Polymer-modified screed systems — balcony waterproofing

System Description

ARDEX A 38 is the primary ARDEX screed system for balcony falls correction and over-membrane protection toppings on external terraces and podiums. It is a site-batched rapid-set screed binder — mixed on site with washed sand and water, with ARDEX Abacrete or WPM 405 polymer additive incorporated into both the bonding slurry and the gauging water. It is not a pre-blended ready-to-use product. As a pre-membrane bonded screed, A 38 is applied directly to the mechanically prepared concrete substrate over a polymer-modified bonding slurry applied wet, with the screed placed wet-on-wet immediately after. This corrects or establishes the drainage fall to the floor waste before the waterproofing membrane is installed. Minimum bonded thickness approximately 15mm. Maximum bay size approximately 40m² — larger areas require saw cuts or planned bays. The screed must cure and dry before the waterproofing membrane is applied — apply a moisture check and consider ARDEX WPM 300 HydrEpoxy as a moisture seal on fast-track programmes. As an over-membrane unbonded protection topping, A 38 is the only ARDEX-engineered screed approved for use directly over liquid-applied waterproofing membranes — placed over a double-layer 200 micron polyethylene slip sheet that isolates the screed from the cured membrane. Minimum unbonded thickness at least 35mm, preferably 40mm — confirm from the current ARDEX Australia TDS. Self-levelling compounds are not approved for this application.

System Description

ARDEX A 48 is ARDEX's pre-mixed rapid-set screed for domestic and smaller-scale balcony remediation. Unlike ARDEX A 38, the cement and aggregate are pre-combined in the bag — only water (and polymer additive where required) is added on site. This eliminates the need to source correctly graded sand separately and simplifies site logistics on smaller projects and strata apartments where batching space and materials storage are constrained. A 48 is positioned for domestic-scale and smaller commercial balcony remediation, while A 38 is better suited to larger commercial balcony, terrace, and podium screeds where the volume justifies site batching. The key performance difference in the balcony context is tile-over time — A 48 is ready to receive most tiles and natural stone after approximately 4 hours, compared to approximately 8 hours for A 38. On programme-critical occupied strata remediation projects where the same area must be waterproofed and tiled within a short access window, the faster tile-over time of A 48 can be a decisive factor. Like A 38, ARDEX A 48 is one of the two ARDEX-approved engineered screed systems for use as an unbonded topping over liquid-applied waterproofing membranes — placed over a double-layer polyethylene slip sheet. Self-levelling compounds are not approved for this application.

System Description

Mapei Mapecem Pronto is Mapei Australia's pre-blended ready-to-use rapid-setting screed mortar for pre-membrane falls correction on balconies, terraces, and podium slabs. Binder and aggregate are pre-combined in the 20kg bag — only clean water is added on site (1.5–1.7 litres per bag). This eliminates site batching variation and the need for separate aggregate sourcing — particularly practical on strata balcony remediation projects in high-rise or city-centre locations where aggregate storage is impractical. Mapecem Pronto is primarily used as a pre-membrane screed — the screed is placed to establish the required falls, allowed to cure, and the waterproofing membrane is then applied. The TDS confirms the membrane can be applied over the screed after 4 hours — confirm this timing with the membrane manufacturer before scheduling on the same day. For bonded applications, Planicrete or Planicrete SP bonding slurry is applied first and the Mapecem Pronto screed applied while the slurry is still wet. For floating (unbonded) applications, isolate the substrate with a polyethylene sheet before placing the screed. Workability time is 20–30 minutes — mix only the quantity that can be placed and finished in this window. Residual moisture at 24 hours is less than 2% — significantly drier than conventional sand-cement screeds on the same timeline.

System Description

Mapei Topcem Pronto AU is Mapei's Australian-formulation pre-blended screed binder that provides a conventional workability time — similar to a standard cement-based mortar — while drying significantly faster than conventional Portland cement screeds. This is the key difference from Mapecem Pronto: Mapecem Pronto sets very quickly (tile over in 3 hours) but has only a 20–30 minute workability window, which can be too short for larger balcony pours or where a smaller crew is placing and finishing the screed. Topcem Pronto AU gives the applicator the familiar working time of a conventional cement mortar without the long drying delays of a standard cement screed — bridging the gap between fast-set and conventional products. On larger balcony terraces and podium slabs where multiple batches must be placed sequentially, or where the finishing work requires more time, Topcem Pronto AU is more practical than Mapecem Pronto. On small domestic balconies or where very fast tile-over is the priority, Mapecem Pronto is the better choice. Like Mapecem Pronto, Topcem Pronto AU is a pre-blended product — only water is added on site, eliminating site batching risk. Bonded and floating/unbonded applications. Do not mix with other binders or aggregates.

System Description

Fosroc Cemtop Screed is a single-component ready-to-use polymer-modified shrinkage-compensated screed distributed in Australia by Parchem Construction Supplies. Only water is added on site — no site batching of aggregate or polymer admixture. It is specifically confirmed for correcting falls in concrete substrates prior to the application of waterproofing membranes and floor finishes — making it directly relevant to balcony remediation. The key characteristic that defines Cemtop Screed's position in this product group is its coverage rate: one 20kg bag covers approximately 4m² at 3mm thickness. This confirms it is best suited to localised falls correction on smaller balconies or targeted low-point correction on larger terraces — not the primary screed solution for a full large-area balcony pour. Where the required screed volume is large, ARDEX A 38, A 48, or Mapei Mapecem Pronto are more practical and economical solutions. Where Cemtop Screed is useful: correcting isolated low points or reverse fall areas on a balcony slab before waterproofing, filling localised depressions, and providing thin falls correction in the 3–15mm range where a site-batched sand-cement screed would be impractical. The 3mm minimum is lower than most site-batched screeds can reliably achieve. Nitoprime 330 primer is required on the substrate before application. Nitobond AR curing membrane is applied over the completed screed. Do not apply below 5°C or above 30°C, or in hot windy conditions. Not for structural applications.