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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. Thank you for your response to my question, however I think I may have confused you...we actually want to use the same outside spotted gum decking on the inside that the outside and inside look the same (other than obvious wearing more on the outside!) What we are concerned about is the moisture content of the wood if it is inside, will that make the wood inside warp or maybe even push the silicon up and out between the planks?....and should it be laid on ply or can it go directly onto the existing floorboards ( in good shape) I'm confused about the ribs that you refer to, our spotted gum decking doesn't have ribs? The reason we wanted to use black silicon is to give the boards room for expansion and contraction and obviously cos there will be gaps that 'stuff' can fall in between and be difficult to vac up! We're not envisaging sanding either outside or inside...just coating with Cutek oil which keeps the red/brown colour and protects the wood. It's amazing that with all the people I've spoken to about this idea that it's never been done before....why is that do you think?...and what do other people do if the outside elements (rain and UV) are going to be an issue? We don't want to use fake plastic wood and all other normal inside wood will be damaged by the elements.

We did understand that you wanted to maintain indoor/outdoor continuity by using decking inside the house as well as outside. As mentioned in our previous answer, it wouldn't be a good idea to try to achieve this by running conventional floorboards outdoors, since they don't tolerate weather exposure. The reference to "ribs" relates to the fact that most decking is ribbed one side and smooth the other, but if your decking is smooth both sides you can just pick the best face to expose. Regarding your comment that you don't envisage sanding the floor inside the house, we were thinking of the long term rather than the short term. It's rare for a timber floor to last its entire life without sanding and re-sealing at some stage. If that were necessary, a sandable filler would be essential. As to why decking isn't used indoors more often, no doubt most people prefer the look of a traditional timber floor rather than the look of a boat deck. There are also some issues relating to weatherproofing the room - it's not clear how you intend to stop rain coming in under the external doors if the decking runs straight under from inside to outside. If rain is likely to come right into the area where indoors joins outdoors then moisture is likely to soak back along the decking causing it to swell. On the other hand if there is a verandah that will keep rain away your idea has a better chance of success.

Q. Could someone please tell me if there is a problem in using the exact same spotted gum decking wood in our alfresco lounge room so that the flow from outside in is the same? We thought we would use black silicon in between the gaps to keep the continuity of look from the deck to the lounge in size. The lounge is extremely open to the elements with huge double sliding doors facing North and East so the weather will affect any type of flooring, hence why we thought we'd run the decking from outside in...

It is correct that it wouldn't be a good idea to use floorboards outdoors. To maintain indoor/outdoor continuity you could use decking boards inside your house - the ribs are usually only on one side, so you could install the decking with the smooth side up. However, filling the gaps with black silicone, as used for caulking boat decks, will make it difficult to sand the floor, should you wish to later. Silicone fillers generally stay soft and smear when sanded. We suggest you try to find a caulking compound that is sandable. Marine shops should be able to advise you further.

Q. I'm trying to find someone to discuss the superior qualities of yellow tongue particleboard underlay to timber flooring versus battens.

Telephone advice is not available through this service, but if you would like to leave a more detailed question we can give you a written reply. If you particularly need to discuss the matter, a telephone advisory service is available from the Timber Merchants Association in Victoria and you can visit their website at We can say that if you are installing timber flooring over a concrete slab, plywood is the preferred underlay due to its better holding power for nails or staples. However, batten systems are equally satisfactory as long as the flooring is suitable for spanning between battens in the same way that it would span between joists. A moisture barrier on top of the slab is recommended with either system.

Q. Our client favours using 130mm hot pressed bamboo fabricated flooring over 210sqm house. All the retail outlets are pushing their product lines and we can't find any independent information on how hygroscopic this product generally is and how much it may want to move once laid. Floating floor system on 2mm foam underlay, 14mm clip and lock boards. Is there any govt dept or independent association that can give us some insight into bamboo flooring in Australia?

The Australian Timber Flooring Association (ATFA) has published a useful guide to the installation and properties of bamboo flooring with the title "ATFA Bamboo Flooring Industry Standard version 1, Feb. 2012". It can be downloaded from the net via this link: Although not strictly a wood product (bamboo is classified as a grass) it behaves like wood in many respects. For example, bamboo swells on gaining moisture and shrinks on losing moisture. However, it swells and shrinks in all directions including lengthwise, whereas wood only swells and shrinks in width and thickness, not significantly in length. It's therefore important that bamboo flooring is installed in a stable environment with an appropriate moisture content. Some suppliers nominate a suitable humidity range, eg. between 30% and 70%, while others recommend allowing bamboo flooring to "acclimatise" by being placed in the intended environment for a period of time before installation so the moisture content of the flooring can adjust if necessary. It's important that your client follows the supplier's instructions in this regard.

