COVID-19: Cleaning and Disinfecting Historic Surfaces

Public Health England (PHE) provides guidance on cleaning in non-healthcare settings and working in heritage locations. These principles should be followed when dealing with historic settings and surfaces.

Advice concerning COVID-19 is updated frequently. This guidance is based on information available as of July 2020 and is subject to change. It is designed to help you decide how to protect and/or disinfect the historic surfaces of fixtures and fittings. It is not intended for historic artefacts, objects and collections that can be moved. If a historic surface is highly significant, sensitive or fragile, please consult a conservator who specialises in the relevant material.

Historic England cannot take any responsibility for the effectiveness of the methods described or for any damage caused by third parties attempting to disinfect historic surfaces.

Please read all of this guidance before undertaking any disinfectant activities.

Cleaning and disinfecting

Cleaning is essential to remove dust and dirt from historic surfaces to prevent damage, and it is often part of a housekeeping routine. It is primarily a ‘dry’ process, involving dusting and vacuuming; the ‘wet’ cleaning of historic surfaces is only carried out when absolutely necessary.

Disinfecting is the process of eliminating or reducing harmful microorganisms (such as viruses, bacteria and so on) from objects and surfaces. Before the outbreak of COVID-19, there was no need to disinfect historic surfaces, but it is now known that a person who touches a contaminated surface then touches their mouth, nose or eyes can become infected.

The amount of time that the SARS-CoV-2 virus which causes COVID-19 (we will refer to it as the COVID-19 virus throughout this guidance) remains active on a particular material varies. Latest research on several materials used in historic surfaces gives a guide time of 72 hours in most cases. For some materials, the persistence time is less than 72 hours (see information below).

To prevent the spread of COVID-19, disinfecting surfaces may be included in routine cleaning in certain circumstances. However, as this is a new virus further research is needed to fully understand how effective different types of disinfectants are and how they will interact with various historic surfaces. For example, standard (commercial, industrial, household) liquid disinfectants and hand sanitisers containing chemicals that eliminate microorganisms can cause irreparable damage to historic surfaces, especially if used repeatedly.

It is always best to avoid or mitigate any virus contamination where possible. Using chemical disinfectants to treat historic surfaces is a last resort. If this is the only option, it is important to manage the risk and follow appropriate health and safety procedures.

The following guidance should be observed by those looking after historic surfaces while COVID-19 is a risk.

Avoid contamination

If a surface cannot be touched, it does not need to be disinfected.

Consider the following:

  • Can access to a room or area with historic surfaces be restricted?
  • Can barriers be put up to keep people away from historic features?
  • Can a ‘no touching’ policy be introduced (with signage to explain the reasons)?
  • Can the historic surfaces be covered?
    • If it is impossible to prevent the historic surfaces being touched, it may be helpful to cover them with something that can be removed and then disinfected or replaced as required. For example, furniture can be covered with a tightly woven or synthetic fabric (such as Tyvek ™) and flat surfaces with polyester (such as Melinex ™), acrylic (such as Perspex ™) or glass sheets. Foam protectors can be fitted where people have to touch historic handrails to use stairs safely. Door handles can be covered with acid-free tissue and then cling film. Floors can be covered with mats. Care should be taken not to leave impermeable coverings on historic surfaces for too long since this could cause a build-up of moisture.
  • Can the historic surfaces be protected?
    • Regularly reapplying wax (for example microcrystalline or bees) on existing waxed surfaces should give additional protection against increased cleaning and disinfecting.
    • Wearing disposable gloves may protect surfaces from becoming contaminated as well as protecting the user. All gloves will need to be disposed of appropriately.
    • Where possible, wash hands rather than use hand sanitiser. Most hand sanitisers contain alcohol and when wet may damage historic surfaces.

If there is good reason to suspect that an infected person may have touched a historic surface, or that an area may be contaminated, it will need to be protected, quarantined or disinfected.

Mitigate the risk

Are there any alternative approaches to using standard (commercial, industrial, household) liquid chemical disinfectants?

