METHOD STATEMENT
Sikafloor®-255 Screed
28.09.20 / V.3.1 / SIKA GCC / SIMON AMBAUEN
THE ADDRESS HARBOUR POINT
TABLE OF CONTENTS
1
Scope
3
2
2.1
2.2
2.3
Description and uses
Description
Products
Characteristics/ advantages
3
3
3
3
3
System build-up
3
4
4.1
4.2
Substrate preparation
Substrate pre-requisites
Surface preparation
4
4
4
5
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
Application information
Professional crew
Temperatures
Weather precautions
Mixing Equipment
Application of primer / bonding slurry
Application of Sikafloor®-255 Screed mortar
Treatment of joints
Curing
Wet on wet / thick bed tile applcation
6
6
6
7
7
8
8
11
11
12
6
Important Considerations
12
7
Health and safety recommendation
13
8
Legal Note
14
Method Statement
Sikafloor®-255 Screed
29.9.20
2/14
Sika UAE
1
SCOPE
This method statement describes application of internal bonded cementitious floor screed for
residential use under floor covering (e.g. tiles, carpet, parquet, etc.)
2
DESCRIPTION AND USES
2.1
DESCRIPTION
Sikafloor®-255 Screed is a one part cement based bonded screed. For levelling and smoothing
uneven floors, and thick bed tile setting applications. Suitable for use in hot and tropical
conditions.
2.2
PRODUCTS
The system consisting of a bonding slurry and screed:
PRODUCTS
Sikafloor®-255 Screed
One-part, economical, pre-mixed, cementitious screeds.
Sikabond® DV or SikaLatex®
Water-resistant bonding agent
2.3
CHARACTERISTICS/ ADVANTAGES
Good workability
Good compaction
Ready to use
Good finishing
Application thickness from 20mm to 70mm
Local application down to 10mm and up to 80mm possible, for areas <10m²
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3
SYSTEM BUILD-UP
CONSUMPTION RATE
Coating System
Product
Consumption
Primer /
Bonding slurry
Sikabond®DV / SikaLatex®
mixed with cement
As per site requirements
Screed
Sikafloor®-255 Screed
~2.25 kg/m2/mm
Method Statement
Sikafloor®-255 Screed
29.9.20
3/14
Sika UAE
4
SUBSTRATE PREPARATION
4.1
SUBSTRATE PRE-REQUISITES
Concrete substrates must be of good condition, minimum 3 months old, with a pull off strength
and compressive strength as mentioned below:
Procedure
Equipment
Pull off Compressive Strength
• The concrete substrate must be sound.
• Compressive strength minimum 25 N/mm2.
• Pull off strength > 1.5 N/mm2.
Air Humidity
• Relative air humidity max. 75%.
• Beware of condensation. The substrate must be at least 3°C
above dew point.
Substrate & Ambient Temperature
• Substrate temperature > 10ºC.
• Ambient temperature below < 35°C.
4.2
SURFACE PREPARATION
Concrete substrates must be mechanically prepared using abrasive blast cleaning to remove
cement laitance, existing coatings and achieve a gripping profile that is clean, dry and free from
laitance, dirt, grease, oil and any other form of surface contamination. Vacuum blasting or
similar techniques are ideally suited.
Procedure
Equipment
Vacuum shot blasting
Concrete substrates must be prepared mechanically using
abrasive blast cleaning or scarifying equipment to remove
cement laitance and achieve a profiled open textured.
Method Statement
Sikafloor®-255 Screed
29.9.20
4/14
Sika UAE
Cleaning of the surface
All dust, loose and friable material must be completely removed
from all surfaces before application of the product, preferably by
brush and vacuum.
Clean substrate
The surface must be clean, dry and free of all contaminants, e.g.
dirt, oils, grease, coatings and surface treatments, etc.
Surface defects
Repairs to the substrate, filling of blowholes/voids must be
carried out using appropriate products from SikaTop®, Sika
MonoTop®, Sikafloor®, Sikadur®, and Sikagard® range of
materials.
Surface roughness
Pre-requisite for a good bond between the substrate and
levelling screed is an appropriate roughness of the substrate.
The mean surface roughness should be as large as possible, but
at least 1 mm.
