Tung Oil, aka China Wood Oil

 

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Referred to by Confucius as early as 400 BC and also known as China Wood Oil, Tung Oil is believed by many to be the finest natural wood finish in the world. It is extracted from the nuts of the Tung Tree - Aleurites fordii - native to east Asia. Legend has it that the Great Wall Of China was sealed with tung oil. It is a component of many products marketed as Tung Oil but which are usually extended with other cheaper oils and also consequently have to contain added toxic dryers and anti-fungals.

Tung oil is a tree nut oil which polymerises naturally and cures to a tough, buffable, water resistant, beautiful finish which patinates better than skin finishes.  Pure tung is safe for use on wooden toys (EN71 compliant) and kitchen woodwork which contacts foodstuffs.

Click HERE to see purchase options for Tung Oil.

Click HERE to see a range of solvent dyes suited to tinting Pure Tung oil.

OIL FINISH or MEMBRANE FINISH


The great majority of Wood finishes can be grouped as either OIL or MEMBRANE finishes.

Membrane or skin finishes include varnishes, shellacs (French polish) and lacquers. These finishes divide further into those which can be reformulated on the fly, where the newly applied finish can meld with the prior coating, (for example some lacquers and shellac), or those modern varnishes such as polyurethane which polymerise (cross link) and which have to be removed, or at least heavily scuffed (sometimes referred to as giving the surface "tooth"), to provide a key for subsequent coats or touch up. (It is precisely the final stage inertness and imperviousness resulting from the completion of the cross linking chemical bond formations that makes modern polyurethanes - either moisture or catalyst cured - so resistant and tough). They do however usually scratch rather easily.

Oil finishes by comparison, for whatever end, flooring, cabinetry etc, are by nature more penetrative and mostly "in the wood" whereas membrane or skin finishes typically sit on the wood and key with the wood with a lesser degree of penetration. Oil finishes can be regarded as preserving the look and feel of the wood better than skin finishes which, critics would say, put a plastic coating on the wood.

Oil finishes can be commercial formulations with names such as Danish Oil, Teak Oil, Tung Oil Finish or Buffing Oil.  The precise ingredients and their proportions is typically proprietary information. Tung oil remains an expensive ingredient so many of these commercial formulations contain a limited amount of tung oil - in some cases as little as 3% - and use cheaper, non drying extender oils which then require toxic dryers to get the extender oils to cure and additional anti fungal additives to deal with the tendency of the extender oils to promote fungal growth.

As a general statement nut oils derived from trees are, for wood finishing purposes, more robust than seed oils e.g. linseed.  The tree nut or seed oils of particular interest to wood finishing are those which have a "drying" characteristic.  They include Linseed (both Raw and so called Boiled, which is, these days, usually raw with chemical dryers added), walnut, poppy seed and tung oils.

These oils can be classed as unsaturated drying oils and it is this characteristic which makes an oil of interest to wood finishers.  A drying oil is an oil which hardens to a tough, solid film after a period of exposure to air. The term "drying" is a misnomer - the oil does not harden through the evaporation of water or other carrier solvents as do many skin finish formulations, but through a chemical reaction in which oxygen is absorbed from the environment (autoxidation).

Oil finishes can be remarkably tough, are usually superior in the patination stakes and the initial application, touch-ups or re-coats are far less problematic than with membrane finishes.  Membrane finishes frequently crack when damaged and this allows penetration of moisture and dirt into the ding or crack which then discolours.  Oil finishes have little skin to worry about and thus suffer less from the delamination due to dings and natural seasonal wood movement which is a given for all solid wood in service outside of air-conditioned environments. They therefore patinate better.

 

When considering a teatment for wood in an environment subject to weather such as decks and garden furniture, the consideration of the ease of on-going maintenance is one of the most important criteria.  The prevalence of harsh sun and weather cycles is not diminishing and in this respect tung oil is an excellent choice - for decking for example hose down and scrub with a stiff brush to remove visible contaminants such as bird droppings, allow to thoroughly dry and using a wide disposable roller re-apply a coat of tung and rub back after 30 or so minutes.  Expect to do this every 18 to 20 months.  

Patina defined - the appearance of a piece, including dents, dings and the aged finish and, while mostly applied to cabinet pieces, also applicable to floors and window and door trim.  Regarded as a positive and desirable attribute easily ruined with unsympathetic restoration.

