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. We are looking after the preservation of the oldest timber church in North Queensland. The flooring consists of the original pine (I think Hoop Pine) boards. Sub floor, there is a void of around 1.5m to the ground. The subfloor ventilation is okay. The boards are cupped to some degree. The aisles are all carpeted - but the areas covered by seating are raw floorboards. We intend upon retaining this arrangement, but are looking at trying to tidy up the presentation of the floorboards. We thought that it would be good to leave as they are, renail to pull the boards hard against the joists, and also fix up or replace any broken boards, give it all a light sand and apply "tung oil" as a protective coating. The boards are cupped, so the sanding cannot be deep.

We thought your approach was fine, but would just add a couple of comments. Although you feel the subfloor ventilation is okay the fact that the boards have cupped suggests it's not totally effective. North Queensland can be pretty damp and you might want to check the ventilation against the requirements of the Building Code of Australia (BCA). Table sets out current requirements. We also point out that tung oil is not particularly hardwearing. Some manufacturers recommend regular maintenance with a floor polish to provide a wearing surface. If the floor is unlikely to be maintained with a polish it might be better to consider polyurethane which doesn't need any maintenance.

Q. I bought a house with blackbutt and forest red gum floor boards. One small section the floor boards have become "wavey" and I want to contact a specialist. Can you please recommend someone for me to contact to come to Bilambil Heights just near Tweed Heads?

Sounds as if the floor was OK when you bought the house but the problem has developed since. Perhaps there is an area where moisture has built up under the floor for some reason. To arrange an inspection you could contact Forests NSW. If you go to their website at and click on the tab that says "business services" you will find a link to their Timber Inspection Service. The Australian Timber Flooring Association (ATFA) also has qualified inspectors available. If you visit their website at you will see there is a tab that says "Request a timber floor inspection". When you click on that it will give you a list of the nearest inspectors.

Q. After installing structural plywood floor directly on timber joists complying to standards, we need to finish the floor by T&G timber floor boards strips Questions. 1. Is it possible to install them any direction regardless the floor joist directions? 2. Are there any written documents or details for this?

If the Structural Grade plywood is an adequate floor in itself, then the timber is just a decorative overlay and can be laid any way you like. The Engineered Wood Products Association of Australasia (EWPAA) has a plywood flooring manual which will confirm whether you have used the right grade and thickness for your joist spacing. You can download the manual via this link:

Q. Further to my question about wooden basins and baths, I am looking at the Francoceccotti range in Italy - here is the link: It seems the basins and bath are just larch.

Quite right, the Francoceccotti range looks as if it’s made out of wood. However, we still prefer the Rapsel approach of having the wood look, combined with the practicality of a stainless steel bowl. Part of your original question was asking whether there were any Australian woods we would recommend, and we didn’t address that point. The answer is that there are a few specialty timbers that would be similar to larch (dimensionally stable and non-staining), for example celery-top pine and huon pine from Tasmania.

Q. There is a European company making baths and hand basins from Larch and I am wondering if there is a timber in Australia that could be used for the same purpose.

Maybe you are looking at the Rapsel range marketed in Italy. However, our understanding is that the actual handbasins are stainless steel, set in wood. The description on the Rapsel website is as follows: LAVABO realizzato con doghe di Larice massello, con vasca in acciaio inox. This translates as "handbasin with slats of solid larch with stainless steel tank". While we like to see innovative uses of wood we feel that wooden baths and handbasins would not give good service in the long term. It's true that hot tubs are made from western red cedar, and it's possible to obtain bathtubs made in a similar style, but we have reservations about their suitability for daily use in an indoor setting.

Q. I was looking for advice on concealing (or minimising the impact of) a 10-12mm expansion gap in the middle of an open plan area (blackbutt flooring). I noticed in an answer to a similar question you mentioned having an information sheet about some of the options available. Would it be possible to have it emailed out to the above address?

It's difficult to conceal a 10mm expansion gap in the middle of an open-plan floor - sometimes it's better to make a design feature of it, hence the strategy of using a polished brass strip favoured by some architects. We will email you the brochure that shows some of the alternatives, as requested.

