For floor installations where downtime must be minimised, ARDEX A 38 allows tiling and stone placement to proceed within hours rather than weeks. This rapid-setting engineered screed cement is dimensionally stable and formulated to receive moisture-sensitive floor coverings, resilient flooring, parquet, and waterproofing membranes on concrete subfloors without the typical shrinkage or extended drying windows of traditional sand-cement screeds.
ARDEX A 38 functions as a binder that, when mixed with graded gravel, creates a high-early-strength screed for internal and external concrete floors. It can be installed as a bonded screed, an unbonded screed over a slip-sheet or insulation, or as a heated screed over floor heating systems. By curing rapidly and controlling moisture internally, the screed achieves an early strength of approximately 20 MPa within 24 hours, meaning the surface can be tiled after 8 hours and meets the AS 1884 dryness standard for resilient flooring after 2 days.
ARDEX A 38 is suitable for both internal and external concrete floor applications. It serves as the subfloor preparation layer prior to installing:
To prepare the subfloor, concrete must be mechanically prepared via shot-blasting, scarifying, or diamond grinding to achieve a clean, sound, open porous matrix. Acid etching, solvents, and sweeping compounds must not be used. Direct-to-earth subfloors require an effective damp-proof membrane or an ARDEX moisture barrier system.
For mixing, combine 20kg of ARDEX A 38 with 100kg of ARDEX Gravel Mix (0–4mm) using a horizontal forced-action mixer or screed pump. Gradually add between 9.5 and 11 litres of clean water. Do not exceed 11 litres of water per bag, do not add other cements, and do not use additives like compound oils. Mix for 2 minutes, ensuring the mixing drum is filled to no more than three-quarters capacity.
For bonded installations, a slurry bonding bridge must be prepared. Mix ARDEX A 38 and ARDEX Gravel Mix at a 1:1 ratio. Separately mix ARDEX P 51 and water at a 1:1 ratio. Combine the wet and dry mixes in equal parts (1:1 ratio), apply the thin slurry to the substrate, and place the screed mix immediately wet-on-wet. Never place the screed onto dry slurry or a dry substrate.
To manage movement, the screed must be placed in bays of no more than 40m², with the longest side not exceeding 8m and a length-to-width ratio of no more than 2. Adjacent bays should be separated by a 2mm gap, which can be joined the following day with epoxy to build larger contiguous panels up to 100m².
All perimeter walls, protrusions, direction changes, and bay divisions must be isolated with compressible foam strip (such as Abelflex) and a flexible sealant like ARDEX RA 040 Polyurethane.
You can install tiles, natural stone, and terrazzo after 8 hours. Resilient floor coverings, textile floor coverings, and parquet can be laid after 2 days. This rapid readiness minimises project downtime.
For bonded screeds, apply at a minimum of 15mm. For unbonded screeds, the minimum nominal thickness is 40mm. The screed can be installed in 50mm increments for proper compaction.
Yes, ARDEX A 38 is suited for floor heating systems. For specific application guidance on heated screeds, consult ARDEX Technical Services.
Yes, for bonded screeds, a slurry mix created with ARDEX P 51 primer and ARDEX Gravel Mix is required. Apply the ARDEX A 38 screed wet-on-wet to this prepared and wet substrate to ensure maximum bond.
| Application | Key benefit | Primary trades |
|---|---|---|
| Bonded screeds on concrete | Achieves 20 MPa compressive strength in 1 day for rapid subsequent trade access. | Concreters, Floor Layers, Builders |
| Under resilient and textile floor coverings | Compliant with AS 1884, dimensionally stable to prevent subfloor movement. Ready for covering in 2 days. | Floor Layers, Builders |
| Under tiles, natural stone, and terrazzo | Rapid readiness for tiling in 8 hours, reducing project timelines significantly. | Tilers, Floor Layers |
| Heated screeds | Suited for floor heating systems, providing a stable and conductive base without compromise. | Plumbers, Floor Layers, Tilers |
| Unbonded screeds | Forms a robust, stable base over slipsheets or insulation layers. | Concreters, Floor Layers |
| Large panel construction (up to 100m²) | Allows for the creation of large, stable floor areas when bays are epoxy-joined. | Commercial Builders, Concreters |
Your concrete substrate must be solid, clean, and free from oil, grease, curing compounds, and any other contaminants. Use mechanical methods like shot-blasting or grinding to achieve a clean, open-porous surface.
