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Important Information:
Stains and Leaching


Timber is a natural material that contains a wide variety of compounds that are termed "extractives". While they are not part of the essential wood structure, they contribute to natural colour, odour, durability and moisture absorbency of a particular species, and may comprise of polyphenols, terpenes, oils, fats, gums, resins and waxes. Extractives may represent from 5% to as high as 30% of the dry wood mass, varying with species, sapwood or heartwood, rate of growth, growth location and season. Many of these extractives are partially or fully water soluble.

Stains On Timber Due To Natural Causes

There are many ways in which wood can become stained by natural causes, from the invasion of organisms and chemical change in extractives, to stains arising from leaching and decay during the service life of the timber.

Stains On Proccessed Timber Arising From Damage To The Living Tree

The rupturing of the protective bark on a tree causes the tree to respond by forming protective compounds which are generally phenolics in hardwoods and terpenes in softwoods. The rupture of the bark also potentially exposes the tree to invasion by a wide variety of organisms. An unsightly coloured/staining effect may appear on processed timber when these compounds and organisms which may also be photosensitive are exposed to oxygen and environmental weathering.

Stains Due To Chemical Changes In Wood Extractives

During the growth of timber, streaks or blotches of different shades are produced, and it is these variations that enhance the decorative value of the timber by adding character. However when processed timber is placed in the environment, oxidation of the natural extractives accentuated by exposure to light often causes these natural colorations to significantly change. Often blonde woods aquire a yellowish tint and red woods become more brown.

Stains And Leaching Due To Water

Exposure of processed timber to liquid and gas phase moisture in the environment often causes difficulty with unsightly leaching. Many extractives are partially water soluble and when the surface of the timber is wetted, some of these coloured extractives may partially dissolve and produce watermarks on the timber surface when it redries. Additonally, some extractives may runoff and stain other surrounding surfaces like concrete, walls, tiles, pavers etc. Tannins (polyphenols) in particular are likely to react with alkaline surfaces such as concrete to form an unsightly red/brown stain. In Australia, eucalypts such as Stringybark and Blackbutt and tropical hardwoods such as Merbau are particularly prone to causing such staining. If left alone to weather, the level of extractive runoff will reduce resulting in a significant reduction in ongoing staining with time. Chemical cleaning and removal of these stains is a simple and easy process.

Stains Caused By Chemical Reaction With Iron

Many species have a high tannin content which reacts with iron to form black and insoluble iron tannates if the timber is in a wet condition. Dark/black discolorations can often be observed on processed timber that has been newly exposed to a wet environment as a result of contact during processing or fixing with a steel blade or tool. Such stains appear suddenly and can be alarming, but are limited to the surface. In Australia we have noticed that Blackbutt in particular is particular is susceptible to this issue. Chemical cleaning and removal of these stains is a simple and easy process. More infomation on iron stain is available here

Pre-Cleaning Susceptible Timbers

Timber with a high level of extractives that are to be fixed in a wet environment where it would be undesirable for leaching to occur, or if iron contamination is suspected; may benefit from a pre-clean using Cutek Proclean prior to coating with Cutek oils. While it is impossible to guarantee that leaching or staining will not occur after this process, experience has proven that such an event is more unlikely, and if it does occur is of a signifcantly reduced nature.

Removing Stains And Leachate

Removal of iron tannates on timber, and leachates on adjacent surfaces is easily accomplished by using Cutek Proclean and following the procedures in the Cutek Proclean factsheet.