Timber is both beautiful and sustainable but by it's organic nature, susceptible to changes in the environment.

This article discusses some of the considerations for specifiers looking to implement timber items of street furniture in the public realm.

In the past, some schemes have had issues with the exterior use of FSC certified Oak. The primary issue is that the oak has a natural property to leach tannins and this can cause staining on the surrounding paving and other items directly below the installed timber .

This staining can be removed but should be dealt with promptly.

This is a temporary occurrence and will eventually stop happening once all of the tannins have disappeared, although this time span varies due to weather conditions and section size of the timber.

Below is part of a recent report on a project we have encountered and provides interesting reading regarding the properties of Oak.

We're certainly not saying that the timber should not be specified but feel it is pertinent for specifiers and clients to be aware of these short term issues.

Timber is a hygroscopic material and consequently by its very nature is subject to a degree of change.

Always conscious of the need for a second opinion, we have taken independent advice from Mr Andrew Allan, Managing Director of Vincent Timber Ltd, on this particular issue. 

Mr Allan  points out that checking occurs most often at the end of a timber section and it is caused by excess moisture exiting at the point of lowest resistance. It will eventually stabilise. 

Instances of surface checking evident on the top side of timber sections are usually caused by stress relief within the timber, and irrespective of the extent to which timber is sorted or graded at the point of machining and/or assembly, is an inevitable occurrence in, what is after all, an organic product. 

As a consequence of checking there may be some slightly raised edges which might need to be sanded down to avoid potential snagging of users clothing. 

Our opinion is that checking issues raised to Woodhouse in our experience have in no way compromised the structural integrity of the goods supplied. The  timber used is not defective or unfit for purpose but can have a detrimental effect on the paving or other furniture elements in the project if untreated.

The Importance of Care and Maintenance

Often demoted post-installation as "someone else's responsibility," entire schemes can be ruined by poor maintenance schedules or over-zealous, insensitive or misinformed techniques.

The guide below should help as a general introduction to timber care, but we're more than happy to help with any specific requests on our products.

Surface Cleaning - General

For minor surface marking a light pressure washing with cold water (only), should be sufficient.

Important – The Pressure Washer spray nozzle should be kept at a distance of no less than one metre from the area being cleaned, and water pressure should be kept low and directed through a nozzle type that omits a broad spray as opposed to a fine jet.  Care should also be taken to ensure that the Pressure Washer is entirely free of any trace of previously used detergents, solvents, etc.

Surface Cleaning - Sanding

Light sanding by hand can be an effective means or reducing or eliminating surface marking that was resistant to pressure washing, but care should be taken to sand the whole bench evenly along its entire length so as to avoid  “bright patches” occurring where localized sanding has taken place. 

Powered Belt Sanders can also be used but care must be taken to ensure a smooth and consistent movement down the full length of the timber section irrespective of whether or not all areas are affected, and under no circumstances should the Sander be held running in a stationery position.

Surface Damage – Minor Dents and Impressions

In instances where timber fibres have been compressed by an impact but not broken, localized wetting of the effected area using cold water (an application method commonly used is to place a saturated sponge or cloth directly on top of the dent or impression), may encourage the depression to “re-level” itself relative to the rest of the timber section. 

Leaching & Tannins

Oak contains large quantities of naturally occurring tannins and these will leach out over time, particularly when the wood comes into direct and prolonged contact with water.

Tannins are water soluble at the point when they first appear and can be easily washed off. Once they are dry they can be removed in most cases by washing and/or sanding though in more extreme cases a dilute solution of Oxalic acid can be used.

Contact with Ferrous Items

Timber staining will occur where ferrous materials come into direct contact with Oak as a consequence of the chemical reaction that occurs creating ‘black iron’ marks which can prove very hard to remove.  Typical causes of this are tools being laid across the timber or as a consequence of contamination from nearby drilling, grinding, etc.

Important – Under no circumstances should Wire Wool or steel-type Wire Brushes be used to clean any part of the Oak surface.

Chemical Cleaners and Colour Restorers

Though no Chemical Treatments or Preservatives are specified or required, should they be of interest Owatrol can offer an extensive range of Wood Cleaners and Colour Restorers which can be viewed at their website www.owatrol.com.

Note these should only be used after taking advice from both Woodhouse and Owatrol’s technical representatives and in all instances, discreet trialing should take place on a concealed area of the timber section, or alternatively please contact us and we will be happy to arrange the free of charge supply of a sample section for testing purposes.