Wood preservatives and timber treatments, insecticides, fungicides and other methods have been used for millennia to control timber decay. The chemicals used generally became increasingly poisonous, persistent and environmentally-damaging during the second half of the twentieth century. But this is not an excuse for not salvaging and reusing reclaimed timbers, most of which were not contaminated and of those that were, many have long since lost their potency for killing woodworm larvae, insects, dry and wet rot - most of which are dependent on an external source of moisture (such external leaks) to affect reclaimed timbers.
 
The planet is deforesting fast. Reclaiming and reusing the hundreds of thousands of tonnes of old demolition timber, much of which is first growth forest wood logged years ago, is vital. Destroying it by chipping (sadly called 'recycling'), burning (known as energy from waste), mulching and composting is an environmental travesty. Sound dimension timber and boarding from demolition is a precious resource which should be carefully dismantled and saved for reuse. We believe that a small proportion of timber reclaimed from demolition and refurbishment may have been treated with chemical preservative in its lifetime but these treatments long ago lost their efficacy and are now relatively harmless to both insects and fungi.
 
Salvo has never used, nor recommended the use of, timber preservatives.
 
In the 1990s Salvo estimated that 2,500 tonnes of reclaimable demolition timber was being landfilled daily, of which around 250 tonnes was valuable reclaimable tropical hardwood. In 1995 Salvo published its Reclamation Protocol (see extract below) which, among many other things, stated the position of some concerned international environmental scientists that demolished materials which could possibly be contaminated, such as chemically treated dimension timbers, are best reclaimed and reused in buildings rather than buried in landfill sites or incinerated. SalvoNEWS then compiled and published a history of timber treatments which we have republished and updated below.
 
Timber contains cellulose, a food source for some microorganisms, fungi and insects. Timber preservatives date back to ancient times and have generally became more poisonous over time, more damaging to the environment, and more persistent or longer lasting. These chemical poisons were often a byproduct of an unconnected industrial process that entailed the creation of poisonous wastes which were then fortuitously placed on the market as timber treatments and were used by mainstream construction and DIYers, often in the housing sector and often insisted on by mortgage companies.
 
The use of timber treatments seems to often be driven by commerce and fashion rather than science.
 
We believe that the modern fad for 'thermally modified' or charred timber is a classic example of this type of trend. Charred wood and its dust contains benzopyrene, a possible carcinogen, which was the reason that creosote was banned in Europe and why fabulous old tropical hardwood woodblock floors laid in bitumen cannot be reclaimed from demolition in Holland and Germany.
 
Nowadays the rapidly spreading use of 'nano' chemicals some of which are now put into wood paints and timber treatments, contain long chains of atoms which some scientists believe may turn out to be as hazardous as asbestos.
 
