Preparation
Concrete
Concrete substrates must be adequately prepared either by use of a suitable mechanical method such as water blasting, needle gunning, or other appropriate means.
Old concrete surfaces contaminated with oil or grease require suitable 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 large area.
New concrete should be at least 14 days old.
Where repairs are carried out, feather edging is not recommended; therefore, the perimeter of area to be repaired should be cut back to provide a square edge, minimum 10 mm.
Before application of webercem keycoat, the concrete should be thoroughly wetted but all surface water must be removed.
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 2 1/2).
Steel cleaning shall include hidden faces at the back of bars and at intersections, and the bonding agent/holding primer applied immediately after. 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.
BS EN 1504 states:- 'Where exposed reinforcement is contaminated with chloride or other material which may cause corrosion, the whole of the circumference of the contaminated reinforcement shall be cleaned by water jets not exceeding a pressure of 18 MPa to remove the chlorides and other contaminants unless electrochemical methods of protection and repair are to be used.'
webercem keycoat bonding slurry
Mix in the ratio of 3 volumes of webercem keycoat to 1 volume of clean water. Slowly add powder to water mixing continuously to a smooth creamy consistency.
Apply the slurry by a stiff brush and scrub well in. The slurry must be tacky when applying webercem mortar.
In hot weather the slurry dries quickly and, therefore, it is advisable that webercem mortar is mixed ready for application before the bonding slurry is applied. lf webercem keycoat does dry, it must be removed mechanically and a further coat applied.
In certain circumstances, especially in warmer conditions, it is more appropriate to use an epoxy primer such as webertec EP bonding aid.
