Ardex A 70 is used to produce unbonded and floating screeds for internal locations. It can also be used for repairs to existing calcium sulphate screeds. It is ideal for situations where early foot traffic and rapid hardening is required. Ardex A 70 is suitable for use over underfloor heating systems. Ardex A 70 must only be used on floors with a functioning damp proof system. Ardex A 70 is not suitable for use in locations with prolonged exposure to moisture.

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• Thickness
• Pack Contents
• Preparation
• Mixing
• Application
• Drying Time
• Surface Finish
• Priming Options
• Repairs To Calcium Sulphate Screeds
• Coverage
• Technical Data

Thickness

Floating screeds

• Min. thickness: 35mm (domestic), 45mm (commercial)

Unbonded screeds

• Min. thickness: 30mm (domestic), 40mm (commercial)

Note: The minimum thickness of cover over underfloor heating elements (e.g. Pipes) is 25mm.

Pack Contents

Packed in paper sacks incorporating a polyethylene liner – net weight 25kg.

Preparation

Floating Screeds

For floating screeds, place a suitable separating layer or damp proof membrane over the insulation before applying the screed mortar.

Unbonded Screeds

For unbonded screeds, ensure that the concrete slab surface is reasonably true and flat prior to applying a proprietary damp proof/slip membrane.

Mixing

A 25kg bag of Ardex A 70 requires up to 5 litres of water. The actual water dosage must be checked, using the flow ring test (target 280-320mm flow) and adjusted where necessary. Use clean potable mixing water only, and add the powder to the water. Do not add additional water.

Ardex A 70 can be hand mixed using a mixer drill or alternatively, machine mixed and pumped.

The working time of the mixed screed mortar is up to approximately 2 hours at 20°C, when kept suitably agitated. This time will be extended in lower temperatures and shortened at higher temperatures.

The fresh mortar must be placed and finished in full before the end of the working time.

Application

Apply at substrate temperatures above 5°C. Do not allow the product to freeze.

Mix and place Ardex A 70 in one layer to meet the defined levels and thickness.

Use a standard flowable screed tamping bar to move and level the Ardex A 70. Work across the full area in two directions, with the first pass being a deep one and the second pass being a shallower finishing pass.

Drying Time

Ardex A 70 will typically be walkable in as little as 6 hours at 20°C. Note that lower temperatures will slow the rate of hardening and higher temperatures will accelerate it.

Ardex A 70 is dry enough to receive floor coverings when a moisture content of ≤ 2% is measured. At 20°C and under good drying conditions this is typically after 14 days.

Application over under floor heating systems: When the Ardex A 70 screed has been laid on a hot water floor system, 3 days should be allowed to elapse before heating the water up to a temperature of 20°C; this should then be maintained for a further 3 days. The maximum floor temperature should then be used and maintained for a further 4 days. Throughout this time, draughts across the screed must be avoided. The floor should then be allowed to cool down to room temperature (above 15°C) before laying floorcoverings.

Once hardened, Ardex A 70 will need sanding to remove any loose materials before receiving further treatment. It is recommended that the surface be sanded 48 hours after hardening and inside 7 days.

Surface Finish

Calcium Sulphate screeds cannot receive cementitious adhesives or levelling compounds directly, and will need priming first. To do so, mechanically prepare the surface to remove all laitance, loose debris and dust to a suitable depth to expose a sound hard surface.

Priming Options

Water-based: Apply Ardex P 51 diluted 1:3 with water in a continuous coat and allow it to dry thoroughly before overlaying.

For subsequent smoothing, Ardex recommend the Ardex range of latex or water-based levelling and smoothing compounds.

Repairs To Calcium Sulphate Screeds

To use Ardex A 70 to repair damaged calcium sulphate screeds, refer to the surface finish notes above with regards to surface preparation and priming.

To bond adjacent repairs when cutting out sections, Ardex recommend preparing clean sound saw cut vertical edges and applying Ardex R 3 E to the vertical edges and whilst still fresh infilling with Ardex A 70.

Coverage

A 25kg bag of Ardex A 70 will cover approximately 0.4m² at 35mm thickness.

Technical Data

Soundness ISCR (BRE Screed Test)

Annex D and E of BS 8204-1 contains advice on the use of the In-Situ Crushing Resistance (ISCR) Test on bonded, unbonded and floating screeds. The installed Ardex A 70 can normally be tested after 36 hours using the BRE screed tester, if required. The depth of an indentation of a correctly mixed and compacted screed should comply with the requirements of the floor finish and category of use.

Moisture Testing

Should the moisture need to be determined, the specific properties and composition of an Ardex A 70 screed mean that the moisture content cannot be determined with electric conductivity or hygrometer methods and instead the Speedy Moisture Tester (Carbide Method) must be used. The DIN standard for testing cementitious floor screeds (DIN 18121-2) is to use the CM (Carbide Method) when laying moisture sensitive floorcoverings and a reading of ≤2% needs to be achieved. Please consult Rawlins Technical for further advice on 0113 2455450 (option 2) or send a message to [email protected].