Self-levelling compounds are designed to be applied in relatively thin layers. If the material is poured too deep, problems can occur during curing and later when the floor is in use. This is a common issue on renovation projects where uneven concrete slabs are being corrected.
Why thickness matters
Most self-levelling products are intended for thin applications, usually around 2–10mm, although some products allow up to 15mm depending on manufacturer specifications. When the compound is installed thicker than recommended, it may not cure properly. The surface can appear solid while the material beneath remains weak or unstable. Over time, this may lead to cracking or sections separating from the subfloor.
Common problems when it’s too thick
Excessive thickness can lead to several issues:
- Cracking as the compound shrinks while drying
- Soft or powdery areas below the surface
- Loss of adhesion between the levelling layer and the base
- Extended drying times before flooring can be installed
- Failure under load in high-use areas such as kitchens, hallways, or garages
These problems are more likely in older buildings where slabs may already have uneven moisture levels or poor preparation.
Why it happens
Self-levelling compound is often misused to correct large differences in floor height. However, it is intended as a finishing layer rather than a structural build-up. In cases where greater depth is required, screed should normally be used instead. Poor priming or insufficient surface preparation can also contribute to failure.
What to use instead
Where a thicker floor build-up is needed, traditional sand and cement screed or liquid screed is usually more appropriate. These systems are designed for deeper layers and provide greater strength and durability.
Why choose LMA Floor Screeding London?
With over 15 years of experience, LMA Floor Screeding London installs screed and levelling systems across London with clear advice and reliable workmanship.