Uses
Tung oil is suited to wooden floors, interior and exterior woodwork including decks, window and other wooden joinery, kitchen tables and bench tops, chopping boards, concrete, stone and terracotta surfaces, rammed earth floors and children's toys. It is a preferred finish for gun stocks and didgeridoos. It is often used as a figure enhancing sealer under other top finishes such as shellacs and varnishes.

Thinning
The high grade pure tung we sell has a viscosity heavier than olive oil and in most cases should be thinned before use.  We recommend Citric Terpene (d-Limonene) which is distilled from orange and mandarin skins and, when more highly refined, is used as a food flavour.  A 50:50 cut with Citric Terpene is our recommended mix however this is frequently adjusted a bit each way to speed penetration in ultra hard or highly absorbent woods. If harder thin more, if very thirsty you can thin less.  

Colouring

Surfaces to be oiled can have their base colour adjusted prior to the application of Tung Oil with the use of wood stains or wood dyes, alternatively, the tung oil itself can be pre-coloured using our range of turpentine/terpene soluble aniline dyes.  See HERE for more on these dyes.

 

Provided you are methodical and make test runs, using tinted oil is a very simple process. To use these dyes a quantity of BLACK and primary colours RED, YELLOW and BLUE are recommended. This pallete will enable you to adjust the oil colour. The most compelling advice regarding the use of these dyes and stains is to measure and test mix ratios and procedure carefully and document what you do so that a successful outcome can be replicated.

 

See HERE for graduated storage and mixing containers.

See HERE for powder/liquid funnels.

 

A set of metal or plastic kitchen measuring spoons is very useful for measuring powders.


VOC and Flamability
Pure tung itself has a zero VOC rating (volatile organic compound - the off gassing compounds found in petrochemically derived thinners which are both deleterious to the atmosphere and often hazardous to breathe or come into contact with). The gases given off by Citric Terpene are in fact the same as nature off-gases from orange orchards which suggests it is a relatively more benign product to thin tung and work with.
Note there are several grades of both tung and terpene - we sell the best quality of tung and a high quality water-white grade of terpene. 

If Citric Terpene is not available Gum Turpentine, also a tree derived product, is a good alternative.

 

Citric terpene, gum turpentine and petrochemically derived mineral turpentine ('turps') are all schedule 3 flammable liquids.  Do not allow smoking in the vicinity and beware of naked flames.

 

Supply & Shipping
Pure Tung can be mailed but be aware that Australia Post has a 20 kg package limit.

Citric terpene is a flammable good and needs to be delivered via road courier.

Please email or call for shipping quotes and timing.

 


TUNG OIL APPLICATION

TESTING

It is strongly recommended that Pure Tung is tested on an off-cut or equivalent piece of the wood that the finish is intended for.  This proving process will determine thinning ratios and your technique and will help to ensure that your expectations are in line with what can be achieved. This advice is especially relevant to oiled finishes which, by their nature, can absorb oil deep into the wood and which are therefore unlike skin finishes which can often be more easily removed with strippers or sanding if you change your mind or are unhappy with the outcome.

PREPARATION
Fill nail holes and dings if desired with an appropriate wood filler and allow to setup.
Sand as finely and evenly as possible. For cabinet and smaller surfaces sand to 600 grit if possible.  For floors this is not feasible but sand to the finest grit attainable. Tung should preferably not be applied over other finishes. On work which is already finely sanded but has been left untreated for some time consider using a wax and grime remover to remove skin oils, tobacco smoke stains etc.  A product widely marketed as sugar soap is recommended to clean most readily removable contaminants.
Vacuum the sanding dust.

APPLICATION
Generously apply a 50:50 mix of thinner and tung oil using a paint roller, wool applicator pad, sponge, brush or cotton rag. Keep the area well wetted with the oil for about 30 minutes. Some areas with differential absorbency may soak up all the mix and will need re-wetting.
After this time vigorously wipe off all remaining surface oil with a cotton rag or similar. This in counterintuitive (and expensive) but essential to achieving a good outcome.  Tung oil needs to be cured in thin coats.  Failure to do this carefully is the most common reason for problems.

Next day repeat with another coat using the same technique.  After a few more days repeat coats as you wish. The golden rule of oil finishing is more and thinner coats is better than fewer and thicker.    

Ideally wait a week during which time the oil will harden.  During any stage of the drying process you can walk on a floor in socks or bare feet. Be ready to wipe away any oil which may bleed from the surface. For external wood treatments pick a period with a few days of dry weather in prospect.

