Shrinking timber weatherboards – there is a problem

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If the large amount of responses I got from it is anything to go by, last month’s article on the problems experienced with shrinking, pre-primed, finger-jointed weatherboard hit a nerve in the industry. Many builders from around the country have suffered from the same issues of boards pulling back in the summer months, leaving an unsightly paint line that no owner could be expected to accept.

This invariably results in expensive repaints, with little support on offer from the manufacturers. In response to my article, New Zealand Wood Processors and Manufacturers Association technical manager Jeff Parker provides a welcome and useful summary of the problem, and how to mitigate the many risks of shrinkage when using pre-primed timber weatherboards.

Please take the time to read this summary which appears on the page opposite. It confirms that unless you are extremel y careful around your choice of board, weather conditions, protection of product and painting times, you will undoubtedly experience problems.

He highlights potential shrinkage of board up to 6.9mm, a huge figure. Hence my comments in last month’s article — that the product now appears to be far more precious than it ever used to be — are certainl y confirmed.

Concerning information

I have also been contacted by manufacturers about the article, and some very enlightening, if not concerning, information has come to hand from digging a little deeper. This is where things get very interesting. As a builder you expect that when you order a pre-primed weatherboard from your merchant that it will be fit for purpose and manufactured to a common standard and process.

A weatherboard is a weatherboard, right? Surprisingly, this is not the case, and it is confirmed in point 3 of the Mr Parker ’s summary: “ Different manufacturers use different methods of treatment and painting. The builder should make himself aware of these differences and ensure that the  appropriate handling, installation and finishing methods are used.”

This puts all the onus back on the builder who would often be oblivious as to where their local merchant might have sourced the weatherboard order from, or what criteria the merchant has chosen that manufacturer on. If your merchant is buying on bottom price or is naive to the risks, you may be getting less than you bargained for, and possible ongoing problems.

For instance, did you know that some weatherboard manufactures use boron treated boards and acrylic primer, whilst other use treatment and oil-based primer. And some manufacturers use two coats of primer while others use only one.

Others actually mix imported board from Chile amongst the New Zealand-produced board to help keep the cost down. If you thought all board was created equal think again.

Unfair for builders and consumers

It is unfair for builders and consumers to have to decipher what they are actually getting when they order a timber weatherboard. Manufacturers should look at the issues their customers are experiencing, then collectively create a board with a treatment level and priming that is robust enough to meet the way we construct — one that repels water long enough to be built in normal circumstances.

Failure to address this problem will result in a loss of market share as builders migrate to less risky product. Sending out weatherboard with varying forms of treatment and priming, along with a list of exclusions and instructions that may or may not be practical, and then relying upon them as an escape mechanism when a problem occurs, is an unfair and impractical approach. It is also a way to turn people off your product.

Timber weatherboards have traditionally stood the test of time and have been a trusted product, and it’s in everyone’s best interests to get them back to a position of favour and trust. However, this won’t happen unless there is some leadership and co-operation between manufacturers. 

This may be difficult because there are many players in the market — some better than others — and they compete financially. However, without a benchmark and cooperation the product will continue to be hit and miss depending on where it comes from and the treatments used.

In the interim, I suggest you check who your merchant is getting their weatherboard from, know what the level of treatment and primer is, understand what that manufacturer’s response is to warranty claims, and where they source their raw materials from.

You need to take control of this or you may get board that is not the best for your application and end up paying dearly after the event. You may need to stipulate to the merchant that you want the board to be sourced from a certain manufacturer, as there are some good ones who do produce a sound product and offer back up. Do your homework.

Finally, if you do use pre-primed, finger-jointed weatherboard, take the wisest suggestion of all from the Wood Processors and Manufacturers Association summary — “paint the lap of the weatherboard the finishing colour before you install them. Any shrinkage will be less noticeable”.

Although there may be a cost associated with this preventative action, it will be smaller when compared to a repaint. Good luck.

• This article contains the author’s opinion only, and is not necessarily the opinion of the Registered Master Builders Association, its chief executive or staff