Interior timber & flooring

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Question: I have some bamboo flooring which has been flooded & has water/mould stains at the joins. Oxalic acid appears to have an effect, I am now seeking an expert contractor or timber chemist to advise/undertake the restoration. Can you please assist?

Answer: Oxalic acid usually removes mould and other stains. The coating might need to be sanded off if mould has progressed under the coating, to allow the oxalic acid to come into contact with the wood. You should be able to tell whether this is necessary. If the floor has cupped after taking up water we suggest waiting for it to dry before sanding. It is likely to flatten out to some extent as it dries. I'm afraid we don't have the names of contractors who can restore the floor, but just make sure you engage someone who has the relevant licence that applies in your State. It would also give you some confidence if the contractor is a member of the Australian Timber Flooring Association (ATFA), and has completed some of their courses. Alternatively, recommendations from previous clients are always reassuring.


Question: Small black spots have appeared on freshly laid Jarrah floors boards after oil dried; how do I remove them? Sanding has not helped.

Answer: Black spots are nearly always caused by metal contamination. Stain that resembles slivers or flakes could be from steel wool. A more even discolouration indicates that the iron was in solution when it contaminated the wood, probably in a contaminated finish. Black spots could be caused by the head of a hammer striking a nail, or by cutting or grinding metal somewhere in the vicinity. The good news is that this kind of stain can be removed with oxalic acid, or with a proprietary cleaner that contains oxalic acid. Most of the major manufacturers of wood finishes produce timber cleaning products that will do the job.


Question: I am considering installing 130mm wide American Oak flooring. I'm told that it's generally not wise to secret nail 130mm floor boards though I've also been told the profile of imported American Oak makes it an exception to the rule.

Answer: We are not familiar with the profile of American oak flooring but doubt that it gives the timber any special qualities. The reason why the Australian Code Residential timber-framed construction limits secret nailing to boards with a maximum width of 85mm is because boards with a greater surface width need more restraint against possible cupping. Floorboards will cup if they are exposed to wetting or drying from one side. For example, flooring suspended over a damp site will absorb moisture from underneath and the underside of the board will swell more than the topside, making it cup. Similarly, flooring exposed to sun shining on it will lose moisture from the top more than the bottom, making the top surface shrink. Again the result is cupping. Narrow boards may still cup under these conditions, but the points of restraint are closer together. Under stable conditions (no moisture underneath and no drying from the top) wide boards will stay flat, assuming they have been correctly kiln dried and installed. Many older buildings have wide floorboards which have given years of good service, but they often have relatively small windows and shady verandas which help to stabilise indoor conditions. If you feel that the area where you are installing the boards is a stable environment, and the boards have been properly acclimatised, you may feel confident enough to ignore the standard recommendation that "secret" or concealed nailing is not recommended for boards wider than 85 mm.


Question: We are proposing to use a painted timber ceiling with open joints above an indoor pool to an apartment development. Insulation will be fixed to the underside of the slab in the ceiling space above the timber boarded ceiling. What timber do you recommend?

Answer: An indoor pool usually generates some condensation, even if not heated. If it is heated then the condensation can be considerable. We suggest a stable timber such as western red cedar that is little affected by changes in moisture content. For that reason it's a popular choice for windows, gates, venetian blinds and other uses where a high degree of dimensional stability is required. We also suggest keeping the insulation away from direct contact with the timber if there is any likelihood of water vapour passing through the timber into the ceiling space. It would be highly undesirable to have any build-up of moisture between the wood and the insulation.


Question: Veneered HMR Pineboard glued with liquid nails to cement rendered wall interior. Ground floor flooded up to 200mm depth, panelling loosening. Is it because of moisture running up cement render? All timber flooring must also be ripped up and replaced.

