TIMBECK Profiles - Two Alternative Fixing Methods
All TIMBECK tongue & groove profiles have been designed with an offset groove which allows the head of a fixing to be concealed by the adjoining board. When it is considered appropriate (as assessed under these guidelines), concealing of fixings can be incorporated into the specification. When the concealed fix option is considered unsuitable or inadequate, face fixing of the same offset profile is appropriate.
Typical Conceal Fix application.
The fixing is through the thinnest section
of the board and the head must be flush
to allow the tongue & groove to properly
Typical Face Fix application to the same profile.
The primary and secondary (when required) fixings are through
the full thickness of the board and have the capacity to offer
significantly greater holding and restraining power.
Concealed Fixing Option
Primarily, there are two situations which favour concealed fixing :
- the aesthetics of not wanting the head of fixings to be visible on the finished surface.
- where cladding boards are prefinished with a film forming coating and there is a preference for not penetrating that film.
Concealed Fixing can be undertaken with either hand nailing, gun nailing or screw fixing – further details for each specie are included under their 'Products' tab and in the further sketches below.
While design trends may suggest that the hiding of board fixings are the fashion today, the overall parameters as outlined in this guide do not change. As attractive as concealed fixings might be, they may be inadequate for some situations. Concealed fixings are also located in the thinnest portion of the board which is counter to the requirements of increased performance.
Face Fixing Option
The interlocking tongue & groove detail on TIMBECK cladding profiles allows the heads of fixings to be concealed but it restricts the securing of the cladding to just one fixing per board at each stud (or batten). That degree of restraint is considered quite adequate where minimal movement of a board is likely to take place.
Where greater movement due to any of the influencing criteria (listed elsewhere) is likely to occur, specifiers may prefer to consider the additional restraint provided by adopting the Face Fix option.
TIMBECK’s guidance for fixing cladding lies with
both Face Fixing AND Concealed Fixing depending on the location, exposure and future maintenance levels of the application.
Either option, complimented with penetrating oil finishes,
(one coat as a factory applied pre-finish with a second coat applied on-site after installation)
will provide the optimum exterior cladding.
T & G Detail for non-cedar Cladding Profiles
The Tongue & Groove detail on TIMBECK Cladding profiles
incorporates a 5 degree splay on the top of the tongue to
assist engagement with the groove.
The face of the splay is also normal to the suggested
5 degrees off-square line of fixing.
The groove incorporates an 8 mm offset which provides the
mechanism to cover the head of the fixing to the adjacent
For Concealed Fixing, the method of fixing chosen is at the discretion of the Specifier - conventional Bullet Head nails have long been used and may require final driving in conjunction with a 'nail punch'.
Most proprietary 'Air Gun' nailing devices will work well - most countersunk screws will require pre-drilling of a pilot hole.
Specifiers are encouraged also to consult the technical advice available from the fixing manufacturers.
The Need to Cater for Expansion of Cladding ??
The TIMBECK detail for tongue & groove cladding profiles utilises a very conventional and well proven tongue & groove detail as shown above.
Some of the more recent cladding profiles to emerge onto the market incorporate a gap in the tongue & groove to accommodate ‘expansion’ of the cladding. If expansion was to occur, it would be due to change in moisture content. The logic behind the theory can be challenged and appears dubious at best.
- Traditional seasoned ‘Shiplap’ cladding has been used for decades without ever being installed with an allowance for expansion. When considering a horizontal installation, the top edge of the lower board is fitted snugly against the base of the rebate in the upper board. An allowance for expansion has never been incorporated and performance problems due to that have never been an issue.
- A simple comparison with timber strip flooring tends to also confirm the view. The Australian Timber Flooring Association’s recommendations to cater for expansion in flooring suggests that there is no need for any requirements in runs of flooring (at right angles to the board direction) below 6 metres. Beyond 6 metres, measures for handling expansion are suggested, but these are to cater for possible ‘crowning’ of less than a millimetre which is very apparent in a gloss finished floor. Furthermore, this provision is related to an installation where the individual boards are physically cramped tight together.
(While this comparison with flooring is related to an internal application, the primary cause of movement in timber is due to humidity changes and not physical wetting – the effects of humidity change on flooring and cladding are therefore virtually identical).
Any expansion in a cladding product will likely be the result of seasonal variation in humidity. It will not be related to kiln drying where the final moisture content is too low. The amount of expansion due to seasonal changes in moisture content is relatively small and will largely be absorbed through some degree of fibre crushing. At worst, it may result in minor crowning, which on an external cladding is virtually unnoticeable.
The incorporation of an ‘expansion gap’ may have some theoretical appeal when the detail is viewed on paper, but from a functional perspective, it is virtually impossible to achieve.
Furthermore, with the taper that is incorporated into the tongue on some of these profiles, if the lower board was to expand, it would increasingly add pressure to the walls of the groove and induce splitting of the outer shoulder of the groove.
The following extracts from a NAFI Data Sheet further substantiate the theory of not needing to provide for the expansion of cladding boards:-
NAFI – Wood Solutions – Data Sheet on Cladding
“Other than exercising proper care and good workmanship during installation, no special precautions need to be taken to compensate for slight expansion and contraction in service”.
“With the tongue facing upwards, the tongue and groove are brought tightly together by using a chisel as a lever”.
A far simpler method of catering for ‘accumulated’ movement on high (horizontal cladding) or long (vertical cladding) runs of wall is to incorporate an ‘expansion absorbing’ detail every 5 to 6 metres (decision influenced by shrinkage rate of specie).
Developments in Fastening Technology
One thing from which the Timber Products industry has derived significant benefit is the technological progress that has been made by the fixing manufacturers. The days of relying on a range of smooth shank bullet head nails to solve all fixing requirements are long gone and specifiers are encouraged to explore the range of non-ferrous fixings from silicon bronze and stainless steel manufacturers.
One excellent example is this dual thread stainless steel screw from Spax Pacific which is an ideal choice for face fixing claddings.
The secondary thread is at a different pitch to the initial thread which assures a rigourous hold between the screw and the cladding.
The relatively small diameter head is very conducive to a face fix application with timber cladding.