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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. Have a major problem, I contract clean a community centre which has 3 floors, main stadium, multi purpose rm and dance studio, I sealed all 3 floors 10 months ago using Gemini floor sealer, over polyurethane floor, have had constant problem with dance floor slippery when doing tap dance, in multi purpose when doing line dancing, floor goes powdery and sometimes slippery, the main stadium which seems to hold out, have stripped and cut back floors, have ask experts but having no luck, need to redo the floors at xmas which is the only time to do them they operate 7 days a week. any help would be most appreciated.

We don't claim to be experts on floor finishes but perhaps the Gemini floor finish is too slippery for these sorts of floors. It is intended as a polish and our impression is that the manufacturer doesn't warrant it to be a non-slip product. Perhaps the floors in question should be regarded as sports floors, given the activities that take place. In that case "Gymclean" marketed by the same manufacturer might be a more appropriate maintenance product since it is specifically claimed that it keeps floors safe from slips.

Q. We've had an Ironbark T&G floor laid on battens over an existing concrete slab fail. The floor has expanded due to slab moisture. No membrane was used as all the battens had to be graded from 20mm to 120mm (slab had fall and undulations throughout). Timber moisture content at 25!! My question is there a way to seal moisture in slab successfully as I'm concerned this will reoccur again especially during wet season? I thought an FC base layer, finished with a floating floor may be the safest solution.

We would strongly recommend a membrane directly on top of the concrete, ie. under the battens. This protects the battens as well as the flooring - if the flooring now tests at 25% there is considerable moisture present and the battens could be a risk of decay in the long term. Of course the fixings penetrate the membrane but little or no moisture escapes in this way and the system works as long as the fasteners are highly corrosion resistant. Your suggestion of a floating floor on an FC base would also work, but won't solve the problem of protecting the battens.

Q. My builder wants to use particle board class 1 flooring in the bathroom as the floor under the tiles what is your opinion please, the ncc does not have any answers.

Class 1 particleboard is an acceptable flooring material in bathrooms and other "wet areas" but there are strict guidelines as to how it is to be installed. Installation must comply with Part 3.8.1 of the Building Code of Australia (BCA) vol. 2, and Australian Standard 3740. If you happen to be building in South Australia there are additional requirements in Minister's Specification SA F1.7. If you don't have access to these documents you can refer to the design manual on the website of the Engineered Wood Products Association of Australasia (EWPAA) which is available via this link: (see page 18 onwards).





Q. Would like to buy timber looking panels for our lounge room. The timber is baltic pine and I would like to buy them in panels, possibly engineered wood, also it has to look like real wood.

We weren't sure what size or shape you have in mind for your lounge room wall panels, but it's unlikely that you could buy them off the shelf. The best approach would be to go to a joinery works and explain what you want to achieve, preferably with a sketch showing measurements. They can then discuss the options with you and prepare a quote to make the panels. They might also be able to coat the timber for you, so you should decide whether you want a lacquered finish, oil finish, etc.

Q. Hi, I have a question regarding the length of time that yellow tongue can sustain moisture. Our bathroom waterproof membrane has failed and there is evidence of water damage under the house and during the flood test the water drained at a reasonable rate through the flooring (tile, membrane and particle board) dripping within minutes. Our builder has proposed repairing the issue by grinding the face of the existing tiles and waterproofing again and laying tiles over the top . We are reluctant as we are unsure if there is any damage to the flooring substrate or whether this will put undue strain on the already compromised flooring. Are you able to provide me with some insite as to the permeability of the yellow tongue flooring, the house is four years old as I mentioned earlier we are unsure how long it has been leaking as it was only 3 months ago that it was noticed that the tiles were becoming loose and the tile grout degrading. Your assistance with this would be appreciated as I am unsure what the best direction to take with regard to repair is. Kind Regards Cassandra

Hi Cassandra,

Thank you for your question.

