SPECIFICATION AND METHOD STATEMENT OF
ARDEX A 37 or A38 SCREED – UNBONDED METHOD
A : Substrate Inspection:
Before starting actual installation, ensure that the following parameters should be
inspected:
1. Substrate or base screed should be laid at least 28 days old or as per
installer’s specification and recommendation, so the setting process is
completed to avoid shrinkage cracks.
2. Flatness of the base should be checked for level to ensure that the specified
thickness of screed can be applied over the whole area.
3. The substrate or base screed should be fully compacted and laid to the
tolerances (+10/-3 mm) within given limits.
4. All expansion and movement joints shall be properly cut and maintained for
terminations as per structural drawing.
5. The area must be handed over to ARDEX Endura and/or its partner company
cleaned by broom, eventual debris of other work steps must be removed by
the responsible agency or the client prior application of the screed
B: Screed Levelling:
1. To control and ensure the level of the screed, divide the surface in panels by
MS Box type Battens (e.g. 50X25 mm) and fix them with adjustment-screws
or suitable method at desired level.
2. Suitable single panel sizes are up to 50 sqm with ARDEX A37 and up to 100
sqm with ARDEX A38 if the sides do not exceed a ratio in length of 1:2
without any required cutting or joints.
3. Screed battens, carefully levelled and trued, should be fixed at the corrected
height for the required thickness of screed.
4. Battens should be removed before laying adjacent bay of screed.
5. Battens must be checked regularly for straightness and cleaned (scraped)
prior use to avoid a layer of cement building up on them.
6. Between the battens apply the screed, compact by either hand or mechanical
means and use additional batten to achieve the desired level between the
frame battens. The batten used for levelling in between the frame must be of
suitable diameter to not bend in the length it is used in.
D : Un-Bonded System
Prior the application of ARDEX A37 or A38 screed, a Polythene sheet is to be
laid on the Base Slab.
2. In order to secure un-bonding effect, a second slip membrane can be installed
onto the first and is recommended from ARDEX.
3. The thickness of the polythene sheet should be not less than 70 microns and
resistant against the wear and tear during application of screed.
4. The slip membrane can be brought up on the walls until FFL if required
1.
E : Aggregate Mix
Sand:
1. The quality of sand, i.e. its concrete –making properties, has a large influence
on the quality of resulting screed and it should be concrete sand –not a plaster
sand.
2. Ideally to be used is riversand, if available. Crushed stone is possible to be used
if grading is maintained as per chart below.
3. ARDEX could supply the sand from a known and certified source and provide
QC on site if awarded the contract for screeding works.
4. To produce a mix that is easy to finish to a smooth surface, it may be necessary
to blend two or more sands.
5. For a 74 mm & 94mm thick un bonded screed we recommend to use 0-8 mm
graded aggregate and the typical sieve analysis of the sand is as follows:
Retention on 8mm – 0.6%
Retention on 4mm – 14.7%
Retention on 2mm – 26.4%
Retention on 1mm – 38.4%
Retention on 0.5mm – 67.3%
Retention on 0.25mm – 95.4%
Retention on 0.125mm – 99.4%
Retention on 0.063mm - 100.0
Water Content:
• The quantity of water used in ARDEX A37 or A38 screed should be kept to
the minimum consistent with the need to compact the screed material fully
approx. 6-11 litres per 25 kg bag depending on moisture content of the sand.
Every batch of mix shall be checked with the squeeze ball test to indicate
ideal water content being achieved.
1. ARDEX A38 has the ability to totally finish it’s shrinking process and dry
out sufficiently within 4 hours (1:5 mixing ratio) or 12 hours (1:6 mixing
ratio) regardless of thickness; therefore subsequent installation of natural
stone can be undertaken after this drying time without any risk of moisture
staining.
2. ARDEX A37 may be covered with tiles or moisture insensitive natural
stone within 3 days of completion, natural stones after 7 days if moisture
sensitive.
ARDEX A37 and A38 screed can be installed internal and external.
Mixing Ratio:
• 1:5 in A37
• 1:5 or 1:6 in A38
Mixing Method:
Only mechanical mixing allowed, it may be Forced Action / Pan
Mixture or ideally through screed mixing-pump.
1. At day work joints all bedding screed beneath the battens should be cut away
to form a vertical joint.
