Trade preambles and specifications

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All materials used in the works shall be new and of the qualities and kinds specified herein and equal to approved samples. Deliveries shall be made sufficiently in advance to enable samples to be taken and tested if required. No materials shall be used until approved and all materials which are not approved or which are damaged, contaminated or have deteriorated in any way do not comply with the requirements of this Specification shall be rejected and shall be immediately removed from the Site at the Contractor’s expense.


All materials used in the works for which a Kenya Standard Specification is published shall conform to latest Edition thereof in every way. Materials for which no Kenya Standard exists but which are covered by a British Standard shall conform to the latest Edition of that Standard.

Where materials are covered by both a Kenya Standard and British Standard the Kenya Standard will override the British Standard where inconsistencies occur.
The Architect reserves the right to demand that the Contractor obtain at his own expense a certificate in respect of any material to state that it is in accordance with a Kenya or British Standard Specification.


All materials used in the work for which no Kenya or British Standard Specification has been published shall be the best of their respective kinds and of a standard to the satisfaction of the Architect. The quality of such materials shall be generally of a standard equal to those for which there is a Kenya or British Standard Specification.


Where materials are specified by their proprietary names or where fittings are specified by catalogue numbers, or descriptions, the Contractor may offer materials or fittings of alternative manufacture which are of equal quality. Such alternatives must be approved before being used in the works and the Contractor shall allow for this, but prior to tendering he may submit to the Architect for approval, the names of any suppliers or manufacturers whose products he intends to use, together with catalogue numbers, and descriptions and/or samples but the decision of the Architect will be final.


The Contractor shall provide the following equipment for carrying out measuring and control tests on the Site and maintain in full working order: -

  1. Straight edges 2 metres and 4 metres long for testing the accuracy of the finished concrete.

  1. A glass graduated cylinder for use in the silt test for organic impurities in the sand.

  2. Slump test apparatus.

  1. 150mm Steel cube moulds with base plates and tamping rods to B.S. 1881. Two 30 metre steel tapes.

  1. One dumpy or quickest level and staff.


    1. The rates set down by the Contractor against each item shall unless otherwise expressly provided to the contrary, or unless there is a separate item for extra labour, cutting or waste, be held to include for waste on materials, carriage, and cartage, carrying in and return of empties, hoisting, setting, fitting and fixing in position, marking all other labours and everything else necessary for the proper completion of each item and or establishment charges and profit.

    1. Throughout the Bills of Quantities generally no mention is made of heights for hoisting and all prices must include for hoisting and fixing at any level within the limit shown on the drawings or include in the general description unless a specific level stated.

    1. The Contractor shall be deemed to have made allowance in his rates generally to cover items of Preliminaries, expenses in connection with Prime Cost Sums or other items if these have not been priced against the respective items.



The Contractor is deemed to have visited the site and to have ascertained the nature of the soil and sub-soils to be excavated. No claim will be allowed on account of these being of a different nature from that for which he has allowed in his prices.
The excavations and fillings shall be carried out in such a manner and order as the Architect may direct.
Cut down and remove shrubs and trees as directed. No shrubs, trees, plants, etc. shall be removed except as directed by the Architect and the contractor shall be held responsible for any damage caused by the building operations to those shrubs, trees, etc., not so directed to be removed.
All grass, vegetable matter etc., must be removed or burned on site at the commencement of the Contract over areas as directed by the Architect.


The Contractor must destroy any white ants’ nest found within the perimeter of the buildings and within a distance of 20 metres from the buildings externally and take out and destroy Queen Ants, impregnate holes and tunnels with approved insecticide and back-fill with hard material well rammed and consolidated.
The excavations are to be executed to the widths shown on the Drawings, and to the depths below existing ground level as directed by the Architect in order to obtain satisfactory foundation. If the Contractor excavates to any widths or depths greater than those shown on the drawings or as instructed by the Architect he shall at his own expense fill in such widths or depths of excavation beyond that instructed or shown with concrete as specified by the Architect.

  1. Level and ram bottoms of all excavations to receive concrete form stepping if necessary or directed to allow for sloping ground and well water excavations before pouring concrete.