Consider the following:

  • Can the rooms, areas or surfaces be quarantined? Using time to let the virus naturally deactivate on historic surfaces is the safest, cheapest and most environmentally friendly method of disinfection.
  • Can you close the affected areas or rooms for at least 72 hours before attempting to clean them? The COVID-19 virus persists for longer on some non-porous materials so it may be necessary to extend the quarantine; please see the information on individual historic surfaces below.

After surfaces have been quarantined for the appropriate period, they do not need to be chemically disinfected and normal cleaning can be carried out.

Manage the risk

How can the risk be managed to minimise potential damage to the historic fabric?

If avoiding contamination or imposing a period of quarantine are not possible and using a chemical disinfectant is the only option, a risk assessment and management approach will be required to achieve a proportionate response. You need to balance the need to disinfect with the potential damage to the historic surface.

Before disinfecting any historic surface, it is important to consider the following:

  • Understand the historic surface you are wanting to disinfect:
    • What is the substrate material?
    • Has it got an applied surface finish? For example, paint, varnish, shellac, gilding or wax.
    • What is its condition? If it is fragile – flaking, cracking or in poor condition, for example – a liquid chemical disinfectant may cause further damage and should not be used.
  • Understand the chemical composition and concentration of the disinfectant, as well as the potential effect of the disinfectant chemicals or proprietary products (for example, wipes, sprays) before using them. Material Safety Data Sheets (MSDSs) for proprietary products should be available, and manufacturer’s instructions for storage and use should be followed.
  • Do NOT use any detergents or disinfectants which are strongly acid or alkaline.
  • Do NOT use any detergents or disinfectants containing chlorine, such as household bleach (containing sodium hypochlorite) and water purification treatments (containing chlorine dioxide). These are effective COVID-19 virus cleaning agents, but may also cause permanent damage to historic surfaces. Such products contain chloride anions, which can react to produce damaging salts.
  • Do NOT use any detergents or disinfectants containing QACs (quaternary ammonium compounds) on any historic surface because they may cause permanent damage. Many commercial biocidal products currently being suggested for disinfection contain QACs. These chemicals can sometimes be difficult to identify in product labelling or MSDSs, so it is best to check on the Internet. QACs can be strongly acidic or alkaline, and either would damage historic surfaces. They may also leave damaging salt residues if not rinsed thoroughly.
  • Do NOT use heat or steam devices. Heat (including steam) destroys microorganisms by breaking down the proteins. Its effectiveness is primarily determined by the temperature and exposure time, as well as the type of material being treated. Latest research indicates that the COVID-19 virus can survive long exposure to high temperatures (60°C for 1 hour). The high temperature and sustained time period required for deactivating this virus (92°C for 1 hour) is not safe for historic materials. Heat treatments used to kill insect pests, and household or garment steamers are unlikely to be effective.
  • Do NOT use UV or UVC (ultraviolet and ultraviolet C) light. Although UVC light (254 nm wavelength) is effective in deactivating the COVID-19 virus (research shows that five minutes’ exposure kills the virus), this method is not recommended for historic surfaces. UV and UVC light is not only potentially damaging to historic textiles, paper, wood and pigments, but it is also a health hazard to skin and eyes. Research into far-UVC light (222 nm) may have application for some heritage settings in the future.
  • Ozone treatment has been suggested, but it has not yet been proved to be effective against the COVID-19 virus and it could be harmful to human health and historic surfaces.

Disinfectant chemicals/methods

The following chemicals have been found to be effective in deactivating the COVID-19 virus on a variety of materials. These materials correlate to historic surfaces (see information below). This information is based on our understanding of currently available research and links to this are given.

Alcohols

Examples: ethanol, industrial denatured alcohol (IDA), such as industrial methylated spirit (IMS), Isopropanol (also known as 2-propanol, isopropyl alcohol, IPA or surgical spirit)

  • Alcohols need to be least 70% (70 parts alcohol, 30 parts purified water) to be effective. Both components play a crucial role in deactivating the virus by breaking down the lipid shell. Consult the manufacturer’s instructions to make sure the ethyl alcohol component is not diluted below 70%.
  • Industrial alcohols can be difficult to buy and transport. You will need to register with HMRC.
  • Methylated spirits bought from DIY stores are not generally suitable for treating historic surfaces because they usually include harmful additives and dyes that could stain historic surfaces.
  • Isopropanol is readily available at 70% and can also be purchased as impregnated wipes. Always read the product labelling or MSDS to check that isopropanol and deionised water are the only ingredients.

