdity
High humidity can contribute to the formation of dew on surfaces, which can then be absorbed by the paint, leading to blistering.