On the 5th August 2018, we started an experiment to see how well applying Osmo UV-oil maintains the natural colour of Western Red Cedar. We have written about this experiment before, but to refresh you, we took three offcuts of Cedar from a project here at Garden Room HQ. On the 5th August, we put one length in a dark corner of our shed and with the other two applied two coats of Osmo Clear UV-oil to half of each board.
We then stood the boards up against a south-facing wall. We set a reminder to take a photo of the Cedar each month, to monitor if there was any significant change in colour. Some of our month by month photos can be seen here.
Cedar will naturally weather to silver grey
If left unprotected Cedar cladding will weather to a silver-grey colour. The speed at which this will happen depends on the exposure of the cladding, and the weathering will not necessarily be even, across the whole of the building.
The change in colour does not affect the durability of the cladding. Western Red Cedar has a maintenance-free lifespan of 20+ years. It is the visual appearance which can look aged. There is nothing wrong with this change; in fact, some garden room buyers want to achieve it from day one. They want to create the mellow grey colour naturally without having to apply paint to colour the cladding.
The silvery grey cladding finish can be achieved on a new building, by using a specialist Siberian Larch product. If this is of interest to you, take a look at this project by Garden Spaces with uses it, and this one by Outside In Garden Rooms.
One year on the Cedar has changed colour - significantly!
5 August 2018
The top half of the boards have 2 coats of Osmo clear UV-oil applied.
5 August 2019
One year on, the unprotected area has turned silver grey. The right-hand board, from the same batch, has been in our shed all year.
On the 5th August 2019, we took photos of our exposed and control boards, exactly one year on. As you can see, there has been significant weathering of the untreated exposed area. There is actually a higher degree of weathering and colour change than we were expecting in a year.
Interestingly, there is very little change in colour between the board with the Osmo UV-oil applied, compared with the unexposed board. This proves that applying the UV-oil is worth the time and expense if you wish to maintain the original colour of Cedar cladding.
Applying UV-oil is an ongoing commitment
If you want to maintain the original colouring of your Cedar cladding and slow the ageing process, you need to make the decision at the design stage. As the UV-oil needs to be applied before the Cedar is exposed to the light.
Some garden room companies will apply UV-oil to each board in their factory prior to delivering it to site. Other companies will apply the UV-oil for you as they finish the build. You will find that there is a charge for this service on top of the cost for standard Cedar cladding and that there are companies who are not keen to stay on-site to apply the finish, so don't offer it.
It is, however, a fairly easy job to do yourself. You can buy Osmo UV oil from sawmills like Millworks and on Amazon - we have personally ordered from both sites. We would recommend either buying a pack of disposable brushes, or a tin of Osmo brush cleaner - which will be useful over the years for cleaning brushes.
The UV-oil is applied by brush, and two coats are needed initially. The oil will need recoating every few years. Here at Garden Room HQ we have added one coat each year since the cladding was installed three years ago, and the cladding still looks pretty much like new!
It's a relatively quick job to keep topped up. Our 5 meter by 4 meter Cedar clad extension takes just over an hour to oil, plus a little extra time to prepare the decks.