Boron timber preservative

We have considerable experience in carrying out timber treatment of dry & wet rot using Boron in the form of Disodium octaborate, which is 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 and also has insecticidal qualities.

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

Unlike most traditional timber treatments, a correctly formulated Boron timber preservative is absorbed deeply into damp timber and has been shown to penetrate up to 40mm into sapwood and heartwood, this treatment and will rapidly kill existing fungal growth.  The Boron stays fixed in the timber for the life of the building, it will also increase the fire resistance of timber and is safe to use near 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 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 as a food preservative 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 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. 

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 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.  By using a suitable Boron wood preservative, some infected timber can be kept.  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.  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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