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
Pre-specification testing should be included as a routine part of the building survey. At least one, and preferably two, ties should be inserted into each elevation at different levels to determine the minimum pull out load obtainable from both the near and far leaves.
This minimum load should be used as the basis for deciding the density of ties to be installed. For a small contract at least 10 ties must be tested; on large projects 5% of all ties should be tested.
For most applications (buildings under 30m high and areas with a maximum wind speed of less than 46m/sec) the minimum tensile proof load is 1kN based on a tie density of 2.5 per m² (900mm x 450mm centres). This excludes cladding form masonry and substrates below 100mm deep. For applications outside these criteria please consult either the Helifix sales team or BRE Digest 401, January 1995.
Part E Acoustic Performance – Helifix 6mm and 8mm diameter wall ties have been independently tested for dynamic stiffness and comply with the sound insulation requirements of Building Regs, Part E for a Type B tie.