Last edited 01 Nov 2023

Deleterious materials in construction

The term 'deleterious materials' is a broad one, encompassing not only materials that are dangerous to health or which are the causes of failures in buildings, but increasingly, materials which are environmentally damaging. Lists of deleterious materials may be prohibited in appointment documents or construction contracts, others may merely have warning regarding their use.

It should be noted however that all materials can be considered deleterious under the wrong circumstances (for example, water can be very damaging and can cause extensive pollution), and whatever materials are selected for use, it is vitally important that the manufacturer's instructions are followed. It is important to also note that some versions of similar products may not be considered with the same risks. For example autoclaved aerated concrete (AAC) is not considered deleterious, some reinforced autoclaved aerated concrete (RAAC) products are, but that is not to say that all RAAC products are considered in the same light.

The following materials are commonly considered to be either harmful to human health or to be the cause of long-term failure in buildings. While some of these materials may now be considered to be 'banned', they can still be found in our historic building stock and other materials are listed here as specifiers should be wary of them in certain circumstance.

Asbestos and Asbestos Containing Materials (ACM): Asbestos is often found in products such as cement fibre boards and roofing and sprayed as fireproofing or insulation. There are strict regulations controlling its removal and disposal (see Asbestos for more information).
Brick slips: These can be made from deleterious materials. There is a risk of poor adhesion and the lack of 'soft joints' can transfer loads to slips and cause delamination.
Cadmium products.
Chlorides: Calcium chloride and sodium chloride.
Chlorofluorocarbons (CFCs), Hydrochlorofluorocarbons (HCFCs) and Hydrofluorocarbons (HFCs) are considered to be 'greenhouse' gases.
Coal tar.
Lead and Lead Containing Materials (LCM) are hazardous materials which are neuro-toxic. Lead in paint is far more widespread than is realised. HSE guidance states: 'if preparing paintwork, lead surveys' are a requirement for pre-construction information. Residual leaded exhaust particle contamination can also be found in floor, ceiling and roof voids. Working with LCMs creates a 'significant' exposure risk, from inhalation and ingestion, as defined by lead regulations.
Hair plaster
High alumina cement: Used as an accelerator for quick setting of concrete.
Urea formaldehyde: Used in furniture and foam products or contained in adhesives.
Urea formaldehyde foam: Used in cavity wall insulation and some insulation boards, however this is not very common in the UK.
Polychlorinated Biphenyls (PCBs).
Polyisocynurate or polyurethane foam. (PIR and PUR) both PUR and PIR products have historically not been considered as deleterious. However since the Grenfell tragedy in which external PIR insulation burnt and release toxic gases, some sepcifiers are wary of its use in certain circumstances but not in all circumstances, for example below ground. For further information refer to the article Celotex RS5000 PIR insulation
Marine sea dredged aggregates (not in compliance with BS EN 1260): Such aggregates may contain salts, such as sodium chloride. If the salts are not washed out there is a risk of corrosion of concrete reinforcement.
Mercury, which can now be found in Compact Fluorescent Lamps (CFLs)
Machine Made Mineral Fibres (MMMF): If the fibres have a diameter of 3 microns or less or a length of 200 microns or less.
Mundic, which is a condition that occurs (especially in homes built from 1900 to 1960 in Cornwall and Devon) when structures deteriorate due to the oxidisation of unstable sulphides (often including pyrite) used in concrete.
Pentachlorophenol: Most commonly found in paint and wood preservatives.
Reinforced Autoclaved Aerated Concrete structural planks. RAAC are autoclaved aerated concrete (AAC) products containing reinforcement elements. Structural safety issues have arisen with these products, in particular where used as structural plank elements and from installations between the 1950's and 1970's, though it is important to note that this may not apply to all RAAC products, see below.
Silica dust. Stone, brick, tile and concrete contain silica. Silica dust (known as Respirable Crystalline Silica (RCS)) can be inhaled and can lead to silicosis, a lung disease that causes permanent disablement and early death. See HSE: Control of Substances Hazardous to Health (COSHH) for more information.
Vermiculite, unless fibre-free: Vermiculite can be found in light-weight concrete, fire protection materials, paints and other coatings.
Volatile organic compounds: Found in paints and protective coatings.
Wood wool: Slabs are often used as permanent formwork and left as a ceiling soffit. This may result in reduced fire resistance, reinforcement corrosion or in extreme cases, loss of structural strength in its use as a permanent shuttering or formwork.

The list of deleterious materials has always remained fluid because as technology advances new products come onto the market and medical research establishes new risks to health.

Clauses in contracts and appointment documents often refer to compliance with 'Good Practice in the selection of construction materials'. Originally published in 1997 by Ove Arup, and sponsored by the British Council of Offices (BCO) and the British Property Federation (BPF), it was an attempt to standardise a chaotic situation where contracts included long lists of prohibited materials that were often not deleterious, or were not enforced.

Now in its 2011 edition, 'Good Practice in the selection of construction materials' has been updated to reflect changing standards in materials specification and the growing importance of environmental concerns.

[edit] Asbestos

The following is a more detailed list of components where the use of asbestos might be detected (ref. list published by Greenhalgh & Co, Chartered Surveyors):

See Asbestos for more information.

[edit] Reinforced Autoclaved Aerated Concrete

In December 2022 the UK Government published 'Reinforced autoclaved aerated concrete (RAAC): estates guidance'. The guidance set out a 5-stage approach to the identification and management of RAAC in educational buildings, where these maybe present in floors, walls and roofs (pitched and flat) of buildings constructed or modified between the 1950s and mid-1990s. This guidance outlined initial steps that should be taken by those responsible for the management of educational buildings, how to procure building professional’s services when specialist advice is needed. It was designed for all parties involved in the identification and management of RAAC, including estates managers and those providing specialist advice, can use this guidance.

In mid 2023 UK ministers Ministers launched a UK government-wide inquiry into the use of crumbling concrete, in particular occurring in reinforced autoclaved aerated concrete (RAAC). Initial indication is that many of the installations at risk are over 30 years old which may be beyond the expected lifespan of the product. Typically these are low-rise flat roofed structures built between mid-1960s and mid-1990s primarily of RAAC blocks.

Towards the end of August 2023, RAAC was increasingly classed as a deleterious material as many school across the UK were unable to open due to safety fears. In the same month the Government published its updated guidance "Reinforced Autoclaved Aerated Concrete (RAAC):Identification guidance"

for further information and history see Reinforced Autoclaved Aerated Concrete, Autoclaved Aerated Concrete and Aerated Concrete.