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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. I have had a floor of American Oak installed over an existing hardwood floor. I think it was glued in place. The boards are solid timber 14mm thick, tongue and grooved. The house was re-stumped prior to installation of the boards. The floor has been sanded and estapolled. After about 6 months gaps have been opening up between the boards at random. These gaps are less than a millimetre. Is this a problem with the timber itself or has the installation been incorrectly handled? We have had a number of trades on site and someone has done some filling of the gaps, these gaps have opened up more since they were first filled. Your advice on managing this situation would be appreciated.

We wondered if the contractor checked the moisture content of the flooring before he started laying it. In this case there was a good opportunity to check the existing flooring and then check the moisture content of the new flooring, and see if they matched. If the moisture content of the new flooring was higher than that of the old flooring, then the new flooring should have been left to lose its excess moisture until it was "acclimatised". Clearly the American oak has shrunk after installation, and wood only shrinks when it loses moisture. Since the oak is now glued in place it would seem that the only strategy is to wait until it has finished shrinking and then fill the gaps, re-sand and re-finish.

Q. Hi, I am having someone installing the timber floor for my new house. I used ironbark for the floor, the dimensions are 130mm x 14mm, selected grade. During installing the timber, I noticed cracks of the tongue on all sites of the nails, which are used to fix the timber to the floor. It is secret nail. Are the cracks normal for the timber? Will this affect the floor in the future? Thank you very much for your kindly consideration. Looking forward to hearing from you.

It sounds as if the contractor is using a pneumatic nailer. The problem doesn't arise if the boards are pre-drilled and hand-nailed, but it's a much slower job and no doubt more expensive. If all the tongues are splitting the contractor needs to stop and work out a solution to the problem, otherwise the boards won't be tight onto the substrate. A few split tongues don't matter, but you don't want them all to split. Things to try are: changing the angle of the nailer, changing the pressure, trying staples instead of nails or, failing all that, talking to the manufacturer of the nailer.

Q. I am looking for some technical detail/information on “floor squeaks/noises” on a timber floor. EG, floor joists, timber floor (highset) construction. If you could please send me some info it will be greatly appreciated.

We assume you are talking about floorboards, rather than sheet flooring such as particleboard or plywood. There are two main reasons why timber floors squeak: the tongue and groove may not be a tight fit, allowing the edges of the boards to rub together when walked upon, or the nails may have worked loose and the boards are rubbing against the nails. You can check whether the tongue and groove connection is loose by locating the squeak and seeing if one board can be moved relative to its neighbour. If so, one way to fix it is to carefully skew-nail the two boards together. This might be best done by a carpenter if you are not particularly handy. Alternatively, if access is available from below, the offending boards can be cleated together so they no longer move independently. If the nails have worked loose, and the boards are no longer held down tightly onto the joists, simply punching the existing nails further in may alleviate the problem. A more permanent solution is to screw down boards where nails are loose. We don't recommend trying talc powder or other lubricants - although recommended on some websites the effect tends to be temporary and the squeaks return.

Q. We have purchased Am Oak solid flooring 195x19 mm and require the technical requirements on how to lay the flooring. Such as how long should we wait for the timber to climatise, what type of nails are recommended to use, the type of glue recommended etc Am Oak solid flooring 195x19 mm.

The period of acclimatisation is somewhat elastic since it depends on the initial moisture content of the timber and the rate of drying. In fact acclimatisation might not be necessary if the timber is already at a suitable moisture content, This can be checked with a moisture meter. The installation of direct stick flooring is too lengthy a subject to detail here, but you will find guidelines in our Technical Design Guide #09 which can be downloaded at this location: Direct-stick flooring is covered in Section 4.4.

Q. A general question regarding direction of strip flooring: If laying a solid strip timber floor over a ply membrane substrate over a slab we would have a choice of flooring direction. If we also have a series of minimal threshold door openings (multi-fold or sliders) along one side it then begs the question whether it is better to orient the boards so that long sides are parallel to the point of possible moisture ingress to minimise exposure of end-grain, or to lay the boards transverse so that the natural board expansion/movement wouldn't occur at thresholds? Any feedback appreciated.

