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Preservative treatments & finishes

Like to know what wood to use building a pergola or framing a barn? How about the difference between tung oil and polyurethane as a floor finish? How to revive decking or deal with merbau stains? Or how to meet the building code or bushfire standards? Or ask about the environmental advantages of wood or forest certification?

Q. I have an "Ironbark" slab, polished and ready for a clear lacquer to be located outdoors in a entertainment area. Would you be able to let me know the best product to use and how best to prepare and apply.

No doubt the slab will be used to serve food and drinks, so you will need a hardwearing finish that can be wiped clean. You will also need a finish that contains a UV filter. We suggest a UV-resistant marine varnish. There are several on the market, eg. Cuprinol High Performance Marine Varnish. Even with a coating such as this it's desirable to shade the slab from direct sun. Exposure to sun will shorten the life of the coating and change the colour of the wood so if you can locate the slab under a verandah, pergola, shadecloth or other protection it will help considerably.

Q. Not sure if you can help me but it never hurts to ask. I am an artist and am interested in putting my art work on to wood. I have recently had some tree work done at my house and have pieces of a holly tree, a crab apple tree and a mulberry tree. I have the wood cut into rounds with the bark intact which I would like to keep on. I am trying to find out what I need to do to the wood to preserve/protect/treat it before I apply my artwork. I have read that it will split if it dries out without me treating it first but can not find how to go about it with these types of wood. Do I need to cut it and glue it back together or soak it in "pentacryl" or something else? Any advice would be greatly appreciated.

If the trees were dead and were standing for some time the wood will have dried out and probably won't split. However, if it is green wood from a living tree it will shrink as it dries, and in round sections a split nearly always occurs, running in to the centre. This can be prevented by a prolonged soak in polyethylene glycol (PEG). You will find more detailed information about this product if you write "wood splitting polyethylene glycol" in your browser. It can be purchased from chemical supply companies.

Q. We are using mixed hardwood timber tongue and groove flooring (character grade) to create a feature wall inside our house. We are wondering what the best product would be to seal it. We know some of the timber is Blackbutt, yellow gum and redgum. We would like to retain the natural colours of the timber so believe an oil would be best. Is this correct and should we use water based or oil based. We definitely do not want to stain the timber. Any advice would be greatly appreciated.

Oils tend to darken with age and also are inclined to collect dust. For indoor timber we generally recommend a matt or satin polyurethane. These finishes bring out the natural colour of the wood and are easy to clean. If you have any offcuts left over maybe the paint shop would coat some samples with different products so you can see how they look. Alternatively they may have some sample boards to show you.

Q. Do you have any recommended suppliers/installers for on site treatment of house frames?

You will find suppliers of boron-based products if you write "boron timber preservative" in your browser. We mentioned ProtecTimber in a previous answer. Another one is TimberSafe. These are not the only suitable products - light organic solvent preservatives such as XJ Timber Protective could also be used. XJ contains the same insecticide that is used in treating H2-F timber. However, note that different levels of treatment are required for house framing, depending on whether the site is north or south of the Tropic of Capricorn. A liberal application of the products mentioned could be considered to provide protection equivalent to the envelope treatment required south of the Tropic of Capricorn (at least for the surfaces available for treatment), but would not match the requirement north of the Tropic of Capricorn. The latter can only be achieved by pressure treatment.

Q. We are in a situation whereby a H2 frame was supposed to have been erected on a particular site and was not. The client is steadfast that they would like the frames to be treated. My question to you is, is there any way to perform the treatment with the frame erected on site?

There are products that could be brushed or sprayed on to give a similar level of protection to H2 treatment, eg. boron-based products such as ProtecTimber. The only difficulty will be applying it to concealed surfaces such as the underside of the bottom plates. Note that we don't recommend reliance on treatment alone, but believe it should be used in conjunction with a barrier system. If the frame is treated, but there are no termite barriers, the frame will be protected but the contents of the building will not. Perhaps your client would be confortable with a treatment applied on site, together with a barrier system.

Q. We have just purchased 2 hoop pine slabs and are using them for furniture; what would you suggest to seal them, we don't want to change the color; we do want a buttery beeswax finish.

We assume the slabs are seasoned and you don't need to set them aside to dry. If so, a couple of coats of matt polyurethane will seal the timber and you can then apply wax to give it nice sheen. Wax on its own is not a very durable finish. For a more detailed explanation, with which we agree, visit this website:

Q. What company uses the treatment registration number 896 64 UC 3A.

Sorry, we've not been able to trace that number. Australian Standard 1604.1-2012 includes timber preservative code numbers, but they are all in two-digit format from 01 to 90.

Q. We are currently renovating and our windows are being delivered and installed tomorrow. The timber is raw western red cedar because we decided that we didn't want to stain the timber. We would like to know what you think the best protective coating for the timber is - we would like to keep the natural timber finish but don't want to have to keep reapplying oil every couple of years because there are about 17 windows over two levels.

Frankly the best thing to do would be to paint the exterior surfaces and have a natural finish on the inside. Natural finishes need more maintenance and if some of the windows are at first-floor level, re-coating could be difficult. Some of the clear coatings with UV absorbers will last longer than oils and if there are any verandahs or wide overhangs that would help. However, we don't know of any natural finish that would last as long as acrylic paint. Also for a natural finish the glass should be installed with wooden glazing beads rather than putty, since putties generally need the protection of paint. If you still intend to go ahead with a varnish-type finish, you might want to investigate products such as Sikkens, Intergrain DWD, etc.

Q. Can you please tell me if there is any problem using copper pipe in contact with blue pine framing. Any possible chemical reaction.

Care is needed when dissimilar metals come into contact because of the potential for accelerated corrosion, but only when moisture is present. It can be an issue with copper-based preservatives such as CCA and ACQ, but Blue Pine does not contain copper. Even with CCA there would be no reaction with copper pipe since the same metals are involved. So the short answer is - no problem!

Q. I am planning to build a 1 metre high by 25 metre long retaining wall along the south boundary of my block. Would you please advise approx how long H4 CCA Treated Pine sleepers would last in ground. The wall will be in rocky dry soil, with occasional run off water. There does not appear to be water seepage along the wall. The sleepers will be slotted into Galvanised "H" beams. I have been trawling the internet, but have been unable to get this information. I would be grateful if you could assist.

The predicted life of H4 treated pine depends on local climate as well as the design of the structure. We think you will find our Design Guide #05 helpful. It's titled "Timber Service Life Design" and can be downloaded at For example, if we consider your sleepers as 200 x 75 rectangular posts in ground contact, located in decay hazard zone C (east coast of NSW), full preservative penetration gives an expected service life of 30 years. This is probably conservative given that the sleepers are only in contact with the ground on one side and it's rocky dry soil, but it will give you an indication.


Did you know?

In 2008 seventy percent of known old-growth are in nature conservation reserves.