Blog · Waterproofing Expansion Joints in Buildings


Expansion Joint on a commercial building on Ngong Road, Nairobi, Kenya.



Water damage caused by a leaking expansion joint


Expansion joints are also called movement joints or isolation joints.

In buildings expansion joints allow for the concrete to move freely as it shrinks, expands or vibrates, thus preventing uncontrolled cracking.

  • Buildings move due to :expansion and contraction caused by changes in temperature
  • Swaying caused by wind
  • seismic events/earthquakes
  • Ground movement and vibration

Because the expansion joint is a separation/gap that bisects the entire building, it goes through all building assemblies like walls, floor slabs, roofs, decks, planters, terraces, columns, etc

The gap must be filled with an expansion joint sealant to make it weatherproof (i.e keep rain and other environmental elements from entering the building) and prevent debris from entering, and enhance appearance of the building while accommodating expected movements of the building.


An exposed expansion joint on a commercial building in Upper hill, Nairobi, Kenya


The two types of expansion joint sealants that are available in Kenya are:

  1. Polysulphide based sealants-most of these sealants can only accommodate 25% movement.
  2. Polyurethane based sealants-which can elongate by up to 300%

However, hybrid sealants have emerged in other parts of the world to create more effective products. The hybrid sealants overcome the fatigue and potential cohesion failures that are common with other sealants.

If the building has a basement, the expansion joint in the basement must be made watertight to ground water during construction using water bars. This must be perfectly done as it is very difficult to seal a leaking expansion joint in a basement as ground water usually subjects the building to high hydrostatic pressure.

Do you have any questions or comments regarding leakages, water damage or waterproofing in your house or building? Do you have any ideas, insights or questions regarding construction in general? We are very approachable and would love to speak with you. Get in touch