Plan joint locations carefully. Install joints at maximum 6m centers. Use proper joint materials.
Surface regularity is defined as the limitation of deviation of the surface beneath a straightedge laid flat on the surface. It measures the “waviness” of the surface and is critical for floor finish performance and longevity.
Sharp, well-graded sand produces stronger, more durable screed
Use sand conforming to BS 882 with grading zone M or C. Avoid fine sands which increase water demand and reduce strength.
Too much water weakens screed and causes surface dusting
Add water gradually until mix just holds together when squeezed. Typical water:cement ratio should be 0.35-0.45.
Plasticizers and fibres can improve workability and performance
Plasticizers improve workability without increasing water. Polypropylene fibres reduce plastic shrinkage cracking.
Clean, sound substrate is essential for good bond
Remove all loose material, oil, paint, and dust. Dampen substrate but avoid ponding water before screed application.
Divide large areas into bays to maintain quality
Maximum bay size should allow completion within 1 hour. Use temporary battens to define bays and maintain levels.
Proper compaction eliminates voids and improves strength
Use mechanical compaction for thick screeds. Hand tamping is sufficient for thin applications but must be thorough.
Rapid moisture loss causes surface weakness and cracking
Cover with polythene sheeting or use curing compound. Maintain surface moisture for at least 7 days in normal conditions.
Temperature and humidity affect curing quality
Maintain temperature between 5-25°C. Use windbreaks to prevent excessive air movement over the surface.
Don’t rush to apply floor finishes
Traditional rule: 1 day per mm thickness. Actual drying time depends on thickness, conditions, and finish requirements.
Regular level checking prevents major corrections later
Use laser levels or string lines. Check levels every 2-3 metres during placement and make immediate adjustments.
Always verify moisture content before applying finishes
Maintain temperature between 5-25°C. Use windbreaks to prevent excessive air movement over the surface.
Don’t rush to apply floor finishes
Traditional rule: 1 day per mm thickness. Actual drying time depends on thickness, conditions, and finish requirements.
Add water gradually and test consistency frequently. Use plasticizers for improved workability.
Clean thoroughly, check for defects, and prime if necessary. Test bond strength on trial areas.
Plan work for suitable conditions. Use protection in extreme weather. Monitor temperature and humidity.
Cover immediately after finishing. Maintain protection for minimum 7 days. Use curing compounds when necessary.
Plan joint locations carefully. Install joints at maximum 6m centers. Use proper joint materials.
Perfect screed consistency: when squeezed in your hand, it should just hold together without excess water appearing
Why It Works:
This ensures minimum water content for maximum strength while maintaining workability
Add water in small increments and test frequently. Once you achieve the right consistency, stick to it.
A properly finished screed surface should not show indentation when you press a coin edge into it after 2-3 hours
Why It Works:
This indicates proper surface hardness and adequate cement content at the surface
If the surface is too soft, it may indicate bleeding or over-working during finishing.
Tap the screed surface with a hammer - a solid ring indicates good bond, a hollow sound suggests problems
Why It Works:
Sound transmission reveals the presence of voids or poor bonding to the substrate
Test systematically across the area. Mark any hollow-sounding areas for further investigation.
Use temporary timber strips as guides - this ensures consistent thickness and level better than screeding to dots
Why It Works:
Continuous guides provide better accuracy and prevent the ridges that result from dot and dab methods
Remove strips within 2-3 hours and fill grooves immediately while screed is still workable.
Essential supervision points for quality screeding based on professional site experience and common problem prevention.
Critical Supervision Areas
Proper supervision prevents the most common screeding problems: inadequate substrate preparation, incorrect mix ratios, poor curing, premature traffic, and inadequate environmental protection. Following this checklist ensures professional results and reduces costly remedial work.
Ideal Mix Proportions
1:3 to 1:5 ratio (1 part Portland Cement to 3-5 parts sand). Use BS12 compliant cement with sand meeting grading limit C or M of BS882. Maximum 10% should pass through 150mm sieve.
Wood floating followed by steel trowelling produces a smooth surface satisfactory for most floor finishes. Ensure the finishing technique is appropriate for the specific final floor finish that will be applied.
Traditional screed requires 110 days good drying time before floor finish application. Laying earlier can trap residual moisture, triggering major flooring problems after final floor installation.
For time-sensitive projects, consider proprietary/modified screeds using water reducing admixtures or special cements. These can accept floor finishes in days to weeks rather than months.
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