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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 have a number of internal walls clad in rough cut timber stained mission brown. Is there a product that can satisfactorily bleach the stain out of the timber that will leave the timber receptive to a new lighter staining or clear finish?

We feel you have a difficult task ahead. Wood stains, whether dyes or pigments, are penetrating finishes that soak in, and Mission Brown is a particularly dark and persistent colour. Techniques that might work will be somewhat impractical indoors, for example applying deck cleaner followed by water from a high pressure hose. An added complication is the rough sawn surface which rules out sanding the wood. Techniques such as bleaching, which might work on a small area, will be very difficult to utilise over a large area without getting a patchy result. There is quite a lot of information on the net if you write "removing wood stain" in your browser. However, you will find that most sites advise the task is difficult if not impossible and we tend to agree. It might be best to just accept what's there or, if you find it really unpleasant, install new panelling over the top.

Q. I have had a client place taun timber from new guinea flooring. The decking was secret nailed and has not accepted the stain finish. Two coats have been put on it and it still seems to want more and there is a possibility of the flooring showing signs of cupping. Can you help?

We don't know of any particular problems with putting a finish on taun. However, if the flooring is cupping it might be worth checking the moisture content to see if that is causing a problem. Cupping often indicates a high moisture content. On the other hand, a high moisture content wouldn't make the wood absorb more stain - it would more likely do the opposite. Maybe it's just a very absorbent batch of timber.

Q. I would like some information on installing timber floor boards over a heated concrete slab. Are there any particular varieties that you would recommend?

The only type of flooring we are comfortable about recommending on a heated slab is laminated flooring, ie. made up in layers like plywood. This is because in laminated flooring the grain changes direction in each layer. The warmth from a heated slab is inclined to dry out the timber, but since wood only shrinks noticeably in one direction (across the grain) each layer in laminated flooring helps to restrain the adjacent one, limiting the possibility of shrinkage. The type of wood is less important than the way it's made, so we suggest you look for laminated flooring (sometimes marketed as "floating" flooring), preferably a brand that the manufacturer specifically recommends for use over a heated slab. Armourfloor, manufactured in Australia by Big River Timbers, is one such product but there are probably others.

Q. Is tasmanian myrtle laminate good for flooring in the entry/family/kitchen area?

We assume this is flooring with a Tasmanian myrtle veneer on top, rather than an imitation laminate. If it is an artificial laminate you will have to seek information from the manufacturer, but if it is a wood laminate we can tell you that myrtle is in the mid-range for hardness. It's significantly harder than most of the pines, but not as hard as some of the eucalypt woods. This means it will stand up to normal foot traffic but would show denting under stiletto heels. If the kitchen and family room are used regularly it could be useful to place mats in high wear areas such as in front of the sink, or where chairs are pulled in and out. Otherwise it seems a suitable choice.

Q. Thank you for the prompt response and valuable information. I would also like your opinion on Expol underfloor insulation in this situation as I have plenty of underfloor space. I'm also looking at Cabot's CFP water based finish to try and avoid edge bonding. I'm so glad I found this site and value your opinions and assistance.

Expol underfloor insulation looks like a suitable product although we have no personal experience of it. It's important to ensure that there is plenty of ventilation of the sub-floor space so the underside of the floor stays dry, but apart from that we don't consider any special precautions are needed. Today's water-based floor finishes are comparable with the older solvent-based formulations with regard to wearing qualities and, as you say, are much less likely to cause edge bonding. The method of application also plays a part. Try to avoid letting the finish run into the tongue and groove joint since this is where the edge bonding problem occurs.

Q. I have an old housing commission house built in around 1960 in Werribee, west of Melbourne. It's been carpeted most its life. The boards underneath have a fine grain and no knots, but colours vary board to board from very light to reddish brown. Do you have any idea what species were used in this area around that time and if they mixed species? I was planning on removing carpet and putting floating timber floor on top for acoustic reasons and warmth, but am seriously considering restoring original floors.

It's likely that floors in Melbourne from that era would be Victorian ash/Tasmanian oak, although the colour would generally be a light-brown straw colour rather than reddish brown. Victorian ash is a mixture of alpine ash and mountain ash, while Tasmanian oak is the same with messmate included. It would probably be easier to restore the original floors than to put a floating floor on top. Laying another floor over the existing one will increase its height and you may then have to cut the bottoms off doors and deal with a small step between areas. If insulation is an issue you could insulate from underneath if there is sufficient access.

