Workmanship on building sites

BS 8000-9:2003 pdf free.Workmanship on building sites Part 9: Cementitious levelling screeds and wearing screeds- Code of practice.
in situ crushing resistance (ISCR)
resistance of levelling screeds to the crushing effect of imposed loads and traffic in service
NOTE ISCR wa formcrly known a oundnt.
4 Materials handling and preparation
4.1 General
Cements and combinations, of strength class 42.5 N, have a compressive strength equivalent to that of ordinary Portland cement conforming to BS 12:1996 (BS EN 197.1). Lower strength classes of cement and combinations used either in concrete bases or in cementitious levelling screeds might need an increase in cement or combination content to obtain similar properties and performance For example, a cement of strength class 32.5 N would probably require an increase in cement content of approximately 10 %. An additional period of curing might also be necessary (see BS 8204-1).
CAUTION Calcium aluminate (high alumina) cement should be used with care. Guidance on the correct use of calcium aluminate cement should be sought from manufacturers and current specialized publications.
WARNING 1 When Portland cement is mixed with water, or even becomes damp, alkalis are released that can be harmful to the skin. The effect depends on the length of contact, any abrasion, the individual and the part of the body involved. Suitable protective clothing should be worn. If eyes are affected, they should be washed out without delay and medical advice sought.
WARNING 2 Screed material and concrete might until set cause both irritant and allergic contact dermatitis.
— Irritant contact dermatitis is due to a combination of the wetness, alkalinity and abrasiveness of the constituent material.
— Allergic contact dermatitis is caused mainly by the sensitivity of an individual’s skin to hexavalent chromium salts.
4.2 Checking., handling and site storage of materials and components
4.2.1 Checking
Check delivery tickets for the materials against what was ordered and, if necessary, refer discrepancies to the supplier immediately.
Check visually that the materials as ordered are as stated on the delivery tickets. In particular observe that:
a) cement is of the type and class specified:
b) sand is clean and well graded:
c) coarse aggregates are of the correct single or graded sizes and are clean.
4.2.2 Handling and site storage
4.2.2.1 Ready.to-u-se retarded screed material
Unload the screed material into clean containers or onto a clean impervious platform. If the screed material is not used immediately on delivery, protect it from the weather and cover it to prevent water loss.
4.2.2.2 Cement in bags
Where the cement is to be stored for later use (unless there are small quantities only), store as follows.
a) Store in a dry, weatherproof, enclosed shed or building with a dry floor. Where there is a solid floor. store off the floor, e.g. on pallets.
b) Stack bags away from walls, closely packed together but not more than eight bags high. Cover stacks with a tarpaulin or polyethylene sheet.
c) Stack bags so that consignments can be used in the order of deLivery.
Check cement for deterioration when taken out of storage and discard if lumpy.
In the case of small quantities for immediate use, if not stored in a shed or building, stand the bags well clear of the ground, e.g. on a pallet, and cover with a tarpaulin or polyethylene sheet so that all the bags are wholly protected from wind and rain.
COMMENTARY. Even if cement is protected from rain, moisture in the air will gradually cause its deterioration. Even in good conditions cement will eventually go lumpy and give lower strength.
4.2.2.3 Sand and aggregates
The following should be observed when storing sand or aggregates.
a) Keep different sizes and types of sand and aggregates strictly separate.
h) Store on a hard, clean base which permits free drainage.
c) Keep free from leaves, rubbish, dirt or other deleterious material.
d) In frosty weather cover the stockpiles to prevent freezing.
e) Store sand and aggregates that are delivered in bags in the bags until required for use.
COMMENTARY. In very cold weather ii might be necessary to use some form of insulating covering to protect the sand and aggregutes. Polyethylene sheets will keep out rain and dirt but do not offer much protection from frost. In very hot sunny weather it is advisable to cover or to shade stocks to prevent them from becoming excessively hot.
4.2.2.4 Re’inforcement
Avoid deformation of the reinforcement during handling. Store off the ground on supports close enough together to prevent the reinforcement from sagging unduly. Cover to keep dry and clean.
