Boron timber preservative

Nigel Foster possesses extensive expertise in treating dry and wet rot in timber using Disodium Octaborate, a boron-based compound. Typically, this compound is dissolved in mono-ethylene glycol. Boron has been a staple in the timber preservation industry for over five decades, primarily in the form of inorganic borates. Its efficacy as a fungicide is well-established, and it also exhibits insecticidal properties.

Boron can penetrate up to 40mm into damp timber
Boron penetrating wood

Unlike conventional timber treatments, a properly formulated Boron timber preservative deeply permeates damp wood, penetrating up to 40mm into sapwood and heartwood. This treatment swiftly eradicates existing fungal growth. Moreover, the Boron remains fixed within the timber throughout the building’s lifespan, enhancing its fire resistance. Importantly, it is also safe for use in proximity to bats.


base active ingredient in born wood preservative

Boron is a rare element, present in the earth’s crust in ubiquitous small proportions. It is never found free in nature but invariably occurs in concentrated forms as an oxide (boric oxide) in combination with oxides of other elements to form inorganic borates.


Inorganic borates have a rich history as cleaning agents, dating back to the days of ancient Greek and Roman empires. In the USA, Borax® serves as a powerful detergent booster and household cleaner. Additionally, in Europe and America, it finds application as a food preservative.

Boron has also been shown to be an essential element for plant growth, although in excess its toxic to plants.


A traditional timber preservative treatment involves the application of an insecticide/fungicide. Various chemicals are used to combine, the preservative ingredients with the spirit or water-based carrier: in most of the cases, they are applied by spray or brush on the timbers have dried down to <22% moisture content. 

A traditional timber treatment typically entails the application of an insecticide or fungicide. Various chemicals are used to apply the preservative ingredients with either a spirit or water-based carrier to create an envelope-only treatment. In most cases, these treatments are administered via spray or brush once the timber has dried to a moisture content of less than 22%.


An eradicative timber treatment for wood boring insects consists of applying wood preservatives to affected timbers to kill the larvae present in the timber or to provide an envelope layer of “poisoned” timber, which will kill woodworm larvae near the surface or when they pupate into a beetle and attempt to emerge through the treatment envelope.


Employing a professional Boron wood preservative containing a carefully formulated carrier enables effective treatment and preservation of infected timber. Unlike traditional chemicals, which struggle to penetrate damp wood, and using a suitable Boron-based solution has the remarkable capability to address dry rot. As a result, it can save substantial sums.

By utilizing a professional Boron wood preservative, you can effectively carry out an eradicative treatment for Dry Rot in timber. This involves introducing a specific loading of Boron disodium Octaborate tetrahydrate. The precise loading requirement varies based on the timber’s size, but as a general guideline, targeting 632 grams of Boron per cubic meter of timber is recommended.

Boron thrives in damp timber, and the wetter the wood, the more effectively Boron can penetrate and disperse within it. Employing an appropriate Boron wood preservative allows for the preservation of certain infected timber. Moreover, this method enables achieving a zero cutback into sound timber, a benefit not typically achievable with traditional treatments.

Traditional wood preservatives cannot penetrate meaningfully into wet timbers, and you must dry the wood down below 22% moisture content to allow some penetration of the active ingredient (BWPDA 1986).


You can now treat the infection and save more original timbers using the correct Boron wood preservative.  In the past, some specifiers may have done more damage treating/repairing the building, than the dry rot infection being treated, due to lack of understanding.

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