Deleterious materials

The other side of the hill

13 May 2010

To understand deleterious materials of the future, says Trevor Rushton, we must learn the lessons of the past

Deleterious materials perform in an undesirable way. We have considered high alumina cement, calcium chloride, asbestos and lead as deleterious or hazardous, but notwithstanding this, all materials have the capability of being in some way deleterious given the right circumstances.

With the drive to cut carbon emissions and provide a sustainable approach to construction, numerous new materials and construction methods are coming on to the market - many of which may indeed perform in ways that were not anticipated by the designer. How can we assess how well these innovations will perform?

The Duke of Wellington once proclaimed

"All the business of war, and indeed all the business of life, is to endeavour to find out what you don't know by what you do; that's what I called 'guessing what was at the other side of the hill'."

The following examples serve to illustrate Wellington's advice.

Don't take information at face value

In January 2010, a short piece in the Daily Telegraph discussed a research paper published in the American Chemical Society's Chemical Research in Toxicology journal.

The paper, Risks of Copper and Iron Toxicity during Aging in Humans (Ref. 1), drew attention to the possible risk of Alzheimer's disease resulting from exposure to water in domestic copper plumbing systems. The author concluded that people with higher intakes of copper and a high-fat diet had 'lost cognition' more rapidly than expected, and that people over 50 should avoid drinking water from copper pipes.

However, before we consider the ramifications of banning the use of copper, let us look at one small fact the Telegraph chose to ignore - the research paper was what is called in scientific circles a 'narrative review'. This gives a comprehensive overview of a topic, but does not necessarily include all data. It is unclear how well the review covers the evidence, or whether it has omitted evidence that contradicts the author.

This review was also written by a single author, as opposed to being a collaborative effort, and may therefore be biased. Furthermore, a majority of the studies covered in the review were animal- or cell-based studies, which means that their direct relevance to humans is limited.

Thus far, information is limited and it would be dangerous to base decisions upon limited and selective examples of research - but watch this space.

Don't overlook the obvious

The mercury from a single CFL is enough to pollute 30,000 litres of water beyond safe drinking levels

Compact fluorescent lamps (CFL) are considered to be 80% more efficient than conventional incandescent lamps, and governments globally are pushing to introduce them as a substitute for tungsten bulbs.

CFL bulbs contain up to 5mg of mercury per bulb. The mercury is required to produce ultraviolet light, which is then changed into visible light by a phosphor coating. However, the mercury from a single lamp is enough to pollute 30,000 litres of water beyond safe drinking levels (source: Mercury Recycling plc).

Under normal operating conditions, a CFL bulb should not break but experience and common sense tells you that breakages in the home are inevitable. Start investigating how to clean up and you will find some alarming advice. In the UK, the Health Protection Agency recommends, among other things (Ref. 2):

  • vacate the room and keep children and pets out of the affected area. Shut off central air-conditioning system, if you have one
  • ventilate the room by opening windows for at least 15 minutes before clean-up
  • do not use a vacuum cleaner, but clean up using rubber gloves and aim to avoid creating and inhaling airborne dust as much as possible
  • dispose of the fragments in a double-wrapped plastic bag and treat as hazardous.

Somehow I do not see the layman adopting this advice. And there's the problem - mercury will find its way into landfill. BSJ readers will recall a recent article on PCBs (Ref. 3) and the biopersistence of these materials - sound familiar?

Research by the Maine Department of Environmental Protection in the US has revealed that, depending upon the clean-up regime implemented, mercury concentrations can be extremely variable. Double re-sealable polyethylene bags did not appear to retard the migration of mercury adequately to maintain room air concentrations below action levels. Also, clean-up material may remain in the home for some period of time and/or be transported inside a closed vehicle, potentially exposing occupants to mercury vapour.

Given the difficulty of monitoring such precautions, one can see that uncontrolled disposal is a possibility, with at least some bulbs finding their way into landfill.

Expect the unexpected

In 2001, BBC2's Newsnight questioned the use of Incinerator Bottom Ash (IBA) as a secondary aggregate in road surfaces and building blocks on account of alleged high dioxin content. IBA is a by-product of industrial waste incinerators - it is essentially composed of those particles of ash that fall from a moving grate into a quenching pool.

IBA has been challenged by some environmentalists and it is possible that the material may yet be reclassified and treated as hazardous waste

The Environment Agency's current classification of IBA has been challenged by some environmentalists and it is possible that the material may yet be reclassified and treated as hazardous waste.

Foamed concrete is often used for void filling and roadway applications; it is a cement-bonded material made by blending an extremely fluid cement paste (slurry), into which is injected a stable, pre-formed foam. Not all foamed concrete products are the same; some contain IBA while others do not.

IBA often contains aluminium so that when it is used with cement, the aluminium reacts with the alkaline cement paste to produce hydrogen gas. In 'normal' concrete made with IBA aggregate, this 'off gassing' can cause swelling of the concrete and subsequent large spalling effects. If the IBA aggregate concrete is a foamed type for use as low density fill, the much greater porosity of the foamed mix will allow the small particle size of hydrogen gas to leach more easily from the mix in wet and hardened state.

In a recent incident, contractors had been filling an old well with IBA foamed concrete over three days. The well was contained within a building and capped with temporary metal plates. It is thought that sparks from cutting equipment led to the ignition of hydrogen gas produced by the concrete. Two workmen received serious foot injuries in the resulting explosion.

The results of the HSE investigation have yet to be published, but as a precaution, The Highways Agency has banned the use of foamed concrete containing IBA until such time as the material is deemed safe.

If something can go wrong...

