Correct drilling techniques are essential to ensure efficacy of the retrofit wall tie, and to minimize aesthetic and structural damage to the property under repair.
The use of Rotary Percussion drill bits for drilling pilot / clearance holes is recommended wherever possible. This keeps spalling of the rear side of the outer wythe masonry to a minimum. Any spalling of the brick / block rear will reduce the effectiveness of the wall ties installed.
Electric hammer drill
This type of electric hammer drill is designed to provide a rotary drilling action, which may be amplified by a light ‘tapping’ action. This light percussion improves the drilling rate but is gentle and permits fragile masonry substrates such as brick, terracotta, mortar, hollow concrete block to be drilled without damage, particularly when the drill breaks through the material into a void or cavity.
The rotary hammer drill, SDS type, is always used to set the Helifix tie into position with either a ‘DryFix’ Power Driver Attachment for masonry stabilization, or a Helifix Power Support Tool for masonry re-facing.
The SDS hammer drilling system is only used for drilling into dense materials such as reinforced concrete, some limestone and sandstone and for blind holes in strong material. Sometimes the method may be used to drill mortar. The drilling of all holes should be tried first with the 3-jaw-chuck type drilling machine and the SDS method should be seen as a “last resort”. It should not be used into cavity masonry as significant break-out is likely to occur in the cavity. A 3-jaw-chuck adaptor fitted to an SDS machine must NEVER be used in place of an electric hammer drill.
The Helifix Load Test Unit is used on site to test the pull-out loads from the actual masonry units within the structure in question. These loads will be more meaningful than laboratory performance figures using selected materials.
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 wythes.
This minimum load should be used as the basis for deciding the density of ties to be installed.