  1. The Contractor shall report to the Architect when secure bottoms to the excavations have been obtained. Any concrete or other work executed before the excavations have been inspected and approved shall, if so directed, be removed and new work substituted after the excavations have been approved all at the contractor’s expense.


  1. Rock is defined as any material met with in the excavation which is of such size or position that it can only be removed by means of wedges, compressed air plant, other special plant or explosives and the Architect’s opinion shall be final. Excavation in any material such as soft coral, hard murram, stiff clay or similar materials which in the opinion of the Architect can reasonably be removed by pick, traxcavator or similar means will be deemed to be included in the prices for normal excavation.

  1. All materials classified as rock may, if approved by the Architects be used as hardcore filling and the measured quantities of imported filling will be adjusted accordingly. All rock so used must be broken to the required size as hereafter described before being so used.


Blasting will only be allowed with the written permission of the Architect. All blasting operations shall be carried out at the sole risk and cost of the contractor and in accordance with any Government regulations in force for the time being, and any special regulations laid down by the Architect governing the use and storage of explosives.
Burrow pits will only be allowed to be opened up on site at the written permission of the Architect.
Hardcore for filling under floors, etc., shall be good hard stone of coral, ballast or quarry waste (not soft coral) to the approval of the Architect broken to pass not greater than 150mm ring or to be 75% of the finished thickness of the layers being compacted whichever is the lesser and graded to contain sufficient smaller pieces to fill all voids so that it can be thoroughly compacted. The filling is to be in layers each of a consolidated thickness not exceeding 225mm and well watered and compacted by hand or mechanical tampers. The top surface of the hardcore shall be levelled or graded to falls as required and blinded with a 75m layer of similar material finely crushed and well rolled and watered immediately before concrete is laid.


Filling obtained from surplus excavated materials is to be free from all weeds, roots, vegetable or other unsuitable materials and is to be filled in layers each of not more than 225mm finished thickness. Each layer to be well watered and consolidated before the subsequent layer is filled in.
No sand, aggregate or other material found in the excavations is to be used in the works without written permission of the Architect.

  1. Where the joints occur there is to be a minimum of 300mm welted lap or joint made with approved tapes.

  1. The Contractor shall ensure that the membrane will not be pierced during the laying and concreting of sub-floors


  1. Insecticide treatment shall be “Aldrex” 48 or “Dieldrex” 18 (to be obtained from Kenya Shell Limited. P.O. Box 43561, Nairobi.) applied in accordance with the Manufacturer’s printed instructions or other equal and approved treatment.

  1. After the hardcore filling has been prepared the whole surface including the top surface of foundation walling shall be similarly treated before concrete slabs are poured. The treatment shall extend 1.5 metres beyond the external wall faces of the building.


Prices shall include for excavating in any material encountered unless specifically measured.
Excavation and disposal of soil are measured net before excavation, filling is measured net after consolidation.
Prices shall include for handling, etc., of extra bulk after excavating, or before consolidating, any extra excavation required for formwork or planking and strutting, circular work, grubbing up any old drains, roots, etc., that may be encountered and for well watering bottoms before laying concrete unless specifically measured.
Prices for returning, filling and ramming or carting away are to include for

removing the excavated materials to temporary heaps or dumps, etc., as required

or made necessary by the progress of the works, site conditions, etc., and for any

re-excavating, re-handling and transporting from such heaps or dumps. All

excavated material has been either returned, filled in and rammed or carted away

and therefore the rates for these items must include for all costs involved in

getting this material to its final position.
The thickness of all soil, hardcore etc., beds given herein is thickness after


The term formation level used in descriptions of work means the level after general excavation to reduce levels of Site or where there is no such bulk excavation the level after removal of surface soil.

The various mixes of concrete are designated in the subsequent measured items

by the following criteria:-

Nominal mixes: By the weight proportions of whole bags of ordinary Portland

cement to fine and coarse aggregate and by the maximum size of coarse

aggregate. The Contractor shall regularly submit details giving specific

gravities and moisture content of aggregates.


The term “tamping” as used herein in conjunction with the phrase treating surfaces of unset concrete” shall mean the final compaction and surface finish to be applied to unset concrete beds, or the like, with steel shod beam tamper, either manually or mechanically operated unless otherwise stated. The resulting surface finish shall have a slightly ribbed appearance.