Answer: Sounds as if the building was flooded. HMR particleboard is more resistant to humidity than standard particleboard and therefore is recommended for kitchens and bathrooms. However, it is not intended to be exposed to water. If the panelling goes right to the floor and the water rose 200 mm up the wall then the panelling will probably need to be replaced. Even if the panelling remained above the water-line it is likely that the masonry wall is quite damp and, as you say, will make the panelling come loose.


Question: Replacing old floor boards and have been reading about timber cupping that would happen to wider timber boards, what would you recommend 130mm x 19mm or 85 mm x

Answer: Floor boards will cup if they are exposed to wetting or drying from one side. For example, flooring suspended over a damp site will absorb moisture from underneath and the underside of the board will swell more than the top side, making it cup. Similarly, flooring exposed to sun shining on it will lose moisture from the top more than the bottom, making the top surface shrink. Again the result is cupping. Narrow boards will still cup under these conditions, it's just less obvious than it is with wide boards. However, under stable conditions (no moisture underneath and no drying from the top) wide boards will stay flat, assuming they have been correctly kiln dried and installed. Many older buildings have wide floorboards which have given years of good service. Note that "secret" or concealed nailing on only one edge is not recommended for boards wider than 85 mm. Wider boards are required to be fixed with two nails at each point where they cross a joist.


Question: We're considering using either Karri or Stringybark for a living room, kitchen and laundry floor. Is the Karri environmentally sound, and are there any other practical issues we should be aware of with either of these. Would a satin PU finish be suitable.

Answer: Both timbers are a practical choice for flooring, although karri is a little harder and therefore more resistant to indentation. Even with karri it's a good idea to limit exposure to stiletto heels so if you are planning any big parties, placing rugs in high traffic areas would be recommended. In the kitchen, wear tends to concentrate around the sink. Here a mat or two will help to extend the life of the coating. In the laundry, water will be the major hazard. The section of the floor that is under and immediately adjacent to your washing machine and laundry trough could be tiled and fitted with a floor drain to deal with possible overflows. Regarding a suitable finish, satin coatings are generally less hard-wearing than gloss coatings. However, advances have been made in recent years, particularly in water-based coating technology. As with all coatings, adequate "film build" is the key to success so make sure the correct number of coats are applied in accordance with the manufacturer's recommendations. Regarding environmental issues, both the timbers you are considering are Australian-grown and therefore subject to stringent management regimes. We don't have enough space here to go into detail, but you can find out more about the management of Australia's forests on the net. Australia's State of the Forests Report gives a particularly good overview and can be downloaded from the website of the Department of Agriculture, Fisheries & Forestry (DAFF).


Question: We have selected 85mm wide Blue Gum for an internal sunroom with polyurethane finish. This floor is to adjoin an external timber deck that is very well ventilated but also quite exposed. Is Blue Gum OK used externally with an oil finish?

Answer: Blue gum is rated Durability Class 2 outside above ground according to Australian Standard 5604-2005, Timber - Natural durability ratings. This puts it in the same category as some other common decking timbers (eg. jarrah & karri) and we consider it is suitable for decking in a moderate climate. Oil finishes need fairly frequent maintenance, but providing you keep up the oil it will retain a similar appearance to your internal flooring. If you don't maintain the oil, the timber will tend to go grey, giving it a weathered look. If you are in a location that experiences a hot summer, it's not a good idea to let the sun shine directly onto your sunroom floor as it may dry out and shrink slightly - some external shading would be advisable.


Question: How long do you need to acclimatise hardwood flooring before laying?

Answer: Most hardwood flooring producers have data sheets outlining recommended installation procedures and it's advisable to work to their guidelines. As an example, one major producer suggests that 14 days is usually enough to acclimatise flooring. However, the actual time required varies according to the moisture content of the flooring on delivery, conditions on site, and the indoor environment of the building. If the flooring is supplied at the usual moisture content of 10% to 12% it will be ready to install, unless the building is in a particularly dry or humid region. Nevertheless, acclimatisation can still serve the purpose of evening out the moisture content of the timber. While the majority of the parcel might be in the desired range of 10% to 12%, it is not unusual to find a few boards that fall below or above this range. A couple of weeks of acclimatisation can help to bring these few odd boards back into the desired range. On the other hand, there's nothing to be gained by bringing the flooring on site before the building is enclosed - it must be placed in a dry, stable environment if acclimatisation is going to be of any benefit. Your timber merchant and flooring contractor should both have moisture meters so they can carry out random tests on the flooring, at the time of delivery and before commencing laying. Further details can be obtained from industry literature available on the net or from timber companies.


