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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. Can you help me with a query about treated pine fascia boards. How long is an acceptable time for paint to last on treated pine without peeling. Our house is just over 3 years old and already the paint on fascia boards is peeling - this is mainly around knots in timber and areas where sap from boards is leaching.

It sounds as if the fascia boards are treated with LOSP preservative, although usually "clear" timber (knot-free material) is used for this purpose. In any case, a paint finish should certainly last more than three years. However, if a dark colour is used it sometimes absorbs heat from the sun and draws resin to the surface. One supplier of pine products recommends scraping off any accumulated resin, wiping the surface with turps or white spirit, sanding for a final clean, and then applying Zinsser BIN primer/sealer, followed by two top coats. If it is a new home this may be something the builder will attend to under your warranty. Note that we have not used or tested Zinsser products, and simply pass on one timber company's recommendation.

Q. We a have new solid timber door in a new house. Our desire is that the door goes naturally grey, is there a product that preserves the timber that still allows the timber to grey?

Cabot's have a product in the US called Bleaching Oil, but as far as we know it's not available in Australia. The nearest thing seems to be a Sikkens product called Silver Grey stain. You can read about it on the net at this location: To inquire further, contact Tenaru, the Australian distributors for Sikkens. Their website is located at this address:

Q. I'm building an overhanging bench-seat on a pond. It will be permapine. Will I have a problem with my fish because of chemicals leaching from the wood?

Fish are particularly sensitive to wood preservatives and this is one situation where we wouldn't recommend treated pine. It's probably OK if there's a relatively small volume of wood in a large expanse of water, but not for a domestic fish pond. So we suggest you consider a naturally durable timber for the bench seat, such as western red cedar, or a hardwood such as spotted gum.

Q. I have been reading your 'Timber Flooring - Design Guide for Installation' looking for answers to an issue that has arisen with the quality of finish on a cypress pine floor that has recently been installed on a project for which I was the architect. I got some useful information out of the guide but was hoping to follow up with someone who was familiar with the common issues arising with timber flooring installation and finishing. The new cypress floor has been laid (secret nailed plus adhesive) on battens on a vapour barrier over a concrete slab in the area of an extension. It matches an existing area of cypress flooring laid (surface nailed) on joists in the original house. The floor is polyurethane finished. In the area of new floor (north facing living areas with significant areas of Low e glazing) there are very noticable pale patches - typically at end to end board junctions in the areas that see most sunlight. Often the neighbouring board (not jointed at that location) is also affected. The contractor claims never to have seen this issue before. It appears as though the patches are getting lighter with time. (Floor was done in mid July). I would be grateful for any insight you can offer.

All varnishes start off as glossy. They are made satin or matt by adding "matting agents", which are finely dispersed particles that scatter light as it passes through the coating. It is possible that the contractor applied the varnish too thickly or in too many coats, and the milky appearance is caused by the matting agents. Maybe the varnish was not stirred thoroughly or often enough, and the matting agents became concentrated in the bottom of the container. The other major cause of milky or cloudy varnish is moisture, which might have had an impact if the wood was damp or the coating was applied at a time of high humidity. If this explanation doesn't seem right we suggest you talk it over with the manufacturer of the coating. Most major companies have a technical help line.

Q. I burn a lot of pine as firewood. I believe it is untreated but wish to make sure. The markings on the timber are as follows: MGP 10 seasoned ASNZS 1748 2210.10-21142 HYNE 25 pt CERTIFIED.

We consider your timber is unlikely to be preservative treated - treatment would generally add some colour to the wood (red or blue for Hyne T2, or green for Hyne T3). However, it's not recommended to burn treated timber in a domestic fireplace, so to be sure we suggest you phone Hyne on 1300 30 4963. They will be able to give you a definite answer.

Q. I'm building a timber framed house in the Perth Hills. It is on 5 acre bush block and I have come across lots of termites. Although I'm planning physical and chemical barriers I'd like the timber framing to be as termite resistant as it possibly can be. Most of the framing timber here seems to be the H2F blue pine. I have concerns about this, as I believe that it is just an envelope treatment. Would it be of any benefit to use H3 CCA treated timber for all of the framing? Are there downsides to doing this? Are different fixings required? Is there a middle ground? Are all H2 treatments equally effective? Are some pressure treated? I don't mind spending a bit more on the timber for peace of mind, I just don't want to encounter any unforeseen consequences of using H3 timber internally. We also have European House Borer here too.

