Screeds (Concrete) Building Codes & Rules

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Manufacturer's Requirement

Preparing Screeds^{Manufacturer's Requirement}

Mix
1:3 to 1:5 cement to sand (as per Manufacturer's requirements)
Batch ingredients accurately (i.e. use bucket NOT shovel)
Add water strictly as directed

Informative

AS 3958.1:2007, 5.4.5.2

AS 4654.2:2012, 2.15.2

Floor Screeds

Compacted to required Levels, Falls & Thicknesses^Informative
Cure screed according to Manufacturer's requirements^Informative
Movement joints^{AS 3958.1:2007, 5.4.5.2AS 4654.2:2012, 2.15.2}
± 10mm wide
≤ 4.5m CTS
Align with control joints
Above load-bearing beams or walls

Informative

Substrate Preparation^Informative

Well compacted
Repair any defect
Smooth, clean, dry, & dust / oil free surface
No sharp edges, back of the shovel finish, nor un-vibrated areas

Screed Risks & Failures

Efflorescence
Debonding
Curling
Cracking

Screed RISKS & FAILURES

NCC 2022 V2

Efflorescence

White stains on surface due to salt deposits
Solutions
Use Pre-bagged Screeds for quality control of ingredients
Add salt retardants to the screed mix
Apply waterproofer acting as a second WPM to prevent salt damage

Debonding

Failure between Bonded Screed & substrate
Solution - to clean up & remove weak top layer of concrete
Allows bonding between screed and substrate's tougher aggregates
Achieved through
Shot blasting - firing particulate grains under high velocity, normally small steel balls, or
Scabbling / Scappling - using compressed air to reduce stone or concrete

Curling & Cracking

Common for Unbonded & Floating Screeds, as they are not restrained by the substrate
Occurs when moisture evaporates off the screed's surface, which then dries and shrinks quicker than the rest of the screed
Solution
Use of steel fabric reinforcement

Efflorescence
Debonding
Curling
Cracking

Slip Rating

Slip RATING

NCC 2022 V3

All Building Classes

NCC 2022 D1P2

May 2023

NCC 2022 Vol 1, D1P2

NCC 2022 Vol 1, D3D15

HB 198:2014, 4.3.2 (Table 3A)

HB 198:2014, 5.2 (Table 3B)

Slip resistance performance requirements according to NCC^{NCC 2022 Vol 1, D1P2NCC 2022 Vol 1, D3D15HB 198:2014, 4.3.2 (Table 3A)HB 198:2014, 5.2 (Table 3B)}

Informative

Benefits^Informative

Prevents concrete settlement, or floor sinking due to considerable pressure
Reinforcement reduces shrinkage cracks
Guards against damp

Manufacturer's Recommendation

100mm thk Unreinforced Screed^{Manufacturer's Recommendation}

Membrane / Polythene

Adhesive

Floor Finish

Manufacturer's Recommendation

40 to 50mm thk Reinforced Screed^{Manufacturer's Recommendation}

Reinforce if required

Tools™ Best Practice

Screed Reinforcement^{Tools™ Best Practice}

Compliant, non ferrous preferred
No mild steel
Locate middle of Screed

Informative

Membrane^Informative

Compatible to substrate & bedding / finishes

Substrate (Concrete Slab)

Informative

AS 3958.1:2007, A.2.3 (b)

Manufacturer's Recommendation

Unbonded Screed

≥ 40mm thk, with reinforcement, prone to curling^Informative
Independent from slab
100mm thk, unreinforced Screed^{AS 3958.1:2007, A.2.3 (b)}
Laid onto membrane with no adhesion^{Manufacturer's Recommendation}
Slab movement will not affect the screed
Ideal for areas in buildings prone to moisture & damp

Internal Waterproofing Overview