Question: How do I know I will get Grey Gum (Eucalyptus propinqua) if ordered from a supplier. There appear to be other common/similar names eg. mountain Grey Gum and it appears less common for flooring use. Who guarantees the moisture content prior to laying?

Answer: Common names of timbers are sometimes confusing. The timber known as "grey gum" is Eucalyptus propinqua, as you say. However, the timber known as "mountain grey gum" is Eucalyptus cypellocarpa, a completely different species. You can generally rely on reputable suppliers not to confuse species. Also, mountain grey gum is less likely to be supplied as flooring (unless it is a feature grade) because of the frequent presence of gum veins. The source of the timber may also help - grey gum comes from the coastal districts between the Hawkesbury River in NSW and Maryborough in Queensland. Mountain grey gum generally grows in Victoria, south of the Alps and near Cape Otway, although it also occurs in the southern tablelands of NSW. Regarding moisture content, we recommend that it should be checked at all stages. The producer, who will have kiln dried the timber, should be able to confirm the moisture content at the time it leaves the mill. The timber merchant should then carry out some random tests before supplying it to site. Finally, the installer should test the timber before laying. If these procedures are followed it becomes much less likely that any incorrectly dried material will slip through the system.


Question: Which of the three timber floorings would be easier to work with Blue Gum, Merbau or Grey Gum (Eucalyptus propinqua)? Are the harder timbers more brittle and difficult to work with and do they require different fixings than with softer timber?

Answer: Grey gum is considerably harder than merbau or Sydney blue gum. The latter two have similar hardness ratings, and are quite hard enough to give good service, but grey gum is unusually hard and is comparable to ironbark. This doesn't make it brittle, but it is harder to work with than less dense timbers. However, no special fixings are required for the usual flooring profiles. On the plus side, it is extremely hard wearing. Note that secret nailing is not recommended for boards wider than 85 mm cover. This is not something that is specific to grey gum - it applies to all timber species. Boards wider than 85 mm require face nailing with two nails at each joist.


Question: Hello I wish to know the required spacing for fixing 12mm v-joint lining boards as a decorative ceiling application.

Answer: Decorative uses of timber do not come within the scope of the Building Code of Australia (BCA), but there are timber industry recommendations for fixing lining boards. If the boards are installed at right-angles to the supports, 12 mm boards are recommended to be fixed at 600 mm centres on ceilings.


Question: Hello I am considering using WA Karri as a solid timber floor. I have heard conflicting reports that Karri "moves" a lot more that other similar timbers (eg Sydney blue gum, Jarrah).

Answer: When we talk about timber products "moving" we are referring to the swelling (or shrinkage) that takes place with a change in moisture content. If there is little or no change in moisture content, there is little or no shrinkage. Timber responds slowly to changes in atmospheric humidity, particularly if it's sealed, so if there are a couple of dry days followed by a couple of wet or humid days, there probably won't be any movement at all. If there is a prolonged period of dry or damp weather, it's true that karri "moves" slightly more than some other timbers, but the difference is small. Australian Standards quote movement figures of 0.3% of the width of the board, per 1% change in moisture content for jarrah, 0.35% for Sydney blue gum, and 0.4% for karri. This means if there is a 2% change in moisture content from summer to winter, a 100 mm wide karri floorboard is likely to "move" by up to 2 x 0.4% x 100 mm = 0.8 mm. The most important thing is to make sure the flooring has a suitable moisture content when it is installed, so movement is kept to a minimum. For most of the southern parts of Australia the moisture content should be in the range 10% to 12%, but this may vary depending where you live. Your timber supplier and/or installer should be able to carry out some random checks with a moisture meter to confirm that the timber is in the right range.