The term“Keying” as used herein in conjunction with the phrase “treating surfaces of unset concrete” shall mean the preparation of beds, or the like, to receive insitu pavings by raking with a standard horticultural rake whilst the concrete is still green and when the concrete is set and cured, protecting the raked surfaces with a layer of clean sand and removing the sand immediately before the insitu paving is laid.
Unless otherwise described in the measured items, precast concrete units are deemed to be basically rectangular in cross section and rough on exposed faces. Reinforcement bars shall have hooked ends. Bedding and pointing mortar shall be either cement or cement lime mortar, as appropriate, and units shall be deemed to be fixed by hoisting, bedding and building in unless otherwise described.

Nominally non-reinforced units may contain any reinforcement the Contractor may wish to Introduce for handling purposes.

The whole of the concrete work and testing thereof shall comply with British Standard Code of Practice No. 114 and with the subsequent clauses of this Document and shall be carried out in strict accordance with the working drawings and instructions of the Architect and the Structural Engineer.
A competent person shall be employed whose first duty will be to supervise all stages in the preparation and placing of the concrete. All cubes should be made and site tests carried out under his direct supervision. This person shall also be responsible for keeping an accurate record of the dates on which concrete is poured.


The Structural Engineer will prepare and provide all necessary bar bending schedules and explanatory details.
The Contractor shall check these bending schedules against the corresponding drawings before any cutting or bending. Any discrepancies shall be reported to the Engineer. The Contractor shall be responsible for any delays or additional work caused by his failure to check the schedules.
Samples of all materials are to be submitted for approval of the Architect at least one week before it is desired to commence deliveries. All condemned materials are to be removed from the site within 24 hours.
Cement shall comply with Kenya Standard as follows:-
Portland cement - K.S. 02-21
Rapid hardening cement - K.S. 02-21
Sulphate resisting Portland cement shall comply with - B.S. 4027
Rapid hardening cement may be used in lieu of ordinary Portland cement only with the prior approval of the Architect or Engineer, provided that all conditions applying to its use are strictly observed. Any additional expense in connection with the use of such cement shall be borne by the Contractor.
The use of high alumina cement will not be permitted. All cement shall be

delivered to the site in sealed bags bearing the mark of the manufacturer. Rebagged cement, cement in plain bags and cement in torn bags will not be allowed on the site.

Each consignment of cement shall be accompanied by the manufacturer’s certificate showing that a representative sample of the consignment has been tested and compiles with the appropriate specification.

From time to time as requested by the Architect, copies of the cement manufacturer’s test certificate shall be delivered to the Architect or his representative on the site promptly, but such documents shall not preclude the Architect from rejecting any cement which does not in every way comply with the specification.
Any cement, which has failed to pass the tests or has been damaged by water or contaminated in any way on site, shall immediately be removed from the site.
Aggregates shall comply with British Standards as follows:-
Fine - B.S. 882 table 2 Zone

1 to 3 only.

Coarse - B.S. 882 graded
“All in” ballast - B.S. 882 graded
Granite - B.S. 1201 graded


Each type aggregate shall be obtained from one approved source, capable of

maintaining adequate supplies of consistently graded material throughout the

contract. Aggregates for exposed concrete shall be free from all impurities

likely to cause discolouration and shall be of consistent colour throughout the

Fine aggregates and sand shall be clean, sharp, coarse, hard material and equal at

all times to the samples which shall be deposited with and approved by the

engineer. The caustic soda test for organic impurities shall show a colour not

deeper than that of the standard solution. The setting test for natural sand shall

be made after being allowed to settle for three hours the layer of silt deposit on

the coarse material shall not exceed 10%.

The contractor shall supply necessary equipment for the testing of fine

aggregate and sand for the use of the Engineer.

Coarse aggregates shall be hard , clean gravel or broken stone from approved

quarries and shall be free from earth, decomposed stone, and extraneous matter.

