Ask an Expert

Ask an Expert

Interior timber & flooring

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'm an architect in Sydney, working on a couple of house projects with plywood ceilings and exposed visible timber structure. I'd like to get information on specifying the visible timber and finishing the timber and plywood. I have the Wood Solutions Design Guides, but they don't seem to have this information. Please advise.

Generally speaking, reference to Australian Standards defines matters such as quality, grade, moisture content etc. However, some Standards require the specifier to make a selection from a range of options within the Standard. For example, an Australian Standard might describe four possible grades of timber from which the specifier must select one. It's also necessary to decide on the type of timber for the exposed members before specifying an Australian Standard. For example there is a Standard for glue-laminated timber, and another for structural timber, and another for non-structural joinery timber. There is also a separate suite of Standards for softwoods as opposed to hardwoods. We weren't sure whether your reference to "exposed visible timber structure" was indoors or outdoors. Either way, much of the information you need is covered in the 68-page Wood Solutions Design Guide 14 "Timber in Internal Design" which can be downloaded from If you need more specific advice, feel free to leave another message.

Q. What causes floorboards to delaminate?

We need a little more information to answer your question. "Solid" floorboards don't delaminate, unless you are referring to the grain lifting, so we assume your floorboards are some kind of engineered flooring, or a floating floor. These floors are made up of layers of wood glued together like plywood. They might delaminate if the product was wet for a prolonged period, or if the adhesive was faulty. If this doesn't answer your question, feel free to leave another more detailed message.

Q. I'm an architect designing an amenities and shower block for a victorian beach environment. We specified marine ply for our internal linings - this forms the internal walls of the shower enclosures as well as general internal partitions. Could we use external grade ply in lieu of marine ply?

Marine Grade plywood manufactured to Australian Standard 2272 is a very high quality material with characteristics specifically suited to boatbuilding, eg. the ability to resist pounding waves. Many people are surprised to learn that it is not necessarily highly resistant to wood rot. A commonly used species for Marine Grade plywood is plantation-grown hoop pine, a species of low durability but one that has the strength and impact resistance required by AS 2272. Hoop pine plywood is suitable for boats that are taken out of the water and stored under cover after use, such as speedboats, racing dinghies, etc. but needs preservative treatment if used in situations where there is prolonged contact with water. This is explained on the Austral Plywood website at Consequently we would be cautious about using Marine Grade plywood for linings in the shower block that are frequently exposed to water. Even with the choice of a durable species and/or preservative treatment, plywood is unlikely to stand up to long term exposure in the actual shower enclosure. For general partitions elsewhere in the shower block, however, plywood is quite suitable but in lieu of Marine Grade plywood which is relatively expensive we suggest plywood designed for exterior cladding, eg. Carter Holt Harvey's "Shadowclad".

Q. We have unpainted cypress internal walls and have various marks including grease marks from dog resting against walls. Am wondering how we can give these walls a good clean without doing harm to the timber eg causing timber surface to become slightly 'furry', for want of a better description!!

When you say the walls are "unpainted" we assume they are bare wood, not sealed with a varnish. If they are varnished, wiping down with any household cleaner and a damp cloth should do the trick. However, if they are bare wood it's a bit more difficult because stains will tend to penetrate into the wood. Wood cleaners that are marketed for cleaning outdoor decks need to be hosed down afterwards, which is hardly practical indoors! However, you could try one of the products in the Wood Master range. You will find more information on the net via this link - And once you have the walls cleaned to your satisfaction we strongly recommend sealing them with satin polyurethane to provide a surface that can be easily cleaned in future.

Q. I want to lay a wooden floor on top of our yellow tongue flooring and want a pale (whitish coloured) hardwood. What wood would you suggest? Is Victorian Ash a suitable wood in colour? Should we lay fibro down first, or just sand the yellow tongue back to smooth?

