Sealing the Facing Product on all Surfaces
As referenced in adjoining web pages, the single biggest threat to product stability is changes in moisture content - this applies to all timber facing products irrespective of their being installed in weather exposed OR weather protected locations.
The application of oils or other surface protecting materials is a recommended means of minimising changes in moisture content, but the performance improvement afforded by these finishes is only optimised when the initial coating of the protecting substance is applied to ALL surfaces AND faces of the facing product.
To achieve this, it is imperative that the facing is ‘sealed all round’ prior to installation. Factory pre-coating is the more cost efficient way of applying an initial coating, but site application can provide a similar result if the application is thorough.
Sarking is one of the most important components in ensuring optimum performance from any timber cladding.
The Importance Of Air Space
To enable weather exposed timber cladding to respond to natural changes in atmospheric conditions (humidity, rain wetting, condensation etc), it is essential that air is able to move freely on both faces of the board. When the cladding is fixed over a vapour permeable membrane and directly to framing members (whether they be studs, noggings or battens), the air space at the back of the board is achieved via the spaces between the framing (irrespective of the presence of insulation batts).
In situations where the cladding is not fixed directly to individual framing members but is fixed over another flat surface (ie a masonry wall or a plywood sheathed frame), the provision of 'free air space' at the back of the board can be achieved by first fixing battens to the flat surface then fixing the membrane and cladding to the battens.
Battens should be seasoned and at centres to suit the specification for the specific cladding product. The minimum thickness of the battens should be 25mm (nominal) but may need to be thicker depending on the length and positioning of the cladding fixing nails (or screws).
Storage on Site
All material should be stored on site in a dry, well protected location. If stored on natural ground, temporary bearers should be packed as necessary to ensure a level platform well clear of the ground.
If stored on a concrete slab or other prepared area, packing should also be incorporated to ensure free movement of air under and around the packs.
All TIMBECK Cladding and Panelling products are produced from seasoned timbers where the moisture content is generally below 15%.
As each project is fundamentally different with respect to geographical location, season of the year when constructed, propensity for excessively wet or dry conditions, it is strongly recommended that boards be allowed to acclimatise to any new environment before being fixed into position.
This is best achieved by removing any packaging, separating all pieces and temporarily restacking under a well covered area so as to allow plenty of free air flow between all pieces.
Acclimatisation is particularly important for interior applications where the moisture content of the material to be installed varies from the average Equilibrium Moisture Content for the in-service environment by more than 2%.
More on Sarking
Sarking is a waterproof but vapour permeable flexible sheet material that is fixed directly behind timber cladding. Its primary function in walls is to prevent wind and storm-driven water penetrating the cladding and to direct it back to the outside of the structure instead of it lodging within the frame.
Sarking will also provide a draught proof barrier to keep wind driven rain or dust out of the wall cavity.
Sarking must be impermeable to liquid moisture yet still allow the free flow of water vapour from the back surface of the cladding.
If sarking restricts the flow of vapour, timber cladding which has taken up moisture during periods of wet weather may tend to cup as the outside face dries.
Only vapour permeable building paper, vapour permeable reflective foil laminate (RFL), or breather type sarking should be used.
Polyethylene film, impermeable aluminium foil, or other nonpermeable material should never be used as sarking immediately behind timber cladding. Building papers with fire resistant properties are also available.
Note that the manufacturers of perforated foil insulation recommend that it not be used for sarking immediately behind timber cladding.
It is good practice to use a vapour permeable sarking on the outside of studs, and directly under the timber cladding. Insulation material should be behind the sarking.
Sarking is considered essential in walls subject to high wind conditions and wind updraughts and also for use where boarding is fixed diagonally or vertically.
The use of wall sarking is not a substitute for well-chosen and properly installed cladding and it should never be regarded as the principal means of weatherproofing.
Vapour permeable sarking should always be used and installed according to the manufacturers recommendations.