Red cedar UV protection

woodingabout

Hi there, interesting questions about discoloration, blacking and cracking, which I think require a few clarifications.

The change in colour of the wood is not due to the fact that colour “leachs out”, the discolouration you see and the initial grey process is the UV breaking down the lignin in the wood. As the cedar resins come to the surface and are eventually less able to resist the absorption of water, the increase in humidity in the wood allows the mould spores that are present in the wood to get activated and you start seeing mould growth (i.e. blackening). Finally, the cracking starts as the rotting process continues, i.e. the UV keeps breaking down the lignin, with the wood greying first, then weakening, then mould spores developing and as the structure of the wood weakens and more water can enter and evaporate it eventually cracks, and the process starts all over again on the next layer.

When I wanted to keep the wood looking as natural as possible I have used Woodoc Wood Dressing clear. It has UV protection and anti-mildew but it’s non-film forming so it is just absorbed into the wood. They explained to me that the polymer in the product forms a loose mesh so that it doesn’t leach out, but because it is clear the colour of the wood will fade over time so they recommend a seasonal application. I think a couple of years should be fine and probably you can keep it a bit longer (if you like a greyish tinge) but the antimildew should keep the blackening at bay for a while. Sorry I have never used the Roxil Wood Protection Cream so I can’t really comment on it.

lastdayofmay

Thanks for your very comprehensive reply to my question.

The company that makes the Roxil cream are sending me a small sample tube in the post for me to try out. I'll try and get hold of a sample of the Woodoc as well for comparison. I'll treat a sample of the Red Cedar with both and also leave an untreated bit to see how they weather. The only problem is that I'm planning on building the garden office at the and of August, so not much time for any weathering effect to show up.

I don't mind the wood fading or discolouring as long as the effect is even. I've seen quite a few examples where the resins in the wood appear to have been washed out (or come to the surface, as you describe) on some sections, but not others (e.g. those protected by a balcony or overhang). This is why I think I need a product with a waterproofing effect (both the Woodoc and the Roxil appear to have this), although I guess UV is also a factor if some parts get more shade than others.

woodingabout

If it is waterproofing that you are looking for, and can treat the cedar before installation, then Woodoc 50Matt (or Gloss) it's your best choice. W50 is a marine grade product which will provide waterproofing and UV protection, but best to apply two coats on all sides (taking care of sealing the end grains) before installing and then the last coat after installation to make sure that the areas where the film is pierced (when the cladding is nailed/screwed in) are resealed. Film build is key for good protection and an extra coat will probably add another 12 months to the maintenance cycle.