Isocrete Fast-K Screed - JHLidstone

Isocrete Fast-K Screed
A screed additive incorporating accelerating, water reducing
and shrinkage compensation compounds to give a high early
strength, early drying screed.
Uses
Fast track construction and refurbishment projects where the
screed needs to be trafficked or overlaid quickly.
Fast K additive can be utilised in bonded (15mm min),
unbonded (50mm min) or floating (75 mm min or 65mm min
for domestic) screed constructions.
Benefits
☺ Early traffic by following trades (8 hours at 20 o C).
☺ Early installation of sensitive finishes (7 days at 50mm
thickness and 20 o C & 60%RH).
☺ Excellent workability properties, easy to use.
☺ Low shrinkage, minimises cracking.
☺ High abrasion and impact resistance.
☺ Use with under floor heating systems.
Project References
Boots, Habitat, Sainsbury, Premier Brands.
Thickness
Bonded with M-Bond to insitu concrete
Bonded with Polymer 70 to insitu conc.
Bonded with Polymer 70 to p.c. conc.
Unbonded on bituminous dpm
Floating on insulation
Domestic only
All other duties
On 5mm acoustic insulation
Min 15mm
Min 20mm
Min 30mm
Min 40mm
Min 65mm
Min 75mm
Min 40mm
Typical Physical Properties
Compressive strength (BSEN196-1) 28 day
1:3 mix 30N/mm 2
1:4 mix 25N/mm 2
ISCR (BRE Soundness to BS8204-1) Category A
10 o C 20 o C
Working time 50 mins 25 mins
Light traffic 18 hrs 8 hrs
Heavy traffic 48 hrs 48 hrs
References
BS 8203:2001
BS 8204-1:2002
Installation of sheet and tile flooring.
Screeds to receive in-situ floorings.
Ambient Conditions
Screeds should be laid and cured above 5 o C. Above 25 o C
working time will be shortened significantly.
SPECIFICATION
Damp Proof Membranes
It is essential to ensure that no rising moisture can delay the
drying of the Fast-K screed and cause failure of the floor
finishes. A damp proof membrane is required on ground floors
and may be required on new concrete slabs to seal in excess
construction moisture in the base.
Isocrete M-Bond Extra can be used as a combined damp proof
membrane and bonding agent for bonded screed
constructions.
Fast-K screed can be laid unbonded over most other DPMs on
the market (min 40 mm thickness).
Surface Preparation for Bonded Screed
Totally enclosed medium shot blasting or scabbling. All
residues must be removed to provide a dry, dust free open
textured surface.
Bonding Agent for Bonded Screed
Use M-Bond for low screed thicknesses of 15-20 mm. The
screed should be applied whilst the M-Bond is still fluid/tacky.
Above 20mm, Isocrete Polymer 70 primer and grout may be
used, but note that drying times will be extended as these are
water based. For the shortest drying times, bond with
Isocrete M-Bond.
Reinforcement
Isocrete Fast-K screed laid unbonded or floating is to be
reinforced throughout with Isocrete PP Fibres (see separate
data sheet) and D49 across day joints.
Model Specification for Isocrete Fast K Screed
Isocrete Fast-K screed to be supplied and laid bonded with
Isocrete M-Bond epoxy bonding agent on a suitable
shotblasted or scabbled and vacuum cleaned insitu
concrete base in accordance with the instructions of
Isocrete Commercial Flooring by one of their approved
Licensees.

Mix Designs
Portland cement Type CEM 1
Class 42.5N to BS EN 197-1. (Other
Classes of 42.5 or higher may be
used but may affect working and
hardening times).
Sand to BS882 Grading limit M with
not more that 10% passing 150
micron sieve.
For screeds greater than 75mm
thickness, 5mm single size coarse
aggregate to BS882.
The amount of water added will vary
with the moisture content of the sand.
Grade M sands are generally
suitable, but should be checked prior
to use to confirm that the water
required to produce a workable ‘earth
moist’ screed gives a ratio for
water:cement of approx 0.35:1 to
ensure good hydration and quick
drying.
Mixing
By forced action mixer. Sequence of
addition as follows:-
1. Percentage of water (if sand &
aggregates are dry)
2. 75% of the sand/aggregates
3. PP Fibres (if specified)
4. Fast-K additive
5. Cement
6. Remaining sand/aggregate
7. Water to provide an earth moist
consistency.
Bay Sizes and Jointing
Lay Fast-K screed in accordance with
BS 8204-1, generally in large areas
without forming bays.
Application
Apply immediately after mixing.
Ensure full compaction, taking
particular care in thicker applications.
Finish with a wooden float and steel
trowel.
Curing
Cover with polythene sheet after
laying & leave for a minimum of 12
hrs before removal to permit drying.
(Optimum strengths are achieved
with longer curing times, but longer
curing times will also extend the
drying times).
To achieve 75% Relative Humidity in
the screed as quickly as possible
after removal of the polythene, good
ventilation is necessary. In good
conditions (20 o C and 60% ambient
humidity), 75% RH can be achieved
in 7 days for a 50 mm thick screed
mix at 1:3 by volume.
1:3 cement/sand mixes will generally
achieve 75% RH faster than 1:4
mixes, so where drying times are
critical, use the heavy duty mix.
Protection
Ensure adequate protection from
other construction trades after
installation.
Packaging
25kg pack, containing 38no nominal
650g units.
Storage & Shelf Life
Stored unopened in dry conditions,
shelf life will be 6 months.
Mix designs for nominally 1:3 and 1:4 by volume batches
Weights of materials required – all figures in kg
Standard Duty Heavy Duty
1:4 Mix (by vol.) 1:3 Mix (by vol.)
Thickness 75mm 75mm
m
Cement 25 25 25 25
Grade M Sand 125 95 100 75
5mm Aggregate - 30 - 25
Fast-K Additive 0.65 0.65 0.65 0.65
Water (approx) 7.5 7.5 7.5 7.5
Total 158 158 133 133
Coverage
Fast-K screed additive is used at 650
g per 25 kg of cement.
At 50mm thickness, the amount of
Fast-K additive required is:
0.55 kg/m 2 for a 1:3 mix
0.44 kg/m 2 for a 1:4 mix
Quality Control Test Methods
In Situ Crushing Resistance
Fast-K screed can achieve high
resistance to indentation, to meet
BS8204-1 Category A (heavy duty) of
the BRE Screed Tester Classification
within 7 days of laying (dependent on
temperature and compaction methods
used).
Screed Moisture Content
This should be measured in
accordance with BS8203 using
calibrated fully insulated and sealed
hair hygrometers.
Health & Safety
Some of the components of this
product may be hazardous during
mixing and application. Please consult
the relevant Health & Safety Data
Sheets, available from Isocrete on
request.
Further information
Where other products are to be used
in conjunction with this material, the
relevant technical data sheets should
be consulted to determine total
requirements. Isocrete have a wealth
of technical and practical experience
built up over many years in our
pursuit of excellence in flooring and
concrete technology. Clients are
welcome to call our Technical Desk
or visit our Technology Centre in
Sandbach, Cheshire.
Important Note
Isocrete's products are guaranteed
against defective materials and
manufacture and are sold subject to its
standard Terms & Conditions of Sale,
copies of which may be obtained on
request.
FastK 15-01-03 JC
Isocrete Commercial Flooring
The Flooring Technology Centre
Booth Lane
Sandbach
Cheshire
CW11 3QF
Tel: +44 (0) 1270 753753
Fax: +44 (0) 1270 753333