~ Salvo's history of timber treatments ~
[Written by the T Kay in 1996 and 1998 and published in SalvoNEWS - updated in 2020]
Definitions:
Fungicide: Material for destroying fungus, dry rot and wet rot
Insecticide: Material for destroying beetles, larvae and other insects
Inorganic: Chemicals not containing carbon atoms
Organic: Chemicals containing carbon atoms - natural and synthetic. (Organic is a term used by chemists, not a description for eco-friendly food)
Residual life: Moderate = months. Persistent = more than a year. Very high = longer than 5 years. Extreme is 20 years or more.
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1600BCE - Ancient Egyptians used charcoal and burnt gazelle dung against fleas and weevils, and bitumen for preserving mummies.
500BCE In ancient times the Greeks used olive oil (and borates, marjoram and coriander for food some of which are still used to the present day), Odysseus used fire and brimstone to fumigate his house, the Chinese used tung oil made from the seeds of euphorbia
200BCE - 200AD ancient Romans painted wood with pitch, Pliny suggested using vinegar (see Accoya below) and pitch for food preservation
[Some of the above borrowed from Natural Insecticides and Insect Repellents in Antiquity: Eva Panagiotakopulu, Paul C. Buckland and from Sheffield Uni Peter M. Day - to whom thanks]
700 - 1000 Norse and Vikings used pine tars, Danish oil and Stockholm pitch.
1030-42 Westminster Abbey and Hadstock church have the oldest working doors in England (made from English oak untreated with timber preservatives)
1000-1800s Tars were used to paint ship and house oak frames, and oak was sometimes limed on oak boards.
1737 Alexander Emerson’s Patent Process – Hot boiled oil mixed with ‘poisonous substances’ applied to timber.
1754 John Lewis’s Patent – Application of a varnish made from the juice of pitch pine plus additives.
1820s Nailing – Broad-headed ‘scupper’ nails sacrificial corrosion by salt-water ‘indurates’ the wood. (Probably harmless)
1823 Some Paints In Use – Nottingham White Lead, Litharge (white lead oxide), Vermilion and Cinnibar (bright red = mercury + sulphur), Red Lead or Minium, Smalt (dark blue = cobalt oxide), Kings Yellow (= arsenic + sulphur), Orpiment (yellow = arsenic + sulphur + other metals)
1832 Kyanizing – Patent process involving soaking timber in chloride of mercury (still in use in the 1930s)
1837 Margary’s Process – Soaking timber in a solution of acetate or sulphate of copper (in use to 1950s, corrosive to ferrous metals.)
1838 Sir William Burnett’s Process – Hot solution of chloride of zinc forced into timber under pressure in cylinders hermetically sealed. This was deemed to render the timber both rot-proof and fire-proof (in use to 1950s, corrosive to ferrous metals.)
1838 Bethell’s Process – Impregnating timber with creosote = coal tar distillate. (In use to 1990s, now banned under EU laws for domestic use)
1841 Payne’s Process – First a metallic solution is forced into timber under pressure, then a ‘decomposing fluid’ is forced in to form an insoluble compound in the pores of the wood.
1860s Leipzig Yellow (chromium oxide)
1890 US Process – Sodium Fluoride. (Still in use 1930s)