They shall conform to B.S. 882 and shall be “Graded Aggregate” 20mm to

5mm. Thin, elongated, friable, flaky or laminated pieces, mica or shale shall

only be present in such small quantities as not to affect adversely the strength

and durability of the concrete. The amount of fine particles occurring in a free

state or as loose adherent shall not exceed 1% when determined by the laboratory

sedimentation test. After twenty-four hours in water, a previously fried sample

shall not gain more than 10% in weight.

Each grade of aggregate shall be stored in the works in separate heaps so that

there shall be no possibility of any inter-mixing. Any materials which have

become inter-mixed shall be removed from the site forthwith by the Contractor.

If, in the opinion of the Engineer, the aggregate is dirty or adulterated in any

manner, it shall be wasted and or/ screened by the Contractor.

Graded samples of all types of aggregate each weighing 10Kg. Shall after

approval, be kept on site behind glass for visual checking of subsequent

deliveries for grading, shape, and where applicable, colour.
Reinforcement shall comply with the following standards: -

  1. Mild steel rod reinforcement shall be – K.S. 02-22

  1. High tensile steel reinforcement shall either be cold worked deformed steel bars of circular octagonal section complying with B.S. 4461 or hot rolled deformed high tensile bars having a guarantee minimum yield stress of 4200 kg/sq. cm (60,000 p.s.i) and other physical qualities in accordance with B.S. 4449.

(c) Welded steel fabric reinforcement shall comply with B.S. 4483.

All reinforcement shall be in the “diameter” and metric range and the substitution of “square twisted” or imperial range shall be allowed but only at no extra cost to the Employer.
The Contractor will be required to submit at his own expense certified test data of the following characteristics; ultimate tensile stress, yield point stress, elongation, cold bend test. Should such certificates not be submitted by the manufacturer, the Contractor shall have the requisite tests made at his own expense at an independent testing laboratory.

  1. Filler shall be Flexcell” impregnated fibreboard joint filler.

Top edges of filler to be covered with plastic tapes as a bond-breaking barrier prior to filling with sealer.

  1. Sealers to be

  1. “Pli-astic” grade 99 applied hot with a machine pourer as recommended by the manufacturers. Prior to application surfaces to be treated with a brush coat of Expandite No. 3 Primer. or

  1. “Plastic joint” hand applied bitumen putty sealant prior to application surfaces to be primed as last. or

  1. “High duty” sealer cold applied to sealant. Porous surfaces to be primed with Expandite No. 20 primer.

iii) The appropriate sealers are specified in the measured work hereafter and must all be applied and used strictly in accordance with the manufacturers’ printed instructions.

Wall ties shall be provided between all columns and walling and shall be of galvanised mild steel strip 25mm wide x 450mm long.
Water shall be from the mains and kept free of any impurities and acid or alkaline substances in suspension or in solution, and shall be stored in proper storage tanks to the approval of the Architect.
Cement shall be kept dry and used in rotation of deliveries. If delivered in bags these shall be stored off the ground in a well-ventilated and weatherproof shed used exclusively for this purpose.
The shed is to be sufficiently large to contain a working stock and provided with partitions or such other means as may be necessary to ensure the effectual separation of the various consignments and type of cement. Stacking of cement in bags over a height of ten bags will not be permitted. Cement may be delivered in bulk containers provided additional suitable arrangements are made for bulk storage on the approval of the Architect.
Aggregate shall be stored at mixer positions on drained concrete paved areas, with stout dividing walls between different sizes and types of aggregates.
Reinforcement shall be stored by type, size and length either off the ground or on clean surfaced areas, and shall be kept free from rust.
The quantity of cement shall be measured by weight and each batch of concrete is to use one or more whole bags. The quantity of fine aggregate and coarse aggregate shall be measured separately by weight-batching plant. Volume mixing will not be permitted.
For grading test the Contractor shall supply and deliver at his own cost to the Approved Testing Authority, samples of the aggregates which the Contractor proposes to use, consisting of not less than 50 Kilograms weight in fine aggregate. It is the Contractor’s responsibility to ensure that the subsequent deliveries of aggregate conform to the grading analysis of the approved samples.
The proportions of materials to be used for the preliminary cube tests and subsequent batching, shall be ascertained by calculation from the results of the aggregate grading tests carried out by the Approved Testing Authority.

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