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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. In March we had our cypress pine floor coating redone by a professional as the colour had become quite orange with age. The flooring was 15 years old and around 150sqm, hidden nails. Original finish trowel puttied and two pack enamel. No gaps, level and a very quiet floor to walk on. A polish like finish. The contractor sanded it back bare. Lime wash stained and applied 1 coat poly sealer and 2 coats of poly-semi gloss he states. 9 months on and the floor now has several gaps up to 5mm in the flooring where the boards have shrunk, 1 the entire length of the house. Bad peeling or delaminating and squeaky floorboards. The entire floor needs to be sanded and re coated. There was some moisture under the house when the job was done. The contractor used metho with the stain and across the floor to clean it. The contractor states the peeling is caused from a reaction between the stain and also what he used on the poly beads after the first coat. What I am really concerned about and what I do not understand is why the floor has shrunk after 16 years of being perfect. He states it was because of the moisture under the house. Do we just putty them up when he does the new coat or will they crack again?

It is hard to understand why a 15 year old floor would suddenly shrink, particularly producing such large gaps. We wondered if the gaps are occurring every five or six boards, rather than between all the boards. If so, this would suggest that "edge bonding" has occurred. This happens when polyurethane finds its way into the tongue and groove joint and sticks the boards together. Shrinkage which should be distributed evenly across the floor is then concentrated into a few large gaps instead of a lot of very small ones. Some shrinkage might be expected if there was moisture under the floor which subsequently dried out, but it shouldn't produce gaps of 5mm. You will find more information on the net about edge bonding if you write those words in your browser. Since there are clearly other problems with the floor (unsatisfactory finish, squeaks, etc.) which are difficult to comment on without seeing the floor, you might wish to have it inspected. The Australian Timber Flooring Association (ATFA) has qualified inspectors available. If you visit their website at you will see there is a tab that says "Request a timber floor inspection". When you click on that it will give you a list of inspectors in your area.

Q. I have a new Tas Oak timber floor installed 4 months ago in my new house and the builder just handed over to me for a month. I found there are lots of gaps on the floor some are small and some are larger and little bit cupping and the floor look like little bit uneven around the whole house. When I touched the gaps I have cutting feeling. I checked the moisture content of the timber and it still has got about 11.5%. I want to redo the floor like deep sanding, gap filling and re polishing to rectify the problem, but I am worried about the timber may not dry enough and shrinking more in the future. Please advise me what I need to do.

It sounds as if moisture might be getting into the flooring from underneath. We assume the flooring is laid over a concrete slab. If the concrete is fairly new it could still contain a significant amount of moisture. When flooring absorbs moisture from below the undersides of the boards swell causing them to cup. The moisture content of 11.5% is not particularly high, but some moisture meters require a correction factor so the actual moisture content could be higher, depending on the type of meter you are using. On the other hand, if there is a moisture barrier on top of the slab (which we recommend) moisture would be unlikely to be coming from the concrete and we would look for other causes. The gaps you are seeing could be shrinkage or they could be a side effect of cupping, since the top surface tends to open up when boards cup. We would certainly not recommend sanding and re-polishing the floor until you are sure it's dry. In fact some of the cupping might flatten out once the flooring is thoroughly dry. It might be worth having your floor inspected to get to the bottom of the problem. The Australian Timber Flooring Association (ATFA) has qualified inspectors available. If you visit their website at you will see there is a tab that says "Request a timber floor inspection". When you click on that it will give you a list of inspectors in your area.

Q. Our floors have big gaps between each board, so we used a black seal and flex between each board. Then we got it sanded and a tung oil put on. We were told that we could walk on it after two days, so we did. The wood was dried, but the tung oil on the seal and flex was not. Now we have marks on the floor from were our feet stepped on the seal and flex tung oiled bits, and have spread them on the wooden bits, and we can't get them off. We spent so much and the floor looks like poo. I hope you can help us . We don't know what to remove them with.

