Twistfix

How to fit remedial wall ties in 3 easy steps

Remedial wall ties - Helical CD Tie

As the title of this guide suggests, it addresses how to fit remedial wall ties into an existing wall. This article focuses on retrofit helical wall ties; explaining what they are, the benefits of selecting them for brick-tie replacement and the technical advantages that the Twistfix CD Tie offers over comparable products.

What helical wall ties are

Helical wall ties are helix-shaped rods having multiple longitudinal threads and a pointed tip. The stainless-steel ties anchor the brick façade of a building to the main walls of the structure. Each tie fixes into a tiny pilot hole, which minimises disturbance to the masonry. The hardness and angle of the winding ridges enable them to cut spiral grooves into a wide variety of masonry components as the tie is driven, by a series of hammer impacts, into brick, block, stone or concrete. Installation is remarkably quick and simple.

Independent test programs, and more than 35 years of use, prove the lasting performance and reliability of helical wall ties. BRE Digest 329 (Table 5) shows them as being suitable for use in all remedial situations, irrespective of the substrate of the building or its fire performance criteria.

Benefits of using helical ties

The mechanical interlock anchorage of a helical wall tie resists tension and compression loads; it exerts no expansive pressure on the masonry, does not rely on chemical adhesives and is unaffected by temperature extremes or fire.

The cross-sectional profile of the spiral wall tie includes high-profile threads, which maximise grip in the masonry, and deep helical troughs which allow it to accommodate differential movements between inner and outer walls. The twisted helix has multiple natural drip-points which prevent the transmission of water across the cavity.

When under load, the threads interact with the host building material to impart an accumulative cone of stress at a tangent to the helix. The helix distributes loads evenly along the full penetrative length of the tie to ensure the reliability of its connection in a wide variety of construction materials.

One-piece stainless-steel helical wall ties are:

  • Robust, combining axial strength with flexibility
  • Corrosion-resistant
  • Non-combustible
  • Quick and easy to fix
  • Easily concealed

Choosing the best helical wall tie system

The criteria for establishing which are the best helical wall ties to use for retrofit applications include considering which provides the most reliable performance over a sustained period and which offers the most cost-effective installation in terms of the combined expenditure on products, tooling and labour.

The manufacture of helical wall ties involves the twisting of pre-shaped and work-hardened stainless-steel wire. The twisting of traditional helical wall ties involves clamping one end of the profiled wire and spinning the other (much like twisting a rubber band on a toy aeroplane by spinning its propellor). The method develops a helix, though the pitch helix varies along its length.

In use, the leading end of a ‘spin-twisted’ tie cuts winding channels or internal threads into the masonry. As installation proceeds and the fastener drives further into the wall, its imprecisely twisted ridges tend to widen the grooves.­  This partial stripping of the internal thread impedes the reliability of the grip that the tie has in the wall.

In contrast, Thor Helical, who manufacture the CD wall ties for Twistfix, use a highly-engineering twisting die technology to control the twist of the helix precisely. The refined, exact twist of the CD Tie (Patent EP1307303) forms tightly mating threads within masonry to ensure a superior interlock along the full length of the tie.

Independent tests for CE Mark compliance show the CD Tie is excep­ti­onally versatile across a wide range of masonry types. Further testing, by Oxford Brooks University, confirms no adverse effect on the performance of the CD Ties, after subjecting them to 100-year service cycles for movement caused by thermal and moisture variations.

Competing helical wall tie systems require multi-part installation adaptors to fit the ties into existing cavity walls. Such lengthy adaptors work with a telescopic action and can be expensive, unreliable, and cumbersome to use.

Conversely, the CD Tie has a unique driving end confi­gura­tion (Patent GB2439633) which allows safe and controlled installation with low-cost, easy to use tooling. The short one-piece setting tool eases the installation process and ends the need for unwieldy and expensive telescopic setting tools.

What makes the CD Tie superior to alternative Helical Ties?

Twistfix CD Ties offer:

  • Reliability in all types of masonry
  • Durability against cyclic movement and seismic shock
  • A precise helical interlock anchorage
  • An engineered upgrade of conventional helical tie designs
  • Independent testing and C.E. Marking
  • A patented tying system in terms of helix consistency and driving confi­gura­tion
  • Quick, simple installation
  • Cost-effec­tiveness

Fitting remedial wall ties in 3 easy steps

Fitting remedial wall ties in 3 easy steps

  1. Drill both layers of a cavity wall to form a pilot hole of right diameter and length using a lightweight hammer drill. After drilling through the first brick, stop drill-bit rotation, to prevent ‘whipping’, before continuing into the second wall. The depth of the bore should be 10mm longer than the length of the tie.
  2. Insert the coloured end of a 9mm diameter CD Tie into the setting tool and drive it into the masonry using a lightweight SDS drill set on a hammer-action mode.
  3. Once the setting tool recesses the tie beneath the surface, remove the driver and disguise the hole with suitably compacted coloured-mortar.

Product specifi­cation

Product: Thor Helical 9mm diameter CD Tie

Lengths (mm): 180, 205, 230, 255, 280, 305 & 330

Material: Austenitic Stainless steel - (304 & 316)

Ultimate Tensile Strength: => 15kN

DECLARATION OF PERFORMANCE
(CONFORMS WITH BS EN 845-1:2013)
Substrate
Type
Substrate
Strength
(N/mm2 )
Pilot Hole
Diameter
(mm)
Tested
Embedment
(mm)
Cavity
Width
(mm)
Mean Load Capacity
(N)
Recommended
Tie
Embedment (mm)
          Tension Compression  
Aircrete (AAC) 3.5 0 85 225 1490 1500 85
Dense Aggregate Concrete 7 6 60 150 2870 2700 75
Common Brick 30 6 60 150 1940 2680 75
Perforated Brick 40 5 60 150 1990 2790 75
Structural Concrete C30 30 7 40 150 2370 2690 50

 
This installation video displays the wall tie installation process and demonstrates how self-tapping helical wall ties work.

Related documents:

How to fix Helical Wall Ties brochure How to fix Helical Wall Ties

Wall Tie Spacing Pattern at 2.5 Ties per M2 brochure Wall Tie Spacing Pattern at 2.5 Ties per M2

Related links