Screed Fault Diagnosis
Curling at Screed Edges
Edge curling is caused by differential drying and shrinkage between the top and bottom of the screed slab, and is often mistaken for debonding.
Curling appears as a slight upward lift at perimeters, movement joints or door thresholds, where the top surface of the screed dries and shrinks faster than the underside. Because the base stays wetter for longer against the insulation or membrane, a stress differential builds up through the depth of the slab and the edges lift away first.
It's easy to confuse curling with debonding from the substrate, but the mechanisms are different: curling is a drying and shrinkage phenomenon within an unbonded or floating floor, whereas debonding relates to loss of adhesion at a bonded screed's interface. Getting the diagnosis right changes the repair approach entirely.
On liquid screed floors laid over underfloor heating and insulation, curling risk is closely tied to how the drying programme was managed and whether the screed was protected from draughts and direct sun during the early curing period.
Curling at Screed Edges — the points that decide it
How to identify curling versus other edge faults
Curling typically shows as a shallow, continuous upward bow along an edge or joint line, rather than a discrete hollow patch. Sounding the surface with a light tap and comparing readings with a BRE screed tester can help confirm whether the substrate bond is intact beneath the lifted section.
Because curling stems from a moisture and shrinkage gradient rather than a bonding failure, readings across the affected area tend to be consistent, whereas true debonding usually shows a sharper transition between sound and hollow zones.
Practical remedies and prevention
Where curling is minor and stable, it may be acceptable to overlay once moisture content is confirmed suitable for the chosen floor finish, using a flexible levelling compound to feather the transition. More pronounced curling at joints may need local grinding or, in persistent cases, cutting back and re-forming the movement joint.
Prevention starts on site: protecting the screed from strong draughts and direct sun in the first days after pouring, following a considered drying programme, and ensuring edge isolation strips and movement joints are correctly detailed at the design stage all reduce the likelihood of curling developing.
Curling at Screed Edges — your questions
Concerned about curling edges on a screed floor?
Call Exeter Liquid Screeders on 07791 510849 for an experienced diagnostic assessment before you commit to a floor finish.
Or call our landline on 01392 237700
In short
Edge curling is caused by differential drying and shrinkage between the top and bottom of the screed slab, and is often mistaken for debonding.
Keep going — closely linked topics
Concerned about curling edges on a screed floor?
Call Exeter Liquid Screeders on 07791 510849 for an experienced diagnostic assessment before you commit to a floor finish.
Curling Screed Edges: Why It Happens and How We Correct It
Curling shows up most often at perimeters, thresholds and around columns — anywhere the screed's edge is exposed to a different drying environment than the middle of the room.
It's a differential shrinkage issue: the top and edges of the slab dry and shrink before the core does, and the mismatch pulls the edge upward by a millimetre or two. It looks alarming but it's a well-understood, manageable problem.
Below we cover why edges curl more than the field of the floor, how we measure it, and the grinding or filling correction that gets the floor flat enough for the next trade.
Why edges move more than the middle of the room
The perimeter of a pour has more exposed surface area relative to its volume, so it loses moisture faster than the centre of a large slab. That uneven drying rate creates a shrinkage gradient, and the edge lifts to relieve the stress.
Direct sun through a patio door, a draught under a temporary door, or a heater positioned near one wall all accelerate this on one side of a room more than another, making the curl worse in that zone specifically.
What we typically measure
Typical curl height: 1–4mm at the edge
Distance affected: usually within 150–300mm of the wall
Correctable by grinding: in the large majority of cases
How we bring a curled edge back to level
Laser survey — We map the floor with a laser level to find every high edge, not just the obvious one.
Grind the high points — Diamond grinding brings curled edges down to the datum line without over-cutting the field.
Latex or leveller fill — Where grinding alone won't reach tolerance, a levelling compound tops up low areas beside the ground edge.
Re-check to SR1 — Final laser check confirms the room is back within SR1 flatness before handover.
Grind-and-level vs full re-pour
Grind and level (usual route): Works for curls up to a few millimetres Same-day correction in most rooms No disruption to the rest of the build programme
Full re-pour (rare): Only needed where curling is severe and widespread Requires the original screed lifting first Adds weeks, not days, to the programme