Crack control
Specifying reinforcement and crack control measures for liquid screed
Liquid screeds already carry a degree of crack resistance from their formulation, but larger areas, restrained edges and heavy point loads still need a considered joint and reinforcement strategy.
Concerned about cracking risk in your design?
Share your floor layout and loading details and we can advise on joint positions and reinforcement.
Or call our landline on 01392 237700
Liquid screeds, particularly calcium sulfate types, are generally more resistant to shrinkage cracking than traditional sand and cement because of their flow characteristics and lower water demand, but this does not mean cracking risk can be ignored at specification stage.
Fibre reinforcement is commonly incorporated into the mix by the manufacturer, and this is different from applying a separate steel mesh, which is uncommon in modern liquid screed practice but occasionally still requested by designers used to traditional screed detailing.
The specification's role is to set out where movement joints are required, how restraint at columns, thresholds and upstands is dealt with, and whether any additional reinforcement beyond the standard mix formulation is justified by the loading or geometry of the floor.
Reinforcement and crack control — the points that decide it
- Confirm whether the specified screed already contains fibre reinforcement as part of its formulation before specifying additional measures.
- Steel mesh reinforcement is rarely appropriate in liquid screed and should not be specified without checking compatibility with the pumped, self-levelling placement method.
- Movement joints should be positioned at changes in direction, large area breaks and junctions with restraining elements such as columns or fixed cabinetry.
- Bay sizes and joint spacing recommended by the manufacturer for the specific product should be followed rather than defaulting to sand and cement screed conventions.
- Restraint at door thresholds, changes of level and perimeter upstands is a common source of unplanned cracking and should be detailed explicitly.
- Point loads from heavy fixed equipment may warrant a locally increased depth or a discussion with the manufacturer rather than relying on standard reinforcement alone.
- Any additional reinforcement beyond the manufacturer's standard formulation should be agreed with them, since it can affect flow, placement and warranty terms.
What fibre reinforcement does and does not do
Fibres distributed through the screed mix help control the width and extent of shrinkage cracking as the material dries, but they do not eliminate the need for movement joints in larger areas or at restraint points. They work at a microscopic scale, holding fine cracks together rather than preventing a joint from being required where the floor genuinely needs to move.
Because fibre content is set by the manufacturer's formulation, specifying additional fibre or a different type without consultation can alter flow properties and is not something to add to a specification casually.
Movement joints and restraint
Joint layout for liquid screed follows guidance from the manufacturer and BS 8204, which typically allows larger bay sizes than traditional screed because of the material's shrinkage characteristics, but restrained edges such as around columns, fixed staircases or built-in furniture still need isolation joints to allow the screed to move independently of the fixed element.
Thresholds between rooms, and any point where the screed changes depth or meets a different substrate, are common crack initiation points if left undetailed, so these should be shown explicitly on the screed layout drawing rather than left to be resolved on site.
When to consider more than the standard mix
In most domestic and light commercial floors, the manufacturer's standard fibre-reinforced formulation combined with correctly positioned movement joints is sufficient. Additional reinforcement tends to be considered in areas with unusually heavy or concentrated point loads, long unbroken runs without natural joint locations, or where a client has a specific concern about hairline cracking on a decorative exposed finish.
In these cases, the sensible route is to raise the requirement with the screed manufacturer's technical team early, since they can advise whether the standard product and joint spacing is adequate or whether a different specification is warranted.
In short
Liquid screeds already carry a degree of crack resistance from their formulation, but larger areas, restrained edges and heavy point loads still need a considered joint and reinforcement strategy.
Concerned about cracking risk in your design?
Share your floor layout and loading details and we can advise on joint positions and reinforcement.
Or call our landline on 01392 237700
Reinforcement and crack control — your questions
Concerned about cracking risk in your design?
Share your floor layout and loading details and we can advise on joint positions and reinforcement.