Q. Hi I have 2 houses which have in the past 2 years had their timber tongue and groove floors replaced as a result of the recent floods. We have removed the original floors to be able to remove damp materials and to ensure good ventilation and subfloor drainage. The floors have been replaced but now they are finding that the floors are opening up over 3 to 4 boards. I suspect that they have used a 2 pack floor sealer. Is there anything which can be done to fix this issue other than replacement of the floor boards? Appreciate any comments.

If there is a shrinkage gap between every third or fourth board, it sounds as if you are right - the floor sealer has stuck the boards together and they are shrinking in clumps instead of creating hairline gaps between all the boards. This is called "edge bonding" and you will find more information on the net if you write that in your browser. There's not a lot you can do about it. It usually means the finish has run down into the joint, creating a strong adhesive bond. Trying to separate the boards with a sawcut is very difficult to do neatly and likely to make the situation worse. Perhaps it will be possible to overlay the existing floor rather than removing it. That is sometimes less disruptive.

Q. I am looking to find somewhere to purchase some round timber posts, similar to those used for fencing. However I would like them to be untreated, so they can be used internally and this is proving problematic. I would like to get about 2m of a 75mm diameter post and also 2m of a 100mm diameter post. Otherwise, do you know where the wood gets treated so I may contact them directly?

If there are any plywood mills in your area they would be a good source of round posts. Logs are turned on a lathe to produce veneer, but there is always a small core left over since the lathe can only peel down to about 100mm diameter. Failing that, you could contact a treatment plant, as you say. However, be aware that rounds sent for treatment are a bit knobbly, ie. they are small logs that are not turned to a perfectly cylindrical shape. In NSW Koppers should be able to help.

Q. How to tell whether floorboards are suitable for sanding. We have just removed foor coverings from our passage in a 1920's weatherboard. We are not sure what type of timber has been used. The timber does not appear to be Baltic pine.

Floorboards of just about any type can be sanded and sealed. Some timbers are harder than others and therefore stand up to more wear. Baltic pine is at the softer end of the spectrum but still makes a very atractive floor when polished. Placing rugs in high traffic areas helps to provide protection from damage. If your floor is some other kind of timber perhaps the floor sanding contractor can identify it for you. However, it's not essential to know the species as long as you are happy with its appearance. You can get a rough idea of how it will look when sealed by wetting a small area.

Q. I've searched your website, but can't seem to find the answer I'm looking for. We are building a house in Victoria (Bulleen) and architect has designed a room which is 80% indoor and 20% outdoor. The flooring proposed is external decking (spotted gum/Merbau) to run across the whole room which spans both outdoor and indoor area. the indoor area will be 80% enclosed by 2 glass doors. Are there any issues using external decking timber for internal house use? (given various temperature and moisture levels.

Decking could be used indoors but there are several factors to consider. The profile is usually ribbed one side and smooth the other, and has rounded edges. Presumably you would want it laid smooth side up. The rounded edges might be a problem since there would be a small inversion where the boards meet, which could collect dirt and dust. Also the edges of decking are not tongued and grooved like floorboards, so if there is any shrinkage there would be a space between the boards which small objects might fall through, depending on the size of the gap. In summary, using decking for an internal floor is not something we would usually recommend, but there is no structural reason why it can't be done as long as the possible disadvantages are understood.

Q. I am specifying an internal timber floor to abut against a polished concrete finish for a new contemporary residential build. Do you have any technical details on how best to achieve this?

We are not aware of any specific details about abutting floors, but if the timber area is to be laid over concrete it will be necessary to provide a set-down if the timber is fixed to battens or plywood, so that the timber and concrete meet at the same level. If the timber is to be glued to the concrete there will be less difference between the two levels, depending on the thickness of the timber. More detailed information can be found in a data sheet published by Timber Queensland. It can be accessed on the net by writing TQL 18 in your browser. There is also a useful design guide available via this link: Go to Guide #9.

Q. I'm looking at using OSB board as a ceiling lining in the public toilets for a shopping centre in Sydney. Is it appropriate for this use?

Oriented Strand Board (OSB) has a fairly rough, textured surface which might be inclined to collect dust in the longer term. Perhaps you should ask for samples to be supplied so you can assess its surface qualities. If you decide to go ahead with OSB we suggest a polyurethane coating which will seal the surface and facilitate cleaning.


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.