webercem spray RS

Preparation

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

Concrete

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

Old surfaces contaminated with oil or grease must be cleaned with a suitable detergent. Care must be taken that the contaminants are removed and not simply spread over a wider area.

The designer may require the sprayed concrete to be reinforced with mesh or bars.

Any reinforcement shall be fixed in accordance with the recommendations outlined in the Sprayed Concrete Association, SCA-Design and Specification and Concrete Society Technical Report 15.

In most cases, no additional mesh reinforcement is required in repairs where existing rebar exists or where thin overlays are applied (i.e. less than 25mm, see SCA recommendations).

Soak the concrete thoroughly and allow any surplus water to drain off.

Steel reinforcement

Steel surfaces, 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.

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 RS 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.

Note that webercem spray RS has a lower water demand than webercem spray DS and will require less water. Keep the water content as low as possible.

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.

webercem spray RS can be applied down to 15 mm thickness but, because of the higher cement content, (due to aggregate loss through rebound) there is the likelihood of greater shrinkage. The recommended minimum thickness is 25 mm. The recommended minimum thickness for protection over steel is 40mm.

Finishing

This material will set quickly and any finishing must take place within 15 minutes of application.

We recommend an ‘as sprayed’ finish is used with webercem spray RS.

Curing

Proper curing is essential to maintain the strength development. As the webercem spray RS is rapid setting, it develops an exotherm that can drive off water that is needed for full hydration. This water needs to be replaced by curing. The best method for curing this product is to spray the surface with clean water as soon as possible as concrete spraying has been finished. On large areas, the water should be applied as soon as the concrete hardens, in sections rather than waiting for the whole area to be completed.

Where possible and where site restrictions are not a hindrance, water can be applied by direct spray at intervals of about 30 minutes or by spray bar, for at least 2 hours after completion of spraying.

Yield

Approximately 11.5 litres per 25 kg bag. An allowance must be made for rebound and wastage.