Oak Windows Finishing advice

[Offcut]

Hello All,
It’s been sometime since I last posted but I’m in need of some expert advice and help.

I have been making new oak windows for a house that I’m building and have become stuck with how to finish them. I'm really after a finish that will give me approx 5 years protection before recoat. Looking at all the professional windows on the market I kept being led towards Sikkens Cetol HLS plus and Filter 7 coating system. On the inside of the windows I intend to use Osmo Polyx oil as it produces a great finish.
I have also had Osmo UV polyx oil on test for about a year but unfortunately it is showing signs of greying and requiring recoat already.
My problem really is that I want the clear wet look finish with a long maintenance period but the sikkens system; despite being labelled as transparent, is in fact a light brown/very orange colour. The house is subject to a lot of sunlight and therefore any varnish finish is unlikely to last very long.

What does everyone else recommend?

Your input would be greatly appreciated.

Thanks Andy

 

[Woodfinish Man]

Sorry Andy but in our opinion there's no better clear exterior finish on the market than the Osmo UV Protection Oil and as you mention this needs reapplying every year.

Unfortunately the technology isn't there yet for clear exterior finishes...it's the wood coatings equivalent of the Holy Grail. At the moment you'd be far better applying a coloured microporous finish if you want to forget about the windows for a few years.

All the best

Ian McAslan

 

[yetloh]

I certainly agree with Ian. In my opinion there is no better finish for external oak than no finish at all, unless you are prepared to keep re-finishing frequently. Just think of all those very old buildings with beautifull silver grey woodwork - all achieved with no finish at all.

Jim

 

[wisno]

You can try to coat with automotive paint. It is for exterior.
Find the clear coat but it has to applied by spray


Thanks

Good luck

 

[The Wood Butcher]

I'm finding that the Osmo UV Oil + works well on the vertical planes of the window and not at all on the sills. Having spoken to Osmo they don't reccomend using it on horizontal planes, so the Holy Grail still waits.

A shame as I really like the look and feel of the Osmo oil.

 

[The Wood Butcher]

You can try to coat with automotive paint. It is for exterior.
Find the clear coat but it has to applied by spray

Won't work, it will be lacking in UV protection.

 

[The Wood Butcher]

I certainly agree with Ian. In my opinion there is no better finish for external oak than no finish at all, unless you are prepared to keep re-finishing frequently. Just think of all those very old buildings with beautifull silver grey woodwork - all achieved with no finish at all

Unfortunately your windows look terrible for the first 75 years or so, but if you think you'll still be around then why not...

 

[yetloh]

Unfortunately your windows look terrible for the first 75 years or so,

Not in my experience.

Jim

 

[yellowbelly]

you could try Silver Nitrate to stain the oak
Silver Nitrate is used on Sycamore to produce Silver Harewood

 

[Offcut]

Unfortunately i'm not a fan of the silver look and the windows will bleed on the granite walls before long and have decided that I really don't like the look of the Sikkens or coloured microporus finish.

Having now applied Osmo UV oil to the windows I have just noticed the wood butchers comments about not working well on cills. Can you expand on this WB? What happens to the wood?

Thanks Andy

 

[RogerM]

A friend uses Owatrol Deks Olje D1 and D2 on his boat, and after 3 years in what must be one of the most hostile environments for any natural wood finish it still looks like new, despite extreme UV exposure, salt, rain, spray etc. For a satin finish just apply 2 coats of D1 saturator, or for a high gloss wipe on D2 over the D1. It's flexible and doesn't blister although not sure if it's microporous. When it needs refreshing it's just a case of cleaning the surface and wiping on a thin coat. Anyone tried using this on exterior hardwood joinery? Not cheap but appears absolutely bulletproof.

 

[Woodfinish Man]

That's really interesting Roger, must try to get some to run a few tests.

Andy, wood butcher is spot on, the Osmo will wear more quickly on the horizontal sills as water seeps in under the edges and gradually turns grey. However, Osmo have a product called Wood reviver (Oxalic acid solution of some type we think) that works brilliantly at removing the grey. Simply pour onto the affected area, scrub with a coarse brush and wash off with water. leave overnight and then reapply the UV protection oil....nearly good as new.

Hope this helps

Ian McAslan

 

[The Wood Butcher]

Having spent the last two days sanding sills and re-oiling the windows I've decided the next windows I buy will be aluminium...

