Thermowood Tongue and Groove Cladding

Tongue and Groove Thermowood cladding is a durable timber which is exceptional for outdoor use. The timber is a Scandinavian Pine which has been heat treated through a steaming process, this process helps to remove almost all of the moisture from the timber in order to make it as stable as possible. All of the resin is also dried up which helps to prevent rotting and leaking onto the surface of the wood, leaving you with a nice clean finish.

Supplied in a Sawfalling grade, you can expect to see a fairly heavy knot content in the boards, the majority of which are sound, live knots. There can be some dead knots though, so we do recommend ordering 10% extra so you can cut these out of the board.

Unpainted Thermowood machines well so you get a smooth finish for your tongue and groove cladding, there are a range of profiles on offer including:

• IWC1
• IWC2
• IWC3
• IWC4
• IWC5

These are a range of horizontal and vertical for with v joint and shadow gap designs. IWC3, IWC4 and IWC5 can all be secret fixed as well. Please make sure that you use stainless steel nails, and we recommend pre-drilling due to the brittle nature of the product, this will help to reduce splits in the timber.

Although you don’t need to treat the timber because of how stable it is, it does take a paint or oil well if you would like to change or preserve the colour. If you leave it, the Thermowood will naturally turn silver grey over time like all timber.

An alternative to Siberian Larch

One of the reasons we are so keen to offer this timber along with our premium range of hardwoods and durable softwoods, is so that we have a suitable alternative for Siberian Larch which is currently unavailable. With Canadian Cedar prices rising to levels we haven’t seen before it has become more important than ever to offer a cost effective and quality option.

Our Thermowood is available as PEFC certified because it is sourced from sustainable sources.

Fitting Guidance

These fitting guidelines are only a rough idea on how to fix your tongue and groove cladding. We do recommend you employ a professional who has experience fitting tongue and groove cladding.

Be sure to read our treatment guidance as treatment needs to be applied prior to fixing your cladding

Breathable Membrane

Consult a fitter to determine if your scenario would require the fitting of a breathable membrane between your wall and the cladding. This membrane stops rain getting to the wall, but allows moisture to escape, helping to prevent internal condensation and mould that can come with it.

Treated Softwood Battens

Treated softwood battens (available from our cladding accessories pages) are most commonly used to fix to the wall (or on top of the breathable membrane) to then fix your cladding to. If you are fixing your cladding horizontally, your battens need to be placed vertically, at around every 600mm (60cm), and vice versa.

Fixing

** Whether you use nails or screws, it's important that they are stainless steel, or silicone bronze ARS, so that the natural tanins in the timber will not corrode them. Never use iron nails for fixing timber.

To help stop the wood from splitting we recommend pre-drilling the timber and then holding it with the screw or nail head when you fit the board to the batten. Look to leave a 3mm gap between the boards, rather than butting them up tight like flooring, to account for any moisture movement and make sure that the tongue is facing upwards otherwise moisture will start gathering in the groove of the profile.

You can also use nails, preferably ring-shanked for extra grip, and again stainless steel so they don't corrode. For lower-density species like cedar, consider using nails with larger heads so the cladding doesn't pull through.

You can fit IWC 1,2,3 and 4 vertically or horizontally depending on the look you want from your timber. Whilst technically you can fit IWC5 horizontally, water can sit in the square channel, which is not recommended.

With each new row of cladding you add, it's preferred that you stagger the joins between each board so you don't create a visible seam.

As already stated, these are just ideas to get you thinking about installation and you should consult a professional installer before fitting your cladding as every scenario is different.

All our claddings are provided untreated. Fresh sawn timber claddings are best left untreated and to go silver grey. There are a wide range of optional treatments available for different species of timber and we recommend talking to the excellent team at www.wood-finishes-direct.com, who know the most up-to-date information on all the newest treatment products.