TILING, FLOORING, SCREEDS, SUSPENDED CEILINGS AND ROOFING

1 TILING, FLOORING, SCREEDS, SUSPENDED CEILINGS AND ROOFING

1.1 Scope

This Specification covers the requirements for tiling, flooring, screeds, suspended ceilings and roofing.

1.2 Tiling

1.2.1 General

Work under this heading shall comprise all required labour, equipment and the supply of the appurtenant materials and structural components including off-loading and storage at the site unless otherwise specified. Tiling and flooring shall be applied in accordance with the finishes, specified in the particular specifications.
Workmanship and construction for tiles to floors and walls shall generally be in accordance with DIN 18352. All materials and structural components not standardized shall be used only with the approval of the Engineer.
All tiles and slabs for which there are several grades shall be of the best standard commercial grade unless grade is stipulated in the specifications.
Before starting the work, the Contractor shall ascertain the Employer's selection of patterns and colours and the Contractor shall furnish the Engineer with duplicate samples of the patterns and colours of the material selected by the Employer.
Tiling shall be free of all defects and any work which shows signs of bond failure, hollow patches, misalignment, cracking or any other defect will not be accepted and shall be removed and replaced with acceptable work.
The Contractor, before the commencement of his work, shall inspect and test backgrounds to ensure that their cleanliness, moisture content, alkalinity, sulphate content, etc., are such that they will not adversely affect his work.
Joint fillers, sealer and adhesives shall be mixed and used strictly in accordance with the manufacturer's instructions.
Additives shall not be used in rendered backings to receive wall tiling.

1.2.2 Materials

In general, tiles and flags shall meet the require¬ments for quality stated in DIN 18155, DIN 18158 and DIN 18166. Where tiles and flags are not standardized, the quality features (e.g. parallelism of the edges, state and colour of the top surface, water absorption) shall satisfy the standard commercial requirements. All floor and wall tiles of a particular type and colour shall be from the same batch. Glazed ceramic tiles for walls shall be either white or coloured, true to shape, flat, free from flaws, cracks and crazing, uniform in colour, keyed on the back and shall comply with DIN 18155. The tiles shall be of a suitable type, size, colour and acid resistant. Ceramic floor tiles shall be oil and acid resistant, true to shape, flat, free from flaws, cracks, uniform in colour and of an approved type, make and colour. Dimensions and tolerance shall comply with DIN 18158 and DIN 18166. PVC (vinyl asbestos) floor tiles shall be to DIN 16951 and DIN 16952.

1.2.3 Tiles - Adhesives

Cement based adhesives shall comply with the requirements of DIN 18156. Other adhesives shall be subject to the approval of the Engineer and mixed and used strictly in accordance with the manufacturer's printed instruction. Mortar materials and adhesives shall not alter or damage the top surface of the covering. Grout for wall tiling shall be to DIN 18156.

1.2.4 General Preparation

Surfaces shall be prepared before covering with tiles is started in accordance with the manufacturer's instructions.

1.2.5 Preparation of Tiles

Tiles, which are to be laid in cement mortar, shall be soaked in clean water for 15 - 30 minutes before fixing and allowed to drain for 10 - 15 minutes. Any surplus water shall be removed from the backs before laying.
Tiles to be fixed with adhesives shall not be soaked or wetter prior to laying. All cutting to tiles shall be fair cutting using a tile cutter.

1.2.6 Placing

In interior finishing works all tiles, flags and mosaic shall only be set and laid before the fixing of window and door frames and trims, and after stop rails, plumbing installations and the application of plaster unless otherwise specified.
All tiles, flags and mosaic shall be set or laid plumb, in true alignment and horizontal or at the slope specified, without any projections, with regard to any specified reference and level lines. In wall coverings, projections shall be allowed only to the extent dictated by the particular type of tile or slab specified.
All tiles, flags, mosaic, or the like shall be set or laid in normal mortar bedding unless otherwise specified below.
Tiles shall be laid so that the key patterns on the back of the tiles lie in the same direction.

