This method is used for repairing holes having a depth nearly equal to greater than the least surface dimension, i.e. for any holes and narrow slots cut for the repair of cracks. This method is not used for shallow depressions; for filling patches where reinforcement is exposed or holes which extend through and through wall or beam.
Dry Pack Method of Repairing Concrete Surface
Before actual operation the hole should be thoroughly cleaned and ensured free from broken pieces of aggregates, washed and dried.
A thin layer of cement grout is applied on the surface. The mix for bonding grout is the mixture of cement and fine sand in ratio of 1:1 to a consistency like thick cream.
After this, the dry pack material is put into place before the bonding grout has dried up. Packing material consists of the volume or by weight a mix of 1 part of cement to 2 parts of sand.
Water requirement for mix is such as to produce a mortar which, when used, will stick together on being moulded into a ball, and will not exude water but will leave the hands damp. If less water is added, it will not make sound solid pack. If more water is added excessive shrinkage will occur and the material becomes loose.
Dry pack material is not to be filled at a time, but should be filled in layers and properly compacted having compacted thickness of about 1 cm.
Each layer is scratched & finished to secure bond for succeeding layer and is compacted over its entire surface by use of hardwood stick and hammer. The size of such stick is about 20 to 30 cm in length and not over 2.5 cm in diameter. Wooden sticks will not polish the surface of each layer and thus better bonding surface is formed. Last layer is finished to match the surroundings.
For better results and when water tightness is a requisite, the holes should be sharp and square at the surface edges, but corners within holes should be rounded. Holes for dry pack should have a minimum depth of 2.5 cm.