Natural external finish on oak windows

[CarolineTheChemist]

We’ve had some beautiful oak windows made to replace the softwood ones that have perished. The old windows were painted with white gloss, which I don’t like at all. After many years of living in rental properties with white gloss slapped everywhere, it has become my nemesis! So we’d like the windows to weather naturally into a lovely silvery grey colour.
Our carpenter has asked me what we’d like to finish the windows with before he fits them and my initial thought was linseed oil. As I wasn’t entirely sure what kind (boiled? Pure?) or how it should be applied, I did a bit of Googling. However, everything I found said that linseed oil paint that is not appropriate for “exterior oak”….

So why can’t linseed oil be used, and what IS appropriate for exterior oak??

Can we leave the windows unfinished? Would it be sensible to leave it unfinished and then once it’s grey in a few years, give it some kind of oil as tlc? What oil would you all recommend?

I’m wary about finishing the oak with anything that might make it look yellowy. I painted our brand new iroko gate with Osmo oil (as recommended by the manufacturer) a few years back and it has now faded in places and looks tatty. I wish I had left it to grey naturally before I painted it.

Also - I read on an old post from 10 years ago that we should be careful about putting oak frames above lead flashing as the oak tannins can stain the lead. Any tips on what to do there?

 

[Cubist]

The essential difference between boiled and natural linseed oil is that the former has a faster drying/curing time making it more suitable for some applications. As far as your window frames are concerned either could be used as could other oils. However, you need to be aware that periodically you will need to refresh the oils as you would with a paint. The key issue for me is to use nothing that allows moisture to be trapped behind the surface.

I have not done it myself, but you could use a strip of the plastic damp course material, trimmed to size, between the frame and the lead in an effort to avoid any risk of discolouration.

 

[88v8]

On external oak I use a 50/50 of boiled linseed oil and turpentine (the real thing, not turps subs).
Soaks in nicely and doesn't prevent the eventual silvering.

However, is the glazing puttied or beaded? Single glazed or units?

 

[Zebra]

88v8's question about the glazing is pertinent. Double glazed panes are bonded together with a material which, I forget why, is supposedly attacked by linseed oil. The linseed oil paint manufacturers issue warnings about its use with double glazed units, not that it can't be done - I did it - but that care must be taken to line the rebates with shellac such that the linseed oil does not touch the edges of the units.
Don't know if that helps at all...

 

[malcolm]

My old farmhouse had oak windows around 100 years old that had not been treated for some time (maybe never) and the sills were suffering. In my current house I've left my exterior oak timber frame untreated but that's vertical and the rain will just run down and it'll be fine. Window sills are much closer to horizontal and would benefit from some protection.

Some sort of oil would probably be good. It's UV light that causes oak to go grey. I think boiled linseed oil would be fine - it has no UV protection so the oak should still go grey. It should get nowhere near the double glazing seal if the window has already been assembled. But it's only an option to apply it in August when it's really hot and will still take a couple of days to dry. Other oils should be OK too and many have faster drying times when they mix stuff in. Your Osmo might have been one of the mixes with UV protection.

I wouldn't worry about oak staining or damaging leadwork.

 

[CarolineTheChemist]

On external oak I use a 50/50 of boiled linseed oil and turpentine (the real thing, not turps subs).
Soaks in nicely and doesn't prevent the eventual silvering.

However, is the glazing puttied or beaded? Single glazed or units?

It’s single glazed, some with iron frames. It hasnt been done yet, but I think the plan is to have some of the windows puttied and some beaded.

Thanks everyone!