Black stains appeared overnight on my new oak windows - help

[mew]

Hi

Ive just had my new solid oak windows and door fitted.

They have a base and top coat of Osmo Polyx oil UV 420 applied. They were fitted 3 weeks ago and on Tues we had torrential rains all day and night. Yesterday when I came home I was mortified to find the sills and georgian bar have leached what I can only describe as black ink some of it looks like small dots other is larger blotches. It cant be mold as it appeared over night so im guessing its the wood's natural tanins. can this be fixed as I dont want it to get worse and I best using something else.

I cant understand why this has happened when its been treated with what I thought was a really could product.

I wanted to keep the the most natural colour oak as possible so have kept to the clear osmo stuff but this no longer seems sufficient from the staining which has appeared, as I dont want to have sand it off every time it rains heavily and appears again. Please help, what can I do. I dont want to use varnish either, would like a more oiled finish to be maintained.

Can it be fixed?

Thanks
MEW

[grahamhobbs]

I think you probably have some steel fixings, perhaps small glazing pins or steel ironmongery?. Steel will stain oak black (or blue/black). Oak should be fixed with non-ferous fixings.

[healer]

I'll ask my OH when he returns but I know the tanin in the oak make oak workers hands purple when they wash their hands - I've many stained towels to prove it!

[healer]

is summary of OH response.

The acid in the oak discolours the iron not the other way round. Marking like shouldn't be that quick. Windows shouldn't be made with iron - it should be copper/brass/stainless steel!

Out of curiosity he has emailed Osmo in Germany to see if they have any ideas. We'll let you know the response.

[Millymollymandy]

I would contant the manufacturers and ask their advice about what products they recommend for their windows/doors. If they say oil is OK, then I would mention the stains and ask for their further advice. Hope you get it sorted as it must be really heartbreaking.

[mew]

Many thanks

There are no steel pins/fixings etc where the staining has occured whatsoever. I can only see pins right at the top of the window under the arch and this area of the windows is fine. The back 2 upstairs windows, the first floor landing window and the front door have no stains whatsoever but these are far more protected from the rain so im almost convinced its something to do with the water since it happened after a full day and night of none stop heavy rain.

Thanks Healer - My joiner has been to see the windows this morning. He's scratching his head a little too. He is contacting his oak supplier/manufacturer to see what they think it might be (who also recmmond using Osmo). He said he is going to contact Osmo also for me. If you hear back from Osmo in the meantime if you could let me know what they say that would be great as it is very heartbreaking yes - so much so ive lost sleep at the thought of this being a recrurring problem and it not being able to be fixed.

At the moment its a case of sanding of the areas which have the stains and re-oiling them. I will attempt a third coat to see if this helps as I was wondering if perhaps 2 coats hadnt penetrated the wood enough.

I just dont know what else to do.

Thanks again

MEW

[healer]

Hi mew - we have a response back from Osmo in Germany. Its in German so OH is translating...
"This reaction can not be caused by treatment with our UV protection oil.
The explanation is as follows:
Oak as a wood has a rich chemical content. The tanic acid reacts very strongly with iron and/or alkalines.
The Osmo treatment is breathable, and moisture transfer happens constantly.
Presumably on the surface of the wood there was either iron dust or cement dust.
In combination with rain or moisture this will lead to a chemical reaction.
Unfortunately these blemishes can only be removed from the wood by sanding."

Hope this helps.

Osmo will always be breathable so it will never seal the oak so you might have to watch out for things like cement dust...
This is verses the breathable coating allowing the frame to dry out and so reducing the risk of rotting.

[mew]

Hi Healer

Yes this response has been extremely useful. Before second coating it I did give the windows a very light go over with a fine wire wool which I then wiped off with a clean dry soft cloth. Chances are I would guess this is what could have possibly kickstarted the reaction.

The plan is to sand the affected areas using only sandpaper this time. Fingers crossed for a better result.

Thank you so much for your help on this. It really is very much appreciated.

Mew x

[Sheffil]

Hi Mew,
I know it's a few years since you posted about black stains on your oak windows, but I wondered whether you have any updates that may be useful for me. I recently had some large French windows built out of oak and installed (last October). We used a high build exterior oil recommended by the installer, and put about 4 coats on before winter. All was fine until this wet last few months, when we started to see specks and lines of black along the sill and lowest part of the doors. I sanded them down and re-oiled them during the present dry spell, and so far so good. However, when I spoke to the installer, he said that oak can often have a naturally occuring fungal spore present on the surface which, if water gets to it, it will start to grow as a black speck or streak. It's possible that since we are using an oil rather than a varnish, that water pounding on the sill managed to force it's way through the oil, or perhaps we just didn't get enough coats on. There was no iron or steel wool in contact with those parts of the doors, so it can't be iron staining. I just wonder whether you have continued to use wood oil, and whether you have any hints or helpful advice for us. The doors were really expensive, so I don't want to risk damaging the wood permanently. If it's simply a case of putting a coat of oil on every few months on the bits that get the most weathering, that's what I'll do. Any comments will be appreciated!
Thanks, Phil

[Thomzo]

Hi Phil
Don't be disappointed if you don't get a reply to this. Mew hasn't visited this site in over 2 years.

However, a few years ago my (now ex) partner and I ran a property maintenance business. We offered a service sanding down and re-treating wooden garden furniture. We investigated a lot of different timber treatments and each manufacturer told us never to use steel wool when sanding down exterior timber. Minute traces of steel are left embedded in the wood which will rust and decolour it. The rust can also cause the timber to rot.

Zoe