Bedding Fixing and bedding of tiles shall be as follows: Adhesives: Thin tiles shall generally adhesive fixed. Backgrounds shall be cleaned and primed according to the manufacturer's instructions and the adhesive shall be applied by the notched trowel technique and trowelled over the area to be tiled at a thickness of 4 mm, and then combed with a trowel having 4 x 4 mm notches at 16 mm centres to form ribs. Tiles shall be pressed in as recommended. Mortars: Thick tiles shall generally be bedded in cement/ sand mortar at least 10 mm thick to a true vertical or horizontal face with continuous horizontal and vertical joints and shall be pointed in neat white or coloured cement. Any surplus which adheres to the face of the tile shall be wiped off with a damp cloth before it sets hard. The external angles and side and top edges of glazed wall tiling shall be formed with rounded edge (bullnose) tiles. At intersections, returned rounded edge tiles shall be used. Joints shall match those of the floor tiling and special approved fittings shall be used at the intersections between wall tiles and horizontal surfaces. Where tiling abuts against wood or metal frames or other tiling at angles and around pipes, etc., it shall be carefully cut and fitted to form a close neat joint. Open irregular joints filled with cement and sand or plaster will not be permitted. Tile fittings: Skirtings, coves, channels and other fittings shall be bedded as tiles.

6.2.8 Jointing The widths of joints shall suit the type of tiles and flags used, the purpose and stress of coverings and the type of jointing chosen. The joints shall be equal in width. Unless otherwise specified, the coverings shall have the following widths of joints: Ceramic wall tiles with lengths of sides up to 15 cm 2 mm Ceramic floor tiles with lengths of sides up to 15 cm 2 mm Glass tiles min. 1.5 mm max. 3 mm Ceramic tiles with length of sides over 15 cm min. 2 mm max. 8 mm

Jointing shall be by the washing-in method unless otherwise specified. Cement mortar shall be used in jointing unless otherwise specified. For jointing wall coverings of glass walling panels, permanently elastic sealing compounds shall be used. All parting, expansion and connecting joints shall be closed with suitable sealing compounds unless other means are specified, e.g. elastic joint sections, open joints. Parting joints in buildings shall extend into the wall and floor coverings at the same point and in an adequate width. No mortar bridging shall occur. The expansion joints of the coverings shall penetrate to the bonding surface. In oil-proof and acid-proof tile and flag coverings, the kind of stress shall be taken into account. The movement joints in tiling mentioned above shall be 6 mm to 10 mm wide, shall be formed around the perimeter of the floors and generally at 3.6 m in both directions of surfaces for the full thickness of tile and bed. The joints shall be filled to not more than 6 mm from the face of the tile with joint filler, and sealed with polysulphide sealant applied by gun and neatly smoothed of f and pressed home. The surface of the tiling shall be protected by the use of masking tape which shall be removed before the sealant has set. Any sealant on the face of the tile shall be cleaned off. Brass junction strip shall be fixed at the junction of tile and other floorings. It shall be set in position before the tiles are laid and shall extend through the full thickness of the tiling and bed. 6.2.9 Tolerances The surface of the finished wall tiling shall meet the accuracy as required in DIN 18202. 6.2.10 Stone, Concrete and Marble Slabs General: Materials and workmanship generally shall be in accordance with the requirements of DIN 18352, DIN 18515, DIN 18155, DIN 18158 and DIN 18166. Cutting: Stone displaying defects such as cracks, chipped edges and corners, shall be rejected, and in no case incorporated in the works. Slabs shall be pre-cut to size, and where the lower edge abuts a staircase flight, the panel shall be scribed to the stair profile. Rectangular holes for switchplates and socket outlets shall be cut with a rebated edge to allow faceplates to finish flush with the panel surface. Joints between individual panels shall be flush pointed to ensure an even and continuous surface between arises or changes of direction. Fitting: Stone lining slabs shall be fitted using cramps and hooks and plaster dabs leaving an air pace of 12 mm behind the slabs to prevent transfer of soluble salts from the backing material. Finishing: All marble work shall be cleaned, polished to a uniform glassy surface and finished with an approved compound. Exposed edges shall be protected with lime putty or the like and finished faces shall be free from scratches or other defects. Fixings: Fixing dowels and restraining hooks shall be of stainless steel to DIN 17440 and shall generally comprise two per slab. Allowance shall be made for drilling holes in the top edge of a slab to receive dowels, and for site drilling dense concrete block-work, and wedging and grouting following insertion of dowels. Mortar used for jointing and bedding shall be in accordance with the requirements of DIN 18156. Marble shall be best quality, for walls grey marble shall be used, cut square and true and shall be uniform in shape and thickness. Window sills shall be bedded hollow on plaster dabs and pointed all around with white cement/sand mortar (1:4 mix). Skirtings shall be fixed solid on a backing 10 mm thick. Joints in skirtings shall be arranged to coincide with joints in adjacent paving. Rounded arises, nosings and mouldings shall be adequately protected by means of timber casings or lime putty coatings. Treads, risers, skirtings and window sills shall be grouted and protected in a manner similar to pavings. 6.2.11 Measurement for Payment Not used.

