Timber maintenance

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Maintenance is an item that needs to be considered at the design stage and is discussed in detail in The Timber Service Design Guide available for download below. When deciding on the quality of elements and fittings that will be specified for a newly designed structure, a designer frequently chooses between items that have relatively high initial costs and low ongoing maintenance requirements and items that are cheaper to purchase but may have more onerous maintenance requirements. In some design briefs, the designer is called upon to devise a maintenance schedule for the completed structure. The Table below gives a list of the items that may need to be considered when drawing up a maintenance schedule.

The key to the durability of timber has already been identified as "keeping it dry". Most of the maintenance requirements outlined in the Table lead to the exclusion of moisture from the timber. Others are concerned with the integrity of barriers that control infestation by termites. The Table provides guidance only, as fittings, coatings and barriers of different qualities and characteristics can be installed and the manufacturers may recommend different maintenance intervals. As well, exposure to sunlight, chemicals, salt, and water may vary with the service environment and all of these affect the maintenance regime required.

Item

Maintenance or Inspection Period

Remarks

Finishes

‑ internal

‑ external

 

~ 10 to 15 years

see Table 1.9

 

Cleaning

Clean non-confined surfaces as required.

Remove build-up of soil against timber near to ground.

Dirt, mould etc traps moisture, increases potential for decay.

Cladding

roofing, weatherproofing

~ 10 year inspections

some environments may make inspection of weatherproofing more frequent

Timber cladding can have design life (5 to 100 years)

Termite protection

 

‑ physical barriers

 

‑ chemical barriers

inspect annually or in accordance with <AS3660>

 

~ 10 years for maintenance of barrier

 

as required by supplier (~2 to 20 years)

Any sign of termites should prompt action

Ventilation

subfloor, wall, roof

Check that vents are not blocked ~ annually or after any new work

Clean as required ~ 10 years

Vents are essential to prevent build up of moisture/condensation

Vapour barriers

subfloor, roof

Check integrity ~15 years or after any new work or other maintenance in the area

 

Metal fasteners

‑ integrity

 

 

‑ corrosion

Retighten bolts, screws and repunch nails if req'd after 6 months and one year if unseasoned timber used

 

Check at intervals dependent on type of corrosion protection used. Inject water repellents for bolts.

Replace any suspect fasteners.

 

Hot dipped galvanised fasteners solve many corrosion problems.

Plumbing

Inspect gutters, downpipes etc 10 years

Repair any plumbing if a leak is noticed

Moisture accelerates decay, deterioration

Decay

Check at the same time as connections

Repair or replace as soon as any decay is noticed

 

End-grain

 

‑ sealants/caps

Inspect 3 - 5 years

Replenish as required by manufacturer and before repainting

 

This Table gives guidance on the maintenance of paints and stains for exterior surfaces. There are significant differences in the expected life of the various coating systems and these can influence the type of coating system selected. Note that clear finishes have a much shorter life than opaque finishes.

Finish

Appearance

Initial treatment

Maintenance of surface finish a

 

of wood

 

Cost

Procedure

Period

Cost

Paint

Grain and natural colour obscured

Prime and two top coats

Medium to high

Clean and apply top coat or remove and repeat initial treatment if requ’d

7 ‑ 10 years b

Medium

Clear

Grain and natural colour unchanged if adequately maintained

Four coats (minimum)

High

Clean and stain bleached areas and apply two more coats

2 years or when breakdown begins

High

Water repellent c

Grain and natural colour - visibility becoming darker and rougher textured

One or two coats of clear material, or preferably dip applied

Low

Clean and apply sufficient material

1 ‑ 3 years or when preferred

Low to medium

Stains

Grain visible, coloured as desired

One or two brush coats

Low to medium

Clean and apply sufficient material

3 ‑ 6 years or when preferred

Low to medium

Organic solvents preservatives d

Grain visible, coloured as desired

Pressure, steeping, dipping, brushing

Low to medium

Brush down and reapply

2 ‑ 3 years

Medium

Waterborne Preservatives

Grain visible, greenish, fading with age

Pressure

Medium

Brush down to remove surface dirt

None unless stained, painted or varnished

Nil

Legend:
a This table is a compilation of data from the observations of many researchers
b Using top quality acrylic latex paints
c With or without added preservatives. Addition of preservative helps control mildew and mould.
d Pentachlorophenol, tri-n-butyltin oxide, copper naphthenate and similar materials.

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