5 Common Causes of Screed Failure (And How to Prevent Them)
Introduction
Screed is the foundation beneath almost every floor finish. When it fails — whether by cracking, crumbling, or debonding — the consequences can be costly: programme delays, remedial works, disputes, and unhappy clients.
The good news? Most screed failures are preventable. After nearly four decades in the industry, we’ve seen the same mistakes repeat again and again. By understanding the most common causes, you can avoid unnecessary rework and ensure a floor that’s built to last.
Here are the five biggest causes of screed failure — and how to prevent them.
1. Poor Substrate Preparation
A screed is only as strong as the surface it sits on.
If the substrate is dusty, oily, or contaminated, adhesion will be compromised — especially for bonded screeds.
Signs of trouble:
Screed lifting or debonding
Hollow-sounding areas underfoot
How to prevent it:
Thoroughly clean and key the substrate before pouring
Use bonding primers or slurries as required by the specification
Carry out a pre-screed inspection to check readiness
2. Excess Moisture in the Screed
Moisture is the silent killer of floors. Laying finishes before the screed is dry can lead to delamination, staining, or fungal growth under vinyl or timber.
Signs of trouble:
Flooring adhesives failing
Damp or discoloured finishes
Warped timber
How to prevent it:
Always carry out moisture testing (calcium carbide, hygrometer, or digital methods)
Respect drying times (typically 1mm/day for traditional screed, faster for flowing screed with additives)
Use moisture suppression systems if programme deadlines are tight
3. Incorrect Mix or Depth
Too much water in the mix, insufficient cement/binder, or screed laid too thin can all compromise performance.
Equally, laying too thick without reinforcement can cause shrinkage or curling.
Signs of trouble:
Cracking or curling
Weak surface strength (dusting)
Screed breaking up under load
How to prevent it:
Follow the specified mix design precisely
Ensure minimum and maximum thicknesses are respected
Use reinforcement (fibres or mesh) where required
Choose the right screed type for the application (traditional, flowing, fast-drying)
4. No or Poorly Positioned Movement Joints
Screed expands and contracts as it dries and with temperature changes. Without properly designed and positioned joints, cracks are inevitable.
Signs of trouble:
Random cracking across large bays
Cracks over underfloor heating zones
How to prevent it:
Install movement joints in accordance with BS 8204
Break up large areas into bays (max 40m² for bonded, 30m² for unbonded/floating)
Place joints around columns, doorways, and changes in construction
5. Underfloor Heating (UFH) Not Pressure Tested
One of the most common and costly mistakes: UFH pipes not pressure tested before the screed goes down.
Leaks or bursts discovered later mean breaking out hardened screed — a nightmare scenario.
Signs of trouble:
Leaks or damp patches after screeding
UFH not performing properly when commissioned
How to prevent it:
Pressure test UFH before screeding (and leave under pressure during install)
Document the test results for QA records
Ensure UFH is commissioned correctly before finishes go down
Conclusion
Screed failures are rarely about “bad screed.”
They’re about missed details, rushed preparation, or skipped testing.
By taking a proactive approach — checking substrates, testing moisture, respecting joints, and documenting UFH — you can avoid costly rework and deliver a floor that’s fast, certain, and ready.
At CSC Screeding, we’ve built our entire process around this principle. With 38 years of experience, our OPTIMA-X delivery system and live QA documentation, we help clients remove screeding as a programme risk.
👉 Want to ensure your project avoids these pitfalls?
Contact us today