1910s Experimental use of radioactive pigments. Possible commercial application.
1948 White lead-based Paints banned for general use.
1920s onwards - Coal Tars - Creosote, polycyclic aromatic hydrocarbons. Organic fungicide used only on external timber. Solvent-based treatment of timber in-situ. Contact & inhalation hazard moderate, especially in recently treated timber – benzopyrene carcinogens and skin irritants.
Environmental hazard negligible in well-burned timber. Aquatic contaminant in discarded or incompletely burned timber. Residual life = years
1930’s to 2020 - Borates, inc disodium octaborate tetrahydrate (DOT). Inorganic fungicide and insecticide, water-based treatment, usually of timber in-situ. Contact & inhalation hazard: None. Environmental hazard: Negligible in discarded or burned timber. Residual life: Months
1940’s onwards - Copper Chrome Arsenate (CCA), chromated arsenical, also sacrificial copper strips on cedar shingles. Inorganic fungicide and insecticide. Water-based treatment by impregnation of bulk timber. Contact & inhalation hazard: None. Environmental hazard: Arsenious and chromium oxides in timber ash become soil and or water contaminants. Copper strip poisoned insects eaten by small birds. Residual life: 20+ years
1940’s onwards - Naphthenates. Organic fungicide. Used only on external timber. Contact & inhalation hazard: Negligible. Environmental hazard: Negligible, burns to innocuous products. Residual life: Months
1950s - 1960s - Chlordane. Organochlorine. Insecticide. Very little UK use. Solvent-based treatment of timber in-situ. Contact & inhalation hazard: Negligible more than one week after treatment of timber. Environmental hazard: Potential for dioxin formation in uncontrolled burning. Sever aquatic and soil contaminant in discarded timber both from chlordane and its degradation product dieldrin. Residual life: 100+ years?
1950s - 1970s - Dieldrin. Organochlorine. Insecticide. Developed in the 1940s as an alternative to DDT, dieldrin proved highly effective insecticide, widely 50s to early 70s. Extremely persistent, does not easily break down. Long-term exposure proven toxic to wide range of animals including humans, now banned in most of the world. Linked to Parkinson's, breast cancer, immune, reproductive, nervous system damage, and is an endocrine disruptor, acting as oestrogen and as testosterone blockers, can adversely affect testicular descent in the fetus when exposed to it in the womb. Wide UK use. Solvent-based treatment of timber in-situ. Contact & inhalation hazard: Negligible more than one week after treatment of timber. Environmental hazard: Potential for dioxin formation in uncontrolled burning. Sever aquatic and soil contaminant in discarded timber both from dieldrin and its degradation products. Residual life: 100+ years
1950s to late 80s - Lindane BHC Organochlorine. Insecticide. Used as an agricultural insecticide and a pharmaceutical treatment for lice and scabies. Lindane is a neurotoxin. In humans lindane affects the nervous system, liver, and kidneys, and may be a carcinogen. Whether lindane is an endocrine disruptor is unclear. The World Health Organization classifies lindane as moderately hazardous, and its international trade is restricted and regulated under the Rotterdam Convention on Prior Informed Consent. In 2009, the production and agricultural use of lindane was banned under the Stockholm Convention on persistent organic pollutants. A specific exemption to that ban allows it to continue to be used as a second-line pharmaceutical treatment for lice and scabies. Solvent-based treatment of timber in-situ. Contact & inhalation hazard: Moderate due to tendency for recrystallisation on timber surface. Environmental hazard: Negligible with well-ventilated burning. Potentially severe aquatic hazard in unburned and discarded timber. Residual life: Months. Elimination half-life 18 hours
1950s to late 1980s - Pentachlorophenol or PCP. Organochlorine. Insecticide and fungicide. Solvent-based treatment of timber in-situ. Some use of water-based soluble sodium salt. Contact & inhalation hazard: Moderate due to tendency for recrystallisation on timber surface. Environmental hazard: Dioxin formation in uncontrolled burning. Aquatic and soil contaminant in discarded timber. Residual life: 10+ years
1950s to 90s - Orthophenol also known as 2-phenylphenol. Organic. Phenolic. Fungicide. Commonly used as a disinfectant. Solvent-based or water-based treatment of timber in-situ. Contact & inhalation hazard: Very low. Environmental hazard: Low in both burned and unburned timber. Possibility of damage to plants growing on or near discarded timber. Residual life: Weeks or months.
1970s to 90s - Permethrin (also Bifenthrin in 2020s). Organic. Pyrethroid. Insect repellent. Solvent-based or water-based emulsion treatment of timber in-situ. Human side effects for use on headlice include scalp irritation. Use during pregnancy appears safe. Permethrin is in the pyrethroid family of medications which works by disrupting the function of the neurons of lice and scabies mites. Permethrin was discovered in 1973 and is on WHOs list of essential medicines. In 2017, it was the 410th most commonly prescribed medication in the United States, with more than 150 thousand prescriptions. Contact & inhalation hazard: Disputed in 1998. British data showed no significant hazard eight hours after treatment. German data showed potential uptake onto house dust and therefore resuspension to the environment. Potential for skin reaction and possibly asthmatic reaction by this route. Data was disputable in 1998 and in view of the reasonable safety record in widespread use over twenty years, probably not significant. Constituent together with Iodopropynyl Butyl Carbamate of Sovereign Chemicals Ltd 'Deep Kill - woodworm and fungicidal timber preservation cream' (in 2020). Environmental hazard: Low in both burned and unburned timber. Possibility of damage to plants growing on or near discarded timber. Residual life: Weeks or months