6.3 Flooring 6.3.1 General All materials and structural components merely to be provided by the Contractor and not, therefore, ultimately incorporated in the structure shall be new and unused unless otherwise specified. They shall be suitable for their intended purpose and appropriately matched to each other. All materials and structural components covered by DIN standards shall meet the respective quality and dimension requirements. All materials and structural components requiring approval by official regulations shall be officially approved and shall comply with the conditions laid down for such approval. Any materials and structural components for which there are neither standards nor official approval requirements may be used subject to the Engineer's consent only. The floorings shall be such as to provide a cover surface that can well be walked on. They must not give rise to any unreasonable inconvenience. Deviations in colour as against the samples may only be slight. 6.3.2 Materials The quality of marble shall be in accordance with DIN 52100. Marble shall be first quality, matched for colour and pattern. Slabs displaying defects such as stains, chipped edges or corners shall be rejected and in no case incorporated in the works. White marble shall be used for floors. Concrete paving slabs shall be 50 mm thick hydraulically pressed precast concrete slabs in accordance with DIN 18500. Terrazzo shall be in accordance with the appropriate DIN standard. The marble chippings shall be of an approved quality in irregular pieces with no flaky pieces. PVC flooring material shall comply with the requirements of DIN 16951 and DIN 16952 and shall have the following properties: temperature resistant within the limits of -300C and +700C, waterproof, abrasion resistant, flameproof, pigment or colour proof to light, evenly coloured throughout, resistant to chemicals, fats, slight acids and alkalines, odour-less, easily laid and flexible, non-porous and slip-proof. All adhesives shall have suitable properties to ensure a firm and durable bond. They must not adversely affect either the flooring or the underlays or the base and shall be odourless once applied. All fillers and levelling compounds shall have a firm and durable bond to the base, provide a good bonding surface for the adhesive and be of suitable property so as to give an adequate support to the covering. They must have no adverse effect on base, adhesive, underlay, or covering. 6.3.3 Workmanship Generally The Contractor shall examine the base to see whether it is in a suitable condition for him to carry out his work. Any doubts the Contractor may have in this connection shall be communicated by him to the Engineer immediately in writing. All materials and structural components whose process¬ing is subject to manufacturer's instructions shall be processed accordingly. The covering must not close any expansion joint in the structure. The Contractor shall clean the flooring and treat it in accordance with the flooring material manufacturer' s instructions. The contractor shall furnish the Engineer with the written instructions for the care and maintenance of the flooring. 