Shrinkable Clay Soils

• Loss of moisture from clay soils causes reduction in volume – “shrinkage”. As the soil shrinks   support for foundations is lost causing subsidence.
• Moisture loss can be caused by evaporation during warm dry spells or by extraction by trees and vegetation.
• Volume reduction can be permanent or temporary (e.g. seasonal). Recovery to the volume greater than that at the time of construction can cause “heave”.
  

Wash-out

• Soil beneath foundations can be removed by ground water causing instability
• Granular soils most at risk
• Common causes: broken and leaking drains, soak-aways positioned too close to property &    inadequate drainage of ground water running off sloping sites

Shallow Foundations and Settlement

Shallow Foundations

• Shallow foundations on extensions are more affected by seasonal moisture changes than the main property causing differential movement.

Settlement

• Consolidation of soil under the additional weight of a new structure can take a number of years to complete.
• Differing soils over a site can lead to different rates of settlement leading to differential movement.

Concentrated Loading

• Structural load exceeds the bearing capacity of the soil.
• Some building designs have inherent load concentrations e.g. Georgian town houses.
• Building alterations can alter load patterns and increase loads, leading to stress concentrations that exceed original foundation design.

Whilst helical wall tie bars can be used to repair, stabilise and strengthen walls, the cause of the problem (that is subsidence), must be addressed to stop the cracks from reappearing. In combination with the range of helical wall tie bars, Helifix provide the total structural stabilisation solution for above and below ground with the cost-effective micro-pile system.

Below we look at the disadvantages of traditional, expensive stabilisation methods.

Underpinning

• Disruptive – major excavation work required
• Time consuming – curing times between sequential areas
• Labour intensive
• Not cost effective for deep bearing strata
• Environmental issues – spoil disposal

Piling

• Access issues – large rigs difficult to manoeuvre in confined areas
• Disruptive  – access may require alterations to other parts of the structure
• Adverse impact on structure  – vibration from driven piles
• Environmental issues  – spoil disposal and noise concerns
• Accuracy – no load test at installation stage

The Helifix Micro-Pile System

Helifix Micro-pile solutions provide a technically superior and more cost-effective alternative to expensive, disruptive and time consuming methods of stabilisation that require extensive excavations. It is especially suited to those projects where access is restricted.

• Piles are sectional and easily transported around congested areas
• Installation is via a small hand held hydraulic drive head
• Rotary installation produces minimal noise, vibration & disruption
• Minimal spoil production avoids potential environmental issues
• Installation torque accurately predicts bearing capacity
• “Pull-Down” grout system increases buckling resistance
• Typical load capacity of up to 225KN
• Pile centres increased by super-structure reinforcing techniques

Backed by more than 80 years of structural engineering experience, this non-intrusive and economical method of overcoming subsidence problems causes minimal disruption to the building fabric or to the occupants, who normally remain in residence while the work is carried out. No mass excavations are needed, work is undertaken externally and noise levels remain low.

Helifix Micro-piles ensure that the affected masonry is fully supported and prevent further property settlement. When combined with Helifix masonry repair products, the above ground structure is reliably repaired, reinforced and secured. On completion all repairs are fully concealed.

Why cost-effective?

Using Helifix reinforcing techniques in the superstructure allow pile centres to be maximised, reducing pile numbers and installation time to provide a cost effective means of stabilisation and repair. HeliBar is used to create Helibeams to span the structure between the piles, thus enabling greater pile spacing to reduce cost and installation time.

Helifix in-house engineers assess each situation and design repairs based on the damage and weight of the individual property and the local ground conditions. Fully trained contractors supply and rapidly install the systems.

Helifix completed one of the UK’s largest micro-pile projects at Disraeli Court in Hereford, where over 400 micro-piles were installed to stabilise a sheltered housing complex rendered uninhabitable due to subsidence damage. Using Helifix reinforcing techniques in the superstructure allowed pile centres to be maximised, reducing pile numbers and installation time to provide a cost effective means of stabilisation and repair. See the case study here.

Since developing the original helical fixing in 1984, HELIFIX has continued to innovate, expanding its range to include specialist helical wall ties, fixings and masonry reinforcement systems for use in both new build and refurbishment.

In addition to full product information, the new brochure ‘Principles, Products and Applications’ also includes a summary of the company’s innovation accomplishments spanning almost 30 years.