 The selected method of preparation will depend on the surface condition, environmental
constraints and availability of services. The method may be selected on the basis of trial areas,
approved by the Contract Administrator. For additional information, please refer to Sika's
Method statement for "Evaluation and Preparation of Surfaces", available upon request.
Method Statement
Sikafloor®-255 Screed
29.9.20
5/14
Sika UAE
5
APPLICATION INFORMATION
5.1
PROFESSIONAL CREW
 The application of Sikafloor®-255 Screed may only be used by experienced professionals and
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therefor requires professional staff in sufficient quantity.
The professional staff must be able to assess the substrate and take the necessary measures if
necessary.
Specifically, the smoothing and compacting work requires trained specialists who are familiar
with the handling of the Sikafloor® products, effects of general environmental conditions and
its changes, and which fully complies with the application limits of the products.
As the installation speed or the daily area size increase, the demand for installation personnel
increases.
The quantitative demand for specialized, trained personnel increases with high installation
performance.
Sika® recommends to start with small sample surfaces and to create test surfaces.
Application window changes with the thickness of the layer, the substrate, the temperature
(substrate, mortar, air, water) of mortar consistency, as well as the sun.
5.2
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TEMPERATURES
The following minimum and maximum temperatures must be strictly adhered to start the
application of the screeds until and when the final strength has been reached:
Minimum temperatures +10° C for product, ambient air and substrate.
Maximum temperatures +25° C for product.
Maximum temperatures +35° C for ambient air and substrate.
Be aware that:
Fresh mortar temperatures ≤ 18 °C retard the strength development.
Fresh mortar temperatures ≥ 22 °C accelerate the strength development.
The fresh mortar temperature follows not linearly the temperatures of the substrate, air and
water.
Should these temperatures vary on the day of application, the mortar binding will vary with
regard to stiffening and curing. Depending on the temperature, water content and layer
thickness, the freshly applied mortar needs up to a few hours to react / stiffens. When the
mortar starts stiffening, however, the mortar can harden very quickly (do not miss the
smoothing / troweling window).
Lower or higher fresh mortar temperatures, than the given temperatures, are outside the
application limits and not guaranteed.
Method Statement
Sikafloor®-255 Screed
29.9.20
6/14
Sika UAE
5.3
WEATHER PRECAUTIONS
In direct connection to the above-mentioned temperatures is the weather. Direct exposure of
the sun on the freshly laid area has a considerable influence. In principle direct solar irradiation
must be avoided. Shrinkage cracks can occur very quickly when a temperature rises above 25
°C . This has to be avoided in any case, for example, the sun's course can be checked in advance
and the installation time / sequence of the application can take place accordingly in the shade.
In particular, sun exposure midday / early afternoon during hardening of the mortar must be
avoided. Combination of the daytime temperature with rising solar radiation and the warmth
of the hardening screed will lead to quality losses and possible appearances of cracks.
Be aware that:
 Shade can be ensured by for example setting up a tent.
 Alternatively, the installation stage can be laid on a night shift. It has been proven in practice
that application during decreasing daily temperature improves the quality of the screed.
 The newly laid mortar must be protect against draft wind and/or draughts. Wind and draught
quickly evaporates the water out of the surface of the mortar and forces a loss of volume, which
in turn can lead to cracks and loss of surface quality.
5.4
MIXING EQUIPMENT
For Small to Medium volumes the following equipment is of use:
▪ Mixing containers
▪ Weighing scales
▪ Water containers
▪ Water measuring container
▪ Double spiral mix paddle & drill (< 500 rpm)
For Medium to Large volumes the following equipment should be used:
▪ Weighing scales
▪ Water containers
▪ Water measuring container
▪ Forced action mixer or rotating pan, paddle or trough type. (Compulsory mixer)
▪ Mixed material carriers/carts ( wheel barrows)
Note : Free fall (tumble) mixers must not be used in any case.
Method Statement
Sikafloor®-255 Screed
29.9.20
7/14
Sika UAE
5.5
APPLICATION OF PRIMER / BONDING SLURRY
Adequate evaluation of the substrate conditions and state will determine the type of bonding
slurry required and allow taking preventive measures to reduce the risk of failures.
Bonding slurry must be used as a wet-on-wet application with the Sikafloor®-255 Screed. The
cement-bonded system slurry must always be mixed like a mortar.