That's a tricky question and perhaps one for the tung oil manufacturer. For example, Feast Watson manufacture tung oil and also produce a special floor cleaner called Floorclean, but we don't know whether it would solve your problem. You might want to contact their Customer Service Team on FREECALL 1800 252 502 and put the question to them. Alternatively you will find several suggested remedies if you search the net, but we haven't tested any of them and therefore cannot make a recommendation.

Q. We have a Boral direct stick 13mm black butt timber floor that was installed around 18 months ago. It has cupped and separated (gaps of 3 to 5 mm in some places) throughout the entire house. Our flooring contractor has told us they can "fix" the problem by resanding and coating the floor, but won't this problem just happen again? Our neighbour has the exact same floor installed by the same contractor, and it is as good today as the day it was finished so it can't be a climatic issue. What should we do?

Wood products sometimes do confusing things, but there are two basic facts: wood shrinks when it loses moisture and swells when it gains moisture. Gaps of 3 to 5mm are quite large. If they occur between all the boards we would say the flooring wasn't kiln dried properly and/or has been exposed to hot conditions such as direct sun through windows. If groups of five or six boards are stuck together and the gaps appear at irregular intervals we would say this is more likely a case of "edge bonding" and perhaps the total shrinkage is within reasonable tolerances. When edge bonding happens the edges of the boards become stuck together with floor varnish and the shrinkage that otherwise would have been distributed evenly across the floor is concentrated into larger gaps. Re-sanding and re-coating the floor won't make any difference - the only thing that would close the gaps would be a significant increase in humidity, but your neighbour's experience suggests this is not a climatic issue. Perhaps the contractor is intending to fill the gaps as part of the re-sanding operation, but filler in a 5mm gap is likely to crack and work loose in the long term.

Q. I have a timber floor - about 18mths old secret nailed and glued to a particle board base. Large gaps are appearing about every 6 - 8 boards. This happened once before but the gaps closed up during the moist part of the year. It has happened again this year during the dry months. I'm pretty certain it is edge bonding. if the gaps close again, do you think surface nailing will stop the gaps from appearing again? Are there any other options short of pulling up the floor and relaying and applying a less adhesive finish?

It is normal for timber to swell and shrink slightly at different times of the year with changes in humidity. However, when edge bonding occurs, the shrinkage that should be evenly distributed across the floor so as to be relatively unnoticeable, is concentrated into a few large gaps. It sounds as if that's what is happening in your case, or maybe the glue that was used squeezed up into the tongue and groove joint. The places where gaps are occurring are places where the boards are not edge bonded, or the bond is weak. If you nail the boards down to try to restrain them they are likely to split since shrinkage forces will be greater than the strength of the wood. Neverthless if you are contemplating pulling the floor up it wouldn't hurt to try nailing first, to see if it helps. You can always relay the floor if it doesn't improve the situation. Other than that I'm afraid we don't have a solution for this problem. But next time if you are using a two-pack hard-setting finish, make sure it is applied very carefully so it doesn't run into the tongue and groove joint. Alternatively, water-based polyurethane is less likely to cause edge bonding.

Q. In 2005 we renovated a California bungalow in Sydney and sanded and stained the Kauri Pine floors from 1928. They looked marvellous. We have since had to move overseas and have leased out the house. The Kauri Boards have been sanded once when we did the renovation and again to prepare for tenants. (that is 2 times) the last tenant left and made series of massive scratches in the Kauri floor boards in one room. How many times can you safely sand back a Kauri Pine floor board. I am loath to keep sanding it back as fear it will thin the boards too much. I adore the lush soft Kauri pine floors. Where is the best information for educating the new tenants to know what they are walking on?

