Fixing Criteria - Factors Influencing a Decision
While a mechanical fixing (nail, screw) is intended to hold a facing (cladding, panelling) against its support medium (stud, batten), its ongoing capacity to do so is totally reliant on the retention of the initial integrity of all three items.
If that integrity is maintained (board remains firm against support, fixing does not lose grip in support, size of hole through board does not increase), the holding capacity of the fixing will remain constant over time.
The single biggest threat to the ongoing holding capacity of the fixing is an inherent movement within the board which is primarily caused by changes in moisture content.
Factors affecting the significance of changes in moisture content include:
- the natural shrinkage rate of the timber specie
(low shrinkage rate, less significant – high shrinkage rate, more significant)
NOTE – Western Red Cedar has one of the lowest shrinkage rates of commercially available timbers while Australian hardwoods have amongst the world’s highest.
- degree of exposure to the elements
(no exposure, negligible significance – high exposure, very significant)
- width of the board
(narrower board, less significance – wider board, more significant)
- maintenance levels of applied protective coating
(well maintained, low significance – no maintenance, significance increases over time to high)
Irrespective of the above mix of conditions, changes in the wood fibre moisture content result in a cycle of board swelling and shrinking. This repetitive action can decrease the support medium’s hold on the fixing and enlarge the hole where the fixing penetrates the board.
The choice of a suitable fixing (and fixing method) which offers appropriate restraint to these movements becomes paramount.
Generally speaking, changes in moisture content to External Cladding will inevitably occur during the life of the product and the effect of that should be taken into consideration when specifying the timber specie and the fixing system.
With Internal Panelling, the changes in moisture content will generally be less significant due primarily to variations in humidity. Specifiers however should not underestimate the significance of that (particularly on some species) and again, choose the fixing method carefully.
Other Influencing Factors May Include
The correct installation of any timber cladding or panelling requires trade skills. Skilled tradesmen invariably have their own favourite, proven and preferred fixing method for each type of job.
Factors influencing a preference may include :
- timber or metal support
- density of support (if timber)
- straightness of support
- size and specie of board being secured.
- hand nailing
- air gun nailing
- length and gauge versus deformed shank
- single shank OR staple
- preferred head shape and size
It is impracticable for the manufacturer of the timber facing product to deal with the plethora of options and provide specific recommendations for all of them. TIMBECK believes that in all cases, the best fixing option for any project not only satisfies the structural requirements but is also determined in conjunction with the fixing tradesman based on his experience, equipment and skills.