In a forced action mixer, combine one 20kg bag of Ardex A 38 with 100kg of ARDEX Gravel Mix (0-4mm). Gradually add 9.5-11 litres of clean water and mix for at least 2 minutes until a uniform, workable consistency is achieved.
For bonded screeds, you must create a bonding slurry. Mix Ardex A 38 and ARDEX Gravel Mix at a 1:1 ratio (powder), and separately mix ARDEX P 51 and water at a 1:1 ratio (liquid). Combine the powder and liquid to make the slurry. Brush this onto the substrate and immediately apply the screed mix 'wet-on-wet'.
The screed can be walked on after 8 hours. It is ready for tiles, natural stone, and terrazzo at the 8-hour mark. Wait 24 hours for smoothing compounds and 2 days for resilient and textile floor coverings.
Danger: ARDEX A 38 Rapid Set Cement Screed is a hazardous chemical. It causes serious eye damage, skin irritation, and may cause an allergic skin reaction. It may also cause respiratory irritation, is suspected of causing genetic defects, and may cause damage to organs through prolonged or repeated exposure.
Wear protective gloves (neoprene rubber or similar), protective clothing, safety glasses with side shields, and face protection. When dust is generated, wear a P3 particulate filter respirator or a full-face respirator for higher protection.
Ensure adequate ventilation during mixing and application. Use only outdoors or in a well-ventilated area. Engineering controls should be used to remove hazards or place barriers between workers and hazards.
Store locked up in original containers in a cool, dry area, protected from environmental extremes. Keep containers securely sealed when not in use. Avoid incompatible materials. Dispose of contents and containers at an authorised hazardous or special waste collection point in accordance with local regulations.
Proper substrate preparation is critical for ARDEX A 38 performance and adhesion, preventing callbacks and premature failure of floor coverings.
Surface prep: Concrete must be solid, clean, and free of contaminants like oil, wax, grease, asphalt, latex, and curing compounds. Mechanically clean the floor using shot-blasting, scarifying, or diamond grinding to achieve a roughened, open-porous surface. Acid etching, solvents, or sweeping compounds are not acceptable cleaning methods. Sub-floors must be dry per AS1884. Direct-to-earth subfloors require an effective damp-proof membrane or an ARDEX MOISTURE BARRIER system.
Primer: Required for bonded screeds. Create a slurry mix using ARDEX A 38, ARDEX Gravel Mix, and a 1:1 mixture of ARDEX P 51 and water. Apply the screed wet-on-wet to this slurry.
| Property | Value |
|---|---|
| Bulk Density | approx. 1 kg/L |
| Fresh Mortar Density | approx. 2 kg/L |
| Material Requirement | approx. 3.1 kg of powder/m²@10mm |
| Working Time | approx. 60 mins |
| Walkability | approx. 8 hrs |
| Compressive Strength (1 day) | approx. 20 MPa |
| Compressive Strength (3 days) | approx. 30 MPa |
| Compressive Strength (28 days) | approx. 35 MPa |
| Tensile Bending Strength (1 day) | approx. 4.0 MPa |
| Tensile Bending Strength (3 days) | approx. 4.5 MPa |
| Tensile Bending Strength (28 days) | approx. 5.0 MPa |
| Suited for Floor Heating | Yes |
| Minimum Bonded Screed Thickness | 15mm |
| Minimum Unbonded Screed Thickness | 40mm |
| Maximum Bay Size | 40m² (up to 100m² with epoxy joints) |
| Shelf Life | 12 months |
Here are some common examples on where Ardex A 38 Rapid Set Cement Screed used by our customers.