6.3.4 Preparation of The Surface The subsurface will be cleaned. The base for coverings to the placed without underlay shall be smoothed with filler compound. In the case of major unevenness a suitable levelling compound shall be used. Any filler or levelling compound shall be applied so that it will bond firmly and durably to the base, will not crack and will adequately withstand pressure. Any screeds such as magnesia and anhydride screed to which the filler or levelling compound will, but insufficiently, bond, shall receive a priming coat. 6.3.5 General Requirements for Application Workmanship generally shall be in accordance with DIN 18352 and DIN 18365. Floorings shall be placed without underlays unless otherwise specified. The courses shall be laid towards the main window wall, in halls and corridors, however, in longitudinal direction, unless otherwise specified. Deviations in colour which are not of minor importance and not due to the flooring pattern shall not be allowed if marring the overall appearance of the flooring. Courses with pattern repeats shall be laid so as to suit these. Where courses run towards doors, recesses and the like, they shall be laid so as to cover also the floor areas of such door openings, recesses etc. Strips or slabs may be used as coverings of such floor areas. Plastic flooring shall not be welded unless otherwise specified or expressly required in the flooring material manufacturer's processing instructions. Any adhesive lodged on the flooring shall be removed at once. Where floorings are raised in grooves on walls they shall be accurately fitted together in the corners of the grooves, if necessary, by inserting adapter sections. 6.3.6 Marble Marble slabs shall be stacked under cover on paving a clean level surface, protected against water penetration from the ground. Units shall be stacked vertically on edge with nonstaining laths or battens placed between each unit. To avoid discolouration, panels shall not be prematurely delivered. to site nor come into contact with rope, straw, hardwood or other materials likely to cause staining, nor shall they be exposed to direct sunlight. Laying: Marble slabs shall be fixed solid on a bed of cement/sand mortar (1:4 nominal mix), 20 mm thick with tight joints grouted in lime putty. A protective slurry of lime putty at least 3 mm thick shall be applied to the marble pavings and subsequently cleaned off. Slabs shall be laid with staggered joints. Treads to stairs shall be fixed solid on a bed 15 mm thick. Risers to stairs shall be fixed solid on a backing10 mm thick. 6.3.7 Precast Concrete Slabs All precast concrete slabs shall be laid in bays not exceeding 10 m in length, the bays being separated by an expansion joint 10 mm wide. 6.3.8 Thin Floor Coverings: Pvc Flexible PVC sheeting or tiles to walls or floors shall be laid on a level and smooth background generally consisting of anhydride screed. The screed surfaces shall be clean, dust-free and dry. Tiles shall be laid and bedded in strict accordance with manufacturer' 5 instructions. Where resilient backing is used, this shall be a rubber underlay, with glass fibre weave surface. 6.3.9 Fitting of Cover Strips and Nosings All skirting boards and cover strips shall be snugly fitted and durably fastened. When not otherwise specified wooden cover strips shall be provided throughout all office rooms, laboratories, residential buildings, etc.. Wooden cover strips shall be fixed at distances not exceeding 60 cm. Stair tread nosings and other edgings of metal shall be screw-fastened at distances not exceeding 18 cm unless any other means, e.g. anchoring, is specified. Any plastic or rubber nosings in stairs shall be fixed to the treads of the steps only.

