Ask an Expert

Ask an Expert

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. We would like to use timber cladding on the top floor of a two storey house. We don't want to have to stain or oil it every year or two due to the cost and inconvenience involved (mostly cost!). We also don't like the pale grey/weathered look. Not a good combination I know. Some neighbours have used Western Red Cedar, which doesn't appear to have greyed much despite their not having oiled or stained it. We are in a bushfire prone area and so need to use bushfire-resisting timber. Any suggestions?

Western red cedar will turn grey in the same way as any other wood when exposed to the weather, but maybe your neighbours have wide eaves overhangs or are in a sheltered location where their cladding is protected. Or maybe it's still fairly new - the greying process takes a while. Cedar is not classed as a bushfire-resisting timber, but can be installed over a fire rated wall. This technique is shown in our bushfire design manual, available as a download from Click on the tab that says "Resources/Events" and then select Technical Design Guides. You are wise to think about maintenance if you don't like the weathered look. Actually, the most practical finish is acrylic paint as it lasts for many years before recoating is needed. If you don't want to paint the timber, an exterior pigmented wood stain is the next most practical in terms of life-span. As you say, clear oils need to be applied every couple of years, depending on exposure.

Q. Can you recommend a penetrating clear sealer for spotted gum exterior cladding? Would it be the same product if new timber or recycled timber?

We assume your cladding will be fully exposed to the weather, not under a verandah or pergola where it would be protected. In exposed situations oils are easier to maintain as they simply erode away, rather than peeling like a varnish. On the other hand they have a shorter life, so it's a trade-off between doing an easier job more often (oiling) or a more difficult job less often (varnishing). We suggest you try decking oil - it will be equally successful on recycled timber as on new timber, so long as the recycled timber is clean.

Q. Can a can of water based pine coloured timber stain be tinted to a darker colour....say Jarrah?

You could purchase a darker water-based stain and mix it with the one you've got to achieve a darker colour, but of course this would increase the total quantity of stain. Wood stains are produced from a limited number of base colours, to which various tints are added in-store. So if you don't want to end up with a larger quantity, and just want to darken what you've got, the best approach would be to go back to where you bought the stain and ask if they can add a darker tint.

Q. The table would be under a typical translucent shelter over a wooden deck, and whilst this would protect it from rain per se, it would be open to the wind and on those really stormy days the rain kind of swirls and goes vertical so there is that level of exposure. That said, using an oil seems to be the best solution. Would I need to re-apply a coat of oil every 6 months, a year to maintain protection? Is a typical outdoor decking oil the best option?

With that level of protection from rain, outdoor furniture oil or decking oil should last longer than six months but you can be guided by appearance. When the wood starts to look "hungry" it's probably time for another coat of oil. A simple test is to splash some water on the setting. If it beads up, the oil is still doing its job. If it soaks into the wood then the oil has lost its water repellent qualities.

Q. Regarding applying oil to mango wood, would a water resistant varnish (after applying oil) in any way help protect it from general moisture?

It's a bit of an overkill to apply oil and varnish - we suggest one or the other. Exterior varnish forms a skin over the wood and therefore excludes moisture very effectively. However, varnishes fail by peeling whereas oils just gradually erode away and are therefore easier to maintain. If you decide to use an exterior varnish make sure it's one that contains UV absorbers, and keep it well maintained before it starts to break down and peel. But if the setting is kept out of the rain, moisture won't be a problem.

Q. I have queries regarding suppliers for fire-retardant coatings to existing joinery in a class 5 building - these are heritage panels.

Presumably you are looking for a clear fire retardant coating, rather than a fire retardant paint. Prudential Coatings have a clear product for interior timber, and you can find out more via this link - You will need to confirm whether it is suitable for applying over an existing coating or whether it is only intended for application to raw timber.

Q. We are building a new kitchen and would like a matt black stained veneer with a very consistent finish and just a slight hint of woodgrain. Which type of wood veneer do you think would be most suitable?

Softwoods (pine, spruce, etc) have much more pronounced growth rings than hardwoods. Although you just want a hint of woodgrain, there's a possibility that black stain would completely obliterate the grain of a hardwood. On the other hand, perhaps a softwood has more grain than you want. The best way to resolve this is to ask your kitchen supplier to stain up some samples for you. Failing that, a specialist supplier of timber finishes should be able to show you some samples. Don't rely on colour cards - you will need to see actual samples of stained veneer.

Q. We have just had our floors sanded in a water based sealer/finish in satin. Prior to this our floors looked a really dark kind of mahogany colour with some lighter planks. Since having them sanded they have come up REALLY light and it now transpires that the wood is grey ironbark. Is there anything I can do to make them darker other than sand them right back, stain and start again!

We suggest you look into the idea of applying a coat of tinted varnish to the floor. This will be much easier than sanding back to bare wood and starting again. You will need to be sure that the colour effect is satisfactory, and that it can be applied without leaving streaks or lap marks. Perhaps the contractor who sanded and sealed your floor could advise you further. You should ask for some test panels to look at, rather than experimenting on your floor. The other option, of course, is to accept the lighter colour if that is the natural colour of the wood.

Q. I have new raw timber bench tops in my laundry and need to waterproof all of the surfaces. Can you recommend a product that is less toxic than those otherwise available?

We suggest a floor finish for best results. The hardest coatings are solvent-based and therefore contain volatile organic compounds (VOC's). Emission of VOC's ceases when the coating has cured but they may persist in the air for a time, depending on the level of ventilation. If you would prefer to use a water-based coating, products are now available with a level of wear resistance similar to solvent-based coatings but make sure you use one that is recommended for floors. It's important to seal all surfaces that will be exposed to water, including edges.


Did you know?

Australia’s native forests, timber plantations and wood products are net absorbers of greenhouse gases, sequestering 56.5 million tonnes of carbon dioxide in 2005, reducing Australia’s total greenhouse gas emissions by nearly 10%.