1970s to 90s - Cypermethrin. Organic. Pyrethroid. Fast-acting neurotoxin in insects. It is easily degraded on soil and plants but can be effective for weeks when applied to indoor inert surfaces. Exposure to sunlight, water and oxygen will accelerate decomposition. Cypermethrin is highly toxic to fish, bees and aquatic insects, according to the National Pesticides Telecommunications Network. It is found in household ant and cockroach killers. Solvent-based or water-based emulsion treatment of timber in-situ. Contact & inhalation hazard: Disputed in 1998. British data showed no significant hazard eight hours after treatment. German data showed potential uptake onto house dust and therefore resuspension to the environment. Potential for skin reaction and possibly asthmatic reaction by this route. Data was disputable in 1998 and in view of the reasonable safety record following widespread use over twenty years, probably not significant. Now considered possibly damaging to bees. Environmental hazard: Negligible in well-burned timber - burns to innocuous products. Very severe aquatic contamination hazard from discarded timber. Residual life: Months
2000 to 2020 - Boric acid. Insecticide and fungicide. Also called sassolite, hydrogen borate, boracic acid, and orthoboric acid. A weak acid of boron often used as an antiseptic, insecticide, flame retardant, neutron absorber, or precursor to other chemical compounds. It exists in the form of colorless crystals or a white powder that dissolves in water. Boric acid is found in volcanic districts in Tuscany, the Lipari Islands and Nevada where it mixes with steam, from fissures in the ground and is also found in many naturally occurring minerals – borax, boracite, ulexite and colemanite. Boric acid and its salts are found in seawater and in plants, including almost all fruits. Boric acid was first prepared by Wilhelm Homberg (b. Jakarta 1652, d. Paris 1715). Borates were used by the ancient Greeks for cleaning, and preserving food. Boric acid is slightly more toxic than common household salt. Boric acid was first registered in the US in 1948 for control of cockroaches, termites, fire ants, fleas, silverfish, other insects. Generally considered safe to use in kitchens to control cockroaches and ants. It acts as a stomach poison affecting metabolism, and dry powder is abrasive to the insects exoskeletons. Boric acid is also believed to be carried back to nests where the poison kills more insects. Boric acid also prevents and destroys existing wet and dry rot in timbers. Borate-impregnated rods are inserted into drill holes of damp timber. It is available as a gel and an injectable paste. Environmental hazard: Very severe aquatic contamination hazard. Residual life: Days or longer.
2000 to 2020 - Iodopropynyl Butyl Carbamate (IPBC). Fungicide. Water-soluble preservative used globally in paints & coatings, wood preservatives (since 2000), personal care, and cosmetics. IPBC was invented in the 1970s and has a history of antifungal use. IPBC is a non-carcinogen with no genotoxicity in reproductive and developmental toxicity studies using rats and mice, IPBC had no significant effect on fertility, reproductive performance, or on the incidence of fetal malformation. It was (in 2020) a constituent of Ronseal wood preserver.
2000? to 2020 - ACQ alkaline copper quaternary. Fungicide and insecticide. Water-based wood preservative. Relatively low risk. Copper oxide and quaternary ammonium compounds. Leaves a dry, paintable surface. Used on lumber, timbers, landscape ties, fence posts, building and utility poles, land, freshwater and marine pilings, sea walls, decking, wood shingles, and other wood structures.
2006-20 - Polymeric betaine, borate. Fungicide. Registered in the United States in 2006. Borate ester that, when applied to wood, breaks down to DDAC (didecyl dimethyl ammonium chloride) and boric acid. Polymeric betaine is applied by pressure treatment to forest products.
2007-2020 - Accoya is a Dutch acetylation process owned by a UK company which impregnates plantation grown softwood (usually P radiata) with vinegar. It is non-toxic and renders the wood rot and insect resistant for 50 years or more. Despite the treatment the wood weathers naturally if left uncoated. Accoya states 'This opened surface structure will both cause a change in colour and also allow surface moulds, yeasts, mosses and algae to penetrate and develop faster. These types of growths can use many sources of nutrients, including extractives in the wood, free sugars, starch, and other available organic compounds, but do not degrade the wood structure itself. However, pigment produced by these moulds and yeasts, may discolour the surface. With Accoya they don’t cause rot, nor with natural wood species – their impact is solely aesthetic!' The process was invented in the early 20thC but was expensive to scale up to an industrial process. Acetylation changes the free hydroxyls within the wood into acetyl groups. The free hydroxyls attract enzymes which result in fungus and insect attack.
2016-20 Charred timber, which may contain benzopyrene, is resistant to insect and fungal attack. It is believed to have been a traditional treatment in Japanese buildings dating back to 700, and has recently undergone a revival.
2016-20 Nanotechnology is able to produce material such as graphene at an atomic level with dimensions as small as a billionth of a metre thick. There are 20,000 products listed on Amazon which use the word 'nano'. In 2019 Global Wood Preservative News reported 'Rising Significance of Nanotechnology in Wood Preservation and Protection'. Wood preservative chemicals market worldwide is projected to grow by US$626.6 Billion, driven by a compounded growth of 4.3%. The rapidly spreading use of 'nano' chemicals is of concern, some of which are now in wood paints and timber treatments, containing long chains of atoms which some scientists believe may turn out to be as hazardous as asbestos.
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~ END ~
 