6.4 Screeds 6.4.1 General Workmanship and construction generally, shall be in accordance with DIN 18353 and DIN 18560. Materials used for mortar shall be measured in proper gauge boxes. All concrete surfaces shall be adequately keyed to receive screeds. 6.4.2 Floor Screeds and In-Situ Finishings The works described below shall generally include the following: • Dense aggregate cement screeds - base and wearing courses. • Granolithic and terrazzo toppings. 6.4.3 Weather Conditions Floor screeds shall not be laid in areas exposed to high temperatures, strong sunlight, strong draughts, or winds, unless protected from such conditions. 6.4.4 Screed Dimensions Screeds shall be as follows: • Floor screeds shall be laid to the thickness, levels and falls according to the approved drawings. When laid "monolithically" a screed shall not be less than 20 mm and not more than 30 mm thick, and when laid "unbonded" on a separating layer, it shall not be less than 50 mm thick. • Thick floor screeds shall be laid in bays of maximum size 20 m2. Bays shall be laid alternately. Floor screeds for thin floorings shall be laid in strips not larger than 3 m wide. • Separation layer shall be a bituminous sheeting or equivalent. 6.4.5 Materials Materials for screeds shall be in accordance with DIN 18560 and set out below: • Cement shall be Portland cement complying with DIN 1164. • Sand shall comply with DIN 1053 and DIN 18550 and shall be rewashed on site if the silt loam or clay content exceeds the requirements described in DIN • Granite for granolithic screeds shall be in accordance with the appropriate DIN standard. • Water shall be clean and free from harmful matter in suspension and solution. Preferably only clean water from mains shall be used. Where doubt exists, it shall be tested in accordance with DIN 4030 and DIN 38404. • Lime shall be to DIN 1060. Anhydride shall be to DIN 4208. 6.4.6 Base Concrete Preparation Base concrete to receive floor screeds shall be prepared as follows: • For screeds laid ‘separate’ - within three to twelve hours of the base concrete being placed, the laitance on the base concrete shall be removed by light or mist spraying with water and brushing to removed prior to laying toppings; or • For screeds laid “separate” - after twelve hours of the base concrete being placed, the laitance on the base concrete shall be completely removed by hacking to expose clean aggregate particles. All loose concrete, dust and dirt shall be removed by thorough washing with water. Any excess water shall be removed prior to applying the cement slurry. • For screeds laid "unbonded" - no special preparation is necessary, except to remove all projecting nibs and sweep the concrete surface clean prior to laying the separating layer. 6.4.7 Screed Mix The mix preparations shall be in accordance to DIN 18550. Materials for a screed mix shall be thoroughly and efficiently mixed dry by mechanical means until a uniform distribution is obtained, and then water added. The water content shall be kept as low as is necessary to allow sufficient workability for laying and compacting. No extra water, or other material, shall be added to the mix after it has left the mixer. Where only small quantities are required, mixing may be carried out by hand, on a clean watertight surface. For this the approval from the Engineer is required. 6.4.8 Placing and Compaction Fixing of forms etc. shall be as follows: Form setting: The side forms shall be fixed rigid on a firm foundation and supported throughout their length so that they will not be disturbed by the spreading and compacting of the floor screeds. Forms shall be set true to line with + 3 mm, and to level within  3 mm, and shall be checked for level immediately before work starts. Placing and compaction: The screed mix shall be placed between the forms (and or other bays) worked around the penetrations, duct covers, manhole covers, gutters, balustrade standards, pipes, etc., and shall be fully compacted by means of a screed board, or other suitable compacting equip¬ment, providing laitance is not brought to the surface. Joints: All edge joints of floor screeds shall be simple butt joints without filler. Screeds laid over construction joints in concrete shall be separated by 10 mm impregnated oakum strips or the like. Joints in wearing courses shall be 10 mm polysulphide to DIN 18540. 