Description
ARDEX A 38 is a rapid-set engineered screed cement designed for use under all types of floor covering, and especially effective where the covering is moisture sensitive. It is mixed on site with ARDEX Gravel Mix 0-4 mm and can be laid as a bonded screed, an unbonded screed on a slipsheet or insulating layer, or a heated screed, internally or externally. Manufactured by ARDEX Australia.
The value is programme time. A traditional sand-cement screed keeps a floor out of action for weeks; ARDEX A 38 is foot trafficable and ready to tile at 8 hours, takes smoothing cements at 24 hours, and accepts resilient, textile and parquet coverings at 2 days – while still reaching approximately 20 MPa compressive strength in the first day. Working time is around 60 minutes. Also written ARDEX A38.
Technical Specifications
| Product type | Rapid-set engineered screed cement |
|---|---|
| Standards | Compliant with AS 1884 |
| Mix design | 20 kg ARDEX A 38 to 100 kg ARDEX Gravel Mix 0-4 mm |
| Mixing water | 9.5-11 litres per bag; must not exceed 11 litres |
| Mixing time | 2 minutes in a horizontal forced-action mixer or screed pump |
| Working time | Approximately 60 minutes |
| Walkability | Approximately 8 hours |
| Ready for tiles, stone, terrazzo | 8 hours |
| Ready for smoothing cements | 24 hours |
| Ready for resilient, textile and parquet | 2 days |
| Minimum thickness (bonded) | 15 mm |
| Minimum thickness (unbonded) | 40 mm |
| Compressive strength (ISO 13007.4) | Approx. 20 MPa at 1 day; 30 MPa at 3 days; 35 MPa at 28 days |
| Tensile bending strength (ISO 13007.4) | Approx. 4.0 MPa at 1 day; 4.5 MPa at 3 days; 5.0 MPa at 28 days |
| Bulk density | Approximately 1 kg/L |
| Fresh mortar density | Approximately 2 kg/L |
| Material requirement | Approximately 3.1 kg of powder per m² at 10 mm |
| Floor heating | Suitable |
| Application temperature | 5 degrees C to 35 degrees C, ambient and substrate |
| Packaging | 20 kg bag |
| Shelf life | 12 months unopened, stored dry at 23 degrees C and 50% RH |
Coverage Rates
A 20 kg bag of ARDEX A 38 mixed with 100 kg of ARDEX Gravel Mix covers approximately 6.5 m² per 10 mm of thickness.
| Thickness | Coverage per 20 kg bag plus 100 kg Gravel Mix |
|---|---|
| 10 mm | Approx. 6.5 m² |
| 15 mm (bonded minimum) | Approx. 4.3 m² |
| 20 mm | Approx. 3.2 m² |
| 40 mm (unbonded minimum) | Approx. 1.6 m² |
| 50 mm | Approx. 1.3 m² |
Water demand varies with the moisture content of the ARDEX Gravel Mix, so allow for site conditions when ordering.
Where to Use
- Bonded screeds over prepared concrete
- Unbonded screeds on a slipsheet or insulating layer
- Heated screeds
- Under tiles, terrazzo and natural stone
- Under parquet, resilient and textile floor coverings
- Under ARDEX waterproofing membranes
- Internal and external floors
How to Apply
- Prepare the substrate – concrete must be solid, thoroughly clean and free of oil, wax, grease, asphalt, latex compounds and curing or sealing compounds. Mechanically clean by shot-blasting, scarifying or diamond grinding to leave a roughened, sound, open porous matrix. Acid etching is not acceptable, and solvents and sweeping compounds must not be used. Subfloors must be dry to AS 1884. Direct-to-earth subfloors need an effective damp-proof membrane or the ARDEX Moisture Barrier system.
- Make the bond slurry – for bonded screeds, mix ARDEX A 38 and ARDEX Gravel Mix at 1:1. Separately mix ARDEX P 51 and water at 1:1. Combine the mixed powder and mixed liquid in equal proportions to produce a thin slurry, and agitate it regularly.
- Mix the screed – using a horizontal forced-action mixer or screed pump, combine 20 kg of ARDEX A 38 with 100 kg of ARDEX Gravel Mix 0-4 mm, gradually adding 9.5 to 11 litres of clean water. Mix for 2 minutes. Fill the drum to no more than three-quarters of its volume; overfilling gives poor mixing. Do not exceed 11 litres of water per bag, do not add compound oils or other additives, and do not mix with other cements.
- Lay wet on wet – while the slurry is still wet, install the screed onto the primed substrate. Never lay the screed onto a dry slurry. Mixing, application, levelling and smoothing must follow each other within 10 minutes, so size each area to what can be completed in the working time.
- Set out the bays – lay in bays or panels of no more than 40 m², with the longest side no more than 8 m and a length-to-width ratio no greater than 2. Separate bays with a narrow gap of about 2 mm; adjacent bays can be joined the next day with epoxy to form panels up to 100 m².
- Detail the joints – changes in direction, protrusions, bay divisions and abutments against perimeter walls must be bounded by movement joints filled with compressible foam strip and a flexible sealant such as ARDEX RA 040 polyurethane.
Important Notes
- Do not install if ambient or substrate temperature is below 5 degrees C or above 35 degrees C. Higher temperatures shorten working and hardening times; lower temperatures lengthen them.
- ARDEX A 38 should not be directly bonded to any ARDEX waterproofing membrane.
- Install to any thickness in 50 mm increments to ensure proper compaction; follow the slurry and wet-on-wet process between additional layers.
- Avoid placing heavy loads such as pallets of tiles or heavy machinery on the screed at 24 hours, as final strength has not been reached.
- For application over floor heating systems, contact ARDEX Technical Services.
- If in doubt about the fast drying properties on a particular job, install a test area first.
- Store in dry conditions in the original unopened packaging; shelf life is 12 months at 23 degrees C and 50% relative humidity.
Frequently Asked Questions
How much ARDEX A 38 do I need per square metre?
A 20 kg bag of ARDEX A 38 mixed with 100 kg of ARDEX Gravel Mix covers approximately 6.5 square metres at 10 mm thickness – a material requirement of about 3.1 kg of powder per square metre per 10 mm. At the 15 mm minimum for a bonded screed that is roughly 4.3 square metres per bag, and at the 40 mm minimum for an unbonded screed roughly 1.6 square metres per bag.
How long before you can tile over ARDEX A 38?
ARDEX A 38 is foot trafficable and ready to receive tiles, natural stone and terrazzo after 8 hours. ARDEX smoothing cements should be applied after 24 hours, and resilient and textile floor coverings and parquet after 2 days. Final strength has not been reached at 24 hours, so avoid placing heavy loads such as pallets of tiles or heavy machinery on the screed at that stage.
What thickness should an ARDEX A 38 screed be laid at?
The nominal minimum thickness is 40 mm for an unbonded screed laid on a slipsheet or insulating layer, and 15 mm for a bonded screed. It can be installed to any thickness in 50 mm increments to ensure proper compaction, and for additional layers the slurry mix and wet-on-wet process must be followed strictly between layers.
