Bonded vs Unbonded Screeds: Understanding the Key Differences

Pedestal Paving Systems: Why They’re Gaining Ground in External Installations

In Episode 14 of the ARDEX Answers Podcast, Monique Fenech and Technical Services Advisor James Bradford get into the nitty gritty of screed systems—specifically, the differences between bonded and unbonded screeds, and when to use each.

What is a Screed System?

A screed system is a layer of material applied over a concrete slab to create a smooth, level surface for floor finishes. How that screed is connected to the slab below determines whether it’s bonded, unbonded, or floating.

Bonded Screeds

Bonded screeds are directly adhered to the concrete substrate, usually using a bonding agent like ARDEX WPM 300 or ARDEX P 51. They’re ideal when:

The screed is relatively thin (typically under 40mm)
You want to maximise floor-to-ceiling height
You’re dealing with a stable, crack-free slab

Unbonded Screeds

Unbonded screeds are separated from the concrete substrate by a slip sheet or membrane. This approach is suitable when:

The substrate is cracked or unstable
You need to isolate the screed from potential movement below
A thicker screed layer is required (typically 50mm+)

Movement and Cracking

James explains that movement control is a major reason to choose an unbonded system. Where there’s risk of shrinkage, slab curling, or latent cracking, unbonded screeds allow the screed layer to perform independently.

Moisture Considerations

Waterproofing becomes more complex in unbonded systems, especially in wet areas. The membrane used underneath needs to be compatible with the overall system. ARDEX offers solutions that integrate both moisture barriers and primers to suit either system.

Best Practice Advice

Always check the condition of the slab before choosing your system.
Consider the environment—commercial, residential, wet or dry.
Think about long-term durability vs install convenience.
Talk to ARDEX for tailored system recommendations.

Need technical support or guidance? Call ARDEX on 1800 224 070 or explore the latest training sessions at the ARDEX Academy.