6.4.9 Finishing Finishes shall be as follows: • Screed base course shall generally be finished with wood float to give and even texture. The sprinkling of cement onto the surface and trowelling in to absorb water will not be permitted. • Screed wearing course shall be tamped with a wood float and trowelled twice with a steel trowel to produce a smooth finish. Matured sub-base shall first be well cleaned, wetted and brushed with a Portland cement grout before topping is laid. Finishing screeds shall be made good around gullies and any penetrations through the floor surface. 6.4.10 Curing and Protection As soon as a floor screed has hardened sufficiently to prevent damage to the surface, it shall be cured for a minimum period of seven days after, by means of either wet canvas, straw mats, rand, polythene or sheeting laid on the surface and kept continuously damp and in position for the full curing period. Protection: As soon as the laying of the floor screed has been completed, it shall be protected against rapid drying out caused by wind, draughts and strong sunlight. 6.4.11 Tolerances Tolerances shall be as follows: General: The finished surface of base course screeds, when laid, shall not depart more than specified in DIN 18202 for accuracy class B. Floor screeds, when laid, shall be free of all defects and any work which shows signs of bond failure, hollow patches, crazing, cracking or any other defects will not be accepted, and shall be removed and replaced with acceptable work by the Contractor. The extent of the work to be removed and the method to be used in the removal and replacement of this work shall be to the approval of the Engineer. All surfaces shall be approved by the Engineer before further work. 6.4.12 In-Situ Toppings In-situ toppings shall be as follows: Granolithic toppings: These shall be mixed with sufficient water to give a matured concrete sub-base, the concrete shall first be well cleaned wetted and brushed with a Portland cement grout. To produce a wearing surface, the granolithic mixture shall be tamped in with a wood float and trowelled twice with a steel trowel to produce a smooth finish. The paving shall be laid in alternate bays not exceeding 9 m2 in area and the bays shall be separated by expansion strips of mastic or other approved material. Terrazzo: This shall be mixed with sufficient water to give a plasticity suitable for laying. The finished thickness shall not be less than 25 mm for pavings and 10 mm for wall facing and skirtings. Terrazzo shall be laid immediately following screed of cement/sand at least 15 mm thick. The concrete sub-base shall first be well cleaned, wetted and brushed with a Portland cement grout. The terrazzo shall be laid in bays not exceeding 9 m2 in area and the bays shall be separated by expansion strips of brass or other approved material truly level with the finished surface. The pavings shall be rolled and trowelled to a dense and even surface. Terrazzo pavings shall be rubbed down to a grit finished surface free from blemishes after the initial set, and cured by covering with waterproof paper or wetted hessian for a period of a least three days. After curing, the pavings shall be filled in with a cement grout of the same colour and polished by approved machine using a suitable carborundum abrasive and potable water until an even and smooth surface is obtained to the satisfaction of the Engineer. Before opening to traffic, terrazzo shall be scrubbed with an acid and alkali-free soap. After 24 hours, all surfaces shall be scrubbed vigorously with hot water and rinsed. No strong detergents or disinfectants shall be used. 6.4.13 Measurement for Payment Not used.

