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?
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Q: I hope you can help. I am looking to externally clad part of my house in quite an artistic fashion....like the following : http://www.archdaily.com/46980/suurupi-house-extension-arhitektid-muru-pere/ But I think Western Red Cedar might be a bit much (colour) for the location. And was wondering if there was a wood product that would age gracefully 'gray' in a way similar to Larch? Is there anything in Australia that would age into a 'gray' like Larch?
30/01/2013
The Suurupi house makes unusual and striking use of timber. Clearly the "matchsticks" are a decorative screen, not a waterproof walling system. We feel western red cedar would be OK for this purpose. It will turn grey after prolonged exposure to the weather, as seen in houses with western red cedar shingle roofs. Ideally the house should have no eaves (like the Suurupi house) since sheltered portions of the wall will retain their original colour for longer, or maybe permanently, while the exposed sections will weather off to a driftwood grey. If you go ahead with this idea, make sure the contractor uses non-corrosive fasteners such as silicon bronze or stainless steel, otherwise you will get rust and black iron staining on the wood.
Q: I'm planning using 100x50mm F7 unseasoned white cypress joists at 450mm centres to support a 130x25mm spotted gum decking board. It is for a domestic roof terrace and the joists will be layed directly onto the roof with packing to match the roof slope. The roof has adequate slope to ensure water drains freely. My question is firstly is the joist size adequate and secondly will using unseasoned joists cause any issues as they dry over time, in particular warping or undulation of the decking boards.
23/01/2013
The joists will be able to span 1.8m at 450mm centres, so if that suits your design the size is OK. There will be some minor shrinkage as the joists dry - up to 2.6% of width and thickness (shrinkage lengthwise is negligible). Cypress is a fairly stable timber so we don't anticipate any significant warping. We assume the decking boards will be kiln-dried. However, it may be a more severe environment than usual if the roof in question is metal and the sun reflects heat onto the timber.
Q: I am writing as I am trying to find a company in Australia that tests Hardwood Timber for structural integrity, grade and quality. 3 years ago we had a deck built using "A grade, external hardwood timber - the best on the market for durability and longevity of a deck. The deck undercover is "as new" but the section of the deck exposed to the sunlight and rain is rotting in several sections (although only one board in each section) We need to find out WHY this has happened so that we can rectify the problem. As we have exhausted all other avenues, we would greatly appreciate any information you may be able to supply.
11/01/2013
Clearly there is something wrong if your decking is rotting after only three years. You don't mention the species of hardwood that was supplied. In our opinion this is an essential first step in getting to the bottom of the problem. Some hardwoods are highly durable while others have a relatively short life when exposed to the weather. If you are not sure of the species of hardwood, and the supplier is unable to tell you, a positive identification can be made by examining a sample microscopically. Each species has a distinctive cell structure and specialists in this field use such characteristics to identify different species. A noted expert is Dr. Jugo Ilic whose consultancy is called Know Your Wood. For details of fees and required sample size send an email to knowyourwood@gmail.com.
Q: I'm after advice regarding plywood roof sheeting that has a gentle curve in some areas. The plywood has a waterproof membrane.
11/01/2013
For information on plywood roofing systems we refer you to a publication of the Engineered Wood Products Association of Australasia (EWPAA) titled "Featuring Plywood in Buildings". The publication can be downloaded via this link - http://www.ewp.asn.au/library/downloads/ewpaa_featuringplywoodv.pdf. There you will find details of recommended radii for bending various thicknesses of plywood, and also the required grade to use for roof sheathing.
Q: Are there any regulations or building practices on fixing timber decking bearers directly on concrete slabs - as in gap between slab and bearer to allow water flow?
06/01/2013
The Building Code of Australia (BCA) doesn't specifically address this issue, although the BCA contains general clauses to the effect that "every part of a building must be constructed in an appropriate manner" and builders must use "materials that are fit for the purpose for which they are intended". Where a deck is installed directly onto concrete, drainage must not be inhibited. If the concrete is not already in place, compacted sand or gravel would be a better base, since they allow better drainage. If water is retained under a deck that is close to the ground it may shorten the life of the timber and cause warping of the decking. The issues involved in building a deck close to the ground are explained in more detail in a data sheet published by Timber Queensland. It can be downloaded by writing TQL 13 in your browser.