The oil curing process is a slightly exothermic reaction. Do not leave oily rags balled up as there is a slight risk of spontaneous combustion.

BUFFING (OPTIONAL)
Some trade customers we supply who, for reasons both of their own health, the results attainable and their customers preference for a natural product, report stunning results using a floor polisher after a couple of weeks.  They prefer to use old carpet on their polishing/buffing machines with the pile side against the floor. Wool carpet is much preferred. Given the oil reaches close to ultimate hardness in about 3 to 4 weeks and, scheduling permitting, buffing can be carried out well after the application. 

CLEANING, MAINTENANCE AND TOUCH UP
For cleaning a damp mop followed by a drying cloth is recommended.  The ability to touch up and spot repair is a major plus for tung compared to many membrane finishes which are impossible to touch up and often require sanding back.  Pure tung can be applied to repair high wear areas at will with no sticky build up. The standard procedure as detailed above applies. Vacuum and damp mop the area, immediately wipe well dry and spritz some oil on and wipe back. A spray bottle of a 50:50 mix works well to mist on a light coat which can then be wiped dry. Water marking can be treated with this touch-up method.

COVERAGE
Any suggestion for coverage is a guess because some wood species are much more thirsty than others and second and subsequent coats will absorb less than the initial coat.  Assuming a 50:50 thinning and work sanded to at least 240 grit, around 18 to 20 square metres per litre is indicated for new (or freshly sanded) work. More highly sanded finishes with second and subsequent coats will require far less oil. After several coats coverages estimates become academic - many dozens of square metres to the litre.

A summary:

  • Pure tung will, in common with all oil finishes, darken the wood somewhat - more so if used straight on the raw wood, somewhat less so if used over a sealer.
  • When considered for use on floors the floor finishing trades are accustomed to getting floor polishing jobs completed very rapidly and commercially formulated products assist with this efficiency. Pure tung demands a more considered approach.
  • For most tradespersons the notion of applying and wiping off a finish is counter-intuitive, they will tend to leave the oil to pond which may be good practice for an oil with dryers but is not the ideal method for pure tung.
  • There is with tung oil no issue of the time window between coats such as applies to some poly-urethane finishes which can require that second and subsequent coats be applied after the solvents in the prior coat have sufficiently off-gassed but before all the chemical bonds have formed in the prior coat.
  • Pure tung is NOT a high build "treacle" finish.
  • Pure tung offers a low gloss 'woody' look.
  • Pure tung is NOT a shiny membrane finish although can be buffed to a quite high lustre.
  • Pure tung MUST be applied with thin "wiped off" coats. Do NOT allow the oil to pond or attempt to cure thick coats.
  • Pure tung will cure to a very tough finish. After a few days the surface of the treated wood will be remarkably hard and suitable for buffing.
  • Tung has, even when used neat, a remarkable affinity for wood and penetrates better than any oil I have used.
  • Pure tung takes longer to cure (it has no chemical dryers added) especially in rainy or humid weather.
  • Tung cures quicker, more completely and to a harder and far less oily finish than linseed oil.
  • Tung does not continue to darken over time as may linseed oil.
  • Tung is not as likely to support mould as linseed oil.
  • Tung has a natural resistance to UV.
  • Pure tung can be touched up with maintenance coats or applied to restore areas of high wear with relative ease.
  • Applications of pure tung do not demand as clean an environment in terms of airborne dust, insects etc as do membrane finishes.
  • Tung oil is very tenacious and the use of expensive application brushes is not recommended because they are impossible to fully clean.
  • Tung oil will last far longer in storage than products with added chemical dryers.  When storing keep sealed off from air, cool and dry, out of the sun and try to expel any air from the head of the container.  Note that we supply 5, 10, 15 and 20 litre consignments in multiples of 5 litre plastic jerry cans filled past their official capacity.  This means only the contents of one 5 litre jerry can at a time need be exposed to air. Stored as suggested, and with minimal air in the head of the container, Pure tung can be stored for at least a couple of years.


OH&S Cautions

Pure Tung Oil in non-flammable & can be regarded as non-toxic. Although it smells somewhat like a salad oil it IS NOT to be used for cooking or salad dressing. Due to the slight exothermic property of the oil while curing (a commonplace feature of drying oils), there is a marginal risk that balled, oily rags may spontaneously combust - spread application rags out to dry. There is some evidence that people with peanut allergies may be affected by contact with Tung Oil.

