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Home Improver Guide 11
TIMBER CLADDING
STORAGE AND HANDLING  |  ESTIMATING QUANTITIES  |  INSTALLATION
  PRE-FINISHING  | STEP BY STEP INSTRUCTIONS   | FINISHING
 

STORAGE AND HANDLING   top
It is important to keep cladding clean and dry because dirt marks and stains are not hidden by stain finishes, also any uptake of moisture may cause problems with movement at a later stage. Make sure the cladding is kept covered, stacked level, well clear of the ground, and the stacks are evenly supported at 450 mm intervals to prevent bowing and sagging. Some cladding, such as western red cedar, is relatively soft and requires care in handling to prevent minor denting.

ESTIMATING QUANTITIES  top
Cladding is normally sold in random lengths. Wherever possible, single length boards should be used on un-sheltered walls and short lengths can be used between windows etc. or sheltered parts of the wall under verandahs, eaves etc. Butt joins should be distributed as evenly as possible.  To calculate the required lineal metres, the following method is recommended:

Lineal Metres = Area to be covered in sg.m. x 1000 + 10% wastage
                            Cover width of cladding (mm)

INSTALLATION  top
Chamferboard and ship-lap cladding profiles will usually be supplied as seasoned. However, cypress and hardwood weatherboard profiles, as well as some western red cedar profiles may be supplied unseasoned. If unseasoned cladding is used the boards are overlapped to allow for shrinkage. Refer to Figure 1.
Unseasoned boards should be fixed as soon as possible after delivery to reduce the risk of cupping or splitting.
Unseasoned boards wider than 200 mm should not be used.

FIXING
When fixing weatherboard profiles, it is important that nails are placed so that movement of boards caused by seasoning does not create stresses sufficient to cause the splitting of the timber. Therefore only one fixing is used per stud and care should be taken so that individual boards are not nailed together. Refer to Figure 2. The design of the edge-joint in seasoned cladding profiles will already allow for minor seasonal movement, so two nails are used per fixing. Refer to Figure 3. Spacing of supports (studs) should not be more than 650 mm centres measured along the board.

SARKING
All external walls should be constructed to prevent the penetration of rain or other water to the inside of the building. Paint finishes on timber cladding cannot be relied upon to meet this requirement because wind driven rain might penetrate through cracks, knot holes or joints. Therefore, unless protected by a verandah, a waterproof but vapour permeable or breather type sarking such as ACI Flamestop Or Antiblaze 121 should be installed behind all timber cladding to prevent such penetration under severe rain and wind conditions. Sarking should be fixed on the outside of studs and directly under the cladding according to the manufacturer's instructions. Refer to Figure 4.

NOTE:- The use of aluminium, foil type sarking directly behind timber cladding should be avoided as trapped vapour can form moisture drops which will wet the back of the timber cladding causing cupping and distortion.

PRE-FINISHING   top
Depending on the final appearance required, a priming coat of either water repellent, stain or paint should be applied to all surfaces before fixing. It is also advisable to apply an undercoat colour matched to the final coat so that movement lines will not be apparent after any shrinkage or movement.

STEP BY STEP INSTRUCTIONS  top

HORIZONTAL CLADDING
Step 1.
Decide which method you will use for joining your timber at internal and external corners. The usual method is the use of timber stops as illustrated in Figure 4. At external corners boards can either be cut in neatly to a stop or left to run through and cut off to a straight edge later and the stop fitted over the cut ends. Alternatively cladding can be mitred at external corners and scribed at internal corners, however this is a time consuming method and requires precision.

Where cladding abuts masonry, enough clearance should be left to prevent moisture in the masonry from being taken up by the boards. Alternatively the ends can be sealed and the joint protected by a cover strip set in mastic.

Step 2.
Select the first board to be fixed. If using weatherboards, undercut the bottom edge of the first board to an angle of about 15 degrees so that water will be shed readily. Refer to Figure 7. inset.

The first board should be laid to a string line. Refer to Figure 7. Mark out the width of one board on both corners of the wall to be clad. Partly drive a nail at these points and run a string line between them. Partly drive nails into every third or fourth stud along the string line. Remove the string line. The first board is placed against this line of nails and fixed. Chamferboard and ship-lap profiles are laid in a similar method with the tongue facing upwards. The rebate or tongue and  groove are brought tight together using a chisel as a lever. Refer to Figure 3.

Weatherboards will require a full-length packing piece under the first board and as necessary over openings. Weatherboards are fixed with only one nail per stud. This nail should be driven as closely as possible to the butt of the board but it must miss the thin end of the board underneath. Lap hardwood and treated pine boards 30 mm and nail them 35 mm from the butt. Lap western red cedar boards 20 mm and nail 25 mm from the butt. A gauge block is used to keep the boards at - the same spacing. Refer to Figure 2.

Joints are placed over studs. Tight fitting joints are achieved by cutting a board slightly over-length, bowing it to get it into position and then snapping it into place. Refer to Figure 5.

Remember to apply a primer to all freshly cut ends and seal all joints, including the stopped ends, with a paint/stain compatible mastic or silicon sealant. Place the mastic on the ends of the boards before fixing them. Nails should be driven with care. Heavy and excessive nailing distorts the wood and may cause splitting during weather changes. Some cladding boards may require pre-drilling of the nail holes at the ends to avoid splitting.

Step 3.
As you progress up the wall, take measurements at the ends of walls, beside openings and at 1800 mm centres along the wall to make sure you are keeping parallel. Refer to Figure 6. This is particularly important either side of openings d the cladding continues above the opening. Joints may be kept apart slightly to correct this d necessary. Catch up over a number of boards K the difference In parallel is great.

Step 4.
Cladding around window and doorframes need not be stopped d the butt jointing is neat. When fixing cladding on the next wall around a corner, make sure the boards are in the same line.

FINISHING  top
After fixing, one or two finishing coats of stain or paint should be applied in accordance with the manufacturer's recommendation. Where cladding is to be painted, nail holes may be punched and filled prior to application of the finishing coats. Filling of nail holes in cladding that is to be stained is not recommended.
                                                                    

Information sourced from TRADAC Home Improvement Guide.
(Timber Research and Development Council)

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