Concentration and minimum effective contact time

Ethanol content

IMS with ethyl alcohol content

Peroxygen compounds

Example: hydrogen peroxide

  • Peroxygen compounds such as hydrogen peroxide can break down the virus’ essential components, but are powerful oxidising agents and can also damage historic surfaces.
  • Peroxygen compound-based proprietary disinfectants are available. Always read the product labelling or MSDS to check that the peroxygen compound percentage doesn’t exceed 0.7% (7,000 ppm).

Concentration and minimum effective contact time

Surfactant/detergent and water

  • Detergents and surfactants are able to deactivate the COVID-19 virus by breaking down the lipid shell around the virus and/or protein components within it. Read more about how detergents deactivate COVID-19. This process reduces the levels of contamination and may be helpful when used in combination with quarantining, but further research is needed to establish its full effectiveness.
  • Detergent/surfactant and water solutions should only be used on surfaces that are able to withstand being damp. Excessive moisture from these mixtures can cause damage, such as lifting coatings or paint layers, and staining porous materials.

Concentration and minimum effective contact time

The following list gives examples of historic surfaces, the persistence of the COVID-19 virus (where known) and the suitability of the selected disinfectant chemicals.

Historic surfaces (in good condition and without surface defects)

Persistence of Covid-19 virus on material: N/A

  • Alcohols: 🚫 Unsuitable
    Risks removal of gilding.
    Seek advice from specialist conservator.
  • Peroxygen compounds: 🚫 Unsuitable
    Risks removal of gilding.
    Seek advice from specialist conservator.
  • Surfactant/detergent and water: 🚫 Unsuitable
    Risks removal of gilding.
    Seek advice from specialist conservator.

Persistence of Covid-19 virus on material: 120 hours

  • Alcohols: ✔ Suitable
  • Peroxygen compounds: ✔ Suitable
  • Surfactant/detergent and water: ✔ Suitable

Persistence of Covid-19 virus on material: 120 hours

  • Alcohols: ✔ Suitable
  • Peroxygen compounds: 🚫 Unsuitable
    May react with irons in earthenware body and cause iron staining.
  • Surfactant/detergent and water: ✔ Suitable

Persistence of Covid-19 virus on material: 94 hours

  • Alcohols: ✔ Suitable
  • Peroxygen compounds: ✔ Suitable
  • Surfactant/detergent and water: ✔ Suitable

Persistence of Covid-19 virus on material: 94 hours

  • Alcohols: 🚫 Unsuitable
    The applied finish could be dissolved by this chemical.
    Seek advice from specialist conservator.
  • Peroxygen compounds: 🚫 Unsuitable
    The applied finish could be dissolved by this chemical.
    Seek advice from specialist conservator.
  • Surfactant/detergent and water: 🚫 Unsuitable
    The applied finish could be dissolved by this chemical.
    Seek advice from specialist conservator.

Persistence of Covid-19 virus on material: N/A

  • Alcohols: 🚫 Unsuitable
    Likely to cause colour change.
    Seek advice from specialist conservator.
  • Peroxygen compounds: 🚫 Unsuitable
    Likely to oxidise surface and cause potential colour change.
    Seek advice from specialist conservator.
  • Surfactant/detergent and water: 🚫 Unsuitable
    Risk of staining and physical distortion from water.
    Seek advice from specialist conservator.

Persistence of Covid-19 virus on material: 120 hours

  • Alcohols: ✔? May be suitable but there are significant risks of damage
    Check for a surface finish such as lacquer or wax which could be damaged
  • Peroxygen compounds: 🚫 Unsuitable
    Risk of corrosion.
  • Surfactant/detergent and water: 🚫 Unsuitable
    Risk of corrosion.

Persistence of Covid-19 virus on material: 48168 hours

  • Alcohols: ✔ Suitable
    Check for a surface finish such as lacquer or wax which could be damaged.
  • Peroxygen compounds: 🚫 Unsuitable
    Risk of corrosion.
  • Surfactant/detergent and water: ✔ Suitable
    Low risk of corrosion.

