Floor Screed
What is flowing (pumped) screed?
Flowing screed is a new generation screeding product. It gives more benefits to specifiers and also increases design flexibility.A flowing floor screed is based on calcium sulfate whereas traditional screeds are based on Portland cement.It offers a great many advantages over traditional screeds
- Speed of application
- Surface finish
- Attainable accuracy of placement and finishing
- Reduction in thickness
- Elimination or substantial reduction of movement joints
Due to the reduced thickness, and efficient delivery method,
one gang of four men can place easily 1000m2 or more accurately in a day.
This is five to ten times more than with conventional materials.
The screed is virtually self-compacting and flows easily into place, filling
all voids and irregularities. It is precisely laser levelled to an accuracy
of equal to or better than surface regularity SR2.
Compared with traditional screeds, shrinkage is minimal and is unlikely to occur.
Therefore, curling is entirely eliminated as there is no differential shrinkage.
It can be applied in all dry locations and in most situations where a
conventional unbonded, floating or heated Portland cement screed could be used.
In some European countries flowing screeds now account for half of all
screeds applied.
Curing
In order that the necessary steps be taken to minimise excessive water loss
in the first 24 hours, any unglazed or missing windows or doors should be
temporarily blocked using plastic sheeting or a similar material.
However, after 48 hours all windows and doors should be fully opened.
Dehumidifiers may be used to force dry the product. Direct sun
should always be avoided during early life.
Hardening and drying
When covering a gypsum based screed for curing, it is essential that the
material is dry. It is classed as “dry” when it has a moisture content of less
than 1% if a permeable covering is to be applied (such as carpet), and
less than 0.5% for any other covering.
The fact that reduced screed thickness is achieved by using flowing screed
leads to shorter drying times overall. The surface may take light traffic after
1 or 2 days, depending on drying conditions.
Authority
The screed complies with the requirements of European Standard prEN CCCC-2,
Screed material and floor screeds, Part 2: screed material properties
and requirements (draft).
Performance
Excellent resistance to impact is provided by flowing screed and it exceeds the
requirements of the most exhaustive test value requirement. Its resistance to
impact easily exceeds that offered by alternative traditional systems.
The screed is self-compacting as it flows into its position, so that voids and
poor compaction can become a thing of the past.
Composition
A calcium sulfate (CaSO4) binder and selected aggregates are precisely weigh
batched in the composition of the screed. Admixtures are used in the formulation
to enhance the plastic properties in order that ease of placing is aided,
as is surface finishing.
Abrasion, impact and indentation
Complies with Building Research Test and indentation requirements of BS 8204, and compared with traditional
screeds offers good resistance to abrasion and impact.
Shrinkage
No drying shrinkage occurs, so movement joints are rarely necessary.
Fire Protection
Non-combustible as defined by BS 476: Parts 4 and 8.
Effect of Frost
Before final strength is achieved suitable precautions should be taken against
frost.
Durability
As calcium sulfate screed is not a wearing course, it requires covering with a suitable surface
finish. It is not recommended for use in continuously wet areas, nor should it
regularly be wetted. Therefore it should not be used for communal baths or
showers, changing / washing areas of sports centres, abattoirs, external yards
or similar.
Application of a bonded floor covering
The screed must be primed in order to prevent drying due to suction when bonded
floor coverings are applied directly. This will make the application of adhesive
much easier and will result in a more uniform layer, which is much smoother.
The appropriate primer to use depends on the chemical make-up of the adhesive.
For example, a calcium sulfate based adhesive will require the use of an acrylic,
epoxy or similar primer should be used. For cementitious adhesives, the two
materials need to be separated by an impermeable layer and so a polymeric
sealer must be used.
Technical Properties
Flow (DIN 1060 test) - 240-260mm
Plastic density - 2060-2130kg/m2
BRE impact test - Less than 2mm
Flexural strength - 4-6N/mm2
Drying shrinkage - Less than 0.02%
Time to light foot traffic - 1 to 2 days
*Drying time - 1 day/mm
Dry density - 1950-2050kg/m2
Fire rating - Non combustible
Thermal expansion coefficient - 0.01mm/mK
PH - 11-12
Setting time - Not less than 3 hours
*at 60% relative humidity +20°C