SUBJECT: TIMBER CLADDING

1 subject : TIMBER CLADDINGDESIGN FOR CLADDINGTo obtain the best possible performance from timbercladding, the designer should give preference to buildingstyles where the CLADDING is sheltered by wide eaves orverandahs. This will give weather protection to thecladding itself, and provide increased comfort for theoccupants by reducing heat build-up on the walls. A studspacing of no more than 450mm should be used in theframe design to minimise the risk of distortion of should be given to the installation ofsuitable thermal insulation behind the sarking, to reduceheat transmission from the external walls to the interior ofthe house. AWall Batts@ are designed specifically for thispurpose, and are specially manufactured so that they willstand up in the wall cavity, and not sag with time as ceilingbatts & HANDLINGT imber CLADDING must be suitably protected fromweather damage prior to storage shed or protective cover must be waterproof,but should also provide for a free-flow of air so that thecladding is not affected by excessive heat build coverings must not trap condensation, andoutdoor storage areas should be chosen so that there isno possibility of water pooling under the covers, whichcould result in moisture uptake into the boards.

2 Inadequate covering can result in:(a)water marking, which can be difficult to cover withtransparent finishes,(b)moisture absorption, which can result in problemswith movement at a later stage,(c)excessive heat build-up, which can causedistortion of the that the CLADDING is stacked level, well clear of theground, and evenly supported at 450mm intervals toprevent bowing and sagging. PREPARATIONT imber CLADDING , exposed to the weather but leftuncoated, will be affected by sunlight, and will absorbmoisture during wet weather and give off moisture in to direct sunlight will eventually result in the surface colour of uncoated TIMBER changing to silver movement will cause the boards to swell andshrink, producing small cracks (surface "checks"), andpossibly cupping. Uncoated TIMBER remaining damp forextended periods may also develop dark discolourationdue to surface impregnation of TIMBER with CCA preservative,whilst giving long term protection against insect attack anddecay, does not prevent colour change, surface checkingof the TIMBER , or other effects of , it is recommended that all TIMBER claddingexposed to the weather be protected with a suitablecoating for extended service on the final appearance required, the surfacesof the CLADDING exposed to the weather should be suitablysealed and prepared so as to provide a suitable base forsubsequent finishing CLADDING should also be sealed on surfaces notexposed to the weather, to prevent moisture movement which can result in board a natural appearance is required, the finish (generally along term water repellent)

3 Should be applied, all roundeach board, in accordance with the manufacturer=sinstructions, before installation. For a stain finish, the firstcoat of the selected stain should be applied all roundeach board before installation, being careful not tooverload the surface, and to brush out any excess to Water repellents should be known brands, rather thanhome made recipes, and should meet the requirements ofAustralian Standard AS : Linseed oil, or mixtures containing a largeproportion of linseed oil, should never be used as anatural finish on TIMBER CLADDING , as the oil encouragesthe growth of mould and fungi which will discolour thetimber. Removal of surface mould is difficult, and it isoften necessary to scrub the CLADDING with a timbercleaning solution and stiff brush before re-coating with asuitable , and some pigmented stain finishes, cannot beapplied over water repellent preservatives and thecompatibility of different systems should be checkedbefore water repellents such as Bar-D-K, will act as asealer on surfaces not exposed to the weather, eg.

4 Therear face. However, Bar-D-K will only give protection infull sun and rain for approximately 6 to 8 weeks before thewaterproofing coating of wax breaks down. Furtherapplications to unseasoned boards may be necessary untilshrinkage stops and the finish coats are applied. If thefinish coats are to be applied before the wax coating hasbroken down, sanding, or washing with Mineral Turpentinemay be necessary for the next coat to be these reasons, we would recommend the use of theintended natural or stain finish as a sealer for claddingrather than Bar-D-K (or similar products).If the CLADDING is to be finished with a paint system, it isadvisable to seal each board, all round, with aprimer/undercoat system, before installation. In the case of unseasoned CLADDING , one coat of theselected paint finish should then be applied to thesurfaces which will be exposed to the weather wheninstalled, including that part which will be covered by theoverlap, (so that shrinkage does not expose theundercoat, which can be damaged from long term sunexposure, causing possible paint adhesion problems).

5 Although seasoned products will exhibit little, if any,shrinkage, it would be advantageous, though notessential, to also apply one coat of the selected paintfinish to the surfaces exposed to the weather, includingthat part which will be covered by the overlap, prior toinstallation,Suitable preparation is possibly more important for CCAtreated pine than it is for CCA treated hardwood, as thereis more movement of moisture in and out of pine, with theassociated danger of board should be suitably protected until required,correctly sealed and prepared, and then installedwithout a natural or stain finish, or paint system is used,the manufacturer's recommendations for application ofpreparatory coats must be followed carefully to achievethe best is a waterproof material that is fixed to the studsdirectly behind external CLADDING .

