webercem spray CP

Preparation

As with all repairs and applications it is essential to apply to a clean, sound surface free from all grease, oil, dust and loose material. 

Concrete 

Concrete substrates must be adequately prepared by a suitable mechanical method such as scabbling, grit blasting, water jetting or needle gunning, or by such other means as appropriate. Concrete must be carefully prepared to give a clean, freshly-exposed surface. The outer limits of concrete patches should be cut square to avoid feather edges. 

Old concrete surfaces contaminated with oil or grease must be cleaned with a suitable detergent. Care must be taken to ensure that the oil or grease is removed from the surface and not simply spread over a larger area. 

A light steel mesh about 2 kg/m2 in density should be used whenever sprayed areas exceed 0·5 m2 and where applied thickness is greater than 25 mm. This mesh helps to evenly distribute stresses due to thermal movement or shrinkage and reduces the risk of cracking especially on corners. The mesh should be fixed in accordance with the recommendations in Concrete Society Technical Report No. 15. 

Soak the concrete surface thoroughly, allowing surplus water to drain off. 

Steel substrates

Steel substrates, including exposed reinforcement, should be free of loose rust and grease. Ideally they should be grit blasted to a uniform grey metal finish to achieve first quality to BS 7079-A1 followed by degreasing with a suitable solvent immediately prior to bonding.

Any formwork or extra reinforcement such as steel mesh should be designed/prepared and fixed in accordance with the guidelines of the Code of Practice.

Application

Guidelines on the method of working are detailed in the Code of Practice for Sprayed Concrete published by the Concrete Society and should be strictly observed.

webercem spray CP should be emptied from the bags directly into the hopper of the dry process spraying machine. The equipment should be balanced so as to produce a steady stream of material with minimal pulsing. The amount of water added at the spraying nozzle will be controlled by the nozzleman - too low an addition will increase rebound and dust emission; too wet a mix will slump. The correct amount of water can be judged by the appearance of the sprayed concrete; any glossiness of the surface should be avoided. In case of a long delay between applied coats of the sprayed concrete, the surface of the newly applied, hardened concrete should be water jetted using maximum air pressure and water flow through the nozzle to ensure that any laitance and all weak or loose material has been removed.

The surface should be allowed to drain before proceeding with the next coat.

Finishing

Any necessary trowelling or profiling should be done immediately after spraying has finished. An 'as-sprayed' appearance is normally acceptable but if overcoating is to follow, finish with a wooden float or damp sponge.

Curing

This product must be properly cured if it is to achieve its optimum properties. Cure immediately with polythene sheeting and/or wet hessian for a minimum of 3 days. 

Yield

Approximately 11·5 litres per 25 kg bag, but allowance must be given for rebound and profiling.