For all remedial ties it is extremely important to use the correct drilling technique to avoid excessive spalling of the near leaf as the drill breaks through into the cavity. Cases have been identified where up to 80mm of the brick thickness have been broken off, bridging the cavity and leaving insufficient material to make either a chemical or dry connection.
Wherever possible rotary percussion drilling should be used with 3-jaw-chuck type drills. This may increase drilling time but damage to the brickwork will be greatly reduced. With the DryFix range, rotary percussion masonry drills should be used as standard to ensure the accuracy of the hole’s diameter and to avoid appreciable spalling.
Where rotary hammer drill bits (SDS type) are used, the size of the drilling machine should be as small as possible and the operator must not lean on the drill as this reduces its effectiveness and increases the likelihood of spalling. Where drilling through the brick face is not acceptable then it will be necessary to consider inserting the remedial ties through the mortar bed. This will be satisfactory where the mortar is strong and in good condition. Angled drilling may also be used in special circumstances.
Wall tie spacing and testing
Proof testing of obtainable pull-out loads can be conducted on site using the Helifix Load Test Unit. The Load Test Unit allows tensile proof loading to a maximum of 3kN. On-site assessment should inform specific engineering design and be conducted during the course of the repair work to suit the requirements of the specifying engineer.
Wall ties should be spaced to suit site conditions and locations and in accordance with the relevant Standards and Building Code requirements (e.g. NZS4210, NZS3604, NZS4229 and NZS4230). Relevant design variables include the wind and seismic conditions that are expected to act on the wall, its material condition and composition. Remedial wall ties may be retrofitted to buildings built in different eras and to earlier building standards, and comprise materials or construction methods that do not comply with the current standards. Specific engineering design will be needed when performance comparable with current standards is required.