Is some sort of finish a must for external oak?

PhilC · 27 Nov 2015

Hi, I have come across various threads that offer advice on how to finish oak to stop it going grey but I have a new oak frame along with oak French doors which I would like to look natural ie go grey in time but.

1) Does the frame and or the doors require an external finish of some sort to prolong the life and prevent issues with the doors changing shape etc?
2) If it does need a finish is there any available that will let the timber go grey but still provide protection from the elements?

Many thanks.

AJB Temple · 27 Nov 2015

In my opinion a finish is not essential. I have built barns from oak, clad in oak and with medieval style oak windows and doors - all left natural and all nicely weathered and rot free. First one was built 30 years ago. I have a pair of French oak front doors that are at least 300 years old and still perfectly usable. It does depend what effect you want: if it is pristine looking then timber preservatives are the way to go but once you start down this route you are on the maintenance treadmill. Oak always goes silvery grey in the end unless it has a frequently maintained joinery finish that you keep intact. I have this on all of the window frames of the house we recently bought in Kent, and wish I didn't.

RobinBHM · 27 Nov 2015

It certainly possible to allow oak to go silvery grey, but:

-On some aspects that receive no sunshine it could go black or green

- It depends on the joinery design, traditional joinery that had no provision for draught sealing or modern locks could cope with a high degree of movement without any problems. If your French doors operate with a multipoint lock then you may find there is a limit to how much it will cope with such movement.

-oak left untreated will initiallly suffer from water staining on the faces, ingress of water into the joints resulting in the joints going black due to tannins, end grain will soak up a lot of water so you may get excessive swelling at the bottom of door stiles etc.

You could try treating the doors with a water repellant like Thomsons which will stop the water staining in the short term and let the sun do its work killing off lignin and turning the surface grey. I would recommend using end grain sealer on bottoms of stiles etc. There is no clear treatment that will protect the oak and allow it to go grey

I now offer customers a low build light oak finish which was actually designed as a decking and cladding stain. It has a matt finish and does not look like the high build transluscent finishes that joinery companies generally offer, which I think look too plastic.

In the joinery industry, the colour 'light oak', is generally accepted as the lightest tint that will provide an acceptable UV protection. Whilst there are clear finishes that have UV inhibitors, they are unlikely to last more than a year. Danish oil is not really worth using outside, it will protect for a few months but will get burnt off quite quickly.

PhilC · 28 Nov 2015

Many thanks for the reply's.
Mmmmm decisions, decisions. Robin, the doors will indeed be multipoint locks so won't take much movement before they become inoperable.
I don't suppose you could let me know what the light oak finish you use is? Or, as I have used Microshield Ultra waterproofing cream for brickwork in the past I wonder how that would work with oak, might try a bit on an offcut. I think I'll head towards some sort of finish on the doors but leave the rest to weather.

RobinBHM · 28 Nov 2015

The product is:

http://www.remmers.co.uk/Product-catalo ... c31.0.html

I dont think you would be able to buy it from remmers but I have some in stock so would happy to give you a pot of it. If by any chance you are near to East Grinstead you could collect.