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3.1 The waterproofing compound shall as approved by the S.O. in the specifications herein, and strictly used in accordance with the manufacturer’s instructions.

3.1.1 Field Test To Determine Level Of Contaminants In Plastering Sand

Carry out field tests as and when required by the S.O for determining the volume of silt and clay in plastering sand.

Prepare a salt solution using one teaspoonful of table salt to half litre of cold tap water. Fill a clean jam jar to about one third of its volume with a sample of the plastering sand. Pour the prepared salt solution into the jam jar to about 90% full. Close lid of the jar, shake its contents vigorously and leave to stand for half an hour. A layer of silt will settle over the top of the sand. Should the layer of silt exceeds one-tenth of the depth of the sand in the jar, the sand is too contaminated to be used and shall be rejected.

The S.O may also carry out a physical inspection of a batch of sand. If it stains excessively or balls up in the fingers when rubbed, the sand shall be removed from the Site at the Contractor's expense.

3.1.2 Cement-sand Plastering for New Works

Unless otherwise specified, plaster shall be applied in two coats to the total nominal thickness indicated. The first coat shall be cross scored to provide a key for the second coat which shall be 6mm thick trowelled or floated to produce a tight, matt, smooth surface in a true plane to correct line and level with walls and reveals plumb and square.

a) Render and set minimum 13mm (for interior plastering), or minimum 25mm (for exterior plastering) thick cement and sand (1:4) plaster gauged with approved plasticiser and steel trowelled smooth to all exposed concrete surfaces such as soffits of concrete slabs, beams, canopy, staircases etc unless otherwise indicated on the drawings.

b) Render and set 20mm (for interior plastering), or minimum 25mm (for exterior plastering) thick cement and sand (1:4) plaster gauged with approved plasticiser and steel trowelled smooth to all exposed common brickwork surfaces unless otherwise indicated on the drawings.

3.2 Plaster angle and stop beads made from hot dipped galvanised steel to BS 2989 : 1982: Z2 quality coating type G275 of approved manufacture shall be used at all

arises, edges, recessed grooves, abutments, corners and joints for plastering and tiling work. The beads shall be manufactured to BS 6542:1984.

3.3 Expanded steel strip mesh shall be used to reinforce plaster along stress lines where cracking is likely to occur, or when plastering over the joint between two different materials, or for plastering over narrow gaps such as service chases. 3.4 Expanded steel corner mesh shall also be used to reinforce plaster at internal

corners. The expanded steel strip mesh shall be made of hot-dipped galvanised steel to BS 2989:1982:'Z2 quality coating type G275' of approved manufacture. 3.5 Carry plaster into grooves and rebates of frames and finish with a slightly coved

internal angle against metal window frames. 3.5.1 Batching and Mixing of Materials

Materials shall be batched by volume in properly sized gauge boxes, one for each material. The materials shall be mechanically mixed or hand mixed on a clean watertight platform and to the satisfaction of the S.O. Mixes containing cement shall be used within two hours of the first contact of the cement with water. All materials remaining after this period shall be discarded and not re-tempered.

Contractor shall submit to the S.O, relevant certification from the approved supplier of the plasticiser incorporated in the plaster mix, as that the quantity used and the dosage is in accordance with the manufacturer's recommendations.

3.5.2 Preparation of Surfaces

Contractor shall rake out joints of brickwork and blockwork to a depth of at least 10mm before the mortar is set in, for the areas to be plastered. Thoroughly hack or the roughen the surfaces to provide a key for plastering. Also, hack off any projecting fins on the concrete work and remove all traces of mould oil, paint, grease, dirt and other incompatible materials by scrubbing with water containing detergent and washing off with clean water.

Brush plastering surfaces to remove all loose particles, dust, laitance and efflorescence, etc and ensure that the surfaces are well wetted before applying each coat. Re-wet to keep damp continuously as required to receive the second coating and to equalise suction.

3.5.3 Movement Joints

Movement joints in the base shall be carried through applied coatings and finishings. Form joints against properly braced timber formwork.

3.5.4 Curing

Work shall be kept damp and adequately cured to prevent shrinkage and cracking. No traffic shall be permitted on insitu pavings or beds until 7 days after laying.

Internal angles shall be slightly coved, external angles and arises slightly rounded true to line and with neatly formed mitres.

3.5.6 Defects and Making Good - All cracks, blisters and other defects shall be made good by hacking out the plaster to,

3.5.7 Edges shall be undercut to form dovetailed keys, surfaces shall be cleaned, cement slurry to be applied and plaster re-applied to match the surrounding plaster.