I've now used an Osmo base coating, called Base Coat WR, on the sills. It's a water and oil based product, very thin and penetrative. It did raise the grain something chronic, but by now I don't care, I just don't want the sills to look rubbish in six months.

 

[Caldinarod]

I found this thread by luck, I am desperate for something which works to put on my oak windows and doors.
Over the last 22 years I've tried all sorts of variations of Sikkens, oils and things I've bought in France, but on my South facing windows in the peak district nothing lasts much more than one season. I like the light oak look you get when Sikkens is new but if you try to re-coat it every year it soon becomes dark oak colour then once it starts to crack and peal on the horizontals it all has to be sanded back to bare wood. SO it is with great interest I read about the Owatrol Deks Olje D1 and D2, it even seems to be specified for this application so I've ordered 2.5 litres. Has anybody else tried it...before I cover the house in it!

 

[RogerM]

Welcome to the forum Caldinarod. I wish you luck with Owatrol. However, comparing a test piece of oak with Owatrol finished teak, it seemed to protect the teak far better than the oak. I think oak is particularly difficult. In fact Sikkens say in some of their technical material that expecting to be able to protect wood against the effects of UV with a clear finish is a bit like expecting untinted sunglasses to protect your eyes in the sun - which kind of makes sense.

I'm running a test in this thread which compares Sikkens with Osmo UV Oil which you may care to follow. Perhaps I should also have included an Owatrol panel. The jury is still out on this one - it's the search for the holy grail for members of this forum.

 

[yetloh]

I fear you are fighting a losing battle. The open grained texture of oak makes it particularly difficult to protect and I doubt that you will ever succeed, other than in the short term. Personally, I rather like the silver colour that unfinished oak takes on quite quickly, so no finish would be the solution that I would adopt.

Jim

 

[Jacob]

....you'd be far better applying a coloured microporous finish if you want to forget about the windows for a few years.
....

Agree. For coloured microporous finish read paint.
All paint is microporous. The thinner the more so. It doesn't really mean anything.
I'd recommend Holkham Hall linseed paints, but oak is a difficult one for windows.

 

[Caldinarod]

I've been sanding them and refinishing them, some for many years, it's amazing how fast they crack and deteriorate once the finish has peeled off, then the rain stains them so the natural bleached silver colour is not really an option in the Peak district, plus the glazing bars are quite fine so can't tolerate too much deterioration. As for paint being the only way to stop UV, surely by now nano-particles as used in invisible sun tan lotion should be finding there way into varnish by now?

Roger, (thanks for the welcome by the way) when you did your Owatrol test did you completely saturate the oak? I only ask because the instructions suggest you should keep the surface fluid for a whole day by constantly re-applying thin coats so that in the end the wood soaks in over a litre per square metre. The tin says you should not treat it as a coating but part of the wood.

I spoke to a guy in the motor paint trade a while ago who was experimenting with car lacquer with additives to give plasticity (intended for plastic bumpers etc) on his windows, I must find out how he got on with it. It seems incredible that in today's world we still can't buy anything to protect oak.
Rod

 

[Phil Pascoe]

Slightly off thread, but worth a comment. A friend of mine, a very good well qualified painter and decorator, was told by the council to take his brand new uPVC windows out as it was a grade 2 listed house and replace them with oak box frames, as was traditional. His reply when taken to court was that he had painted probably thousands of windows in his career, and he had never come across an oak one - because oak is not a good choice of wood for a window.
I walk past the plastic windows daily.

 

[Jacob]

..... I kept being led towards Sikkens Cetol HLS plus and Filter 7 coating system. .....

In the last couple of days I've seen two lots of oak finished with some highly recommended sikkens product.
First was a floor. 5 years old? Where traffic light the surface is a shiny pale orange/yellow but where worn it looks like you'd expect oak floors to look i.e. dark and dingy.
The other was some garage doors (3 years perhaps). The same shiny yellow except where the weather had got in so it now looked like oak but in patches - dark and dingy but weathering to silver.
In other words they would have been better painted yellow to start with - they could then be touched up indefinitely.

Linsed oil is the best but it ends up black - but you can paint over it with linseed oil paint. I wouldn't bother with any of the magic modern materials, they are all rubbish.

And yes I never encountered much oak in my window days - the occasional cill, not necessarily showing any obvious durability compared to the rest of the redwood window.