Helifix products have proven an effective cure for common structural defects in most construction materials including masonry, timber and concrete. Repair and refurbishment is increasingly acknowledged as the more sustainable alternative to demolition, in terms of architectural value, materials usage, cost and environmental impact. Illustrated within the new literature are informative examples of how Helifix’s engineering expertise and products can avoid disruptive dismantling and costly rebuilds.

John Heseltine, Helifix Technical Manager says,

“Our unique helical bar is extremely versatile and can be used to overcome a wide range of structural faults. We can restore integrity to virtually every type of structure from houses and tower blocks, to masonry bridges and listed buildings. In our portfolio, there is almost certain to be a fixing and repair technique to provide a long term solution to any structural problem.”

Helifix-branded products, combined with their concealed non-disruptive installation techniques, are now recognised worldwide. The company has a network of Approved Installers in the UK, distributors throughout Europe, and overseas businesses in USA, Australia and New Zealand. Helifix products are manufactured in the UK.

Download our Product/Application Overview (2MB)

Download our Full Product/Application Brochure (6MB)

Following the ABE Yorkshire & Humber Region AGM, James Plaskitt, the local Area Manager of Helifix Ltd, presented  an educational seminar about the benefits of using Helifix concealed non-disruptive repair methods with regard to cost-effectiveness, aesthetic impact, project timescales and limiting design implications. The seminar was held at the Think Low Carbon Centre, Barnsley in front of 40 mixed building professionals.

James gave an introduction about the Helifix original one piece stainless steel helical fixing, which was first created 30 years ago. Helifix is now the market leader in the design and manufacture of specialist helical wall ties, fixings and masonry repair systems. He went on to discuss common masonry defects such as cracked bay windows and arches, cracks near corners and openings, stabilising bowed walls, replacing cavity wall ties, crack stitching and creating masonry beams.

James explained in detail about modern masonry repair techniques to overcome these problems. Using Helifix techniques such as crack stitching, a quick and simple means of stabilising cracked masonry using  stainless steel HeliBars into appropriate bed joints or cut slots. HeliBar can be used in bricks, blocks or stonework, with HeliBond cement grout. The seminar was completed with some case histories followed by a questions and answers session.

Basil Parylo , Regional ABE Yorkshire & Humber Chairman commented “A big thank you to Helifix for a brilliant seminar, one to repeat again!”.

If you would like a Helifix CPD Seminar for your company, please contact Helifix.

Many of these are over one hundred years old and were originally designed to support the loads of a typical horse and cart. All the bridges in the UK have now been assessed for strength and an estimated 45,000 masonry arches are under-strength for their modern usage patterns.

Substantial upgrading of these bridges is required to accommodate the increasing load requirements from today’s traffic, such as heavy goods vehicles and the ever increasing volume of traffic on the roads.

Common concerns over masonry bridges

•    Not designed for present day traffic (often only meant for horse and cart)
•    Designed by rules of thumb (with variable results)
•    Suffered from neglect
•    Difficult to quantify material properties
•    No agreed method of analysis

The Helifix repair system provides a solution for strengthening and rehabilitating masonry arch bridges and tunnels

•    It involves minimum inconvenience to the travelling public
•    Retains the existing appearance of the structure
•    Maintains structural integrity
•    Involves simple technology which is cost effective
•    It is quick and easy to install

How the Helifix system works

•    Each bridge undergoes a full structural assessment
•    Appropriate repair and strengthening is designed, using the proven MARSYS software, to suit the individual needs of the bridge and the client. For bridges that are being upgraded beyond their original design capacity, the increase in soil pressure under abutments is checked to determine that it is within acceptable limits.
•    For the temporary condition, when the slots have been cut, the load capacity of the bridge is checked using the ASSARC software.
•    The required grid pattern is marked out on the bridge soffit
•    Narrow slots are cut just 12mm wide and 40mm deep
•    Services are avoided and environmental issues observed
•    Radial CemTies installed throughout the grid
•    Stainless steel HeliBars are installed into the slots
•    The reinforcement is encapsulated with Marflex structural adhesive, a durable polyureide resin with high bond strength, particularly to damp substrates, that is elastic and can be colour matched or coated with a layer of masonry dust taken from the slot cutting machine.

The stabilisation and installation techniques employed minimise the disruption to road and rail services and avoid the need for expensive re-building by combining with and conserving the existing fabric.

This makes the Helifix repair system ideal for historic and listed structures, which are left repaired but visibly unimpaired with no unsightly external plates or restraints.

Click here to view Helifix examples of Bridge strengthening projects.