In 2006, a fire at a site in Colindale consumed a six-storey timber-framed (TF) building in less than nine minutes. Last year, a fire on a site in Peckham was fanned by high winds and destroyed 39 new homes, spreading to flats in adjoining estates and a public house.

According to the ABI... the cost of fire damage in 2008 in the UK rose by 16% on 2007 to a record £1.3bn, i.e. £3.4m every day

Typical features of these fires are early structural collapse and fire spread to neighbouring buildings. But not only are TF buildings at risk during construction, the poor installation of fire stopping, plasterboard finish quality and cavity barriers can pose serious risks of fire spread in a completed building.

According to the Association of British Insurers, the insurance industry is increasingly concerned about rising fire losses: the cost of fire damage in 2008 in the UK rose by 16% on 2007 to a record £1.3bn, i.e. £3.4m every day (Ref. 4). New building techniques, including TF are highlighted as being a factor.

All of the above factors point to growing concern about the use of TF construction and recent rumours suggest that insurance companies will withdraw cover for these types of buildings.

Read the instructions

Building is now a process of assembly, with craft-based skills now diminishing. However, it is vital that new systems are fully explained and understood throughout the chain. Not only does TF construction demand attention in respect of fire, proper consideration of shrinkage and load paths are essential.

For example, we are currently involved with repairs to a recently constructed block of 15 flats arranged over four floors. The building is of platform construction whereby the external walls are constructed of prefabricated timber panels bolted together on site. The timber panels support prefabricated floor and ceiling 'cassettes'.

Figure 1: Remedial work in progress to a TF building. The vertical load from the post in the centre of the picture was supposed to be transferred by a set of site-fixed studs below (now installed) but these were originally missing. The resultant distortion of the frame led to severe water penetration from a balcony. (© Watts Group/Trevor Rushton)

The design was fully detailed by designers and required 'loose studs' to be inserted within certain internal wall panels to increase the load-bearing capacity of the panels to support point loads from the roof structure. The building was clad in brickwork.

Fairly soon after construction, residents were alarmed by distortion that began to occur in the building, windows no longer fitted and floors became uneven - in the most severe cases, differences in level developed of up to 75mm across a single room. The downward motion of the floors caused the external balconies to distort, with the result that water flowed back into the building.

Figure 2: The same floor in the TF building seen from below. That the building merely distorted is testament to the flexibility of this form of construction. The vertical support studs have been installed as remedial work. (© Watts Group/Trevor Rushton)

The propensity of a TF building frame to shrink is well documented; suitable provision has to be made. However in this case, investigations revealed that many of the additional loose studs had not been fitted. Furthermore, some of the floor cassettes had been laid reverse-handed so that double-joisted sections no longer occurred beneath partitions or load paths. That the building did not collapse is testament to the inherent flexibility and strength of TF construction, but remedial work, involving decanting the flats is costing in excess of £0.5m.

Understand the need for water management

In Canada, a problem known as 'Leaky Condo Syndrome' lead to the collapse of the British Columbian equivalent of the NHBC - the New Home Warranty Program in 1998. The syndrome involved the decay of TF houses arising from water penetration behind external wall insulation (EWI) systems.

Mineral wool, cellulose fibre and phenolic foam all have the capacity to retain water and, if coupled with a form of construction that resists drainage and evaporation, can lead to serious decay. Phenolic foam in particular contains acidic compounds that when released in wet conditions can have a very corrosive effect upon lightweight galvanized steel sheeting or structural elements. Applying impervious insulation and render systems to old walls can have harmful effects - it can prevent existing water management (breathability) of the fabric and exacerbate problems such as dampness, condensation and mould. The ability of the wall to release water is reduced and as a result, the increase in moisture content reduces the U-value. Problems such as these are typically encountered in older buildings without an effective DPC.

Figure 3: Although a common form of construction and one that can perform well in service, insufficient care in the sealing of joints can lead to air leakage and, in the right conditions, severe condensation on the underside of roof coverings causing the oriented strand board (OSB) to rot. Good construction systems can be given a bad name by poor assembly and detailing. (© Watts Group/Trevor Rushton)

NHBC Standards include detailed guidance to control the risk of rain penetration. For example, they require that external insulation systems over TF include a 15mm drained and ventilated cavity, and over light gauge steel frame a 15mm drained cavity. However, this is controversial and while the EWI industry acknowledges that in some cases a 'second line of defence' is needed, there are no recognised methodologies to determine when such a system would be required.

Furthermore, we come across plenty of examples where the render system has been used as the primary means of defence without auxiliary back up. Damage arising from normal wear and tear, alterations such as the insertion of vents and flues, new windows and the like all create potential for moisture penetration and waterlogging.

In Japan, where structurally insulated panel systems (SIPS) are popular, water ingress and decay problems have been encountered. These result from faulty or insufficient jointing techniques and a failure to seal the joints to prevent vapour transfer from the inside of the building to the cold outside face where it condenses on the sheathing around the joint. SIPS panels are becoming popular in this country, but unless the principles of water management and moisture control are properly understood and implemented, this sound method could become problematic.

The cases that I have outlined here are interesting in that they do not reveal 'new' defects or characteristics. However, what is of concern is the way in which previous lessons have not necessarily been learned, with the result that avoidable problems have been ignored or treated with a Nelsonian eye. Surveyors are well equipped to offer advice and it is worrying, for example, that of the key stakeholders selected to form the working party on the London Assembly's investigation into fire safety in tall and TF buildings, RICS is not represented.

My six principles are essentially matters of common sense - using what we already know to find out what we do not. Sadly, the catalogue of failures illustrates one fact that is often missed - that common sense is not common enough.

Trevor Rushton is a Technical Director with Watts Group and author of Investigating Defects in Commercial and Industrial Buildings

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