Salvo recommends reusing reclaimed timbers even if they may have been treated with preservatives in the past.
1. There have been no adverse medical effects of working with reclaimed timber by reported to Salvo by workers or customers.
2. Neither Salvo nor any of the hundreds of reclaimed timber dealers with which we have had contact in the past thirty years, nor any of their hundreds of thousands of customers, to our knowledge have experienced effects resulting from timber treatments from the reuse of reclaimed timber.
3. All timber preservatives break down over time and lose their strength.
4. Most reclaimed timbers earlier chemical preservatives are no longer toxic to insects and fungi, let alone humans.
5. If it were the case that reclaimed timbers are a toxic threat then millions of existing old buildings in Britain must be more toxic due to repeated applications of wood preservative on floors, joists and roof timbers, particularly from the 1970s onwards.
6. Salvo Code dealers agree 'to the best their ability and knowledge, to sell material free from toxic chemicals, excepting those natural to the material, traditional to its historical use, or resulting from atmospheric pollution'.
7. Reclaimed timber and flooring dealers sometimes use timber preservatives on reclaimed wood, but usually at customer's request.
8. Reclaimed creosoted railway sleepers should never be reused indoors and should be protected from young children outdoors. Most dealers supply reclaimed railway sleepers subject to customers agreeing their conditions of supply.
9. DIYers sanding of old timber or floorboards should keep rooms ventilated, wear PPE and dispose of waste safely.
10. Some people are allergic to certain untreated timber species. For example the sawdust from western red cedar or opepe may give some people nosebleeds.
11. Reclaimed timber is not toxic. Most has not been treated in its lifetime. By not reusing reclaimable timber society is rejecting a valuable resource.
 