Jim Charlton of Gateshead Housing said “Many thanks for a really well received presentation, feedback from all I have spoken with has been very positive. The technical content was appropriate with real local case studies of interest.”

If you would like a seminar with examples of solutions to common structural masonry problems, Helifix projects and seminars take place nationwide. Feel free to contact us.

With the continued pressure for more homes it is essential that the existing housing stock is both maintained and improved to meet current standards. As housing associations across the country continue to assume ownership of homes from local authorities they become responsible for their upkeep and repair. 

Chasing out the mortar joints between storeys on a tower block

As council houses and housing association properties continue to be upgraded, in addition to general maintenance and improvements to domestic facilities, many of the older properties also require attention to resolve a variety of structural problems. Among the most common faults which can result in cracked masonry are lintel failure, differential temperature movement and corroding or failed wall ties. Of particular concern is lintel failure, which is often discovered – causing significant problems – during current widespread window replacement programmes.

When rectifying such faults, housing associations need to consider several factors:

•    are they receiving secure and reliable long term structural solutions?
•    are the specified products and repair techniques well tested and proven?
•    does the contractor have a trained workforce with the appropriate expertise?
•    can he provide insurance-backed guarantees for his work?
•    will the methods employed cause minimal disruption to the building fabric and the occupants?

With traditional repair practices the time, and therefore the cost, and the disruption involved could all be considerable. The cost-effective approach, pioneered by Helifix, uses slim, one-piece stainless steel ties, fixings and reinforcements that are rapidly installed, are fully concealed in the masonry and avoid time consuming and expensive taking down and rebuilding – providing both practical and cost benefits for the building’s owners, its occupants and the structure itself.

Cleaning out the cut slot

Creating and reinstating lintels

During window replacement programmes to upgrade single glazed steel frames to modern double glazed units, the discovery that the existing lintels have failed or never existed can cause major problems. Local authorities and housing associations have found that in many cases there are no lintels above the existing windows as the masonry was built directly off the steel frames and removing them will probably result in structural movement. The traditional approach of installing a new concrete  or Catnic type lintel is expensive and disruptive to both the property and the tenants. Brickwork must be removed to allow for the new proprietary lintel, and masonry above the opening has to be supported during the process.

Grouted HeliBar reinforcement into the grouted slot

However, bonding concealed HeliBars into appropriate channelled-out mortar beds above the windows enables lintels to be formed within the existing brickwork and is proven as a rapid, economical and viable alternative. The helical stainless steel bars and cementitious grout operate in a composite action with the masonry to create masonry beams which support the brickwork above and spread the structural loads. Where appropriate, in conjunction with the horizontal HeliBars, DryFix ties are installed vertically through the brickwork above the window to provide additional structural security. The whole process is quick and simple, with all work carried out externally. The speed of installation – with labour being the primary cost of most contracts – means that important savings can be made compared with traditional methods. Once re-pointing has been completed there is little visible indication of any repair work.

Grouted Helibar installed at two levels. Top level has been re-pointed

Window replacement

Step 1. Using a wall chaser, slots are cut 500mm either side of the opening and above the window in the specified horizontal bed joints, removing mortar to the required depth.
Step 2. Small pilot holes are drilled up through the bottom brick course at the required angle and depth for the DryFix ties.
Step 3. Having flushed out the cut slots, a bead of HeliBond cementitous grout is injected to the back of the slot.
Step 4. Continuous lengths of helical stainless steel HeliBar are then inserted and pushed into the grout.
Step 5. A second bead of grout is injected, followed by a second HeliBar and a third bead of grout which is ironed into the slot leaving 10mm depth for re-pointing.
Step 6. DryFix remedial ties are power-driven into position, via the pilot holes, requiring no grouts or resins.
Step 7. Steps 3 to 5 are repeated on the upper cut slot.
Step 8. DryFix holes are made good, re-pointing of the slots is carried out and any cracks filled and weatherproofed with all repairs being fully concealed.

Installing vertical DryFix ties

Once the grout has cured the old windows can be safely removed and the new ones fitted without risk to safety or costly additional damage due to masonry movement. The whole process is quick and simple and avoids contract delays or disruption.

A growing means of achieving these goals is through the use of rendered external insulation panels, both on traditionally built solid wall properties and the mass of various prefabricated housing, of which there are around 20 different types, and pre-cast concrete high rise buildings, all constructed after World War II. These have either no cavity or a very narrow one, so the use of cavity wall insulation is not feasible. The use of exterior insulation cladding and specialist external rendering will, in most cases, improve the thermal U value of the walls by some 75%.