6.5 Suspended Ceilings 6.5.1 General The standard of workmanship for these works shall be of the highest standard and in strict accordance with manufacturer' 5 instructions. The terms "suspended ceiling" or "ceiling" mean all component parts of an integrated ceiling installation including all junctions to perimeters, cores, columns, etc. The ceiling panel surface shall be of a consistent appearance and the Contractor shall ensure that the surface finishes are uniform in colour, texture and appearance throughout. No fixing screws, cleats1 etc., shall be visible on the ceilings. 6.5.2 Materials Materials used in suspended ceilings shall in general comprise one of the following: • Mineral fibre ceiling tiles; • Aluminium strip acoustic ceiling; • Plasterboard ceiling. Ceiling installation systems shall have the fire classification approved in accordance with DIN 4102. Ceilings shall include a concealed, clipped metal suspension and framework system, installed in accordance with the manufacturer's written instruction. Additionally, a framework shall be provided of galvanized mild steel angles supported from the structure above by means of galvanized mild steel hangers. Ends of hangers shall be threaded and bolted to the framework in such a way as to permit reasonable degree of adjustment to achieve the required levels and effect. All metal components shall be corrosion resistant. Plasterboard used in metal stud partitions or suspended ceiling systems shall be 12.5 mm wall board to DIN 18184 or equal approved. The inner lining to walls providing one hour fire resistance shall be board comprising a gypsum core. The suspended ceiling or any of its parts shall not contain any substance which, as a result of overheating or combustion, will emit abnormally toxic fumes. 6.5.3 General Requirements The suspended ceiling shall be capable of sustaining and transmitting to its point of support all loadings resulting from its dead weight, and the dead weight of integral lighting fittings, without deflection, fracture or permanent deterioration of its performance. No irreversible deformation or progressive creep shall occur beyond the tolerances given herein from such applied force. Ceiling panels and their method of fixing shall be sufficiently robust to withstand removing without permanent damage or disfigurement (especially during commissioning or any air conditioning installation). Any changes in dimensions and shape of the suspended ceiling system or its parts, due to changes in temperature or humidity, shall not affect its performance. The construction method proposed shall include bracing stiffeners, etc., to render the finished work rigid, free from deflection, distortion, bending, warping, etc. In addition to the above requirements, all work shall remain securely fixed without free play. Finished ceilings shall be level and true to line in all directions. Joints between tiles shall be straight and level and no deflection shall be apparent at butt edges between tiles and other components. Any variation from true level shall not be more than 3 mm in any 3 m. 6.5.4 Coordination The Contractor shall ensure that an adequate number of permanent access hatches are incorporated in all suspended ceiling systems. Particular attention is drawn to the requirement that the component parts of the works shall be fixed by tradesmen normally responsible for such work, e.g. electrical work and light fittings fitted by electricians, ceilings by ceiling firms, etc. The method of construction shall allow for prefabrication and other forms of off-site manufacture as necessary to suit the nature of the works and the incomplete state or otherwise of the project at the time of construction. 6.5.5 Suspension Systems Suspension systems shall be adequate and suitable to meet the specified requirements. The method of construction shall take account of the following restrictions with regard to fixings: • Fixings and suspension systems shall not be connected to any services installation. All ceiling suspension members shall be fixed clear of all services or insulation. • Fixings to reinforced concrete beams and slabs shall be made using a fixing method approved by the Engineer. • Fixing to steelwork shall be by drilling and bolting. Clip-on fixings will not be permitted. 6.5.6 Setting out Tiles Acoustic and other tile ceilings shall be set out each direction from the centre of the room, on either the centre of a tile or a tile joint as agreed in each case by the Engineer. 6.5.7 Fixing Devices Metal fixing devices shall be manufactured entirely of non-ferrous metals or be otherwise thoroughly protected from corrosion. Timber fixing devices shall be pressure impregnated with an approved preservative. Brackets, plugs or bolts shall be of a type, make and pattern approved by the Engineer. The Engineer's approval shall be obtained for all proposed methods of fixing. 