Ardex A 38 Mix has been specially formulated to produce ultra-rapid drying floor screeds for internal and external locations. With "Rapidry Plus Formula" Technology, an Ardex A 38 Mix screed can be walked on just 3 hours after application and ceramic and natural stone tiles can be installed after just 4 hours irrespective of thickness, making it ideal for fast-track tiling projects. Resilient floorcoverings such as carpet, vinyl and wood can be installed after 48 hours irrespective of thickness.

Ardex A 38 Mix achieves rapid strengthening and will pass a BRE Screed (ISCR) Test after just 6 hours. After a day, it will also exceed the acceptable minimum compressive and tensile bending strengths attained by ordinary cement screeds after 28 days.

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• Thickness
• Pack Contents
• Preparation
• Mixing
• Application
• Drying Time
• Surface Finish
• Coverage
• Technical Data

Thickness

Ardex A38 Mix can be applied to the following thicknesses:

• Bonded screeds: 15mm - 40mm
• Unbonded screeds: 50mm+
• Floating screeds: 75mm+ or 65mm+ in lightly loaded/domestic locations

When used for screed repair, Ardex A 38 Mix can be applied to the full thickness of the existing cement/sand screed. Please consult BS 8204: Part 1 or BS 5385: Part 3 for additional information/guidance.

Pack Contents

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

Preparation

Bonded Screed

Ardex A 38 Mix can be laid as a bonded screed by firstly applying an Ardex A 38 Mix or Ardex A 18 grouting slurry to a suitably prepared concrete base. The Ardex A 38 Mix screed must then be placed and compacted on the base ‘fresh in fresh’ whilst the grouting slurry is still wet and workable.

To prepare the grouting slurry for dry concrete in internal locations, dilute Ardex P 51 Primer & Bonding Agent with an equal volume of water. Then add Ardex A 38 Mix powder  with the diluted Ardex P 51 to produce a grouting slurry of a creamy consistency or Ardex A 18 can be used.

For external locations, wet areas, damp concrete and below a DPM Ardex A 18 can be used.

Note: The concrete surface must be prepared using suitable mechanised equipment to expose the coarse aggregate and be free from all barriers to adhesion and be at least 6 weeks old.

Unbonded Screed

For unbonded screeds, it is good practice to ensure the concrete slab surface is reasonably true and flat prior to applying a proprietary damp-proof/slip membrane. For uneven areas which require levelling or filling, consult the Ardex A 46 datasheet for localised areas and the Arditex NA datasheet for larger areas.

Floating Screed

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

Note: Ardex A 38 Mix is suitable for direct application to concrete bases which are insufficiently dry (above 75% RH), direct to ground or ground supported without an effective damp-proof membrane, as well as areas which are subject to rising damp. It is however recommended for projects installing resilient floor finishes such as carpet, vinyl, rubber & wood that the use of a damp-proof membrane is incorporated as follows to protect the finish from moisture in the underlying substrate.

For unbonded and floating screeds, install a proprietary damp-proof/ slip membrane as recommended by BS 8204 1+A1 and BS 5385-3 before laying the screed; for bonded screeds, it is recommended screeding is followed by an application of Ardex DPM 1 C/Ardex DPM 1 C R after 3 hours. Should the concrete base be affected by residual construction moisture and is below 95%RH, Ardex MVS 95 can be substituted for the Ardex DPM and can be applied after 4 hours.

Mixing

Mix to a normal screed mortar consistency. When a sample of the mortar is squeezed in the hand, the sample should retain its shape and not crumble, and the hand should be left slightly moist.

When a sample is compacted on the base, no film of water should form on the surface.

Mixing should be performed using a pan, trough or other forced action type. Normal ‘free-fall’ mixers are not suitable for mixing semi-dry screed mortars. Use clean equipment and do not use other cements, lime or screed additives etc., in the mix.

Application

The working time of the mixed mortar is approximately 1 hour at 20°C, therefore mixing, placing, compaction and trowelling off must proceed without delay. The amount of mortar mixed and the area to be screeded should be limited so that trowelling off and finishing can be completed within this time.

Where a new bay is laid against a set and hardened screed, it is recommended that day work joints are vertical and treated with the grouting slurry as described under Preparation.

Apply Ardex A 38 Mix at temperatures above 5°C.

Application over underfloor heating systems:

When an Ardex A 38 Mix 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 25°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.

Note: Ardex A 38 Mix screeds can be thermally loaded up to 65°C (water temperature).

Drying Time

Ardex A 38 Mix can be walked on just 3 hours after application and ceramic and natural stone tiles installed after just 4 hours, irrespective of screed thickness.

Resilient floorcoverings such as carpet, vinyl, rubber and wood can be installed after 2 days. The screed will be fully dry after 48 hours.

Surface Finish

Before fixing ceramic tiles and quarry tiles, etc., the screed should be finished with a wood float. Prior to laying thin floorcoverings e.g. vinyl sheet, a very smooth surface may be obtained using any of the Ardex levelling compounds which should be selected with the final floor finish in mind. Please see the relevant Ardex datasheets for further information.

Note: Screeds are not designed as wearing surfaces, and should be given adequate protection once dry against damage, wear and contamination during subsequent building operations. Protective coverings will also minimise any curling and lipping at joints in unbonded screeds.

Coverage

Material requirement is approximately 1.85kg of Ardex A 38 Mix per m² per millimetre of screed thickness i.e. approximately 0.5m2 at 25mm thick or 0.8m² at 15mm thick per bag.

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 38 Mix can normally be tested after 6 hours using the ISCR 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 38 Mix 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].