However, a problem can arise with the use of external panels as the external elevations may be unable to support the additional load of the new boards, render and decorative finish. Consequently, where weak, corroded or insufficient wall ties are present these need to be replaced or supplemented with new ties. This often creates a further problem if the inner skin or pillars are constructed from clinker blocks, concrete or dense material making remedial wall tie installation very difficult. The tie often will not penetrate the material, or will be unreliable in that no secure fixing can be obtained. At the same time engineers may well specify higher pull-out loads of 1.5kN minimum, rather than the usual 1kN, in order to account for the additional loading.

Few wall ties are able to satisfy these varied conditions while at the same time providing property owners with a rapid cost-effective solution. One that has proven to be successful in meeting these demands is the Helifix DryFix tie, which has been successfully used on ‘Cornish’, ‘Hawksley’, ‘Wimpey No-Fines’ and ‘Laing Easiform’ homes, amongst others.

A simple, one-piece, helical, stainless steel remedial tie, DryFix, unlike many traditional ties, has the major advantage of not requiring any grouts, resins or mechanical expansion. Consequently, it is rapidly installed, saving time and money – respectively, important factors to insulation contractors on a tight schedule and clients wishing to keep costs down. Furthermore, as there is no curing time involved, it can be load-tested immediately to establish its security of fixing.

DryFix is very quick and easy to install. A small pilot hole is drilled, through the outer leaf and into the back-up material. The DryFix tie is then loaded into the patented Power Driver Attachment (PDA) tool fitted to a SDS hammer drill. As the tie is then driven into the pilot hole its helical profile augers into the material to provide a secure and reliable connection, usually well above the required poll out value. It can therefore achieve the higher loadings specified by project engineers and deemed necessary to support the weight of the new external cladding. The requirements of the engineer, the insulation contractor and the property owner are therefore all satisfied, quickly and economically.

An additional benefit is the ability of the PDA to recess the installed DryFix below the face of the outer leaf. This means there is minimal disturbance to the external material (normally brickwork but DryFix are equally effective in other materials) so the small pilot hole entrance can easily be caulked with matching brick dust to seal the tie. In these circumstances the external masonry will be hidden behind the insulation panels but in normal remedial tie situations it means there is little visible evidence of the tie installation.

Case Study

At Penywaun, a village near Aberdare in South Wales, 170 properties owned by RCT Homes, the largest social landlord in Wales, are being upgraded to meet current thermal insulation requirements. Built by the local authority in the 1950s and 60s, the houses were constructed with a clinker block internal skin, a concrete external skin and just a 50mm cavity.

Before the membrane and Rockwool panels with waterproof render could be fixed to the external elevations, the project engineers, Michael Dyson Associates, determined that load bearing capacity of the external walls needed to be upgraded with remedial wall ties to bear the weight of the new system. They also stated that the new ties must have an enhanced minimum pull-out of 1.6kN while the contractor, Specialist External Render Systems, wanted ties that could be easily installed and would rapidly provide a reliable solution as the contract was on a tight timescale.

Following on-site testing, DryFix remedial ties from Helifix were specified by the engineers as they satisfied all the necessary project requirements. Installation was rapid and trouble free and the project was able to remain on schedule.

The Helifix Group with operations in Europe, USA, Australia and New Zealand, strengthens CRH’s position in these key territories, while for Helifix this change of ownership will allow local entrepreneurship to benefit from large company resources.

Fred Paterson, Helifix Sales and Marketing Director, said,

“This is fantastic news which brings immediate operating benefits and secures the long-term development of the business. We are now an integral part of an international construction group that is committed to supporting our growth plans and will ensure we reach our full potential.”

“I’m delighted that this process is now complete and that the business can move forward with renewed vigour and heightened optimism.”

The existing Helifix management remains in place and, despite talk of exciting future plans, company founder and Managing Director Bob Paterson confirms the current focus is unchanged.

“Our customers can be assured that it is ‘business as usual’ at our London headquarters. The immediate priority for the Helifix team is to continue to provide the high quality products, technical support and excellent customer service that the market has come to expect from us”.

CRH has a turnover of circa €18 billion and employs over 75,000 people at 3,600 locations worldwide. The Helifix Group will join the existing Engineered Accessories division of CRH that comprises a number of other market-leading manufacturers from across Europe.

