Repair Systems — 01
Polymer-modified screed systems — balcony waterproofing
Technical product reference for polymer-modified screed systems used in balcony and terrace waterproofing remediation. Covers falls correction, pre-membrane and over-membrane screed positions, polymer modification, bonding systems, application thickness ranges, and brand comparisons for Australian Class 2 strata building applications.
What are polymer-modified screed systems?
Screeds are the falls-and-bedding layer of a balcony/podium build-up — they set the slope to the drain and provide a sound, level base for the membrane and the tile/paver finish. This category covers rapid-set and quick-dry premixed screeds (just add water) and the SBR/acrylic polymer modifiers used to make a site-batched sand:cement screed bond better and resist water. Screeds are not membranes; selection turns on set/dry speed, thickness (bonded vs unbonded), and the falls and residual-moisture requirements of the chosen membrane and finish.
Product Reference
Individual products — one card each — scroll to view all
ARDEX Australia
ARDEX A 38
Rapid-set cement screed (premixed)
ARDEX A 38 is a rapid-set premixed cement screed for bonded, unbonded (slip-sheet/insulation) and heated screeds — falls and bedding for tiles, natural stone, Terrazzo, resilient and parquet finishes. Walkable and tileable from 8 h; bonded ≥15 mm, unbonded ≥35 mm (preferably 40 mm).
ARDEX Australia
ARDEX A 48
Rapid-set cement screed preparation (premixed)
ARDEX A 48 is a rapid-set premixed cement screed for bonded and unbonded falls/bedding beneath tiles, stone, membranes, resilient flooring and parquet. Walkable and ready for tiles/stone at 4 h, membranes at 24 h, resilient at 2 days; bonded ≥15 mm, unbonded ≥35 mm. Dimensionally stable and shrinkage-free; ~1 m² per 10 mm per 20 kg bag.
Mapei Australia
Mapei Mapecem Pronto
Pre-blended rapid-set/dry screed mortar (controlled-shrinkage)
Mapei Mapecem Pronto is a pre-blended, ready-to-use, quick-setting and quick-drying (24 h), controlled-shrinkage screed mortar — just add water (≈1.5–1.7 L per 20 kg). Light foot traffic 2–3 h; ceramic/stone at 3 h; resilient/wood at 24 h (residual humidity <2%). Consumption 20 kg/m² per cm of thickness; workability 20–30 min.
Mapei Australia
Mapei Topcem Pronto AU
Normal-set, quick-dry screed binder (controlled-shrinkage)
Mapei Topcem Pronto AU is a normal-setting, quick-drying (4 days), controlled-shrinkage hydraulic binder for screeds that only requires the addition of water — eliminating on-site sand/cement batching. Trafficable in 12 h; ceramic tiles at 24 h, natural stone at 2 days, resilient/wood at 4 days.
Fosroc / Parchem
Fosroc Cemtop Screed
Cementitious screed — corrects falls before membranes
Fosroc Cemtop Screed is a strong, durable cementitious screed applied 3–40 mm to a wide variety of substrates to correct falls in concrete prior to the application of waterproofing membranes and floor finishes. Apply between 5 °C and 30 °C (not in hot windy conditions); 20 kg bags (Parchem/DuluxGroup).
ARDEX Australia
ARDEX Abacrete
Acrylic bonding agent / liquid polymer additive (screed modifier)
ARDEX Abacrete is an acrylic bonding agent / liquid polymer additive that improves the shear and tensile bond strength, water resistance and thermal-movement tolerance of sand:cement screeds, renders and cement-based adhesives — used as a bond slurry and as a gauging additive to produce polymer-modified screeds. Slurry coat ~100 m²/20 L; screed ~9 m²/20 L.
ARDEX Australia
ARDEX WPM 405
SBR concentrated liquid polymer additive (screed modifier / bond slurry)
ARDEX WPM 405 is an SBR, multipurpose, concentrated liquid polymer additive that improves the bond strength, flexibility and workability of mortars and screeds and reduces the water:cement ratio for stronger screeds. Also used as a preparatory bond slurry and (mixed with cement) as a temporary waterproofing — it does not create falls or independently waterproof.
System Comparison
Polymer-modified screed systems — confirm all selections against the current manufacturer TDS before specifying.
Scroll the table sideways to see every column →
Do not confuse polymer-modified screeds with:
- Self-levelling underlayments and compounds (ARDEX K 15, Mapei Ultraplan and similar) — these are flow-applied floor levellers for internal use, not polymer-modified sand-based screeds — listed on the screed SL page
- Waterproofing membranes — screeds are structural levelling and bedding layers, not classified waterproof membranes — a polymer-modified screed does not replace a membrane in the waterproofing system
- Concrete repair mortars — structural repair mortars such as ARDEX FG 8, Sika MonoTop, or Fosroc Renderoc are designed for structural repair, not falls correction or tile bedding — different thickness ranges, compressive strengths, and system positions
- Tile adhesive mortar beds — polymer-modified adhesives (Mapei Ultraflex, ARDEX X 7 and similar) are thin-bed or medium-bed tile adhesive systems, not structural screed layers
- Polymer admixtures used neat — ARDEX Abacrete, ARDEX WPM 405, and similar polymer liquids must be gauged into a cement-based mix — they are not standalone screeds and must not be applied as a finished layer on their own
Screed system coordination — critical requirements
- Falls to drains — minimum 1:100 fall to all waste outlets is required by AS 3740 and NCC for wet areas — confirm that the screed design achieves the required drainage gradient across the full balcony or terrace area
- Screed position relative to membrane — confirm whether the screed is specified pre-membrane (falls correction below the membrane) or over-membrane (protection bed above the membrane) — both positions cannot be assumed interchangeable without redesigning the system build-up
- Tile finish thickness — the total screed thickness must account for the waterproofing membrane DFT, tile adhesive bed, and tile thickness — coordinate with door threshold heights and adjacent finished floor levels before pouring
- Door threshold and door sill heights — failure to coordinate screed build-up with door thresholds is a common error on balcony remediation — inadequate threshold height allows water ingress at the junction regardless of the membrane quality
- Curing time before membrane — pre-membrane screeds must be cured and achieve the moisture content specified by the membrane manufacturer before primer and membrane are applied — confirm moisture testing method and acceptance criteria with the membrane manufacturer
- Movement joints — polymer-modified screeds are rigid after cure — movement joints must be incorporated at the perimeter, at columns, at any existing slab joints, and at bay size intervals specified by the manufacturer — typically 25–30 mm wide joints at ≤ 4.5 m centres
- Bond breakers at coves and upstands — the membrane must not be bonded to the screed at cove and upstand junctions — a bond breaker strip must be applied before the membrane to allow differential movement without splitting the membrane
- Bay size limits — large unjointed screed areas will crack — confirm the manufacturer's maximum recommended bay size and ensure joints are cut or formed before the screed achieves initial set
- Manufacturer confirmation — always confirm the selected screed product is compatible with the specified waterproofing membrane system above or below it — not all membrane manufacturers allow direct application of all screed types in contact with their membrane
Disclaimer
This page provides general technical information only. Final product selection must be confirmed against the current manufacturer technical data sheet, project specification, substrate condition, substrate moisture content, required screed position, NCC requirements, AS 3740 fall requirements, and applicator warranty conditions. Do not rely on this reference as a substitute for professional engineering or waterproofing consultant advice.