Screeds, bases and in situ floorings
BS 8204-7:2003 pdf free.Screeds, bases and in situ floorings一Part 7: Pumpable self-smoothing screeds一Code of practice.
To enable each party to have full knowledge of the particulars of the work so that they can co-operate in producing the conditions required to complete a satisfactory job, it is essential that consultations and exchange of information between all parties concerned with the building operations are arranged at an early date.
4.2 Selection of screed to be applied
It is essential that, in the design and construction stages, there should be full consultation with the manufacturer of the proprietary pumpable self-smoothing screed to ensure that the product selected is entirely suited for the conditions both during application and in subsequent service. Consideration should therefore be given to whichever of the following are applicable:
a) intended use of the floor, including the type, extent and frequency of trafficking:
b) whether in use the area will be basically dry or permanently damp;
c) type of flooring to be applied (if any);
d) type of construction bonded. unbonded or floating);
e) thickness of screed required;
fl time available for the application, curing and drying of the screed;
g) category of screed and in situ crushing resistance (soundness) required:
h) class of abrasion resistance and/or slip resistance (for wearing screeds only):
i) age, specification, where known, and nature of the base:
j) the existence, or otherwise, of a damp proof membrane;
k) any information about any previous use that could affect adhesion;
I) any preparatory treatment required.
4.3 Information to be provided to the screeding contractor
It is essential that all relevant information be provided in good time to those responsible for installing the screed and to others whose work could be affected, including whichever of the following are applicable:
a) description, situation and address of site and means of access;
b) those conditions of contract that could practically affect this particular work;
c) degree of weather protection afforded by the structure;
d) location and areas of floors to be covered;
e) age and nature of the base and any preparatory treatment required;
minimum time intervals between stages of work and the application of heat in the building.
4.4 Information to be provided by the screeding contractor
It is essential that the screeding contractor provides, in good time to those responsible for the building. details of the conditions needed for the installation of the flooring, including whichever of the following are applicable:
a) the extent of areas to be provided for the storage of raw materials and whether these are to be weatherproof or heated;
b) the extent of areas needed for the siting of mixers and pumps and for access by delivery trucks;
c) ambient conditions required in the area to be screeded, including information on the degree of weatherproofing. draught-proofing, temperature of the base and the air, humidity, etc;
d) power and lighting requirements in the area to be screeded;
e) power, lighting, water supply and any other service requirements in the screed mixing and pumping area;
F) minimum time period after the screed is installed before allowing foot traffic and following trades;
g) protection necessary for the flooring between installation and the laying of floor finishes or final handover.
4.5 Time schedule
In considering the time schedule, in addition to the usual intervals between commencement and completion of work by the various trades involved, allowances should be made for the following:
a) completion of the building envelope to allow construction of a screed protected from rain, wind and sun;
b) delays due to frost and cold weather;
c) laying underfloor services; this should preferably be completed before the base is formed, as there is a risk of subsequent cracking if the services are embedded in the flooring;
d) curing and drying of the base concrete andior levelling screed before a flooring is laid (see 6.17); e) period of protection of the screed from damage by other trades, including the period of restriction of access.
Pumpable self-smoothing screeds will be proprietary formulations such that the manufacturer of the screed material is responsible for the formulation, the types, the quality and the correct proportioning and blending of the raw materials.
The formulation will either be for a complete screed material requiring only the addition of water (or a proprietary gauging liquid), or for a complete screed material delivered to the site with the water already added and ready to lay.
There are two principal types of pumpable self-smoothing screeds, one predominately based on cementitious binders and the other predominately based on calcium sulfate binders.
5.2 Wager, this should he clean and free from materials deleterious to concrete and screeds in their wet and hardened state. In general drinking water is fit for this use.
5.3 Gauging liquid, a liquid, usually a polymer dispersion, which is to be the material supplied by the screed manufacturer and is to be used as instructed by the manufacturer.
5.4 Reinforcement for crack control, fibres or mesh, alkali resistant if used with cement.
6 Design considerations
6.1 Selection criteria
Most pumpable self-smoothing screeds are designed for use where rapid installation is required in dry. internal locations, The designer and contractor should be aware that the rate of installation of most pumpable self-smoothing screed materials is much quicker than for cement sand screeds. The advantages of pumpable self-smoothing screeds are not realized until relatively large areas can be made available for screeding in one visit. By their nature, they cannot be laid to significant falls.
Cement based pumpable self-smoothing screeds will often be chosen when there is a requirement to lay a thin screed section, when the screed is to be a wearing screed or receive a synthetic resin flooring for an industrial floor, or when quick drying is a requirement.
Calcium sulfate based pumpable self-smoothing screeds will often be chosen when the screed section is to be thicker, when there is a requirement for an unbonded or floating screed or when there is time in the programme for the drying out time required before application of floor finishes. Calcium sulfate screeds are generally not suitable for use as wearing screeds.
On direct-to-ground concrete slabs or on concrete bases that still contain a high level of construction moisture, it is essential that there is suitable protection against rising damp so that the normal drying properties of the screed will be achieved (see 6.16 and 6.17).
In wet internal locations, where the hardened and dried screed will become wet in service, the material used for the screed and any necessary bonding treatment should be stable and maintain satisfactory strength characteristics when wet. Calcium sulfate based self-smoothing screeds and many rapid drying cement based screeds will be unsuitable in such circumstances. Calcium sulfate is corrosive to steel in damp conditions.
If a designer specifies the use of a thin sheet or tile floor, then the use of a smoothing compound should be specified in certain circumstances (see 7.8J0).BS 8204-7 pdf free download.Screeds, bases and in situ floorings