Guide
Why Does Floor Screed Crack?
A crack in screed may be a drying defect or a sign that the substrate and floor system are moving. Check its stability and surroundings before repairing or covering it.
Floor screed cracks because of shrinkage, thickness changes, a weak or moving substrate, excess water or unsuitable drying conditions. Before laying laminate, tile or a self-levelling compound, establish whether the crack is stable and whether movement continues below the screed.
Causes within the screed system
- The layer dried unevenly or became much thicker in local areas.
- The base was weak, dirty, damp or insufficiently prepared.
- The mix or application conditions differed from the product instructions.
- Rapid drying created stress near walls, openings or changes in material.
- The floor is moving because of the substrate, services or the surrounding construction.
How to assess a crack
Record its direction, length and location, then check for a step between the sides, a hollow response and signs of moisture. Cracks near walls, doorways and changes between materials deserve particular attention. A growing or through-crack with deflection is not just a cosmetic line.
What may be repaired locally
A stable surface defect can sometimes be treated with a compatible repair system after its cause is understood. The method depends on the screed construction and the planned covering. Filling a crack cannot stabilise a floor that is still moving or wet.
When to postpone the covering
Delay work for multiple cracks, hollow areas, crumbling edges, visible deflection, dampness or a defect that is growing. A membrane, adhesive or underlayment should not be used to hide a serious floor problem.
The calculator has a different job
The screed calculator estimates volume and dry mix from area and average thickness. It does not choose the floor construction or identify why cracking occurred.
Frequently asked questions
Can I tile over a cracked screed?
Only after the crack and the system have been assessed and the selected tile assembly allows it. A covering does not automatically stabilise the screed.
Why did a crack appear near the wall?
Shrinkage, restraint, thickness changes and movement can all contribute. Inspect the joint and surrounding floor rather than assuming one cause.
Will self-levelling compound hide cracks?
It may not stop movement or moisture. Address the screed condition and product compatibility first.
Do I need to remove all the screed?
The required scope depends on whether the layer is sound and stable. Widespread failure needs a professional assessment.