Cemtop Screed: High Performance Cementitious Flooring Mortar

Overview

Cemtop Screed is a high-performance cementitious flooring mortar specifically engineered to provide a strong and durable cementitious screed suitable for a wide variety of construction applications. The product consists of a blend of selected cements, graded aggregates with polymers and flow agents, enabling fast and easy application to internal and external cementitious substrates.

Product Description

Cemtop Screed is supplied as a grey powder that requires only the addition of potable water to produce a highly consistent, easy-to-trowel mortar. The product is classified as RCS (Respirable Crystalline Silica) Hazard Free, containing less than 0.1% RCS in accordance with Australian Inventory of Industrial Chemicals.

Primary Applications and Uses

Cemtop Screed is used to:

• Provide strong and durable screeds that can be applied to concrete, concrete blocks, aerated concrete blocks (AAC), and fibre cement substrates
• Correct falls in concrete substrates prior to the application of waterproofing membranes and floor finishes
• Eliminate traditional sand cement screeds by enabling direct application onto prepared concrete floors
• Create consistent, level flooring surfaces ready for finishing materials

Key Advantages

• Specifically formulated for fast and easy application to internal and external cementitious substrates
• Can be applied directly onto prepared concrete floors, eliminating the need for traditional sand cement screeds
• Demonstrates excellent adhesion to prepared substrates
• Single component product eliminates site batching requirements
• Shrinkage compensated for dimensional stability
• RCS (Respirable Crystalline Silica) Hazard Free
• High early strength development allowing practical use after 24 hours
• Full strength and resistance capability achieved after 28-day curing period

Design Criteria and Specifications

Application Thickness

Cemtop Screed must be applied at:

• Minimum thickness: 3mm
• Maximum thickness: 40mm
• Coverage area: Up to 5m² per application

Substrate Requirements

• Concrete substrate must be at least 14 days old
• Surface must be structurally sound and strong
• Must be clean, sound, and free from loose material and contamination (including curing compounds, oil, paint, and grease)
• Structural defects must be repaired prior to application

Physical and Mechanical Properties

Compressive Strength (AS1478.2:2005)

• 1 day: 15 MPa
• 2 days: 21 MPa
• 7 days: 25 MPa
• 28 days: 37 MPa

Modulus of Rupture – Flexural Strength (AS1012.11-2000)

• 1 day: 4.2 MPa
• 7 days: 5.7 MPa
• 28 days: 6.8 MPa

Indirect Tensile Strength (AS1012.10-2000)

• 1 day: 2 MPa
• 7 days: 2.9 MPa
• 28 days: 3.8 MPa

Drying Shrinkage (AS1478.2-2005)

• 7 days: 516 microstrain
• 28 days: <800 microstrain

Working Properties and Setting Times

• Pot life: 2 hours @ 23°C
• Initial set: 3.5 hours @ 23°C
• Final set: 5 hours @ 23°C
• Traffic time (Foot): 16 hours @ 23°C
• Traffic time (Vehicle): 24 hours @ 23°C

Temperature Performance

• Application temperature range: 5°C - 30°C
• Service temperature range: 3°C - 60°C

Mixing Instructions

Water requirement per 20kg bag: 2.6 to 2.8 litres of clean, cool water

Mixing procedure:

1. Pour the mixing water into a clean mixing vessel
2. Add powder slowly to water while mixing continuously
3. Use a heavy-duty mixer fitted with a suitable spiral paddle
4. Continue mixing for at least 3-4 minutes until a smooth consistency is obtained
5. Do not mix more material than can be reasonably laid within the pot life

Surface Preparation Requirements

Before Cemtop Screed application, surfaces must be:

• Structurally sound with all defects repaired
• Cleaned thoroughly to remove laitance through light scabbling or captive shot blasting
• Vacuumed to remove dust and debris
• Free from contamination including oil, grease, paint, and curing compounds
• Properly primed with Nitoprime 330 (or Nitobond AR as alternative)

Priming System

Recommended primer: Nitoprime 330 (in concentrate form)

Application instructions:

• Dilute Nitoprime 330 at ratio of 1 part primer to 4 parts clean water
• Apply with brush or broom to porous surfaces
• Allow to reach "damp dry" or tacky state (do not allow complete drying)
• Reapply if substrate is porous
• Do not apply more than 2-3 minutes before Cemtop Screed application

Alternative primer: Nitobond AR (diluted 1:1 with clean water)

Application Methods

Trowel or Screed Application

• Place mixed Cemtop Screed onto primed surface and tamp to required thickness
• If using a screed, work in two directions at 90 degrees to each other
• Avoid over-working to prevent excess moisture surfacing
• Finish small areas (2-3m²) before moving on
• Use short nap mohair roller (for rough finish) or sponge trowel (for smooth finish)
• Do not place more material on surface than can be finished in 15 minutes
• Wash all tools every 30 minutes to prevent buildup

Multi-Layer Build-Up

For sections exceeding 40mm thickness:

• Apply multiple layers
• Scratch-key the surface of intermediate layers
• Cover with polythene sheeting secured at edges
• Allow minimum 7 hours (at 23°C) between layers before continuing
• Reprime before applying subsequent layers

Curing and Strength Development

• Benefits from curing compounds such as Concure A99 or curing aids like plastic sheeting
• Achieves full strength after 28-day curing period
• Allows practical use after 24 hours due to high early strength
• Mechanical removal of curing compound may be necessary before applying waterproofing or flooring products

Coverage Data

• Cemtop Screed: 11.5 litres per 20kg bag; approximately 4m² @ 3mm thick
• Nitoprime 330: 6-8 m²/litre (after dilution as specified, depending on surface porosity)

Shelf Life and Storage

• Shelf life: 3 years from date of manufacture
• Storage requirement: Keep in original, unopened packaging
• Storage conditions: May be reduced if stored at high temperatures and/or high humidity
• Do not use if: Lumps are present in product or loss of workability is experienced (requiring additional water)

Limitations

• Do not apply at temperatures below 5°C or above 30°C
• Do not apply in hot windy conditions
• Not designed for structural applications

Supply and Packaging

• Supplied in: 20kg bags
• Product code: FC602057-20KG

Associated products:

• Nitoprime 330 1 litre: FC605120-1L
• Nitoprime 330 5 litre: FC605120-5L
• Nitoprime 330 20 litre: FC605120-20L

References

• [1] Fosroc_Cemtop_Screed_TDS.pdf
• [2] Fosroc_Cemtop_GP_Advanced_TDS.pdf
• [3] Fosroc_Nitobond_SBR_TDS.pdf