Description
Ardex A38 Floor Screed has been specially formulated to produce ultra-rapid drying floor screeds for internal and external locations.
With ‘RAPIDRY PLUS FORMULA’ Technology, Ardex A38 Floor 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 A38 Floor Screed 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.
Ardex A38 Floor Screed is used to produce bonded, unbonded and floating screeds for internal and external locations, including wet areas such as swimming pools. It can also be used for large repairs to existing cement/sand screeds. It is ideal for situations where early foot traffic and rapid hardening is required.
The product should be applied to the following thicknesses as recommended by BS 8204: Part 1 or BS 5385: Part 3:
Bonded screeds: 15mm – 40mm.
Unbonded screeds: 50mm+.
Floating screeds: 75mm+ or 65mm+ in lightly loaded/domestic locations.
It is also available as a pre-blended mix with graded aggregates for easy application – Ardex A38 MIX.
When used for screed repair, Ardex A38 Floor Screed can be applied to the full thickness of the existing cement/sand screed.
Substrate Preparation:
Bonded Screed: Ardex A38 Floor Screed can be laid as a bonded screed by firstly applying an Ardex A38 grouting slurry to a suitably prepared concrete base. The 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 P51 Primer & Bonding Agent with an equal volume of water. Then add A38 powder mixed with an equal volume of screeding sand with the diluted Ardex P51 to produce a grouting slurry of a creamy consistency. Or Ardex A18 Screed Bonding Cement can be used.
For external locations, wet areas and damp concrete, and below a DPM, Ardex A18 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.
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 A46 datasheet for localised areas and the Ardex 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 manufacturers recommendations.
NOTE: Ardex A38 Floor Screed 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.
Mix Proportions:
Sand: Mix maximum 1 part by weight of Ardex A38 Floor Screed cement to 5 parts screeding sand. The screeding sand used should be good quality 0-8mm sand and, recommended by BS 8204-1/A1, classified to BS EN 13139 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 grading table on the product datasheet linked below provides a workable screeding mortar with good compactability.
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 should remain within the product’s normal mix ratio of 1 part by weight Ardex A38 Floor Screed cement to 5 parts sand/aggregate e.g. 1 x 25kg bag of Ardex A38 to 3 x 25kg bags of screeding sand and 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 A38 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 38 mixes.
Water: Add sufficient water to obtain a workable mix. With an evenly graded, fairly dry sand, the water requirement will normally be 10-11 litres per 25kg bag of Ardex A38 Floor Screed. To achieve rapid drying and rapid strength development etc. as stated, not 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 Ardex A38 Floor Screed 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 Substrate Preparation.
Apply Ardex A38 Floor Screed at temperatures above 5°C.
Application over underfloor heating systems: When an Ardex A38 Floor 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 A38 screeds can be thermally loaded up to 65°C (water temperature).
Drying Time:
Ardex A38 Floor Screed 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 (below 2%MC) 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 A38 Floor Screed mixes using a proprietary screed pump. Contact our Technical Support Team for further details.
Coverage:
Using the recommended 1:5 mix, material requirement is approximately 0.31kg of screed per m2 per millimetre of screed thickness i.e. approximately 3.2m2 at 25mm thick or 5.4m2 at 15mm thick per bag.
Technical Data:
Weight of fresh mortar approx. 2kg/litre
Working time at 20°C approx. 1 hour
Walkability at 20°C approx. 3 hours
Compressive Strength Using 0-8MM Graded Aggregate:
After 1 day 25.0 N/mm2
After 7 days 40.0 N/mm2
After 28 days 45.0 N/mm2
Tensile Bending Strength (1:5):
After 1 day 4.0 N/mm2
After 7 days 4.5 N/mm2
After 28 days 5.5 N/mm2
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