Category: Finishes
Prepared by Eng. Ahmed Fathy, Projects Manager ·
Definition
Joint sealants such as silicone, polyurethane and polysulphide seal joints between different materials, expansion joints, and around sanitary ware and windows. They sit on a foam backer rod at a depth suited to the joint width, often about half the width.
Why it matters on a project
A well-sealed joint keeps out water and dust; the wrong material cracks or debonds within a year.
Measurement and pricing
In linear metres, stating joint size and material.
Worked example
A 20 mm expansion joint: sealant about 10 mm deep over a backer rod; a 30 m joint means 30 linear metres of sealant and rod.
Common mistake
Filling an expansion joint with mortar or ordinary silicone without a backer rod, so it cracks at the first movement.
Frequently asked questions
Silicone or polyurethane?
Silicone around sanitary ware and glass; polyurethane for floor and facade joints that move.
Why a backer rod?
It sets the sealant depth and stops it bonding to the joint base, so it moves freely.
Related terms
- Expansion jointA joint allowing the building to expand and contract thermally without cracking.
- Flexible polyurea sealantA flexible joint filler tolerating movement and chemicals, used in industrial floors.
- Aluminium windowsWindows with aluminium frames, sliding or hinged, single or double glazed.
- Sanitary wareWCs, basins, mixers, showers and accessories.
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