MIXING & APPLICATION
Prior to the application of the system bonding slurry the absorbent mineral based substrate
must be pre dampened with sufficient water (warning: no standing water/puddles) to a
saturated, surface dry condition (SDD) substrate that helps to prevent the subsequent bond
slurry for drying out. Our recommendation is to pre-wat substrate 3 days (vigouresly), 24 hours
and 3 hours prior to screed application.
The bonding slurry must always be mixed to a mortar before application in suitable ratio which
is defined through site trials for specific project, considering surface absorption, temperature,
humidity, etc.
The bonding slurry must be applied uniformly over the surface at a thickness of ~ 1 mm. Avoid
excess thicknesses of the material (even in local areas), by suitably prefilling any surface voids
with appropriate Sika® mortars as required.
The Sikafloor®-255 Screed mortar has to follow wet-on-wet on the bonding slurry. Therefore
apply an area of ~2 m² in front of the application of the Sikafloor®-255 Screed. Application of
the bonding slurry on the prepared and pre-dampened (SSD) substrate by brushing vigorously
into the substrate with stiff bristle brushes.
Make sure that the freshly applied bonding slurry does not start to dry out. Do not mix more
bonding slurry than can be used for each area within it’s potlife, always make it up fresh.
The freshly applied bonding slurry must be covered with fresh Sikafloor®-255 Screed mortar
within 10 minutes (at 25°C) of its application (wet-on-wet application).
5.6
APPLICATION OF SIKAFLOOR®-255 SCREED MORTAR
In order to achieve the quality characteristics according to the product data sheet, it is essential
that the application is according to the specifications as given in the product data sheets and
this method statement. Specifications of main importance are: water content, machine
technology, personnel resources and qualification as well as the treatment after troweling of
the applied mortar.
Method Statement
Sikafloor®-255 Screed
29.9.20
8/14
Sika UAE
MIXING WITH HAND MIXER
When mixing manually add the right amount of clean cold water, as per recommendation in
Product Data Sheet, into a suitable mixing vessel before slowly adding dry powder. Work
accurate with the amount of water and always mix full bags. Do not split the bags. Do not mix
with cement or other cementitious products. In case of high temperatures, water can be cooled
by using clean ice.
For measurement of the water use a balance or a
measuring cup.
Thoroughly mix the Sikafloor®-255 Screed in the
specified ratio with an electric hand mixer (approx.
300-400 rpm.) until lamp free, smooth and
homogeneous mixture. It is important to mix for min.
3 minutes. It is recommended that a double spiral
mix paddle is used.
MACHINE MIXING
Use only mixing equipment as advised. Free fall (Tumble) type mixers must not be used.
For measurement of the water use a balance or a
measuring cup.
Water ammount is depending of the size of the mixer.
Always follow Sika’s recommendation in terms of
water to powder ratio.
Method Statement
Sikafloor®-255 Screed
29.9.20
9/14
Sika UAE
Transportation of Sikafloor®-255 Screed mortar.
APPLICATION
Immediately apply mixed mortar screed mix wet on wet onto the bonding slurry, ensuring
sufficient compaction by pouring the mixed product to the surface and spread to the level, 10
mm above the pre installed batten (e.g. steel guides adjusted to the desired height), giving it a
surcharge. Than tamp down the screed heavily to the level to give full compaction. Strike off
excess screed material until the top level (above the batten) by running a straight edge ruler
alongside it.
The use of laser height leveling is recommended, or previously applied mortar dots combined
with steel guides.
Ruling off and final screed finishing must be accurate enough to meet the requirements of the
specification. Wood or plastic float finishes maybe acceptable, but generally a closed, flat steel
trowelled finish is preferred.
Acheive the desired finishing by final troweling to make it rough or smooth, depending from
specification of final covering. At the time when the mortars gets a bit stiff and has nice
troweling properties (tested by hand troweling) the final surface finishing should take place.
In case of conduits and pipes running through the screed, it must be mechanically fixed to the
substrate and reinforced by using wire mesh wrapped over them.
The recommendations set out in relevant standard (e.g. BS 8204-1, SIA 252, FeRFA, etc.) should
be followed during the application.