Q. We are an architectural firm from Melbourne and we specified Grey Box timber lining for a stair in office building. Timber lining to stairs is fully structurally supported (by folded steel plate ). Specified treads 280mm wide by 1150mm long and 42mm thick. Specified timber is Kiln Dried. Builder claims the this particular type of timber when 42mm thick will deflect (cupping). We believe that if timber is adequately kiln dried, and especially that thick, and that sort of timber (very hard) shall not deflect. I am seeking independent advice about the issue.

If the timber is properly kiln dried to 10% to 11% we are confident it will remain stable. Kiln dried hardwood is available in 45 mm and we assume that the treads will be planed down ex 45mm. However, it is important to be sure that the moisture content of the material supplied to site meets your specification. We suggest the supervising architect or site supervisor makes some random checks with a moisture meter when the treads are delivered. If the moisture content is significantly higher than 10% to 11% there is likely to be shrinkage, particularly in an air conditioned office building, so perhaps that is what is troubling the builder.

Q. I am specifying Spotted Gum T&G end matched floor boards to replace a an existing floor on timber joists. There are options to either secret nail, face nail and even glue (Ultra Set). When is each technique required? Some suppliers have warned that a 130mm wide board is prone to move and cup much more than a 85mm wide board. Are the risks far greater?

We assume you are specifying a residential floor - end-matched boards are fine for domestic work, but not recommended for floors subject to impact loads, such as sports floors, gyms, etc. The Code for Residential Timber-framed Construction (AS 1684) advises that boards over 85mm cover width "shall be fixed with two face-nails at each joist". Wider boards are more securely fixed by face-nailing, but we don't see any need to use glue when fixing to timber joists. UltraSet is one of the adhesives recommended for direct stick to concrete. Regarding moving and cupping, wood only moves when it changes moisture content. If you are replacing an existing floor it seems likely that sub-floor conditions will be fairly stable, in which case there shouldn't be significant movement, assuming the moisture content of the wood itself is appropriate. The point about wide boards is not so much that they are more prone to movement, just that the movement is proportionally greater. For example if two 65mm boards shrink by the same amount as one 130mm board the gaps will be half the size.

Q. We are after a recommendation of timber species to be used as stair treads in a commercial building. The treads will be sheeted with vinyl.

If the treads are to be fully sheeted with vinyl and appearance is not important Medium Density Fibreboard (MDF) would probably be the most economical option. The front edges of the treads should have some kind of nosing, or a "pencil round", as a sharp edge will be inclined to chip. If you prefer solid timber, clear (knot-free) pine is available in suitable sizes from some timber merchants. There are a number of suitable hardwoods (Tas oak, merbau, etc) but it seems a bit of an overkill if the treads are to be covered.

Q. I would like some advice about moisture content. I have some recycled Tas Oak to lay in a room to match (as best as I can) some existing floor. The average moisture content is about 13%. Apparently AS2796 cites 10-14% as being OK to lay. Elsewhere I see references (and indeed interpretations of AS2796) to less than 10%. I have not seen AS2796 myself. Can you help me? This floor is a bit of a saga and I am keen to get the floor (my own home) finished as soon as possible.

Australian Standard 2796, Timber-Hardwood-Sawn and milled products, Part 1: Product specification actually states that the moisture content of strip flooring shall be not more than 14% and not less than 9%, "or as otherwise specified". The reason for the fairly wide moisture content range is that AS 2796 is a national Standard intended for use Australia-wide where the climate varies considerably. If you live in a tropical area, or a part of the country with a high rainfall (eg. Tasmania) then timber in service will have a relatively high equilibrium moisture content and 13% is probably OK. For most parts of southern Australia we would prefer to see indoor timber with a moisture content of 10% to 12%. Is it possible to spread the flooring out in the room in the hope that it will drop 1-2%? You can check the moisture content which you should be aiming for by testing some of the existing flooring.


Did you know?

A government report showed there is no evidence proving that harvesting timber from native forests has reduced overall forest biodiversity or led to the extinction of any species of plant or animal.