Question: I'm laying a timber floor that is greater than 6m in width (8.3m). Do I really need to put in an expansion joint? If I must, do I have any choices other than cork or a metal coverstrip?

Answer: We have a brochure we can post or email you which shows the various options for creating expansion joints in timber floors. Meanwhile, have a look at our answer of 26th February which talks about expansion joints in more detail. If you are still uncertain, feel free to leave another message.


Question: I am preparing to lay 80mm brushbox flooring on a particleboard platform floor secret nailed with adhesive.I have bostik ultra set in sausage form and 15 gauge x 38 mm staples. How is the adhesive best applied and what c/c should I be stapling?

Answer: To secret fix 80 x 19 flooring to particleboard, space your staples at 450 mm centres. The adhesive should be applied in a zigzag pattern to achieve approx. 25% glue contact area. Apply the adhesive midway between fixing points at 90° to the length of the boards to minimise possible squeaks and provide secure fixing.


Question: I want to have a European Oak floor stuck directly to the concrete slab floor in a family room. The room is about 5 metres wide. Please advise how much space needs to be left each side of the floor to allow for expansion - I assume this would be corked.

Answer: Floorboards only expand and contract noticeably across the grain, not along their length. This means expansion gaps are only needed at walls parallel to the floorboards. The Code for Residential Timber-Framed Construction calls for a minimum 10 mm gap, plus an intermediate expansion gap for floor widths over 6 m. The need for expansion gaps varies according to the local climate and the initial moisture content of the timber. For example, dry timber installed in a humid climate where indoor conditions are uncontrolled may expand. In most parts of Australia, timber that has been properly kiln-dried and acclimatised is unlikely to expand if installed onto a dry concrete or timber base, in a controlled indoor environment. Nevertheless, expansion gaps are a useful precaution. Gaps at the sides are usually covered by skirting boards and do not need to be filled with cork. Intermediate gaps can be filled with a compressible material such as cork, or covered with a decorative brass strip.


Question: I'm installing some exposed Slash Pine Glue Lam beams in a hydrotherapy pool. The Eng has requested that they be finished with 2 coats of polyurethane. Our subcontractor has put forward to use "Cetol TSI Satin plus, which was rejected. Can you recomend ?

Answer: The answer depends on how likely condensation is in the pool enclosure. If the pool is heated and the enclosure is not ventilated, condensation will form on any cool surface. That could be a hazard for the timber beams and they would then need to be coated on all surfaces with a highly moisture resistant coating, which perhaps is why the engineer has specified polyurethane. While Cetol is an excellent outdoor finish, oddly enough a pool enclosure can be more hazardous if timber is constantly damp. Cetol is a "microporous" coating which allows wood to breathe, i.e. it keeps out liquid water but if moisture gets into joints in outdoor structures it is able to evaporate through the coating when the rain stops and the sun comes out. It won't work the same way indoors. On the other hand, if the enclosure is ventilated and/or air conditioned with a system that controls humidity and removes moisture from the air, it doesn't really matter.


Question: My dance school concert will be on a stage with tarket (rubber) floor. My tap dancers need a wooden floor to tap on. Do you suggest MDF sheets? Particleboard? Ply? Minimal warping is important! & Teenagers need to carry the sheets on & off stage.

Answer: We think the best product for your tap dancing floor would be plywood. However, we were concerned about possible wear and tear from the tap shoes. For this reason we suggest plywood floor panels with a hardwood face, such as the Big Rivers Armourpanel product. We suggest the smallest sheet size for ease of lifting (1200 x 1200), in the 15mm thickness. These panels come with a substantial face veneer of 3mm and you can find out more about the product from the Big Rivers website. Other producers may have similar products.

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