TWA Heavy Oil Preservative

APVMA Registered Product No: 60813


TWA HEAVY OIL PRESERVATIVE is a general purpose oil based timber preservative for exterior out of ground contact applications. It is an excellent treatment against fungal decay and is most suited for use for untreated hardwoods in applications like decks, fences, landscaping,
wharves, bridges and other engineering structures.


The non volatile oil base carrying the copper naphthenate penetrates by creeping into checks and cracks in the timber surface. The copper component bonds to the cellulose structure of the timber and the oils dry on exposure to sunlight and air. The end result is that the product gives the
timber resistance to weathering and protection against biological degrade.


Paints and Stains

Painting over HOP is generally not recommended, it often leaves a very oily and water repellent surface. If painting is necessary allow at least 6 weeks
drying. The surface should be dry and free of any oiliness. Use only oil based primers and paints and avoid light colours as they may be discoloured by the copper naphthenate.

Fasteners and Metals

HOP Is not corrosive to any common metals. In all cases for exterior timber work galvanised nails and plates are recommended.

Appearance: Dark green liquid (black In bulk)
Density: 0.95kg/litre
Viscosity: >1 00cP at 20°C
Odour: Oily
Flash Point: >180°C



HOP can be applied by brush roller or spray. For exterior applications two coats are generally recommended with particular attention to endgrain
joints and interfaces (also see IN-GROUND PASTE). Clean up with mineral turpentine.

Surface Preparation

New timber should be reasonably well weathered before application. This is particularly important with naturally oily timbers such as Tallow Wood
and Jarrah. Dressed timbers, when new, should be allowed to weather for a few weeks prior to application. Thinning the product with mineral spirits or kerosene may also improve absorption and drying speed in these cases. For old timbers and remedial treatments it is essential that any decayed and weathered wood or old paint be removed prior to application.


Apply moderately as excess product will not absorb readily in most timbers.
Coverage will be generally 6-8 square metres per litre.

After Treatment

Timber coated with HP will Initially be a strong dark green colour. With hardwoods this colour will change to rich variable brown tones, particularly when exposed to strong sunlight. This is due to a reaction of the preservative with hemicellulose which is usually abundant in hardwoods.
Softwoods, with their lower hemicellulose content, tend to remain an olive green colour which may weather eventually to light brown. Colour
development is dependent on the type of timber and will be much less pronounced on heavily weathered surfaces. Drying time may vary
considerably with the moisture content of the timber and local drying conditions. With dry timber and fine warm weather drying will take 2-3 days. This may be considerably longer for the second coat or with unseasoned timber or in cool weather. If possible wait at least one week before applying additional coats. Absorption and performance of the product will generally be better on rough sawn rather than dressed timbers.


Generally the product should be reapplied after 2-3 years. This may be shorter or longer depending on the severity of local conditions. The
preservative value of the product will persist long after much of the original colour has apparently weathered away. As the treatment is a penetrating
oil type, re-application is easy as the new coat can go directly over the old without additional preparation.



Copper naphthenate is well recognised as a safe and effective timber preservative. For personal hygiene, it is recommended that the following
precautions be taken. A Safety Data Sheet (SDS) is available on request for further Information.

Handling the Product

Oil resistant gloves should be worn when using
the product. Excessive contact with the product
can cause dryness and mild irritation to the skin.
Similarly eye protection should be used when
working overhead or with spray guns. Wash hands
with soap and water after use.

Environmental Considerations

Avoid contamination of waterways and sewers as
the product will form an oil pollution hazard.


Store in the closed container in a secure place out
of reach of children.


Exempt from dangerous goods classification.


  • 2 litre can
  • 4 litre can
  • 20 litre drum
  • 200 litre drum (on request)


Preschem provides free technical advisory service on all aspects of timber preservation including the use of this product. Call us Toll Free now on 1800 641 711.

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