6 The primary function ofsarking in walls, is to direct any water that may havepenetrated the CLADDING back to the outside of thestructure. It also provides a draught proof barrier to keepwind driven rain or dust out of the wall sarking is fixed on the outside of the studs, from thetop plate down, and over the bottom plate and flashing, orotherwise, in accordance with the vapour permeable, fire-retardant, building papershould be used as sarking behind TIMBER this application, the use of aluminium foil type sarkingshould be avoided, as trapped vapour may wet the backof the CLADDING , possibly causing cupping and sarking is not a substitute for properly installedcladding and it should never be regarded as the principalmeans of of the correct fastening nails is important to theperformance and appearance of TIMBER dipped galvanised or other non-corrosive nailsshould always be used to fasten TIMBER CLADDING .

7 Plain steel nails should not be used, as they are likely torust, causing, unsightly stains, and gradual deteriorationof the TIMBER around the head nails may be used to provide additional restraintof treated pine and Western Red Cedar CLADDING . Siliconbronze nails, although expensive, produce a superiorappearance when Western Red Cedar is coated with anatural or stain finish. When using gun nails, particular care must be takento ensure that the head type, shank size and length,and protective coating, is suitable for the claddingbeing nail sizes for fastening are given below:For Weatherboards - one nail per board at each studFor hardwood and cypress frames -65mm x (plain shank) galvanisedhand nails, or65mm x (plain shank) galvanisedgun nailsFor softwood frames -65mm x (annular threaded) galvanised hand nails, or65mm x (annular threaded) galvanised gun nailsFor 19mm Chamferboard or Ship-Lap CLADDING -2 nails per board at each studFor hardwood and cypress frames -50mm x (plain shank) galvanisedhand nails, or50mm x (plain shank) galvanisedgun nailsFor softwood frames60mm x (annular threaded) galvanised hand nails60mm x (annular threaded) galvanised gun nails(Source - TRADAC Technical Data Sheet 5) Finishing T-Nails are not suitablefor fastening external gun nails mentioned above are framing nails whichcannot be punched below the surface of the board,because of the size of the head.

8 This fact may influencethe user's choice of fastening method to achieve therequired experience is that hand nailing with the correct sizegalvanised nail has generally proved more successful than fastening with gun nails. However, where there havebeen problems with CLADDING fastened with gun nails, ithas often been the result of incorrect nail boards should be fastened as soon aspossible after delivery, to reduce the risk of cupping CLADDING on walls should finish at least 150mmabove ground level. Adjacent earth or pavement should besloped away from the wall, otherwise moisture uptake mayoccur, resulting in deterioration of the CLADDING near bottom edge of the bottom boards should be cut toslope inwards and upwards from the front face at an angleof 15 degrees so that water will be readily shed from thefront stops are attached first, positioned so that the bottomof the stop is at the same level as required for the bottomof the CLADDING , generally bottom of bearer or slightlyabove the bottom of the chamferboard flashing (to allowdrainage).

9 Run a stringline between the bottoms of thestops and check that there is no sag in the line. On longwalls, it would be advisable to use a dumpy level to checkthat there is no sag in the line. Nails can be used forsupport if any sag present cannot be removed bytightening the line. If using weatherboards, use a full length packing board topush out the bottom of the first weatherboard, so that it willbe at the same angle as those above (see diagramfollowing). To protect it from water damage, the packingboard should be sealed all round, including end grains,and fastened a constant 10 - 15mm above the packing board should also be installed above wallopenings to maintain the correct angle. The packing board can be planed before installation (orafterwards, provided that the fastener has beencountersunk sufficiently not to damage planer blades) sothat the angle on the front approximates the angle of theweatherboard, for a neater the end grain of TIMBER is particularly porous, the endsof each board must be effectively sealed, prior toinstallation, to prevent moisture absorption duringrainy conditions.

10 Moisture absorption into the end graincan result in paint peeling, and also prematuredeterioration through rotting, as the moisture is trapped inthe board by the finish coats. For natural or stained finishes, apply a liberal coat (orpreferably two) of the intended permanent finish to the For paint systems, apply a liberal coat (orpreferably two) of prevent water entering the frame during rainyconditions, joints between adjacent boards, and attimber stops, should also be sealed with a paint/staincompatible mastic or silicone sealant. Place themastic on the ends of the boards before installing cutting to length and sealing, position the bottom ofthe weatherboard close to but not touching the stringline. Tack the board at the stop end while applying handpressure against the stop, then tack in position along thestringline.