Q: Need some advice re external verandah specification provided to me by Architect/Engineer. They want to use F17 unseasoned h/wood bearers & joists framing followed by a T&G Tallowwood flooring over. Is shrinkage of the bearers & joists going to cause issues with the T&G Tallowwood flooring given it's being used externally/ exposed on verandah facing NE & NW?
01/01/2013
Some caution is needed with this specification. Total shrinkage will depend on the total depth of the bearers and joists. For example if the bearers are 150 mm deep and the joists are 100 mm deep, total shrinkage will be the same as the shrinkage of a 250 mm section. Some hardwoods can shrink by up to 6%, so worst case scenario would mean shrinkage of around 15 mm, depending on the type of timber. The architect and engineer need to consider carefully whether the structure can accommodate this level of shrinkage without distress. If not, it would be better to use kiln-dried timber. Regarding exposure of the verandah floor to the weather, this can also be problematic if it is likely to be rained on. Old buildings often used tongued and grooved flooring, but today spaced decking is preferred as it allows for swelling and shrinking of the timber with wetting and drying. If it is a heritage building and t & g flooring is required, make sure the flooring is just lightly pushed together, not tightly cramped, and also use hot dip galv nails (or stainless). I guess the design is already locked in, but it's also better if the flooring runs parallel to the external wall rather than at 90°. The outer 1 m or so will receive more weather than the area further under the verandah. If the boards are parallel to the external wall, the outer boards can be replaced later without necessarily replacing the whole floor. If the boards are laid at 90° the ends of all the boards will eventually be weathered, possibly needing complete replacement at a later date.
Q: I suffered extensive damage to a very large pergola on April 9 due to a tornado which smashed the pergola. Insurance only covered $10,700 and I had to pay $9,000. My query is that I notice there are knot holes in the many treated pine rafters. The knot holes were not filled prior to painting. Can you advise if this could present a problem, i.e. dry rot in the future?
19/12/2012
We would regard the use of timber with knot holes as a little careless from an appearance point of view. If only a few pieces have knot holes it's often possible for the carpenter to use them where timbers have to be cut to length, thus providing an opportunity to cut out the knot holes. Aside from that, knot holes won't be a problem if they were present at the time of treatment because the preservative will have penetrated into the holes, so dry rot won't be an issue.
Q: My client has requested that I design the handrails of a deck I am constructing in a method that I have concerns with the effects of shrinkage & movement. He wishes that I continue the handrails (merbau laminated timber) over the top of the 90 mm square softwood posts mitred at the external corners. As I am concerned of the effects of weather and timber could you please recommend a method which would minimise the opening of the mitres.
16/12/2012
You are wise to approach this with caution. Mitred corners look neat when they are new but as soon as the wood moves, the mitres open and close. Even a relatively stable timber such as merbau will swell and shrink slightly with wetting and drying and a mitred joint can't accommodate any movement. If the client insists on mitred corners make sure it's clearly documented that you advised against it, and take no responsibility if the mitres open (which we think is highly likely). Maybe a halved joint would be a satisfactory compromise if there's enough thickness in the handrail. There is still likely to be a bit of movement where the two sections meet, but at least you don't see open space if they move apart slightly. Another option is to cut a mitre with an intentional gap, which at least looks as if it's meant to be there. A good explanation of the problem can be found via this link - http://www.deckmagazine.com/framing/question---answer.aspx. You might want to show it to your client.
Q: I got a decking completed with Merbau a year ago. It was oiled once. There are lots of dusts and bird droppings on it and would like to get it washed, just a wash to remove dirt and not going to oil it. What product should I use? Is it safe to use Napisan?
13/12/2012
The easiest way to clean your deck is to use a power washer with plain water. However, there is a lot of information on the net about the problems that can arise when the pressure is too high. If you don't feel able to use a power washer safely, there are many deck cleaning products on the market that will remove dirt and debris. The general idea is scrub the deck with a stiff bristle brush and deck cleaner, and then hose off the residue. Suitable products include Cabot's Deck Clean, Dekswood Cleaner & Brightener, etc. You will find information about these products, and more, on the net.
Q: I am undertaking a landscape gardening project. I need some information on suitability of timbers for different landscaping projects. I also need to list which timbers need treatment with preservatives etc. Can you advise?
12/12/2012
Your question needs an answer that is too comprehensive to post on our website. However, you will find a technical data sheet on the net that should help. If you write TQL 25 in your browser a data sheet titled Outdoor Timber Performance will come up, produced by Timber Queensland. This data sheet sets out the natural durability ratings of commonly used timbers and explains when preservative treatment is needed.
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