Before you buy a garden room, you’ll probably want to know a bit about how to care for it — especially when it’s timber. When you’re left in the dark about timber care your garden room dream can quickly turn into a nightmare. God forbid, you try to coat your Radiata Pine ThermoWood with varnish, or even worse, gloss paint!
No one wants to get it wrong when it comes to looking after a building that you’ve invested in. We get that. It’s one of the reasons we’re so crazy about aftercare advice here at Gillies & Mackay. And that’s where this blog post comes in. This is your detailed guide to Radiata Pine ThermoWood, so you can look after your cladding like a professional.
What are the benefits of Radiata Pine ThermoWood?
As the name suggests, we make each of our Radiata Garden Rooms with Radiata Pine ThermoWood cladding. When designing these Garden Rooms back in 2024 we chose Radiata for its longevity, moisture resistance, and of course its gorgeous brown tone.
Radiata Pine ThermoWood is heat treated to protect the timber from insect damage, mould and decay. The ThermoWood process also makes the wood extremely weatherproof and resistant to shape changes. All these properties combined makes it an excellent choice for garden rooms in Scotland, and allows us to offer a 30-Year Guarantee on our Radiata Garden Rooms.
We coat our Radiata Pine ThermoWood with a preservative base coat in our workshop, to protect it during delivery and assembly. The base coat also gives the Radiata cladding an extra layer of defence against rot, insects, swelling and shrinkage — we need all the help we can get in Scotland’s wet climate.
Timber has a reputation for being high-maintenance, but with Radiata Pine ThermoWood you can choose a maintenance route that suits you. Because Radiata cladding essentially comes with protection already built-in, it’s not necessary to treat it. You have the option to leave the timber to weather naturally, or to oil the cladding to maintain the tone.
Can I leave Radiata Pine ThermoWood to weather?
If you want the lowest-maintenance option you can leave your Radiata cladding to weather. Left untreated the dark brown timber will gradually turn to a pale blond colour and eventually weather to silver.
Weathering is a completely natural process that results UV and weather exposure. This is a cosmetic change and doesn’t impact the integrity of your Garden Room. If you’re happy with these colour changes, or prefer the look of light coloured Radiata, then you don’t need to worry about treating your building.
Can I oil Radiata Pine ThermoWood?
If you want to maintain the dark brown tone of the Radiata cladding you can oil your building using Osmo UV Protection Oil (Osmo Oil). Osmo Oil protects your building from UV and delays the discoloration caused by weathering by 12 times compared to untreated wood.
If you want to oil your Radiata cladding, we recommend adding a coat of Osmo Oil (Light Red Cedar 431) to your building around 3 weeks after installation. During the first 3 weeks after delivery your Garden Room timbers can shift slightly as they get used to their new spot. Waiting 3 weeks before coating ensures that each board is fully covered with the first coat.
There’s also the option to let the Radiata Pine ThermoWood weather slightly before maintaining it with Osmo Oil. This approach involves letting the cladding lighten to a soft brown before oiling, to preserve a lighter finish rather than the original dark brown colour of the wood. How long you leave the cladding to lighten is completely up to you.
After your first coat of Osmo Oil we recommend re-oiling your building once a year to upkeep the colour. Remember that your cladding is always protected regardless, so there’s no need to panic if you miss an oiling session.
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What shade of Osmo Oil should I use on Radiata Pine ThermoWood?
Osmo Oil comes in a number of different shades. At Gillies & Mackay we use two on our display Garden Rooms: Clear Osmo Oil and shade Light Red Cedar. Light Red Cedar is very close to the natural tone of Radiata Pine ThermoWood but slightly darker.
If you haven’t oiled your Radiata Garden Room and find that the timber has lightened more than you’d like, Light Red Cedar is perfect — it will restore and deepen the tone back towards the natural colour. Clear Osmo Oil will slow down the lightening process but won’t darken the cladding.
For your yearly maintenance, you can use either shade (we trust you!). If you’re happy with the current tone of your timber, clear Osmo Oil will help preserve it. Or, if you’d like to maintain or deepen the tone of the wood, Light Red Cedar is the best choice. You can always use clear Osmo Oil and then switch to Light Red Cedar further down the line, or vice versa.
How do I clean Radiata Pine ThermoWood?
Before you add another coat of Osmo Oil on top of the initial coat we recommend cleaning the cladding with Osmo Decking Cleaner (I promise this article isn’t sponsored by Osmo). This allows you to clean off any dirt or debris that is sitting on the surface of the timber before you seal it under a coat of oil.
To clean Radiata Pine ThermoWood dilute Osmo Decking Cleaner with water in a bucket. You can dilute the cleaner with anywhere from 1:25 cleaner:water (weak) to 1:1 cleaner:water (strong). We’d recommend starting with a weaker dilution and then working up to a stronger dilution if the cladding is particularly dirty.
To clean the cladding, use a stiff bristle brush to scrub the cleaner along the grain of the timber boards. Then rinse off the cleaner, and any dirt, with clean water. Please don’t use a pressure washer on your lovely Radiata cladding, though, as it will make the timber (and us) very upset. Leave the cladding to dry and then you can go in with your coat of Osmo Oil.
You don’t need to clean your Radiata cladding if you’ve chosen to let it weather, but if you fancy giving it a freshen up, the same cleaning process applies.
What else can I do to protect Radiata Pine ThermoWood?
Beyond weathering, oiling, and cleaning there are some little things you can do to protect your Radiata Pine ThermoWood cladding. Regularly cleaning out your gutters ensures that water easily flows off the roof and into the perimeter soakaway (a gravel border around your building) or a water butt. This stops water from hitting the ground, splashing up onto the cladding and damaging it over time.
Another good practice is to cut back any grass, plants, or bushes that are butting up against your building to prevent moisture build up.
Further Reading: How much maintenance does a Radiata Garden Room need?
How do I look after Radiata Pine ThermoWood?
Radiata Pine ThermoWood naturally resists insects, rot, and moisture, giving you the freedom to choose a maintenance plan that suits you. Whether you choose to leave the Radiata cladding to weather naturally, or to regularly oil it, your Garden Room will always live up to its 30-Year Guarantee.
For more information on taking care of your Garden Room take a look at our full Radiata Aftercare Guide. And remember that you’re never on your own when it comes to timber care, — we’ll always be here to answer any questions.
