oak window cills splitting

[cats paws]

Dear All I have welsh oak box sash windows that were made for me a couple of years ago and I have treated them with danish oil every couple of months, but I see after this winter that some of my cills have cracked along the top. Any help with this.

 

[biffvernon]

Hard to say much from the limited description. The oil has probably made no difference. The cracks probably don't matter.

 

[cats paws]

Hi Biff.
The cracks seem to be not very deep and they are on the surface of the cills and running in straight lines a couple of millimeteres deep. Should I fill them with wood filler or continue to just oil the windows, is Danish oil (I use Fiddes) the best product to use or should I use something else?

 

[Andrew Bodenham]

Hello cats paws,

Are these the outside sills that you're talking about? I presume you're oiling the oak to try and keep the nice 'fresh oak' colour. Any chance of a photo?
The cracks sound like the sort of surface degradation that's typical of weathered timber, i.e. wood that's subject to the sort of alternating wet/dry cycle that our weather dishes out. Structurally speaking the cracking will not be a problem, though anything which lets water deeper into the wood is clearly undesirable. So long as it can dry out again there shouldn't be any long term problem, but the finish and appearance of the wood will deteriorate (or become more natural, depending on your point of view). At some point you have to decide to let nature take its course and allow the timber to weather to grey, or to intervene with a coating of paint, oil etc. to keep the water out and preseve the surface finish. Most people tend to take the second route.
Paint is good because it blocks the uV light which doesn't seem to do wood much good. Clear finishes are trickier because they don't have the uV blocking pigments, and so tend to not last so long. I'm not getting into the "which is best" debate because that would take all night - suffice to say that there are hundreds of products in tin for putting on wood, most of which claim to be better than the next in terms of performance, durability, ease of application etc. If you're not careful you can get into some very expensive experimentation. Everybody has their favourite treatment. For what its worth I wouldn't use Danish oil on anything.

 

[biffvernon]

Yes, I really wouldn't worry about such minor cracks at all. It's what oak does. In a couple of centuries there will still be cracks in the cill but you may not be around to notice them. Use Danish oil if it makes you feel good but it really won't do anything much. Danish oil is just tung oil with some added driers to make it set faster. Linseed oil is cheaper if you prefer that look, but on exterior surfaces nature will always win in the end so I'd give up now, enjoy the weathering process and do something more interesting than watching oil dry.

(You know 'catspaws' is what we call the pretty little knots you get in pippy oak?)

 

[cats paws]

The cills are cracking on the outside the inside are fine. Biff suggests leaving it to nature and not putting any treatments on at all, but would this not damage the oak still further. The joiner who made them suggested either danish oil/linsead oil, or sikkens.

 

[biffvernon]

Look at a really old building with oak external joinery a couple of centuries old. See if you can find a piece without cracks.

Relax, it will be just fine, it's the way oak is.

 

[Penners]

Biff suggests leaving it to nature and not putting any treatments on at all, but would this not damage the oak still further.

I don't have anything like Biff's experience with oak, but I second his views on this. The only problems that the cracks are likely to cause is to make you worry. Stop calling them cracks and call them "character" instead, and all will be well.