Resi Flex
During the 1970's research was conducted into the need for replacement wall ties. The actual durability of the protective zinc or galvanised coatings of the original built in wall ties was studied and this now affects the design and use of walls ties for both new build and replacement. The results of the research was found to be quite beyond any previous expectations:
- Vertical twist ties ("fish tails") were found to have a life expectancy of only 30 years - half of that originally intended.
- Wire ties ("butterflies") were found to have a service life of only 15 years.
- Mortar is alkaline which actually protects and enhances the working life of wall ties
- A reaction between mortar and the air causes a process called carbonation which turns the mortar acidic which then attacks the wall ties.
Early attempts at producing a method for replacing existing wall ties highlighted many of the pitfalls that were to be encountered. The expansion type of tie has been found to induce additional stresses into the masonry - similar to the expansion caused by the existing, rusting walls ties - and were costly to make and fit. The use of heavy section re-bars was soon outlawed because of the need for flexibility to allow the necessary differential horizontal and vertical movement between each leaf using a bar of 8mm diameter or above was found to act like mini crowbars and would eventually work themselves loose. The introduction of BSI DD140, BRE Digest 329 and the more recent BRE Digest 401 at last gave guidance for manufacturers and specifiers of remedial wall ties.
The System
The Resi Flex system of wall tie replacement is available in 4.5mm and 6.0mm diameter. It offers the advantages of a non-expanding resin fix on both near and far leaf through a 10mm rotary-percussion drilled hole - eliminating spalling of the brickwork. Proof testing of the far leaf using a Target Fixings Load Test Unit can be performed randomly as installation proceeds. Because the fixing method employed does not induce additional stresses into the substrate Resi Flex can be used in many and varied materials, and by drilling with a rotary-percussion drill - a three jaw chuck - any spalling of the masonry is minimised thus eliminating the need for cavity clearance.
The design of the Resi Flex remedial tie ensures that any potential for installer error can be minimised. The multiple drip design of each fin allows the Resi Flex to be installed at an angle of up to 25° towards the inner leaf without the possibility of any water transfer across the cavity. It is recommended, however, that each Resi Flex is installed horizontally.
Special Features
- One piece design - no moving parts to lose.
- Simple proof testing of connection.
- Multiple drip points to deter water transfer.
- Flexible design allows natural building movement.
- Minimal disfiguration to buildings.
- Fixes into all commonly found building materials.
- Quick and easy installation.
- One diameter for all applications.
Installation Procedure
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- Drill a 10mm hole for the 6.0mm tie using a rotary percussion drill. The hole should be 25mm from the end of any brick and on its horizontal centre line and penetrate 55mm into the far leaf.
- Thoroughly clean the holes in the near and far leaf using a hand pump to blow out debris.
- Using a resin nozzle extension inject Target Fixings Polyester Resin across the cavity and into the far leaf hole until it is full.
- Insert the Resi Flex tie through the near leaf hole and into the far leaf hole allowing it to rotate as it is installed.
- After leaving to gel for about 20 minutes the holding capability can be checked using a Target Fixings Load Test Unit. As a general rule a proof test load of about 1kN in tension is an adequate bond.
- After an acceptable proof test is performed the near leaf connection is made using Target Fixings Polyester Resin. The brick may then be colour matched for a near invisible finish.
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Materials
Resi Flex ties are manufactured from grade 304 or, for more aggressive atmospheres, Grade 316 austenitic stainless steel. The 6.0mm diameter Resi Flex has a tensile strength in excess of 1.0kN. The manufacturing process produces fins that act as multiple drip points across the length of the tie, and a flexible core to allow normal movement.
The fixing in both leafs may also be achieved by the use of Bond Flex XL cementitious grout. Where there is a need for a fire resistance in excess of 30 minutes only Bond Flex XL Cementitious Grout should be used.
Epoxy resins are not recommended for normal installation as it has been noted that many of these resins are not reliable due to their accurate mixing requirements. Epoxy resins should only be used when fixing into diamond drilled holes.
Fixing Densities
In general terms the fixing densities for Resi Flex remedial wall ties would be the same as new build - 2.5 per mē or 450mm vertically and 900mm horizontally in a domino five pattern. This density would, however, be subject to on site testing to ensure that the required tensile loadings are being achieved. It should also be borne in mind that around all the openings - doors and windows - ties should be installed at no more than 300mm vertical centres and no more than 225mm from the edge of the opening. BRE Digest 401 gives more information on the proof test load requirements.
If the masonry is so weak or friable that the required proof test load for standard density fixings cannot be achieved, it is quite acceptable to increase the density of fixings to ensure that the overall loading per mē is achieved. Lowering the density below the standard is not recommended.
Testing
Because Resi Flex ties cannot be randomly tested on site, it is necessary to perform comprehensive preinstallation tests.
There are several different methods of performing tests, but the most straightforward way is to drill into both leaves as described in the Installation Procedures section above. The near leaf hole may then be overdrilled to 12mm. The Dri Flex tie should then be installed into the far leaf and a test performed using the Target Load Test Unit. The fixing capability into the near leaf material may ascertained by drilling into the near leaf as in the Installation Procedures section above and inserting the tie to a maximum depth of 80mm and then test using a Target Load Test Unit. It is recommended that testing is performed in accordance with the requirements of BRE Digest 401. Only in exceptional circumstances does the proof test load requirement exceed 1kN.