Q. I want to build a sprung wooden floor over an existing concrete floor. Do you have specifications/design information on how to do this.

Harlequin Australasia offer sprung floor systems which can be installed as floating floors, over existing floors. You can phone them on (02) 9869 4566 or visit their website at It's also possible to build a sprung floor from scratch, either by using resilient pads or by installing a double system of battens to give extra flexibility. We will email you a specification for building a sprung floor to show you what is involved.

Q. Damaged spotted gum T & G floor - client had a T& G floor overlaid on yellow tongue particle board floor. This would be approx 450mm above ground on a timber subfloor system. Originally laid approx 2007 then in 2011 Toowoomba had floods and at this time no water went over the floor, but the floor cupped and buckled up leaving 2 boards approx 50mm high. The client left the floor to see if it would shrink and go back to normal. Weight was placed on top. There is a floor to ceiling built-in cabinetry running the length of the room parallel to the boards as well. The client doesn’t have grounds for insurance (apparently). I was contacted in November to rectify. I came up with a solution of cutting a board and sacrificing it then replacing it and screwing through the particle board from underneath then having a cork strip for expansion along one edge of the new replaced board. I haven’t yet checked to see if there is still correct clearance between the floor and the bottom plate, however I will check before I proceed. What would you presume would occur in the future noting the floor would no longer act as a full diaphragm and move as one. Also after further research from Timber Queensland moisture could be still under the floor between the 2 surfaces as they are unable to be dried by air.

It's just over two years since the 2011 Toowoomba floods so assuming the property hasn't been affected again by recent floods one would expect the floor to have dried significantly. However, the advice from Timber Queensland is quite right - it takes much longer for a floor to dry if moisture is trapped between two layers. If you have access to a moisture meter, that will tell you whether the floor still contains excess moisture. Regarding the effect of cutting through the floor to rectify the "peaked" area, this will depend on the thickness of the T & G flooring. If it is relatively thin overlay flooring that relies on the particleboard for support you may need to reinforce the area under the sawcuts by installing nogging. However, if the flooring is of a thickness that could span between joists without the particleboard underlay, the effect will be less significant. On the other hand if the tongue and groove has been destroyed, nogging under the affected area may still be a good idea.

Q. Please could you advise whether it is possible to use OSB under mosaic parquet for a dance floor. Usually double plywood crosslaid with rubbers to provide the 'flex' are used but we are wondering if OSB may be used similarly.

As far as we are aware there is no Australian Standard that provides for the structural use of Oriented-Strand Board (OSB). However, it is certainly used for structural flooring and roof decking in Europe and North America, and European Standard EN 13986 defines the properties required for such uses. In Australia Hyne Timber market OSB for wall bracing and may be able to give you some guidance as to its suitability for a dance floor. You can find out more via this link - It's also possible that the Engineered Wood Products Association of Australasia (EWPAA) might be able to help. They have a website at where you will find contact details.

Q. Re: Installations to slabs by direct adhesive fix 1: preferred installation recommends a poly sheet over the slab with boards fixed over this. Q: How are the floor boards held in place with this method? 2: Slab moisture content. Q: What is the optimum moisture content of the slab if the poly sheet is not used.

Polyethylene sheet can only be laid over the slab if the flooring is installed on a plywood base or on battens. The polyethylene barrier is placed under the plywood or battens - it's not possible to glue timber flooring to a polyethylene moisture barrier. However, there are several liquid moisture barriers on the market that can be applied to concrete prior to installing timber flooring. Regarding slab moisture content, this is a complex topic and there are various ways of testing a slab. A detailed summary of the various tests is provided in a data sheet published by Cement Concrete & Aggregates Australia (CCAA), available on the net via this link The general recommendation is that the slab should not have a moisture content higher than 5.5% For example, Boral make the following recommendation for the installation of their flooring: "A concrete subfloor should be moisture tested in accordance with AS1884-1985 to ensure the concrete subfloor has a moisture content (MC) of less than 5.5%. If MC is greater than 5.5%, a moisture seal must be applied as per the manufacturer’s recommendations." Note, however, the limitations of relying on a moisture content test, as explained in the CCAA data sheet. A humidity test may give a more reliable indication of how much moisture is present.


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%.