Does Microcement Crack?
Microcement itself does not crack. Understanding how substrate movement causes surface cracking and how to prevent it.
Direct Answer
Microcement itself does not crack — it is flexible and durable. However, cracks in the underlying substrate will telegraph through to the surface. Proper substrate preparation and movement joint planning are essential to prevent cracking.
Understanding Microcement and Cracking
One of the most common concerns potential microcement clients raise is cracking. The good news is that the microcement material itself is inherently flexible and does not crack under normal conditions — it can accommodate the minor thermal and structural movements that occur in all buildings without failure. The cracking that is sometimes observed in microcement installations is almost always a reflection of a problem in the substrate, not a failure of the microcement itself.
Think of microcement as a highly sophisticated and very thin coating applied over a structural surface. If that structural surface has a crack in it — whether pre-existing or developing after application — the microcement, being only 2-3mm thick and bonded to the substrate, has no choice but to follow the movement. The result is a visible crack in the microcement surface directly above the substrate crack. The solution is therefore to address the substrate, not the microcement.
Prevention: Substrate Preparation
Before any microcement is applied, the substrate must be assessed for existing cracks. Hairline cracks less than 0.2mm wide in concrete or screed can typically be addressed by filling with a compatible filler and allowing it to cure before application. Cracks wider than 0.2mm, or cracks that show evidence of ongoing movement, must be fully investigated and repaired before microcement can be specified. Applying microcement over an active crack will produce a visible crack in the finish and the repair will fail.
Prevention: Movement Joints
Movement joints must be planned and installed at all structural transitions — where the floor meets the wall, around columns, at changes in substrate type, and at any existing structural expansion joint in the building. These joints allow the building elements to move independently without transferring stress to the microcement. They are a standard detail in any professional microcement installation and their omission is one of the most common causes of cracking in both professional and DIY applications.
Reinforcement Mesh at Stress Points
Fibre mesh reinforcement embedded in the scratch coat provides additional crack resistance at areas of stress concentration — internal corners, junctions between substrates, and zones adjacent to door frames and fixed elements. This is standard Cementec practice and is specified as part of every installation carried out by our certified applicators.
Causes and Prevention of Microcement Cracking
Substrate Cracks
Pre-existing or developing cracks in concrete, screed or tiles telegraph through to the microcement surface. Address before application.
Missing Movement Joints
Joints must be planned at all structural transitions. Omitting joints concentrates movement stress in the microcement.
Fresh Screed Too Early
Applying microcement over screed that has not fully dried and shrunk causes cracking as the screed continues to move.
Over-Thick Coats
Applying scratch or finish coats too thick increases the risk of cracking during drying. Thin consistent passes are essential.
Mesh Reinforcement
Embed fibre mesh in scratch coat at all internal corners, substrate junctions and adjacent to fixed elements.
Professional Assessment
A certified applicator will identify all substrate issues and movement joint requirements before any microcement is applied.
Frequently Asked Questions
Prevent Cracks with Professional Installation
Cementec certified applicators carry out thorough substrate assessment and movement joint planning on every project.
Based in Kinsale, Co. Cork · Serving all of Ireland