Before H2F timber was introduced to the market it was tested in the field, with envelope treatments of permethrin and deltamethrin, and found to be effective against termite attack. The test program is described in a paper by Brenton Peters and James Creffield, published in the US Forest Products Journal, ref. Forest Prod. J. 54(12):9-14. Producers of H2F timber (marketed as "Blue Pine") offer a 25-year warranty against termite attack and as far as we are aware there have been no claims made to date. Therefore the timber industry is confident that H2F Blue Pine will adequately protect timber that is used south of the Tropic of Capricorn. North of the Tropic of Capricorn, termites include more voracious species and H2 treatment is required to be a pressure treatment rather than an envelope treatment. The preservative used for H2 may be the same as the one used for H2F, or it may be CCA or one of the other approved preservatives. H2 framing suitable for use north of the Tropic of Capricorn is marketed as Red Pine to distinguish it from Blue Pine, eg. Laserframe Terminator Red, Hyne T2 Red, etc. You may feel more comfortable specifying H2 Red or H3 in place of H2F (Blue Pine), although we feel Blue Pine is adequate for Perth, particularly in conjunction with barrier systems. Note that a concrete slab floor is classed as a complying termite barrier if there is 75 mm slab edge exposure and all construction joints and plumbing penetrations are protected with stainless steel mesh or similar. Obviously termite barriers do not provide protection against European House Borer, but Blue Pine is considered to be protected.

Q. A question whether gluelam portal frame is appropriate for covered spa structure 11mL x 8mW x 5.5mH with 0.875m overhang not including 4 sides eaves gutter. 1 long & 1 short elevation has glass balustrade/open above. 1 elevation has glass louvres/stud wall. 1 elevation has a store room. It is a covered structure with recessed spa but quite open. I am less concerned about the moisture with correct preservative treatment due to the 2 open elevations but it is a BAL 29 area. What manufacturer would be best to discuss moisture, cost benefit for charring vs intumescent paint (suggested by the builder/client)?

Moisture from the spa is unlikely to be a problem for the portal frames if the structure is open, since there will be a high level of ventilation. We assume water will not collect around the base of the portal. Regarding fire resistance, bushfire regulations have no impact on free-standing non-habitable structures that are 6m or more from the main building, eg. garages, carports and similar roofed structures. We consider the spa enclosure would fall within this category. If the spa enclosure is attached to the subject building, the regulations aim to prevent fire spreading from the roof of the enclosure into the roof of the building. So if the enclosure is under the main roof, its roof must meet all the requirements for the main roof. If the roof of the spa enclosure is separated from the main roof by a complying external wall, the roof timbers can either be one of the defined "bushfire-resisting timbers", or the rafters can be lined on the underside with 6mm fibre cement sheeting. If the timber portals are not made from one of the timbers listed in AS 3959 as "bushfire-resisting", a fire-retardant coating can be used to satisfy this requirement, providing test certificates can be produced to show that the coating achieves the required fire resistance and (if exposed to the weather) withstands the accelerated weathering test. The weathering requirement is waived if the timber is covered by a roof projection at 30° or greater to the vertical. For further information we refer you to Australian Standard 3959-2009.

Q. I bought a 25 year old pole house on a steep slope. We live in an area prone to termite and bushfire attack. The treated pine poles show some minor cracks due to age. Is there a product to treat the poles to extend their longevity and resistance to decay/termites, (and potentially make them more fire resistant)?

Minor cracks in treated pine don't necessarily mean there is any increased risk of decay or termite attack, assuming they were properly treated in the first place. However, it is possible to provide extra protection with boron sticks, as used for electricity poles in some States. You will find more information on the net about these products at this address: Regarding fire resistance, various intumescent paints are available and again you will find more information on the net. Just make sure the product you select is certified for weather-exposed situations.

Q. I am going to use vertical 20mm hardwood to clad the exterior of my house. I plan to allow the timber to age naturally to grey. Could you advise me, please, what noggin spacing should be used, the interior will be clad with pine shiplap, and also should the external timber be treated with a preservative.

Spacing of noggings is a maximum of 1.35m for a structural timber wall frame, which caters for walls up to 2.7m high in brick veneer construction. However, timber lining and cladding need to be fixed at closer centres, so we suggest three noggings between top and bottom plate, which provide support at 600mm spacing in a wall 2.4m high. For more detailed information we suggest you consult one of the installation guides available on the net, eg. Outdoor Structures have a comprehensive guide available via this link: Regarding a finish, this will only retard the natural greying process. In the US Cabot produce a special bleaching oil to accelerate the natural weathering process but as far as we are aware it's not available in Australia, so you have to rely on the weather to do the job. Note that full exposure to sun and rain is needed to achieve an even grey - areas under verandahs and wide eaves will weather slowly if at all.

Q. I have built an end grain jarrah cutting board! What is a recommended food safe oil that I can seal this with. Thank you for your help.

It's OK to leave the wood bare but it will eventually grey off with repeated washing. Don't put a wooden cutting board in the dishwasher or leave it soaking in the sink. If you want to keep some colour the recommended finish is food grade mineral oil. There's lots of info on the net on this topic - for example, paste this link into your browser: Some use cooking oils (olive oil etc), but there's a risk they will go rancid after a while and taint the food.


Did you know?

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