Ardex A 35 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 Proportions
• Mixing
• Application
• Drying Time
• Surface Finish
• Pumping
• Coverage
• Technical Data

Thickness

Ardex A35 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 repairs, Ardex A 35 can be applied to the full thickness of the existing cement/sand screed.

Pack Contents

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

Preparation

Bonded Screed

Ardex A 35 can be laid as a bonded screed by firstly applying an Ardex A 35 grouting slurry to a suitably prepared dry concrete base. The Ardex A 35 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, dilute Ardex P 51 Primer & Bonding Agent with an equal volume of water. Then add Ardex A 35 powder mixed with an equal volume of screeding sand with the diluted Ardex P 51 to produce a grouting slurry of a creamy consistency. Alternatively apply Ardex A 18 bonding cement with colour indicator.

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

Unbonded Screed

For unbonded screeds, it is good practice to ensure that 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. The insulation board should be fit for purpose for the application intended and have been laid in accordance with the manufacturer's recommendations.

Note: Where the concrete base is insufficiently dry (above 75% RH), direct to ground or ground supported without an effective damp proof membrane, or if the area is subject to rising damp, Ardex A 35 must be laid over an effective damp proof membrane. For unbonded and floating screeds, install a proprietary damp proof/slip membrane as recommended by BS 8204-1+A1and BS 5385-3. For bonded screeds, firstly apply Ardex DPM 1 C/Ardex DPM 1 C R to a suitably smooth surface and allow to cure, and then apply Ardex R 3 E Moisture Tolerant Epoxy Primer; fully sand blind whilst wet and allow to cure, sweep and vacuum clean before finally applying the Ardex A 35/ Ardex A18 bonding slurry. Alternatively, Ardex A 35 Ultra Rapid Drying Cement for Internal & External Screeds may be applied direct to damp concrete using Ardex A 18 bonding cement for the bonding slurry; for further technical information, please refer to the Ardex A 35 datasheet or contact our Technical Team on 0113 2455450 (option 2) or send a message to [email protected].

Screed Repairs

Repairs should be cut back vertically to sound screed material. The cut edges should then be treated with a bonding coat of Ardex A 35 grouting slurry or Ardex A 18; to prepare the grouting slurry, see Bonded Screed section further above. The Ardex A 35 screed mortar should then be compacted into the bonding coat while it is still wet and workable, i.e. fresh in fresh.

Mixing Proportions

Sand

Mix maximum 1 part by weight of Ardex A 35 cement to 4 or 5 parts screeding sand, depending on mix design and screed purpose.

The screeding sand used should be good quality 0 -8mm sand and, recommended by BS 8204-1+A1, classified to BS EN 1 3139 standards. Alternatively, a fine 0 - 8mm aggregate with fines category 1 with range MP should be used. Experience has shown that sand complying with the following grading table provides a workable screeding mortar with good compactibility.

Where the available screeding sand is good quality but does not have the required coarse fraction, a nominal 6mm aggregate can be mixed with the screeding sand. The ratio of screeding sand to 6mm aggregate will depend upon the actual gradings involved and the workability of the mix, however it should remain within the product’s normal mix ratios e.g. 1 x 25kg bag of Ardex A 35 to 3 x 25kg bags of screeding sand and 1 or 2 x 25kg bags of nominal 6mm aggregate.

Where the screed thickness is going to be consistently greater than 50mm, a fine concrete mix can be produced for easier compaction by partially replacing some of the screeding sand with 8mm or 10mm single-sized aggregate. To achieve good workability as well as the required soundness category, the optimum mix proportions for this application should still be determined within the product’s normal mix proportions and up to a maximum of 2 parts 8mm or 10mm single-sized aggregate added to 3 parts screeding sand and 1 part Ardex A 35 cement.

Note: Any screeding sands or aggregates used should not contain lime lignite or any other materials that could be detrimental to the workability of the screed mortar or the performance of the set and hardened screed. Do not add any other cement or lime materials to Ardex A 35 mixes.

Water

Add sufficient water to obtain a workable mix. With an evenly graded, fairly dry sand, the water requirement will normally be 6-8 litres per 25kg bag of Ardex A 35. To achieve rapid drying and rapid strength development etc. as stated, no more than 11 litres should be added per 25kg bag, including the water contained within the sand/aggregate.

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 35 at temperatures above 5°C.

Application over underfloor heating systems:

When an Ardex A 35 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 35 screeds can be thermally loaded up to 65°C (water temperature).

Drying Time

Ardex A 35 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.

Pumping

It is possible to pump Ardex A 35 screed mixes using a proprietary screed pump. Contact our Technical Team for further details.

Coverage

Using a 1:4 mix, by weight material requirement is approximately 0.37kg of Ardex A 35 per m² per millimetre of screed thickness i.e. approximately 2.7m² at 25mm thick or 4.5m² at 15mm thick per bag.

Using a 1:5 mix, material requirement is approximately 0.31kg of Ardex A 35 per m² per millimetre of screed thickness i.e. approximately 3.2m² at 25mm thick or 5.4m² at 15mm thick per bag.

For slurry bonding, allow an extra 2 x 25kg Ardex A 35 cement and 3 x 5kg of Ardex P 51 bonding agent or 9 x 25kg Ardex A 18 per 100m².

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 test on bonded, unbonded and floating screeds. The installed Ardex A 35 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 35 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].