Boron timber preservative

We have considerable experience in carrying out timber conservation work using Boron in the form of Disodium octaborate normally carried in a mono-ethylene glycol.  Boron has been used for over 50 years in the timber preservative industry, in the form of inorganic borates, and is well established as an effective fungicide with insecticidal qualities.

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

Unlike most timber treatments a correctly formulated Boron timber preservative will penetrate damp timber rapidly and has been shown to penetrate up to 40mm into sapwood and heartwood and will act as a preventative treatment, as well as supply a rapid kill of existing fungal growths.  The Boron stays fixed in the timber for the life of the building, it can improve fire resistance of timber, and does not give of any vapour, which is liable to affect the inhabitants, including children, bats and fish.


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 been known as cleaning agents since the days of the ancient Greek and Roman empires, and is used in the USA as Borax® which is a detergent booster and household cleaner and also use as food preservatives in Europe and America.

Boron has also been shown to be an essential element for plant growth, although in excess is toxic to plants, and effective herbicides have been developed to exploit this.


A preventative timber treatment usually involves the application of an insecticide and or a fungicide carried in either white spirit or water. Various chemicals are used to combine the active ingredients with the spirit or water-based carrier: in each case the active ingredients are normally applied by spray or brush. 

These traditional preventative treatments often use Permethrin as an insecticide, or Polyphase etc, as a fungicide.  The problem with all such treatments is that they involve the release of the vapour from the carrier into the atmosphere in which you live. In addition, such treatments can only be fully effective on the surface of materials, and their penetration is generally insufficient to be useful against anything other than Common Furniture Beetle (woodworm) attack in softwoods.


An eradicative timber treatment for wood boring insects consists of applying wood preservatives to affected timbers in order to kill the larvae present in the timber or to provide a 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.


Using a professional wood preservative with Boron in a carrier formulation will allow you to treat and retain infected timber which a tradition chemical can’t, as they have significate problems in penetrate damp timber, it is this ability, which has saved my client’s thousand pound due to ability to treat dry rot.

Using a professional Boron wood preservative, you can achieve an eradicative treatment for Dry Rot, in timber, this is achieved by introducing a loading of Boron disodium octaborate tetrahydrate.  The loading varies with the size of timber but as a guide 632g of Boron per m3 of timber is the target.

Boron loves damp timber and the wetter the better for rapid penetration and dispersal of the Boron into the timber.  Using a suitable Boron wood preservative with the correct Boron loading, some infected timber can be kept if it is of use.  Also, you can achieve a zero cut back into sound timber unlike 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 of the original timbers by using the correct Boron wood preservative.  It’s sad to say in the past some specifiers may have done more damage to the building, than the dry rot infection being treated, due to lack of understanding.

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