If there is a possibility of moisture ingress (rain?) entering over the threshold, that could cause problems whichever way the flooring is oriented. It would be better in theory to run the boards parallel to the threshold, so moisture isn't absorbed into the end-grain, causing "tenting" of the boards, but water could still get under the floor which would also cause problems. So we would strongly recommend some strategy to prevent the entry of moisture in the first place.

Q. I'm interested in purchasing some pre-finished engineered flooring (DIY project), but continue to be frustrated by the various retailers who, as one would expect, claim that their particular product is the best. What I really need is an unbiased recommendation as to what brand/s of engineered flooring have proven to be or are regarded as good quality products. Have looked at brands such as Quick Step, Embelton and Boral to name few and all claim to be high quality, but just need an independent perspective. Hope you can help. Maybe engineered flooring is not the way to go. Your view on this would also be appreciated.

It can be difficult to sort out the facts from the hype and it's difficult for us to recommend one brand over another given that we haven't actually tested any. One approach is to check where the flooring is made. We generally have confidence in the Australian-made products (Boral, Big River, etc.) Another useful test is to see whether any suppliers can direct you to a showroom where the flooring has been down for a while or, better still, a public building (shop, cafe, etc) where you can see how it stands up to wear and tear. You can also compare the thickness of the face veneer - this varies, and the thicker the better. If it is quite thin it limits the possibility of sanding and re-sealing at a later stage. Also not all products are the same type of timber all the way through. In general we consider that engineered flooring is a good product from a technical point of view as it is made like plywood with the grain direction alternating in each layer. This tends to enhance dimensional stability so it has less tendency to swell and shrink than "solid" timber.

Q. Are you confirming that 1 nail/staple (fixed via a secret nailing gun) per 80mm board would suffice without glue? - (my joists are at 450mm centres). - The floorboards have a secret nail profile but I cannot find a secret nailing gun with staples longer than 50mm - do you think this would be adequate? I have read that due to the joists being softwood 65mm nails/staples are recommended. Thank you once again for your opinion.

In our previous answer we were only talking about nails. If you are going to use staples, 50 x 15 gauge is considered OK but staples need to be used with adhesive, ie. a continuous bead of approximately 6mm of polyurethane flooring adhesive applied to the top edge of the joist. This is covered on page 25 of our Technical Design Guide no. 9, available for download via this link:

Q. We have specified 19mm marine ply (2400x1200mm) to be fixed to the underside of purlins (purlins spaced at 1200 centres). The contractor has concerns that the marine ply will sag and has recommended an additional top hat framing at 400mm centres. Can you advise if there will be a deflection in the plywood?

We consider that 19mm Marine Grade plywood will be quite OK fixed to purlins spaced at 1200mm centres. In fact the Engineered Wood Products Association of Australasia (EWPAA) recommends 12mm plywood for ceiling lining supported at 1200mm centres, as long as the face grain runs across the span, ie. at 90° to the purlins. Refer Table 6 in the EWPAA design guide available at this address:

Q. Which is the best way to fix 19mm x 80mm jarrah floorboards, onto new 90 x 45 treated pine joists? * 1 x Secret nail per joist and glue * 2 x top nail 65mm x 2.8 galvanised bullet head nails Which is stronger? Would 2 nail holes per board over the whole floor take the look off the finished job Any advice would be appreciated.

Secret nailing with 65 x 2.8mm nails is quite OK for boards up to 85mm in width. We don't see a need for glue as long as the nailing is competently done. These days flooring nailers give the best results as they drive the nails at the correct angle. With a machine nailer, 65 x 2.5mm nails are recommended. For best results the boards should be a secret nail profile, ie. with the tongue and groove offset slightly. Top nailing is an alternative option and once the nail holes are filled they aren't obtrusive, but you can certainly see where they are.

Q. We are looking to install a vaulted ceiling in an apartment. It would be lined with timber boards with a clear finish and I was enquiring as to what timber would be best suited to a project such as this. Also, would the timber need to be fitted as tongue and groove or would there be a more effective alternate method?

A wide range of different timbers can be used for linings and it would be best to contact a timber merchant to see what is available in your area. It's a good idea to look at some samples since different timbers vary in colour and grain pattern. Interior linings are marketed under names such as "matchboard", "v-joint lining", "v-joint panelling", etc. The term "v-joint" refers to the tongue and groove joint where the boards meet with a small "v", although other joint designs are available.


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.