Water staining on cedar cladding?


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Established Member
17 Jan 2021
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So I think my Cedar cladding is water stained. See pictures below:

overall view of staining / blotchiness
big view.jpeg

mid way through the oiling process, some oiled, some not oiled
mid way oiling.jpeg

  1. do you agree this is water stating?
  2. what is my best plan to remedy?
Extra background knowledge
  • The cladding was fitted to my garden room and then left a few weeks without protective oil on (I wont go into reasons why). It's oiled now, in Osmo 420 clear, but I think the staining happened when it got wet in the unprotected period
  • Oil was applied with a microfibre roller
  • Oil can was shaken prior to application (it didn't say you needed to stir it on the can, so I just gave it a thorough shake, could this be an issue no stirring it?)
  • It could be just the way I applied the oil (as opposed to water staining) - I notice some areas near the edges of the trims where it looks blotchy and inconsistent, its like a stripe where i ran the roller down the edge.
  • see the mid progress picture - you can see that the un-oiled section looks pretty smooth and not water stainy - HOWEVER, it did look blotchy BEFORE I sanded it all back, so I figured I had removed the staining. However, the oil seems to have brought it out again (see second picture)
  • its 'high grade' cedar, I think they call it 'number 2, clear and better' and it doesn't really have any knots at all so I'm reluctant to blame that
  • in the early morning, the staining looks quite bad, I assume because it's absorbed moisture overnight, becuase it all looks darker. After an hour in the sun it lightens up and it looks pretty good, almost perfect actually
Its kinda bugging me, as its nice Cedar, and it doesn't quite look right. I want to rectify it to get it perfect.

My remedy options:
  1. sand it back, re-stain but try a brush this time
  2. sand it back, apply vinegar solution (?) to remove water stains, re-oil with a brush
  3. your ideas???
thanks for any help you can provide

Here are some additional pictures:

zoomed in pic of some staining:

zoomed in pic of some boards closer to top that do not appear to be stained, but this could be that their natural lighter colour means they don't show it, who knows:
good boards.jpeg

Hi Martin - very smart looking room!
It looks like moisture staining to me, I have no experience of whether sanding this back will remove the discoloration as have only done this in the past with oak - which did remove the water marks.
By way of comparison this is my cedar shingle covered workshop - so no sealer and around 11y of weathering -


It may be water staining. Personally, I wouldn't get very excited about it and just go ahead and oil as is. Given time it will all end up looking much the same as imageel's workshop in any case unless you're prepared to undergo major refurbishment effort every year. I'm quite happy to leave outdoor wooden items to age naturally, as in the example below, an oak outdoor table that had a quick coat of oil when new just to get a pretty photograph. After that it's been left to just get on with it outside all year round, as in the lower image, taken about seven years after the table was built. Because it's a table off which we eat from time to time, the top every now and then gets a scrub down to remove black gunk, lichen and whatever else can be scrubbed off. Slainte.


320-outdoor table.jpg
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Trying to get exterior wood perfect, is a real rabbit hole to get sucked into.
As @Sgian Dubh says, unless you're prepared to execute a comprehensive
renovation every year, it will weather.
As above, let it be....
But if you #really# have to, sand it back then apply oxalic acid , lightly rinse off and leave to dry, then oil. But i wouldnt bother, ive seen far worse water staining, its not all that noticeable
Thanks for the replies. I know the consensus is leave it but I'm a little OCD unfortunately and it will continue to bug me. The oxalic acid seems like best option so far but I do have one other thought....

Could it be that my pre-sanding has taken care of the original water staining but introduced another problem at the same time. The new problem would be one of two things:
1. Rough sanding.... A rough surface, sanded only to 80 grit is maybe too rough for the oil... should I try 140 or something?
2. Inconsistent sanding... possibly not all sanded to exact same level of roughness, could that cause the oil, once applied, to be patchy?

I did a job a few years back with cedar cladding. The customer ( a competent and intelligent person ) sanded the cladding to 180g, but from memory de silva ( the supplier ) recommended 80g ( with the grain )

If you go too fine it reduces the amount of penetration by the finish.

How many coats are you putting on? It may be worth picking a couple of the 'worst' boards and coating again, the finish will probably get more even with subsequent coats.
Thanks that's good to know. My cedar is from Silva too. I was hesitant about putting more oil on but did wonder if that would help even it out.... I might try it like you say on the worst offenders.
I'm doing two coats. Only done one so far
Sgian Dhu says it all, above

Just slap on more oil, or not bother at all , as the fancy takes you. Whatever you do will weather dramatically, unless you paint it every few years.
Cedar needs no treatment if fitted properly and will weather to a light matt grey, like most woods. Oil will darken it over time.
Bit of a thread resurrection:

Is this stuff likely to do same job as oxalic acid for removing water staining on my cedar: Link

When I searched for oxalic acid that came up in the search so I assume there is a reason for that....
I tried clicking on the link but my s/fix app opens instead and doesn't show a product, just homepage ( its really annoying when it does that )
Anyway, you can get oxalic on ebay, amazon, any boat chandlers.
It comes from rhubarb
Just leave it, after a while it will mellow and blend. The cedar on my shed is a few years old now I did it with osmo uv oil.
It looked fresh for a couple of months but then you just forget about it anyway, it has melowed and greyed a good bit. These tiny marks will likely dissapear pretty quickly.

I tried clicking on the link but my s/fix app opens instead and doesn't show a product, just homepage ( its really annoying when it does that )
Anyway, you can get oxalic on ebay, amazon, any boat chandlers.
It comes from rhubarb
Thanks. I did find it on Amazon but I want to buy it NOW as I'm in impatient mode 🙂