Persistence of Covid-19 virus on material: 4 hours

  • Alcohols: ✔ Suitable
    Check for a surface finish such as lacquer or wax which could be damaged.
  • Peroxygen compounds: 🚫 Unsuitable
    Risk of corrosion.
  • Surfactant/detergent and water: 🚫 Unsuitable
    Risk of corrosion.

Persistence of Covid-19 virus on material: 72 hours

  • Alcohols: ✔ Suitable
    Check for a surface finish such as lacquer or wax which could be damaged.
  • Peroxygen compounds: 🚫 Unsuitable
    Risk of corrosion.
  • Surfactant/detergent and water: 🚫 Unsuitable
    Risk of corrosion.

Persistence of Covid-19 virus on material: N/A

  • Alcohols: 🚫 Unsuitable
    Risks removing painted details.
  • Peroxygen compounds: 🚫 Unsuitable
    Risk of colour change.
  • Surfactant/detergent and water: 🚫 Unsuitable
    Risks removing painted details.

Persistence of Covid-19 virus on material: N/A

  • Alcohols: 🚫 Unsuitable
    Risks removal of paint.
  • Peroxygen compounds: 🚫 Unsuitable
    Risk of colour change.
  • Surfactant/detergent and water: ✔ Suitable

Persistence of Covid-19 virus on material: N/A

  • Alcohols: ✔ Suitable
  • Peroxygen compounds: ✔? May be suitable but there are significant risks of damage
    Risk of reacting with calcium carbonate to produce salts.
  • Surfactant/detergent and water: ✔ Suitable

Persistence of Covid-19 virus on material: N/A

  • Alcohols: ✔ Suitable
  • Peroxygen compounds: ✔? May be suitable but there are significant risks of damage
    Risk of reacting with calcium sulphate to produce salts.
  • Surfactant/detergent and water: 🚫 Unsuitable
    Plaster of Paris is moderately soluble in water so this could dissolve detail.

Persistence of Covid-19 virus on material: 72168 hours

  • Alcohols: ✔? May be suitable but there are significant risks of damage
    Check if plastic type is alcohol sensitive
    Can cause swelling or dissolution.
  • Peroxygen compounds: ✔? May be suitable but there are significant risks of damage
    Check if plastic type is hydrogen peroxide sensitive
    Likely to oxidise the surface and lead to embrittlement and/or discolouration.
  • Surfactant/detergent and water: ✔? May be suitable but there are significant risks of damage
    Check if plastic type is water sensitive
    Can cause swelling or dissolution.

Persistence of Covid-19 virus on material: 72 hours

  • Alcohols: ✔ Suitable
  • Peroxygen compounds: 🚫 Unsuitable
    Risk of reacting with calcium sulphate to produce salts.
    Risk of oxidising, resulting in discolouration.
  • Surfactant/detergent and water: 🚫 Unsuitable
    Alabaster is moderately soluble in water so this could dissolve detail.

Persistence of Covid-19 virus on material: 72 hours

  • Alcohols: ✔ Suitable
  • Peroxygen compounds: 🚫 Unsuitable
    Risk of oxidising, resulting in discolouration.
  • Surfactant/detergent and water: ✔ Suitable

Persistence of Covid-19 virus on material: 48 hours

  • Alcohols: 🚫 Unsuitable
    Drying and embrittling of fibres, risk of dye bleed, tide marks and irreversible staining.
    Seek advice from specialist conservator.
  • Peroxygen compounds: 🚫 Unsuitable
    Drying and embrittling of fibres, risk of dye bleed, tide marks and irreversible staining.
    Seek advice from specialist conservator.
  • Surfactant/detergent and water: 🚫 Unsuitable
    Risk of irreversible staining, colour loss, tide marks, dye bleed, distortion of fibres (swelling and shrinkage) and abrasion to fibre surface.
    Seek advice from specialist conservator.

Persistence of Covid-19 virus on material: N/A

  • Alcohols: 🚫 Unsuitable
    Highly sensitive and damage is extremely likely.
  • Peroxygen compounds 🚫 Unsuitable
    Highly sensitive and damage is extremely likely.
  • Surfactant/detergent and water: 🚫 Unsuitable
    Highly sensitive and damage is extremely likely.