Moisture can have a detrimental effect on particleboard flooring (e.g. Yellow Tongue) and can cause swelling of the wood-based material and potential loss of structural performance.  There is a Technical Guide (Number 12) on the WoodSolutions website titled “Impact and Assessment of Moisture-affected Timber-framed Construction”.  In this Guide, there is a section on particleboard flooring (Section 1.2.4) describing the effect of prolonged weathering (wetting) and how this can be determined. 

You can download the guide here.

Q. We are considering putting 12mm pine lining boards on the ceilings of the home we are constructing. We have had various opinions from builders as to how they should be fixed, and would appreciate your advice. We have already had some pine lining boards put on a wall and they have buckled and the joins separated. The builder simply put two nails in the front of the boards on the noggings. With regard to the ceilings, one builder has said that secret nailing (one or two nails?) and glue on the ceiling joists will be the best way to do the job. Another builder has said he does not think this will be sufficient and recommends nails in the face of the boards as well as secret nailing and glue. Most of the joists are 600mm apart, with a few 450mm. What is the best way to proceed?

The general industry recommendation is to fix 12mm boards to the undersides of rafters or ceiling joists spaced not more than 600mm apart. Double face nailing at each rafter, or secret nailing combined with gluing, will secure the boards. There's no need to secret nail and glue as well as face nailing. For other useful advice on installing lining boards refer to Tillings "Archi-Text no. 2.3", available from their website at You can also refer to a data sheet produced by Timber Queensland, that gives guidelines for installing wall and ceiling linings. It can be found at

Q. I am an architect and would like some advice on the most appropriate filler for knots, etc for a jarrah (recycled timber) floor. The floor in question has been sanded and sealed, however some areas that have been filled are not well done (bad colour match and matt finish C.F. satin floor finish). Could you suggest a product or products that would be a suitable filler?

If there are actually knot holes in the floor (ie. the knots have fallen out) the best technique would be to fill them with plugs of jarrah. This can be done using a special plug cutter drill bit. For more info write "plug cutter drill bit" in your browser. However, if the knots are sound but have void spaces around them, we suggest a two-part epoxy, tinted to match the jarrah. This will set hard so it can be sanded. Some experimentation will be needed to get the tint right.

Q. I am after advice regarding hardwood timber floor construction over new concrete stairs. Do you know where I could source advice regarding this construction method?

There are several ways to tackle this - obviously all methods will add some height to the stair treads, so you need to think about what happens when you get to the top of the stairs. Each riser should be the same height, otherwise the stairs will feel odd under foot, and possibly dangerous if they cause someone to miss their footing. This means that ideally the upper floor and any landings should be raised by the same height as the stair treads. Perhaps that is your intention. The simplest method, and the one that adds the least height to the treads, is to direct-stick the flooring to the concrete. You will find information on the net about this if you write "direct stick flooring" in your browser. Other methods include attaching plywood to the stairs and fixing the flooring to the plywood, or battening the stairs and fixing the flooring to the battens.

Q. I am after some information about plywood for internal application. I am based in WA.

We weren't sure what specific plywood application you were inquiring about (flooring, wall lining, ceiling lining or something else). However, information is available on practically every use of plywood on the website of the Engineered Wood Products Association of Australasia (EWPAA). If you go to you will find electronic copies of all EWPAA publications.

Q. Is there a specific Janka value or Janka requirement to be used in a ballroom application for timber flooring? Is there a set standard for Janka use?

We don't know of any reference that relates Janka hardness to the end-use of a wood floor. The desired hardness depends very much on the type of foot traffic. If the ballroom dancers are likely to be wearing stiletto heels, hardness will be an important consideration to avoid indentation. If stiletto heels are unlikely, and the floor will only be used for ballroom dancing, hardness is relatively unimportant. The finish can also play a part. Some pre-finished "engineered" flooring products have an aluminium oxide finish which increases resistance to scratching and denting. On the other hand, polyurethane is resistant to scuffing and abrasion but not particularly resistant to indentation.


Did you know?

About 6% of Australia’s 147 million hectares of native forests are public forests potentially available for timber harvesting. Timber is harvested from about 1% of those public native forests each year.