In 1995 Salvo published its 'Reclamation Protocol' which contained a section on toxicity, some of which is probably still relevant today. In 1995 Salvo was fighting a lone battle to encourage reuse of reclaimed building materials. The circular economy had very few supporters.
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~ The 1995 Salvo Reclamation Protocol ~
Even if reclamation were to be encouraged by governments there are still tricky problems to overcome. Moves towards greater use of healthy construction materials means some older materials may no longer meet today’s higher standards. This may not apply if the materials are already located in an old building but may be less likely to be allowed if the demolished materials are to be reused in another building. While it may be reasonable to argue that upon demolition a view can be taken on the safety of the future use of old materials, the EC are very likely to take an unnecessarily negative view in questionable circumstances. This is encouraged by new building materials manufacturers, many of whom (such as makers of treated timber products) are still pre-contaminating materials before they are even used, thus reducing chances that they will be reusable in future.
The alternatives to reuse can, however, be environmentally worse. It is obviously best to bury demolished asbestos. However, a body of opinion believes that some demolished materials, such as chemically treated timber is best reused in buildings rather than buried in landfill where dioxins can leach into the water supply, or incinerated in power plants, where dioxin plumes may be spread over large areas. This is especially true when it is now known whether the timber has been chemically-treated.
 
Toxicity of reclaimed materials may come in one of two forms - embodied and acquired. This is what is meant:
EMBODIED TOXICITY : The material itself is toxic e.g. asbestos, some hardwoods, metals, plastics and even some stone.
ACQUIRED TOXICITY : This is material that would not normally be considered toxic which has been contaminated by a toxic substance.
 
Acquired toxicity may result through a recognised building process such as the treatment of timber with chemicals, or the setting of woodblock in asphalt. Alternatively material may be contaminated through usage, such as flooring from a factory where chemicals were stored. The definition of a toxic substance or hazardous waste is not uniform. Woodblock set in asphalt is considered hazardous waste in Holland and Germany but not in the UK. So hardwood woodblock laid in asphalt would routinely be incinerated in Holland and Germany but reclaimed woodblock, recovered, cleaned and palletted in the UK can be sold back to both Holland and Germany for reuse.
 
An example of this occurred in 1994 during the construction of a new airport terminal in Germany, much to the chagrin of a German reclamation dealer (one of the very few in Germany at the time). A couple of kilometres away acres of mahogany woodblock were being burned during a demolition job, while similar woodblock that had been reclaimed and cleaned in England was being imported for reuse on the airport floor.
 
A group of scientists from ISCOWA (International Association of Alternative Construction Materials), based in Utrecht, Holland has been looking at the toxicity of reclaimed materials. Their provisional findings recommend that materials with hidden toxicity, either a currently known toxic risk or a possible future one, are better reclaimed and reused above ground in a building than buried in landfill or dispersed into the atmosphere via incineration. Point and click instruments will be developed that will be able to find and measure levels of toxicity, but criteria will constantly shift as hitherto safe materials are declared toxic.
 
In future, Codes of Practice will be developed for reclamation. It is already established through euro-law that special precautions need to be taken when demolishing buildings with a known toxic hazard, and the materials derived cannot be offered for resale. However this has not prevented one or two instances where toxic materials have been transported across national boundaries complete with a clean bill of health.
 
Salvo is trying to establish a Code of Conduct for the reclamation industry (we succeeded in 1995 with the Salvo Code) which will progressively identify areas of concern and recommend means of tackling them. Toxicity is one of the items on our agenda, although the reclamation industry is less than enthusiastic about the prospect of ‘unnecessary restrictions to trade’. Who can blame them when, for instance, despite the ban in the use of lead in paints since 1948 in the UK, the conservation lobby including state-owned ‘quango’ English Heritage (who also, we have good reason to believe, has a covert anti-reclamation policy), and the National Trust, now recommend the use of lead paint to re-toxify the nation’s more important buildings. Last year (in 1994) Medicins Sans Frontiers reported that at least 10,000 toddlers in each of the five main French cities were suffering from lead paint poisoning (saturnisme) from flaking old lead paintwork in the rundown apartment buildings in inner city areas. Where are the green movement when it comes to issues like this? It is reclamation dealers who tackle lead-based and other toxic heavy metals in painted Victorian woodwork and treated timber.
 
The UK DoE recommended a code for the production of recycled aggregates to conform with action in other European countries. This mentions known toxic materials, but of course, cannot adequately deal with concrete that has been contaminated with hidden toxicity during the use of an industrial building. In an increasingly toxic built environment selective disposal methods will continue, in the short term at least, to favour those with most muscle to the detriment of reclamation and reuse.
 
There are no recorded cases of health hazards caused by the use of any reclaimed material, although there have been cases of toxic recycled material (hardcore) being supplied for reuse by demolition contractors which has had to be subsequently removed.
 
The simple short term practical solution then, is to ensure that old architectural items are either stripped and sealed, or repainted and not flaky. The fashionably flaky paint look [now called 'shabby chic'] should be discouraged, unless it has been recreated using modern, preferably, eco-paints.
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