Healthy Environment, Healthy Community, Healthy Business

Environment Protection Authority

Environmental Issues

Chemicals and pesticides

Light organic solvent preservative (LOSP)

LOSP treated timber uses a solvent such as white spirit as a carrier for insecticides and fungicides.

losp treated timber

LOSP treated timber

LOSP may include synthetic pyrethroids, imidacloprid, azoles and/or copper naphthenates.

Sometimes waxes or resins are also added to make the end product water resistant.

LOSP is applied under pressure.  Because it is not water based the timber remains dimensionally stable, i.e. doesn’t shrink, warp or expand.

Hazard level: H3

See the Hazard levels and chemical treatment types chart for more information


Moderate decay, borers and termites. Not effective against soil-borne fungi.

Typical uses


Weatherboard, fascia, pergola posts (above ground), window and door joinery, framing and decking, bargeboards, exterior cladding


Outside, above ground

Because they are ineffective against soil-borne fungi, LOSP treated timbers should not be used in the ground and cut ends should be properly sealed.


LOSP timbers may give off an odour when the solvent evaporates. They should be stored (under cover) in a well ventilated environment.

Gloves that protect from splinters should be worn during general handling of LOSP timber. If the timber is still wet from the treatment, solvent resistant gloves are recommended and an impervious work apron should also be worn.

LOSP timbers should not come into direct contact with food or drinking water.

LOSP timber should not be transported in an enclosed space with passengers.

Laminated veneer lumber (LVL) can also be treated with LOSP to H2 or H3. It is important to note installation guidance if using LVL outside when there is potential for it to be exposed to moisture.

More about safe handling.

Page last updated: 12 May 2016