Timber preservation - the alternatives

Key Issues

Insect and fungal attack happens when:
• wood is poorly dried
• wood becomes wet and fails to dry out

Use naturally durable wood

Unfinished external joinery

Use:
• European Oak (durable)
• Sweet Chestnut (durable)
• Western Red Cedar (European grown) (moderately durable)
• Larch (Moderately durable)
• Douglas Fir (Moderately durable)
( more information on species )

- Use seasoned wood

- Avoid using sapwood, especially when using moderately durable wood

- European Oak and Sweet Chestnut contain a great deal of tannin. This will initially stain but then wash off. However, use corrosion resistant fixings (eg ss) and protect surfaces below during this period.

- Be aware of expanding and shrinking glazing beads due to moisture content differential. The glazing sealant used should be able to expand into the gap between glazing and beading.

- Unpainted wood will gradually lose it's original colour and fade to a light grey.

Unfinished cladding

Use:
• European Oak (durable)
• Sweet Chestnut (durable)
• Western Red Cedar (European grown) (moderately durable)
• Larch (Moderately durable)
( more information on species )

- Avoid using sapwood, especially when using moderately durable wood

- ‘Green’ wood can be used and dries naturally. Allow sufficient fixings to absorb shrinkage.

- European Oak and Sweet Chestnut contain a great deal of tannin. This will initially stain but then wash off. However, use corrosion resistant fixings (eg ss) and protect surfaces below during this period.

- There is a relationship between cladding longevity and the depth of eaves. 600mm should be the optimum

- Design a splash zone of no less than 150mm above the ground

- Ventilate behind the cladding

- Ensure the sawn ends are treated

Use seasoned wood

- Drying wood below the fiber saturation point renders it impervious to fungal attack

- Where possible, use air-dried wood in preference to the more energy intensive kiln dried wood. An emerging alternative is wood dried in solar-powered kilns

Heat treatment

Originating in Finland, the heat treatment of timber is still a relatively new concept in the UK. The treatment involves heating the timber in an oxygen depleted at temperatures between 100 – 150C.
Heat treatment changes wood properties permanently. In particular, it improves its resistance to rot and mould by changing timber's internal structure so as to prevent fungi attack.

Recycled plastic lumber

Recycled plastic Lumber (RPL) is a wood-like product made from recovered plastic or recovered plastic mixed with other materials, which can be used as a substitute for concrete, wood, and metals.

The technology for manufacturing recycled plastic lumber has been in place since the early 1980s. Plastic lumber is most commonly manufactured from post-consumer high density polyethylene (HDPE), but linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) are also used. These plastic feed stocks are derived from such raw materials as post-consumer milk jugs, soda bottles, grocery bags, plastic wrap, bubble rap, detergent bottles, and water bottles, and other used plastic commodities.

The recovered plastic is cleaned, shredded, and ground. The material is then melted and mixed with foaming agents, UV stabilizers, and color pigments. Then it is molded or extruded into lumber or forms. The product is then cooled and inspected. It is now transformed into 'Recycled Plastic Lumber'. The lumber is formed to specified dimensions through either a molding or an extrusion process. This plastic lumber can then be transformed by consumers and manufacturers into a wide range of products including decks, docks, landscape timbers, parking stops, picnic tables, benches, rubbish bins and planters.