Tung Oil is "Non hazardous" rated by Worksafe Australia Criteria and is able to be mailed
Pure tung has no UN hazardous goods code
Specific Gravity at 20 deg.C.    - 0.9375
Moisture & Impurities             - 0.01%
Flash Point                           - 288.90 deg. C
Auto ignition Temp.                - 457 deg. C


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ORIGINS AND INFORMATION RE-CAPS FROM www SOURCES

Tung oil comes from the seeds of several species of Aleurites, primarily Aleurites fordii, a deciduous shade tree native to China. It belongs to the Euphorbia Family (Euphorbiaceae) along with the candlenut tree (A. molucanna), another species with seeds rich in unsaturated oils. For centuries tung oil has been used for paints and waterproof coatings, and as a component of caulk and mortar. It is an ingredient in "India ink" and is commonly used for a lustrous finish on wood. Some woodworkers consider tung oil to be one of the best natural finishes for wood.

 

 

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Tung oil tree (Aleurites fordii) showing two male flowers and one female flower (left) in which the petals have fallen off exposing the pistil.

Other unsaturated plant oils, such as castor oil and linseed oil, take longer to dry and leave an oily residue until they soak into the wood surface. Tung oil's ability to dry quickly and polymerize into a tough, glossy, waterproof coating has made it especially valuable in paints, varnishes, linoleum, oilcloth and printing inks. The oil-rich seeds are produced inside a thick, woody endocarp layer and are the source of tung oil used on fine furniture.

The word Tung is an ancient Chinese term for heart. Today, the term also refers to the large, dark green, heart shaped leaves of the Tung tree. This is a fast growing, deciduous tree that reaches a height of about forty feet when mature. The life span of a Tung tree is about thirty years. Fruit bearing begins in the third year of tree growth. The Tung fruit occurs in clusters, each of which bear four or five nuts. When the nuts are dried and pressed they yield about twenty percent oil. Under favorable conditions an acre of Tung trees will produce about two tons of nuts and eight hundred pounds (one hundred gallons) of raw Tung Oil annually. Successful cultivation of Tung trees requires exact climatic conditions, including the proper ratio of warm and cool days. The major growing areas include China, Argentina, Paraguay, and parts of Africa.

The first record of Tung Oil appears in the writings of Confucius dated about 400 B.C. . Even then, the Chinese recognized the amazing qualities of Tung Oil. Throughout their history, the Chinese have used Tung Oil to waterproof the masts and sails of junks (boats), to finish furniture of royal families and according to legend, to seal the Great Wall! When Marco Polo returned from China, he brought tales of the wonderful "China Wood Oil". But Tung oil was unable to capture the attention of the West until this century.
TUNG OIL VERSUS OTHER FINISHES

In recent years, those who appreciate the warm richness of beautiful wood have begun to realize what the ancient Chinese knew; when turned into a finishing product, Tung Oil is the finest natural wood finish in existence and has yet to be duplicated synthetically!

Man's ingenuity has created many synthetic finishes, including lacquer, shellac, and varnish all of which protect wood with a hard impervious layer. But these surface finishes prevent the development of patina, the lovely depth and tone that only natural aging can produce. Eventually synthetic finishes will break down and discolor, when that happens the entire surface must be removed by labor intensive stripping and sanding before another coat is applied.

Penetrating finishes formulated with linseed, soy or paraffin oils actually go into the wood and enhance its natural beauty, but these oils often dry incompletely and fail to form a hard and durable surface. Furthermore, they develop a gummy build-up when additional coats are applied. Linseed oil, the most commonly used penetrating finish, darkens and changes color with time and finally disintegrates.

A Tung Oil finish is hard yet flexible, waterproof and impervious to alcohol and many food acids. Tung oil as a penetrating oil allows wood to continue its aging process and to develop its patina. The wood's rich color and grain are enhanced by the natural ambering (coloring) of Tung oil over time. Any sign of wear disappears when a thin "maintenance" coat of oil is rubbed in. The maintenance coats, rather than cause a build-up, actually improve the patina as they protect and preserve the wood. A floor, a piece of furniture, or any other wood object finished and maintained with Tung Oil will never have to be stripped again. The finish will become more beautiful with time.

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Updated March 2012

Click HERE to see purchase options for Tung Oil.