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How Water Behaves and Building Leaks Occur

Water has an interesting structure and its properties help explain how building leaks can occur.

Surface Tension

When water molecules bond together they create a kind of skin effect called surface tension. Some building materials such as gloss-painted weatherboards or glass are hydrophobic, meaning they repel water. Surface tension cannot form so the water runs off. 

However, when water comes into contact with absorbent materials such as uncoated concrete or unpainted timber, a bond can be formed and the surface tension causes water droplets to cling to the surface. At this point there is a risk that the water may penetrate and cause damage.

Capillary Action

Similarly, capillary action is where water bonding occurs on adjacent surfaces and the water is drawn upwards between them. Wind pressure can drive it upwards even further.

Surface tension can be addressed by incorporating a drip edge, weather groove, flashing or drip moulding on a home. Capillary action can be prevented by including a gap of 6 mm between surfaces. Using weather grooves, seals or hooks/seams on a flashing can also help.

Moisture Transfer

Once water has been absorbed into a building structure, it will move from warm to cold areas and may also be absorbed by other adjacent materials. For example, once water is absorbed by a poorly coated cladding it could then be absorbed by a wall underlay and ultimately penetrate the timber framing.


When air is cooled by contact with a cold surface, the released vapour forms as condensation which can be absorbed, causing damage to building materials. The threat of deterioration can be managed with proper ventilation and by incorporating absorbent wall underlays or cladding materials with absorbent backings which hold the condensation until it dries.

For help with leaky home repairs, contact the team at Sure Coat for professional advice.