Protecting & Curing Freshly Laid Screeds: The First 7 Days
The first seven days after laying a screed are critical. How you protect and cure the screed during this period directly determines its final strength, surface quality, and long-term durability. Neglecting proper curing is the single most common cause of preventable screed defects.
Why Curing Matters
Cement-based screeds gain strength through hydration — a chemical reaction between cement and water. This reaction requires moisture to continue. If the screed surface dries too quickly (from wind, sun, or heating), hydration stops prematurely at the surface, resulting in a weak, dusty, friable top layer even though the bulk of the screed may be fine.
Proper curing keeps moisture in the screed for long enough to allow hydration to reach adequate levels throughout the full thickness.
Polythene Sheet Curing
The most common and effective method. A sheet of polythene (minimum 500 gauge / 125 micron) is laid over the screed surface within hours of finishing, typically as soon as it can support the sheet without marking.
Duration: Minimum 7 days for cement-based screeds. Some products require longer — always follow manufacturer guidance.
Key points: Seal all edges and joints with tape to prevent air circulation underneath. Overlap sheets by at least 300mm. Remove any trapped air bubbles that could cause localised drying. Weight the edges to prevent wind lifting the sheet.
Water Spray Curing
An alternative to polythene, particularly useful for large areas or where sheet application is impractical. The screed surface is kept damp by regular misting with clean water.
Frequency: Typically 2-3 times per day in moderate conditions, more frequently in hot or windy weather.
Duration: Minimum 7 days. Water spray curing requires more site management than polythene but can be more effective in very hot conditions where polythene can create a greenhouse effect.
Curing Compounds
Liquid curing membranes sprayed onto the screed surface form a film that retains moisture. These are convenient for large areas and eliminate the need for ongoing management, but they can interfere with adhesion of floor finishes — the membrane must be fully removed (typically by grinding) before applying adhesives or coatings.
Curing compounds are most appropriate where the screed will receive a mechanical finish (grinding, polishing) or where no adhesive-bonded finish is planned.
Environmental Controls
During the curing period, control the environment around the screed:
Temperature: Maintain minimum 5°C — below this, hydration slows dramatically and may stop entirely. Ideal range is 10-25°C. Avoid direct sunlight on the screed surface.
Wind: Eliminate draughts and wind exposure. Close windows and doors where possible. On exposed sites, temporary screens may be necessary.
Heating: Do not use direct heating (space heaters blowing hot air onto the screed) during the curing period. This drives moisture out too rapidly. If heating is essential for ambient temperature, use indirect heating (radiators, UFH at low temperature) and ensure adequate humidity.
Anhydrite Screed Curing
Anhydrite screeds have different curing requirements from cement-based products. They must be protected from water — do not spray with water. Instead, ensure good ventilation after the initial 48-hour set period to encourage controlled moisture loss. Protect from rain and water ingress throughout the drying period.
Common Curing Defects
Surface dusting: A weak, powdery surface caused by premature drying. Prevention: proper curing for minimum 7 days.
Crazing: Fine surface cracks caused by rapid moisture loss. Prevention: polythene curing, avoiding draughts.
Curling: Edges lifting due to differential drying (top dries faster than bottom). Prevention: proper curing and gradual drying.
Getting Expert Advice
Related Reading
Proper curing is essential for screed performance. Call us on 0118 370 2060 for advice on curing requirements for your specific product and conditions. We offer free delivery on orders over £600 ex-VAT.