4.3 Preparation of work, materials and components
NOTE Levelling screeda provide surfaces that are intended to receive a flooring. Wearing screeds are intended to provide the
finished surface. Screeds are liable to crack or curl mainly from the influence of drying shrinkage. Screeds can be crushed under load due to insuflicient cement, inadequate mixing andIor compaction. Careful design and skilled workmanship can minimize the risk of these defects. When a failure does occur, it is often inconvenient and costly to remedy as 11 can occur during practical completion of construction or when the building is occupied. Disregarding the guidance and requirements given in this part of 118 8000 is likely to increase the risk of failure.
4.3.1 Effect of 8ta nda rds of workmanship on screed performance
The effects of standards of workmanship on the various tasks carried out in constructing screeds and the consequent screed performance are summarized in Table 1.
4.3.2 Inspection and preparation of bases
4.3.2.1 Level
Check the base for level before preparing it to receive the screed (and insulation if specified), to ensure that the specified minimum thickness of screed can be laid over the whole area. If the base is too high, seek further instructions.
4.3.2.2 General
The wearing screed material should not be placed on the base concrete until any bleed water Ofl the surface
has disappeared.
4.3.2.3 Monolithic wearing screeds
No special preparation of the surface of the base concrete is necessary when the wearing screed is laid monolithically.
COMMENTARY. It is important for the complete bond of a monolithic wearing screed to a base that it should be applied and compacted on to the fresh concrete base while its surface is still plastic. i.e. within three hours of placing the base concrete (or a shorter time in hot weather).
4.3.2.4 Surface roughening and cleaning of hardened in situ concrete bases for bonded screeds Surfaces of hardened in situ concrete bases for bonded screeds should be roughened and cleaned as follows.
a) Mechanically roughen the entire surface to remove laitance and to expose cleanly, but not loosen, the coarse aggregate particles.
COMMENTARY. Brushing to rcmoLrt’ las lance from o fresh concrete base is inadequate preparation before laying a bonded screrd and is not recom mended,
b) Use equipment that avoids heavy impacts on thin bases if there isa risk that cracking or damage could occur.
c) Remove all loose debris, dirt and dust by appropriate means, preferably with vacuum equipment.
d) Carry out the preparation of the surface with as little delay as is practicable before the screed is laid so as to reduce the risk of contamination.
COMMENTARY, hcre the base isa thin layer of conerete (under 100 mm) lwd on precast concrete, mechanical two bbling can cause damage. Contained shot blasting is equally effective and is recommended.
4.3.2.5 Surface cleaning of roughened precast concrete bases for bonded screeds Surfaces of roughened precast concrete bases for bonded screeds should be cleaned as follows.
a) Thoroughly wash and clean surfaces left rough from casting and remove all adhering dirt. Take precautions to ensure that water does not remain in the cores of hollow units.
b) To reduce the risk of contamination, carry out the preparation of the surface with as little delay as is practicable before the screed is laid.
COMMENTARY. Preparation depends on design requirements and further informotwn should be sought. if usaring screrds are intended to act structurally with precast concrete, it is possible that the surface of the base will need lobe contained shot blasted as described in the commentary after 4.3.2.4d).
4.3.2.6 Bonding treatment for screeds on hardened in situ concrete bases for bonded screed-s The bonding treatment may be carried out in either of the following ways.
a) After the base has been prepared and cleaned as described in 4.3.2.4 and before laying the screed material, thoroughly wet the base with water and leave it for several hours (preferably overnight) while keeping it wet. Remove surplus water. Not more than 30 minutes (or less in hot weather) before laying the screed. brush a thin layer of cement grout of creamy consistency well into the surface. Ensure that the grouting is applied at such a time that it will still be wet when the screed is laid on it.
b) As an alternative to applying a thin layer of cement grout, use approved proprietary bonding agents strictly in accordance with manufacturer’s sitework instructions relating to covering rate and the condition of the base when the screed is laid.
COMMENTARY. The use of bonding agents does not eliminate the nerd for the preparation of bases.
4.3.2.7 Surface cleaning and making good of bases for unbonded levelling screeds Surfaces should be cleaned and prepared as follows.
a) Sweep the surface clean and remove loose debris and dirt before laying the screed material or placing the separating layer if specified.
b) Check the surface for defects. Seek and obtain instructions if the making good of any cracks, hollowness or surface roughness is considered necessary.BS 8000-9 pdf download.Workmanship on building sites