Many of our Australian hardwoods are reddish brown in colour, so Victorian ash would be a good choice if you prefer a pale straw-coloured hardwood. It's not essential to put fibro over your yellow tongue. For more detail there's an informative Technical Data Sheet produced by Timber Queensland that outlines the procedure for installing a new timber floor over an existing floor. There is too much detail to reproduce here, but you can access the data sheet via this link -

Q. About to lay T 6 G 130 x 19 mm Blackbutt flooring over existing particle board floor. Using a simple moisture meter i am getting 11-13% moisture across the particle board. We were going to fully trowel glue and secret nail. Standard advice is to top nail. What if we fully trowel glue, secret nailed but top nailed but not necessarily at 450 centres...perhaps at 900?

Timber Queensland has produced an informative Technical Data Sheet outlining the procedure for installing a new timber floor over an existing floor. There is too much detail to reproduce here, but you can access the data sheet via this link -

Q. We are laying a spotted gum floor onto an existing pine floor and finishing with Tung Oil. I would like to know how soon after laying the floor (glue and nail) we need to wait before finishing with the oil? I was advised that the glue needs to dry or cure for a week - is this the case? I am very short on time!

Your best source of information about the curing time of the glue is the manufacturer, since the time varies according to the type of glue. Some adhesives are solvent-based, some contain water, and some are moisture-cured, ie. they contain no moisture but set and cure in the presence of ambient humidity. Adhesives that don't contain water are preferred for gluing flooring. We are not sure why an adhesive would take a week to cure - that seems an exceptionally long time. In our experience most adhesives will be fully cured in 24 hours, although the actual time can vary from 6 to 36 hours. If it takes a week we would feel there's something wrong, but we emphasise you should check with the manufacturer.

Q. We are carrying out repairs to a property that was flooded in March this year. Could you advise us please what the moisture level reading should be for the internal framing, before we begin to re-sheet the walls.

For best results the moisture content of the timber framing should be around 15%. If it's much higher than that there is a risk of shrinkage and possibly some distortion as drying continues. If the building has been well ventilated during the last six months and drying conditions have been favourable we would expect it to be close to the mark by now.

Q. In relation to placing timber floorboards (floating timber floors) onto concrete slabs. What are the requirements for residential apartments? Is there any underlay etc placed on the concrete slab? What requirement does the concrete floor need to be for application (ie within a certain tolerance -/+ 6mm etc). Or just as long as it flat, if so does this need to be requested prior to pouring concrete?

Industry recommendations are that where the slab is greater than ± 2-3 mm out of level over any 1500 mm length, a concrete topping (levelling compound), grinding or packing should be used. Slabs on ground should be constructed with a continuous under-slab vapour barrier (e.g. 0.2 mm thick polyethylene), and most suppliers recommend a vapour barrier on top of the slab as well. The flooring should not be installed until the concrete slab has a moisture content less than 5½% (generally achieved after slabs have cured for approximately 4-6 months). We assume your flooring is to be installed at ground floor level. If the floor is an upper storey floor with a different occupancy below, certain sound transmission limits apply. You will find some helpful guide documents on the net, eg. at

Q. My four year old boral timber floor is splitting before my eyes... I can hear it splitting. I have the type that is suitable for a concrete slab and now it's splitting along the joins however it is causing it to splinter along the edges and even appears to be lifting - a massive issue is my house is up for sale! What do I do ??

It sounds as if your floor boards are shrinking, which is odd so long after installation. Perhaps your home heating was running at higher than usual levels through winter. Usually problems, if there are any, show up in the first six months or so. The splitting might have been caused by the edges of the boards being stuck together and then trying to shrink. Polyurethane coatings have a very strong adhesive effect if they run down into the tongue and groove joint - the glue bond can be stronger than the wood, with the result that the edges tear away. You will find more information on the net if you write "timber floors edge bonding" in your browser. What to do about it is a more difficult issue. I guess your first stop would be the builder or installer to see if they are prepared to have a look and perhaps accept some responsibility if it turns out that edge bonding is a factor.


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%.