6.5.8 Measurement for Payment Not used. 6.6 Roofing 6.6.1 General The work shall consist of supplying, laying and finishing complete insulation and roof coverings and shall include provision of all necessary skirtings, copings, flashings etc. as required. On completion, all roofs shall be left sound and watertight and in a neat and clean condition. All roof finishes shall be carefully worked or fitted around pipes or openings. Roofing systems shall be in general the "inverted root" or "protected membrane roof" system where the waterproof membrane is laid directly onto the structural slab. The insulating layer is then laid on the membrane and protected by a layer of files. Any special working details that may be prepared by the Contractor shall be submitted to the Engineer for approval. This work shall be done in good time, prior to commencement of construction. Falls for rainwater drainage shall slope away from movement or other joints where practicable. 6.6.2 Waterproofing The structural slab or surface screed membrane shall be primed with primer before application of the membrane according to the manufacturer's instructions. 6.6.3 Roof Insulation Roof insulation board shall have a minimum density of 35 kg/m3. 6.6.4 Precast Cement and Sand Roofing Tiles Precast cement and sand roofing tiles shall be formed with a minimum 10 mm facing of one part white cement and three parts of sand, set on a backing of sulphate resisting cement mortar with a minimum cement content of 305 kg/m3. 6.6.5 Aluminium Flashing Flashings shall be formed out of 0.8 mm super purity aluminium with natural mill finish. Accessories such as hooks, nails, screws and clamps shall be of the same material and alloy. 6.6.6 Screeds Cement, sand and water for screeds shall be as described in the section for concrete. Lightweight aggregate shall be a proprietary type approved by the Engineer. 6.6.7 Rainwater Outlets Rainwater outlets shall be a proprietary type approved by the Engineer. Outlets shall drain from the top interface between the waterproof membrane. 6.6.8 Workmanship Workmanship shall be carried out in accordance with DIN 18338. The roof surfaces shall be uniform, compact and free from all debris. Waterproof membranes shall be 1.5 mm thick self-adhesive rubber bitumen applied strictly in accordance with the manufacturer's instructions. The membrane shall be continuous and taken up abutments and pipes to above the insulation layer. Exposed membrane shall be solar protected. The waterproof membrane shall be carried up walls, beams, etc., over fillets to form a skirting continuous with the roof covering. The waterproof membrane shall be dressed and bonded into rainwater outlets and under flashings. The insulation boards shall be not less than 50 mm thick closed cell extruded polystyrene loose laid in a single layer with tight staggered butt joints in accordance with the manufacturer's instructions. The boards shall be trimmed to fit any fillets used under the waterproof membrane. Flashings shall be sheet aluminium neatly cut to a width and length required. Aluminium shall be carefully bent using a slightly rounded former so as to avoid surface cracking. Where surface fixing is required, the sheet shall be pre-drilled and fixed with inoxydisable screws to proprietary fixings or hardwood grounds let into the surface of the base concrete or brickwork. Where flashings are built into joints or tucked into rooves, the aluminium shall be set to full depth. Where set into grooves, aluminium shims or wedges shall be used at 450 mm intervals to secure the flashing. The exposed edges above the flashing shall be neatly flush pointed with cement mortar. Lightweight screeds shall be laid in accordance with the manufacturer's instructions and to falls not less than 1 in 40 with a minimum thickness of 100 mm. The screed shall be laid in two courses, the lower course not less than 50 mm thick and in bays not exceeding 15 m or 1.80 m in width laid alternately and finished with a 10 mm thick topping of 1:4 cement/sand mortar. Screeds shall be trowelled smooth. Immediately after laying, the screed shall be protected from wind or strong sunlight and upon hardening shall be protected with waterproof sheeting for a period of not less than 7 days. Screeds shall be laid to a tolerance in accordance with DIN 18202 accuracy class with high spots between drainage outlets, and shall be thoroughly cured before the roof finish is laid. Care shall be taken to avoid damage to screeds prior to installation of the roof finish. 6.6.9 Galvanized Iron Sheet Covering (Pitched Roofs) In the case of a pitched roof with galvanized iron sheets, corrugated galvanized iron sheeting shall be new sheets of 0.65 mm thickness fixed with forge headed screws and rubber and leather washers or special mastic into 8 cm x 5 cm hardwood purlins. All ridges, cappings, flashings, etc., are to be of galvanized iron 0.65 mm thick. 6.6.10 Timber Roof Structures (Pitched Roofs) Where timber roof structures are foreseen, the timber for trusses and the timber for purlins and joints shall be selected hardwood. Trusses are generally to be constructed in the connected double-wood system and bulldog connectors and all necessary ironmongery are to be allowed for. Unless otherwise indicated, timber trusses shall be spaced 2 m apart, and shall be wall-plated, secured to beams, or string course by means of rag-bolts, rag-bolted angle cleats with bolts, cast-in reinforcing bars, or cast-in hoop irons to the approval of the Engineer. If open soffits are indicated, all visible members of trusses shall be planed and painted with three coats of oil paint. All timber utilized in the construction of roof structures shall be well sawn, sound, free from warps and other defects, and shall be treated in accordance with the general specification for painting and protective coatings.