Method Statement
Sikafloor®-255 Screed
29.9.20
10/14
Sika UAE
5.7
TREATMENT OF JOINTS
Building separation joints, dilatations and connecting joints in the substrate and different
components must in all cases be incorporated into the new screed covering and appropriately
executed. Joints design is project specific and should be recommended by designer.
Generally, following should be taken into consideration:
 Always transfer (mirror) the joints from concrete slab below screed (both expansion and
construction joints)
 Include joints in all areas where there is a major change in screed thickness
 Include joints in all areas where substantial change of shape occurs
 Include joints under doorways
 For slab on grade max. length between the joints should not exceed 5m. This is not required
for suspended slabs, in this case only follow construction and expansion joints mirrored from
the suspended slab
 Saw cuts can be used to create control joints in the applied screed with a recommended depth
of min. 70% of the screed thickness (2/3)
 General application practice applies
 Always refer to relevant international standards for bonded screed installation and application
(e.g. BS 8204 – Part 1, FeRFA)
5.8
CURING
Curing must start immediately after application by covering finished areas with polyethylene
sheet (with all leading edges lapped and secured), and left covered for a minimum 3 days.
Covering by polyethylene sheet is essential to prevent premature drying. Failure to carry out
adequate protection early enough can lead to edges curling and/or a dry friable surface through
moisture loss.
Alternateviely, depending from site conditions, wet hessian curing method can be combined with
polyethylene sheeting.
Protect against wind, sun and rain for minimum 10 days.
Method Statement
Sikafloor®-255 Screed
29.9.20
11/14
Sika UAE
Next day the surface could show some discoloration [white blush] marks or may show trowel
marks. This does not affect properties of the placed screed.
5.9
WET ON WET / THICK BED TILE APPLCATION
Alternative to previous described curing method non-moisture sensitive tiles can be applied
immediately into the wet screed by thick bed application method. For non-absorbent tiles like
porcelain an additional suitable thin bed tile adhesive has to be applied as contact layer in a
suitable manner. Refer to relevant standards, guidelines and good industry practice.
6
IMPORTANT CONSIDERATIONS
 During summer season or temperature higher than 35°C, working area should be covered to
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prevent the direct sun effects. Water can be cooled down by using clean ice.
Protect the floor screed after levelling from direct sunlight, wind and rain.
Do not use where negative hydrostatic pressure is evident (i.e. rising damp)
Only for residential and internal use (no heavy traffic, etc.).
Raw material-related variations in the color, texture, pores on the surface are in mineral
systems (floor leveling compounds) normal and no reason for complaint.
Under certain circumstances (drafts, sunlight, low humidity, etc.) fine "hairline cracks" can be
expected. This is normal with cementitious screed system and it is no reason for complaint.
Confirm required moisture content of substrate prior to application of overlayments which are
not tollerant to moisture (e.g. vinyl, parquest, etc.)
Prepare the screed as per requirements of overlaying material, rough or smooth.
Do not mix Sikafloor®-255 Screed with cement or other cementitious products.
Do not add extra water or other ingredients. Mix only full bags.
Method Statement
Sikafloor®-255 Screed
29.9.20
12/14
Sika UAE
7
HEALTH AND SAFETY RECOMMENDATION
For information and advice on the safe handling, storage and disposal of chemical products, users shall refer to the
most recent Safety Data Sheet (SDS) containing physical, ecological, toxicological and other safety-related data.
Method Statement
Sikafloor®-255 Screed
29.9.20
13/14
Sika UAE
8
LEGAL NOTE
The information, and, in particular, the recommendations relating to the application and enduse of Sika products, are given in good faith based on Sika's current knowledge and experience
of the products when properly stored, handled and applied under normal conditions in
accordance with Sika’s recommendations. in practice, the differences in materials, substrates
and actual site conditions are such that no warranty in respect of merchantability or of fitness
for a particular purpose, nor any liability arising out of any legal relationship whatsoever, can be
inferred either from this information, or from any written recommendations, or from any other
advice offered. The user of the product must test the products suitability for the intended
application and purpose. Sika reserves the right to change the properties of its products. The
proprietary rights of third parties must be observed. All orders are accepted subject to our
current terms of sale and delivery. Users must always refer to the most recent issue of the local
Product Data Sheet for the product concerned, copies of which will be supplied on request.
Sika UAE
Version given by:
Simon Ambauen
Version reviewed by:
Tarek Sallam