webercem lightweight

Preparation

Concrete

Concrete substrates must be adequately prepared to a clean, freshly-exposed surface, whether by use of a suitable mechanical method, such as scabbling, grit blasting or needle gunning, or by such other means as appropriate.
Old concrete surfaces contaminated with oil or grease require preparation such as steam cleaning in conjunction 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. New concrete should be cured for at least 14 days using an approved curing technique, e.g. polythene film. Spray-on curing membranes are unsuitable for use on new concrete where toppings, renders, finishes, etc, are to be subsequently applied.

Where repairs are carried out, feather edging is not recommended; therefore the perimeter of the area to be repaired should be cut back to provide a square edge, minimum 10mm deep.

Steel

Steel reinforcement which has been exposed during preparation should be completely uncovered to the full circumference of the bar. Rust scale, corrosion products and other deposits shall be removed from reinforcement by grit blasting or other approved methods to achieve first quality to BS 7079-A1 (equivalent to Swedish Standard SA 21/2). Steel cleaning shall include hidden faces at the back of bars and at intersections. Bonding agent/holding primer must be applied immediately after cleaning.

In many instances where chloride-induced corrosion is absent, and where grit blasting is not practical, wire brushing or other techniques may be acceptable to the engineer, provided that care is taken not to polish the surfaces of the rust on the steel.

Mixing

Bonding slurry

Mix webercem keycoat in the proportions 1 volume water to 2 volumes of webercem keycoat, adding powder gradually to the water and stirring continuously until a smooth, creamy consistency is obtained.

Lightweight patch repair mortar

A low-shear, forced-action mixer must always be used e.g. Mixal Mixer or Creteangle. Hand mixing is not recommended for this product.

Mixing time should be kept to 2 minutes from adding the powder to the water.

Over mixing will entrain air and reduce compressive strength. Do not over mix.

Water addition is 2·4 - 2·7 litres of water per 20kg bag. Start at 2·4 litres of water and adjust as required upwards to 2·7 litres.

Use only potable water for mixing.

Do not add extra water above stated quantities.

Application

Apply webercem keycoat immediately to the prepared concrete surface which must previously have been thoroughly dampened with water. Use a stiff brush to scrub the slurry well into the surface. The approximate application rate is 1·5 m2 per litre. Place the repair material on to the slurry whilst it is tacky. In hot weather the slurry will dry quickly once it is applied and it is prudent to mix the mortar ready for application prior to applying the slurry. If the webercem keycoat does dry, it should be removed mechanically and a further coat must be applied.

Apply webercem lightweight mortar to the substrate whilst the bonding slurry is still tacky and compact well into place.

Curing

Unless a coating or other system is to be applied to the surface, cure with a suitable membrane, applied immediately after finishing.

Where a coating etc. is to be applied, cure with close contact polythene for a minimum of 7 days; the polythene should be tight on the surface and taped around the edges.

Although shrinkage is minimised, some very fine cracking may occur particularly in large flat areas, or in adverse drying conditions – even when curing with polythene. Bond and durability are not affected and a decorative treatment of webercote should be applied.

Important Notes

When replacing faulty cover on reinforced concrete, using webercem keycoat and webercem lightweight, the minimum thickness of cover must be 12 mm. Below this figure, the concrete should not be pre-wetted but the following procedure should be taken:

Apply one coat of webertec EP bonding aid to the freshly prepared steel reinforcement and allow to become tack-free (3 to 6 hours). Where time restraints do not allow continuous working, to ensure adequate bond, this first protective coat should be dusted with fine, clean, dry sand and allowed to cure thoroughly. Excess sand and any dirt should be removed before the repair process is continued. Apply a second coat of webertec EP bonding aid to both the steel and concrete and whilst this is still tacky, apply the webercem lightweight using a gloved hand. The surface of the mortar should then be finished with a clean, steel float.

Where very thick sections are required, multiple applications may be necessary. Intermediate surfaces should be scratched to give a good mechanical key. Successive applications require the use of either webercem keycoat or webertec EP bonding aid.

When cured, webercem lightweight and webercem keycoat are stable to freeze/thaw conditions but following good concreting practice they should not be applied in freezing weather or at temperatures below 5°C.

Yield

Approximately 15 litres per 20kg bag, i.e. about 1m2 at 15mm thickness.