2. The screed material should be spread on the prepared base with adequate
surcharge, thoroughly compacted, either by heavy tamping or by mechanical
means, and levelled with a batten and/or screed board.
3. Every mix shall be checked by the foreman responsible with the squeeze ball
test to ensure the water content is correct. Detailed description of the same
and training will be given by ARDEX Endura.
4. If the mix is found unfit for purpose, e.g. if too much mixing water is used, the
entire batch shall be removed and not be used.
5. The approved mix shall be carried to the application area in wheel barrows (or
any suitable method) or directly pumped to the required place within shortest
6. possible time so the remaining working time is long enough to compact and
finish it properly.
F : Laying & Compaction of Screed:
1. After screed battens, surrounding the panels on which the screed has to be
laid, have been attached to the prepared base as described above, the screed
should be spread, compacted by either hand or mechanical means e.g.
power-floater.
2. ARDEX screeds can be laid unbonded over pipes and conduits if the
thickness of minimum 45 mm above the conduits is maintained; ideally the
joints of bays should be chosen for such undertaking, technical approval of
ARDEX Endura technical staff preconditioned.
3. The mixed material is supposed to be installed in such a manner and speed,
that at any time the wet edge is maintained
4. If the mixed material dries within a panel prior completion, it shall be either
removed and installed newly or suitable action undertaken as per ARDEX
technical recommendation. Cold joints are not acceptable.
Finishing the levelling screed:
1. The levelling surface should be finished to suit the type of flooring.
2. The screed surface should be finished with Power Floater or in small panels
also hand-trowel ling is suitable.
3. The finished surface should be free from excessive friability.
4. No water/cement slurry or additional cement may be used during power
floating as it will form a weak layer due to inadequate cement/water ratio.
5. Slightly rough and porous surface is acceptable and even preferred for
subsequent tiling/natural stone fixing, because a mechanical key will be
achieved, not solely a chemical adhesion.
Protection of Green Screed:
1. Freshly laid levelling screed surface should be given adequate protection
against damage or wear during subsequent building operations and until the
final flooring is laid.
2. Immediately after finishing of the screed, protect with barricading to give
adequate protection against damage or wear during subsequent construction
operations until the final flooring is laid.
3. Direct sunlight should be avoided during initial drying period.
Subsequent work steps / use of areas after screed installation:
3. ARDEX Endura allows subsequent trades and companies to utilise the
installed ARDEX A38 screed on the very next day (24 hours) and ARDEX
A37 after 3 days (72 hours) if
- the installed area is signed and approved by authorised person /
agency on levels, surface finish, etc
- suitable action is taken to protect the newly installed screed from
contamination which hamper subsequent installation of natural
stones or other floor coverings as per specification
4. ARDEX A38 has the ability to totally finish it’s shrinking process and dry
out sufficiently within 4 hours (1:5 mixing ratio) or 12 hours (1:6 mixing
ratio) regardless of thickness; therefore subsequent installation of natural
stone can be undertaken after this drying time without any risk of moisture
staining.
5. ARDEX A37 may be covered with tiles or moisture insensitive natural
stone within 3 days of completion, natural stones after 7 days if moisture
sensitive.
Joint Cutting
1. Where the joints are present in the base, they should be continued through
the screed as well as all subsequent layers, so that joints in screed and base
line up exactly.
2. Joints may be formed with screed battens, if the screeds on each side are
cast at different times.
3. Each panel size should be limited in size to
– 50 sqm in ARDEX A37
_ 100 sqm in ARDEX A38
4. 8-10mm compressible spacers should be installed around the walls & corners
as well as around the floor penetrating features like columns or pillars in the
full thickness/height of the screed.
Inspection:
The work should be inspected during progress and after completion, attention being
paid to the following points:
1. Materials
2. Preparation of base, if the levelling screed is to be bonded.
3. Mixing and mixing ratio of different materials.
4. Proper Compaction & Correct Finishing
5. Level and Surface regularity
G : Testing
After completion of the work, the following tests should be carried out in a joint
approach between all concerned parties:
1. Levels and surface regularity of levelling screeds
2. If bonded, Adhesion of bonded screeds to the base.
3. Soundness
4. Assessment of cracks.
5. Overtaking of joints from concrete mother slab to screed and natural stone level