Slip film and sliding bearings are aids that reduce the friction between two building parts, so those parts can move freely relative to one another. They prevent shrinkage, expansion and deflection from leading to cracks or built-up stresses.
Slip film
Slip film is a thin plastic foil (usually PE) placed between two layers to decouple them. Common applications:
- Under a floating screed — the film separates the screed from the sub-floor so the screed can shrink freely
- Under a cement or flow screed — prevents bonding and cracking from differential movement
- As a separating layer between concrete and insulation, or between two concrete pours
Sliding bearing
A sliding bearing is a support (bearing point) for a beam or floor slab, made so that the element can slide over the support. This uses a sliding layer of, for example, PTFE (Teflon), neoprene or two layers of foil.
Application
- Precast beams and hollow-core floors — one support is fixed, the other is a sliding bearing, so the floor can move with temperature changes
- Bridges and long spans — sliding bearings absorb expansion
- Wall plates and beams — to prevent twisting and cracks in the masonry
Points of attention
- Decide which side absorbs the movement (one fixed point, one sliding point)
- The sliding layer must stay permanently smooth and not stick
Related Terms
- Expansion joint
- Screed
- Bearing
- Sliding anchor
- Hollow-core floor
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