Ask an Expert

Ask an Expert

Joinery, cabinetwork & furniture

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. We have bought a new timber dining table and have covered it with thick clear plastic. We have been advised that having the plastic directly on the table will cause moisture and ruin the stain on the table. Is this correct? If so, would glass be more appropriate to use? Thanks.

Putting plastic directly on the table won't "cause" moisture, but if there is still some excess moisture in the wood the plastic will create a barrier, stopping moisture from escaping into the air. Then moisture will accumulate under the plastic and it might affect the stain. Once the timber is fully seasoned, and all solvent has evaporated from the stain, we don't see any problem putting plastic over the table to protect it. Glass is just as impermeable - it's the barrier effect that creates the potential problem. However, plate glass is commonly used to protect wooden tables without any difficulty and plastic shouldn't be any worse. We just suggest you wait a while.

Q. Hi there I was wondering about the little "did you know" about not being able to use plantation timber like wood from native forests. Can you explain this further please? Also I am looking for someone to make low/no formaldehyde cupboards in SA, pref in south. many thanks.

Plantations provide a high proportion of the timber used in Australia - as stated in another of our "Did You Know" items, "Australia’s 1.9 million hectares of timber plantations produce about two-thirds of the timber products consumed by Australians each year". While most of our softwood construction timber comes from plantations, it is more difficult to produce high quality hardwood in plantations. Hardwood is much slower to grow and when we try to increase the growth rate the quality often drops. Consequently, hardwood for furniture, flooring, decking and other high quality products is best sourced from sustainably managed native forests. In Australia we are also limited with regard to areas that are suitable for the establishment of plantations. Australian-made particleboard and MDF is produced to low formaldehyde emission levels, and any joinery works should be able to produce cupboards for you. Autralian Standard 1859.1, Reconstituted wood-based panels - Specifications, Part 1: Particleboard, provides for two levels of "formaldehyde potential", E1 and E2. Our understanding is that Australian producers manufacture to E1, with some producing an E0 board. You can find out more about these products by browsing the internet.

Q. I wish to know what material I can use to seal an ash table without developing a honey colour as the polyurethanes do. Thanks Nole

Some of the newer formulas are much less inclined to yellow the timber than the older polyurethanes - the water-based products are particularly good, eg. Cabot's Crystal Clear. Polyurethanes remain the most practical finishes for tabletops and other surfaces that need to resist liquid spills. They are easy to wipe clean and have good wearing qualities. Also be aware that some of the yellowing of pale coloured timber is due to the wood itself changing colour slightly over time, due to the effects of ultra violet light. This will be minimised if the table is kept away from direct sunlight.

Q. I have a Stainless Steel framed outdoor Kwila topped table. It has been protected by Spa-N-Deck 100% Acrylic by Flood, and is too heavy to shift easily. As I am going away for two months would it be wise to cover the table with a sheet of durable plastic?

A cover is quite a good idea if there is no protection from a pergola or verandah, but there are a couple of potential problems. If a plastic cover is laid directly on the table, moisture may be trapped between the plastic and the surface of the table, particularly during periods of high humidity, a problem often described as "sweating". If you try to keep the cover raised off the table, say with wooden blocks, rain will collect in the cover. If you feel you can avoid these problems, by all means cover the table. Otherwise, assuming the tabletop is slatted so water can drain through it, rather than being a solid top that will collect water, we would be inclined to leave it without a cover. Kwila is a durable, rot resistant wood that generally stands up to the weather well.

Q. I have kitchen cupboards made of African Ash installed in1995. I wipe the cupboards with a damp cloth each day to maintain their condition after cooking. Because of the grain, particles of dirt built up and I need to clean them. Can you please help?

The critical issue here is not so much the wood, but the coating applied to it. Essentially what you are wiping down each day is the coating (unless it has all worn off). In an area such as a kitchen we recommend polyurethane coatings because they are hardwearing and easy to keep clean. Oils and waxes look nice in the short term but are not very durable. You don't mention the type of finish used on your cupboards, but perhaps it is time to rub down with a fine grade of sandpaper and then re-seal with a satin polurethane. For best results apply three coats.

Q. What are the main reasons for loosing veneer defects in furniture? We suffer this specially in veneers like Russian Walnut, French Walnut, Circassian, Cluster Maple, Olive Ash Burl and Mahogany Plates 12, 13, 31. We use hot press with urea-formaldehyde.

When bubbles or loose patches appear in veneered surfaces it's often a moisture-related problem. Urea formaldehyde is an excellent adhesive but in a hot climate it will have a shorter assembly time. Perhaps the glue is curing too quickly and leaving patches where adhesion is poor. If a water-based coating is applied it could cause enough stress in the veneer to create bubbles, or even high humidity outside the press might have this effect. We don't know of any problems with the particular veneer types you mention, so it seems more likely to be process-related. Try a shorter assembly time and see if it overcomes the problem. Also be careful that the moisture content of the veneers is tightly controlled, and not causing the veneers to bubble. I'm sorry we can't be more specific, but perhaps these general comments will help.

Q. We are building a solar passive house in Central West NSW in 2011. We will be using timber doors & windows. Is River Red Gum a suitable timber for this application. We do have access to logs & a mill. Many thanks. Kim

River red gum is a durable, rot-resistant timber, so from that point of view it would be a good choice for doors and windows. However, if you are milling your own timber you will have to dry it before it can be used for joinery otherwise you will have unacceptable levels of shrinkage. You should also be aware that gum veins are common in river red gum, so unless you are aiming for a rustic look the timber will need careful selection to obtain high quality material. It's also a good idea to select straight-grained material if possible. Grain direction can be assessed by looking for any fine cracks in the wood as it dries, as cracks and checks always follow the grain.

Q. Which is the better wood for Kitchen cabinets? Maple, Cherry, Oak or Birch?

The four woods you mention are all suitable for kitchen cabinets - it's really a question of the look you want. All have similar hardness ratings - white oak is a little harder on average than the others, but there's not much in it. Just make sure you choose a hardwearing finish that can be wiped clean without damaging it, for example polyurethane. We don't recommend oils and waxes in kitchens. They look nice in the short term but don't stand up to moisture too well.

Q. I would like a pine entertainment unit made for me. Do you have a store nearby in the Wantirna area, eastern suburbs Melbourne?

We don't have any stores, we just provide an advisory service for people who need to know about different wood products. Perhaps you could find a local joinery works in the Yellow Pages, or maybe your friends could recommend someone to make a pine unit for you. However, if you need any information about timber, get in touch with us again!

Q. Is there a way to reliably use wide (eg 200mm) strips of solid timber in the top of a bathroom cabinet, to give the appearance of a single piece of timber whilst avoiding problems with “cupping”? What is the recommended approach for bathroom tops?

Wide planks can be edge-glued to make up benchtops, but unless you are a skilled handyman it might be best to have the work done by a joinery shop. If you intend to do it yourself, make sure the timber is properly dried to a moisture content of 10-12% and use a water-resistant glue. It is also very important to install and seal the top correctly. The sealer must be applied to all surfaces, including edges, forming a complete envelope. A detailed guide is available on the net and you can download it via this link If you follow the recommendations, there should be no problems with cupping.


Did you know?

In 2008 seventy percent of known old-growth trees are in nature conservation reserves.