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.