Persistence of Covid-19 virus on material: 3 hours

  • Alcohols: 🚫 Unsuitable
    Risk of irreversible staining and tide marks, drying and embrittlement of paper fibres, risk of loss to decorated surface layer, and bleed of some paint types.
    Seek advice from specialist conservator.
  • Peroxygen compounds 🚫 Unsuitable
    Risk of irreversible staining and tide marks, drying, embrittlement and potential long term damage to paper fibres, risk of colour change and bleed of some paint types.
    Seek advice from specialist conservator.
  • Surfactant/detergent and water: 🚫 Unsuitable
    Risk of irreversible staining, tide marks, loss or bleed of decorated surface layer, detachment from wall and linings, distortion of fibres (swelling and shrinkage) and abrasion to painted surface.
    Seek advice from specialist conservator.

Persistence of Covid-19 virus on material: 48 hours

  • Alcohols: 🚫 Unsuitable
    Risks drying out the wood, leading to cracks and surface alteration.
  • Peroxygen compounds: 🚫 Unsuitable
    Risks oxidising the natural colour of the wood.
  • Surfactant/detergent and water: ✔ Suitable
    Very low risk on flat surfaces, but avoid veneer, marquetry and complex carved surfaces because the risk of damage is greater.

Persistence of Covid-19 virus on material: 48 hours

  • Alcohols: 🚫 Unsuitable
    Risks removing wax finish.
  • Peroxygen compounds: 🚫 Unsuitable
    Risks oxidising the natural colour of the wood.
  • Surfactant/detergent and water: ✔ Suitable
    Potential to cause white bloom under wax finish unless sound wax layer has been applied.

Persistence of Covid-19 virus on material: 48 hours

  • Alcohols: 🚫 Unsuitable
    Risks removing surface coating.
    Can cause delayed lifting to veneer and marquetry.
    Seek advice from specialist conservator.
  • Peroxygen compounds: 🚫 Unsuitable
    Risks damaging surface coating.
    Can cause delayed lifting to veneer and marquetry.
    Seek advice from specialist conservator.
  • Surfactant/detergent and water: 🚫 Unsuitable
    Risk of water staining to surface.
    Can cause delayed lifting to veneer and marquetry.
    Seek advice from specialist conservator.

When disinfecting historic surfaces, the following guidance should be observed:

  • Wear appropriate Personal Protective Equipment (PPE), as advised by PHE and according to health and safety precautions in relation to any products, chemicals or methods being used.
  • Always carry out a trial in a discreet area and check that no damage has been caused. If damage is noted, do not use the disinfectant chemical or proprietary disinfectant product.
  • Apply disinfecting chemicals in a controlled way, applying the chemicals to a clean cloth or paper towel (not the historic surface), and paying close attention to the effective contact time (see information above). This can be achieved by careful and repeated wiping. The wiping action also helps break down the virus cells. If the surface is dirty or greasy (which could reduce the efficiency of the surfactant at breaking down the virus), it is advisable to repeat the treatment. Remove any residue from the surface using a clean cloth or paper towel. Detergent/surfactant and peroxygen compound residues should be removed with a clean cloth, dampened in deionised water. Minimise excessive moisture as this can easily cause damage. The surface should then be dried immediately with another paper towel or soft cotton cloth.
  • Apply standard disinfectants to non-historic surfaces carefully to avoid accidental contact with historic surfaces. Fogging, misting or spraying (including electrostatic spraying) should not be carried out in spaces that contain historic surfaces, fixtures and fittings, objects or collections (even if they are in display cases).
  • When disinfecting other surfaces, take care to avoid accidental contact with historic surfaces. For example, the wooden elements of a door should be protected when cleaning a metal door handle with a disinfectant chemical.
  • Take care not to damage other adjacent historic surfaces. For example, the wooden elements of a door should be protected when cleaning a metal door handle with a disinfectant chemical.
  • Dispose of all cleaning and disinfecting materials as advised by PHE.
  • If in doubt, seek advice from a conservator who specialises in the historic surface you are trying to treat.
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