Why is timber preservation important?
Timber has been used as a structural material for millennia and is in many ways ideal for the job. It can be described as strong, beautiful and sustainable – basically, wood is good! However, wood-rotting fungi and the wood-boring larvae of certain insects (also known as woodworm) feed by breaking down wood cells and, if left unchecked, ultimately destroy the timber in your home. Fungi and woodworm consequently threaten the structural integrity of your home, leading to substantial financial costs and potential danger for inhabitants.
Common timber problems
A new-build house should be constructed with timber preservation in mind. However, most of us live in houses that we haven't built and inherit timber problems along with the property. The three most common problems likely to affect timber are woodworm, dry rot and wet rot.
Click here for advice on Control
. This guide will focus on:
, which refers to a particular species of fungi - Serpula lacrymans
– and Wet rot
, which is a more general term, encompassing a range of fungi.
How can I identify wood-rotting fungi?
breaks down wood cellulose and causes timber to become dry and powdery. Serpula lacrymans
grows in strands, digesting adjacent timber until it “fruits” and discharges fungal spores. Fugenex
produce a sensor which detects the presence of incipient dry rot, and costs about £7.50 . It's a useful DIY test and only involves drilling a small hole in the timber - if the sensor changes colour you know there is a dry rot problem and you can call in the experts!
is more easily identified than dry rot, quite simply because affected timber will feel damp to the touch. With painted timber, the area may look and feel sound superficially, but the underlying timber may be rotten – try pushing a knife into the timber, you should feel resistance after a few millimetres. Timber affected by wet rot feels spongy and looks darker than surrounding wood. When dried, timber affected by wet rot cracks and crumbles into fine particles.
Rot will only affect timber that is physically damp. Dry rot requires a modest moisture content of 20%, while wet rot needs an elevated level of moisture (28-30%) to become established. Thereafter it can persist in timber which has a minimum moisture content of 20%. You may wish to employ a specialist, but here are three DIY steps it's worth trying first:
STEP 1 - remove the source of moisture
The most common reasons for damp timber are leaking appliances, poorly sealed sinks/baths, leaking roofs and overflowing drainpipes and rising damp.
STEP 2 – promote rapid drying conditions
If you can find and fix the source of the water and allow timber to dry out properly, you can control and ultimately eradicate the rot. To speed up drying, ensure good ventilation and increase the ambient temperature.
STEP 3 – remove and replace affected timber
Badly affected timber should be removed and replaced. Sections of rotten timber can be replaced with epoxy resin. This is especially appropriate for repairs to valuable/historical beams, as work can be done in-situ - see below for further sources of advice.
Initial treatments may be insufficient - it's not always possible or practical to keep timbers dry in the long term. This is where other measures need to be taken to eradicate rot and prevent re-infection. Remedial treatments are outlined below, and are likely to require the services of a specialist contractor. It's worth familiarising yourself with the options, so you have some idea of the what contractors can offer.
Physical containment of rot
Dry rot can pass through materials like brick and masonry to reach a fresh source of wood. Wood can be isolated by physical containment, using joinery lining or masonry sterilisation.
Application of fungicidal renderings and paints
These substances form a chemical barrier between the timber and the surrounding environment, and are often based on zinc oxychloride.
Chemical treatment of timber
This will either be in the form of in-situ treatment of existing timbers or replacement with pre-treated timber. Both of these options are detailed below.
Available chemical treatments
In-situ chemical treatments include:
- Surface spraying, often using a boron-based preservative dissolved in an organic solvent. Glycol is a particularly effective carrier, and allows the preservative to mix freely with any moisture resident in the timber.
- Application of fungicidal pastes consisting of an oil and water emulsion. This method is not effective for very damp wood, as the moisture prevents the fungicide from penetrating deeply enough.
- Fluid injection of fungicides using plastic valves. Distribution of the fungicide is good as the fluid is injected under pressure.
- Insertion of water-soluble borate rods into the timber. Not appropriate for timbers that are already at an advanced stage of decay, but rather for prevention of rot.
Methods of timber pre-treatment include:
- Surface treatment using a range of timber preservatives, many of which are potentially toxic. Water-based borates and glycol borates are both effective and “greener” than some alternatives. You should note that, since 2003, the use of creosote as a wood preservative has been prohibited. There are also restrictions on the use of creosote-treated timber. Contractors should be aware of this legislation.
- Pressure and/or vacuum-treated timber. "CCA treated” timber was commonly used until domestic use of this timber was banned in 2004 due to concerns about the health hazards of the chemical used, Copper Chrome Arsenate. Safer alternatives now available include Tanalith E ® and Osmose Naturewood ®, preservative treatment that are both based on copper and an organic biocide.
Some treatments prevent rot and woodworm as well as increasing timber hardness, strength and durability, such as the Indurite wood hardening system from Osmose®. Treatments like this add value to softwood timber, which is often a more sustainable and environmentally friendly option than hardwood. However, bear in mind that treated wood is considered toxic waste at the end of its lifespan and must be disposed of accordingly. GreenSpec
provides information on alternatives to chemical wood treatment. Ask your timber supplier or the contractor carrying out remedial work for advice and to establish whether these products are appropriate for your home.
How do I locate a timber preservation specialist?
You can find specialists in your local business directory or through an online search facility. Companies or individuals who are members of the Wood Preserving and Damp-Proofing Association
are recommended. The BWPDA regulates and monitors member companies and ensures that they follow a code of practice and comply with relevant health and safety legislation. Allied to the BWPDA, the Property Care Association
has a searchable online database of approved contractors.
A service offered by many companies is a free survey of your home. This can be genuinely useful but you should bear in mind that a commercial contractor has a vested interest - the worse their diagnosis, the more money can be made! Try to get two or three quotes and if you're still unsure, it may be worth employing an independent surveyor. You can find a qualified timber surveyor online at www.specifiypga.com
. Expect to pay a minimum of £45 per hour for their services.
Is the treatment expensive?
That really depends on how extensive the problem is! As with most professionals, timber specialists will charge an hourly rate for their work - in the region of £40. It's usual for contractors to provide a quote for the whole job - shop around for the best price but try to strike a balance between quality and value-for-money. The materials used for treatment are themselves relatively inexpensive - boron gel treatment, for example, costs around £20 for 4 square metres. The bulk of what you pay covers labour costs. As a rough guide, most wood-rotting fungi problems can be eradicated for a few hundred pounds, but extensive remedial work might cost £1000 plus - a survey is the only way to be sure.
Before you begin any treatment...
- Establish which type of treatment is appropriate for you – it can't be overstressed that whatever secondary measures you employ to control wood-rotting fungi, it is essential that you first identify and remove the source of damp.
- Check if your home is a listed building (one judged to be of "special architectural or historic interest"). Contact English Heritage (England), Cadw (Wales) or Historic Scotland (Scotland) for advice and guidance. Financial help may be available to fund high-quality repairs using traditional materials and specialist craftsman, particularly if these conserve original features. Specialist contractors should be familiar with the restoration of ancient timber, but you could contact The Society for the Protection of Ancient Buildings for further advice.
- Consider the environmental impact of your actions - up to 150,000 remedial timber treatments are carried out in British homes each year, many of them unnecessary. Overuse of toxic chemicals in residential settings puts occupants at risk so it's preferable to avoid unneeded repeat treatments. Property Guarantee Administration, will identify active timber treatment chemicals from a small timber sample which you send them, for a fee of £95.00 plus VAT. This could avoid unnecessary chemical treatment and save substantial amount of money if further treatment proves unnecessary.