As expected from a major international group, being part of CRH will bring enhanced focus and continual investment in health and safety, innovation and sustainability.

New Helifix company and technical literature will be available shortly.

Key characteristics

• Non-shrink grout  which exhibits excellent thixotropic properties
• Flows easily under pressure to fill voids
• Rapidly develops compressive strength
• Cures to 45N/mm²
• Ready-to-mix components supplied in two-pack sets to reduce waste

HeliBond is suitable for bonding HeliBars into most common masonry-type substrates, including brick, stone, pre-cast concrete and Aircrete blocks.

Why is it important to only use HeliBond grout?

HeliBond grout has undergone numerous tests, including CE Marking in accordance with BS EN 1504-6.

It is important for property owners to be aware that if HeliBars are installed with any grout other than HeliBond, then any relevant Structural Repair guarantee for the remedial work carried out on the property will be invalid and void. For more information on 10 year guarantees, click here.

Frequently asked questions

Does HeliBond grout create hard spots in a building?

Only a very low cross sectional area of HeliBond is typically required,and the HeliBars are flexible. This will allow normal building movements to be readily accommodated. So whilst being effective in tension, the usage of HeliBond Grout will not create stiff elements within the masonry with the potential to cause damage.

Is HeliBond suitable to use with lime mortar masonry?

Yes it is, HeliBond works differently to most common hard cementitious grouts. HeliBond is applied as a thin layer, with the ability to micro-crack, providing high tensile reinforcement to strengthen low compressive strength lime mortar masonry, whilst not stiffening it. HeliBond Grout has been used on a number of Listed Heritage Structures constructed using Lime Mortar, under the guidance of English Heritage.

Why is HeliBond thixotropic?

HeliBond grout has been formulated to be readily injectible, whilst also holding its form on reaching the location that it is being injected to. HeliBond has a low liquid to powder ratio creating a thixotropic grout that avoids wastage and eliminates issues with slumping of the material prior to curing.

Can I use any applicator gun?

HeliBond should be injected with an applicator with a re-usable cartridge. Helifix sells a Crack Stitching Gun, and a Heavy Duty Gun suitable for Crack Stitching and CemTies. It is mixed using a power mixer in the supplied bucket and then transferred into the cartridge. When used for Crack Stitching the applicator must have a nozzle suitable for reaching into the relevant bed joint height. When using CemTies the Heavy Duty Gun should be used and appropriate Pinning Nozzle manufactured by Helifix will be required. Helifix also sell 4mm and 9.5mm wide Mortar Nozzles for use with their guns for Crack Stitching.

How do I clean my tools after using HeliBond grout?

Immediately after use, always clean all tools, mixers and containers with fresh clean water. Ensure that no grout remains within the mechanism. A spherical (toilet) brush is useful for cleaning the barrel and around the mechanism. If the pail is to be used more than once ensure that the pail is completely clean before loading fresh material.

When can I re point after installing HeliBars and grout?

Re-pointing may be undertaken immediately, although ideally the HeliBond should be recessed adequately below the surface and left for a few hours to start to ‘skin’ before re-pointing.

How much coverage can I achieve with HeliBond?

HeliBond is supplied packed in a pail containing two-packs of dry powder and two packsof liquid ready for mixing as a “set”. The formulation includes an expansion agent, to compensate for normal cement hydration shrinkage, to maintain a tight bond in its hardened state. A 3 Litre tub of HeliBond Grout provides enough coverage for approximately 10 linear metres of single HeliBar Crack Stitching.

Visit the Video page to see a live installation of Crack Stitching and how to mix HeliBond Grout.

Hosted by RICS, the seminars will take a practical approach to the subject and examine the properties of common materials and the various agencies of decay. Welcoming both members  and non-members of RICS, attendees will gain a further understanding of;

• Building defects – typical problems in various building types – what and where to look
• Problems arising from different construction periods
• Chemical and electromagnetic agencies

The seminars will take place at the following venues;

13th November 2012: Hilton Leicester Hotel, Junction 21 Approach, Town Centre, Leicester, LE19 1WQ. 5.30pm – 7.00pm. To book, click here.

22nd November 2012: Cardiff Marriott Hotel, Mill Lane, Cardiff, Wales, CF10 1EZ. 6.00pm – 7.00pm. To book, click here.

29th November 2012: Best Western the Russell Hotel, 136 Boxley Road, Maidstone, Kent , ME14 2AE . 6.00pm – 7.30pm. To book, click here.