It's hard to say how many times a floor can be sanded because it depends on how heavily it's sanded each time. You are right in thinking a timber floor should not be sanded more than absolutely necessary. An indication of the state of the boards can be obtained by inserting a thin probe (such as a piece of paper or a knife) into the tongue and groove joint and seeing how much thickness remains above the tongue. Future tenants should be warned that they will be liable for damage, and you might want to encourage them to place rugs in traffic areas, or perhaps do so yourself before re-letting. If you want some documentation to give to future tenants, Boral have quite a good information sheet that explains the main issues. It can be downloaded from this web address:

Q. I refer to the following website and extract of information confirming cause to floorboard ‘cupping’. “a board swells on its side that is most moist. So on an interior floor like the one shown at left, the fact that the center of the floorboards is cupped "down" we infer that it is the down-side of these boards that is more moist than the finish side facing the room. We find this condition in homes with finished wood flooring installed over a damp or wet basement or crawl space. At our page top photo the finish floor boards seem to be cupped "up" - suggesting that this floor has been wet from above.” We have floorboards that have a prominent ‘Cupping Up’ moisture damage and need confirmation as to whether this suggests high moisture levels on top of the floorboards, or underneath. If you could please confirm at your earliest convenience, it would be greatly appreciated.

The terms "cupped up" and "cupped down" are perhaps a bit confusing. We have visited the website you mention and what Inspectapedia means by "cupped down" is that the centre of the board is lower than the edges, which are curled up. They quite correctly explain that this occurs because the underside of the board contains more moisture than the top side as, for example, when flooring is installed over a damp sub-floor space. If your floorboards are curled up at the edges when viewed from above ("cupped down" according to Inspectapedia) it means there is moisture coming from below. This could be from a plumbing leak, inadequate sub-floor ventilation if the floor is suspended over bare earth, or some other cause.

Q. I am looking for an appropriate flooring solution that meets the following criteria. Recycled timber preferably spotted gum, sprung so that it is suitable for small dance classes to be held on it. Could you also advise relative (ballpark) costs for this type of floor in comparison to a normal timber floor?

We are not able to quote prices, but a contractor should be able to advise you on the cost of building a sprung floor. Of course, this will depend on the method used. Harlequin Australasia offer sprung floor systems which can be installed as floating floors, over existing floors. It's also possible to build a sprung floor from scratch, either by using resilient pads or by installing a double system of battens to give extra flexibility. We could email you a specification for building a floating floor if that would help.

Q. Re: Installations to slabs by direct adhesive fix 1: preferred installation recommends a poly sheet over the slab with boards fixed over this. Q: How are the floor boards held in place with this method? 2: Slab moisture content. Q: What is the optimum moisture content of the slab if the poly sheet is not used?

The poly sheet can't be installed if the boards are directly fixed to the slab - that's only an option if the floor boards are fixed to a plywood underlay, or to timber battens. The poly sheet then goes under the plywood or battens. When the direct-stick method is used the surface can be sealed with an epoxy sealer prior to gluing. Regarding the desirable moisture content of the slab, this and other factors related to direct-stick floors is explained in detail in Section 4 and Appendix C of the Wood Solutions Design Guide #09, available via this link

Q. We had our floorboards sanded and polished 10 years. We got them sanded and polished again 18 months ago. We are finding that the lacquer is coming off in certain areas mainly between the boards. We have been told because of the movement between the boards that when we mop the floors that the moisture is causing the delamination. This was not occurring when we first got the floors done. We are cleaning the boards the same way. Spoke to the someone else and they said the movement in the boards is contributing the delamination but isn’t the cause. The boards weren’t prep correctly. Are you able to provide some reason to why this might be occurring?

It's difficult to comment on the cause of your problem without seeing the floor. We assume the boards were not waxed at any stage? If the lacquer is peeling from the edges of the boards it suggests there might be some contaminant in the tongue and groove joint that is preventing proper adhesion adjacent to the edge. Alternatively, if the lacquer is tearing and presenting a jagged appearance, that would suggest the boards were stuck together and the lacquer was damaged when the boards moved. However, we feel it will need an inspection to get to the bottom of the problem. The Australian Timber Flooring Association (ATFA) has qualified inspectors available. If you visit their website at you will see there is a tab that says "Request a timber floor inspection". When you click on that it will give you a list of inspectors in your area.


Did you know?

Logs from plantations cannot produce the sawn hardwood timber produced from logs currently harvested from native forests.