How can I treat and protect new outdoor oak

[michael]

Slightly off topic but I’ve just had two pairs of old cast iron bench ends fitted with new oak slats. ( I dont think its seasoned)Can anybody advise the best product for protecting oak in an outdoor environment? I’ve considered linseed oil, not sure if this should be boiled or otherwise, but I’ve heard that this can go a bit gooey with age. Other web research has highlighted both Tung oil and Danish oil but some it would seem have had problems with black fungus forming on the wood using these products. Should I perhaps be considering a chemical wood preservative as well as an oil?

 

[Penners]

Oak doesn't really need protection from Mother Nature's puny efforts to destroy it. It will still last for yonks, even if you don't coat it with anything at all.

But if you want to do something, my personal favoruite teatment is linseed oil. Boiled is probably better, for the reason you've mentioned, but unboiled would still be fine, so long as you don't overdo it.

Bear in mind that the oak will probably stain black around the points where it's in contact with the iron. This is only a cosmetic effect, and won't affect its longevity.

 

[michael]

Thanks Penners. I’m quite happy for the oak to go silver with age. Will the linseed oil prevent this from happening? I’m also a bit worried that some types of oil might turn the wood bright orange making these charming old benches look like something from my local DIY store. Is this the case with linseed oil? On the other hand I don’t want the wood to warp or go black so I’m trying to find a happy medium. If I opt for the linseed oil how many coats are generally required. Would one coat be sufficient as I understand that multiple coats can build up to a gloss finish which may also look a bit newish and out of place?

 

[Flyfisher]

My lazy streak might be influencing me here but I'd say the beauty of oak is precisely its natural longevity, wonderful silver ageing and lack of maintenance.
Once treated, there'll just be another annual maintenance task to add to the list and therefore less time to enjoy sitting on the bench!

 

[Penners]

I don’t want the wood to warp or go black

I fear you may not be able to prevent it from going black where it's in contact with the iron - it's all to do with the acids in the oak reacting with the iron.

To prevent warping (as much as is possible - which isn't much) you'd be best to oil both sides of the wood - or neither side. Plus, of course, all edges and end grain. But warping happens due to a complex mix of causes - the part of the tree that the board came from, the grain run in the board, more sunshine on one side than the other, more rain on one side than the other... and so on. Your best bet is to try and ensure that you fix the boards firmly across their width, to try and resist movement. But ultimately it's down to a fair degree of luck.

I've used linseed oil on oak and it certainly didn't turn it orange, although it does enhance the grain (rather attractively, IMO). As to the number of coats, that's up to you. I started with one, and then just wiped on another thin coat whenever the wood started to look dry.

 

[Flyfisher]

I may have posted this before regarding how many coats of linseed oil to apply, but I was told this saying by an old gamekeeper many years ago:

Once a day for a week
Once a week for a month
Once a month for a year
Once a year for life.

It was in the context of walking sticks, though, and is probably overkill for such a durable wood as oak.

 

[biffvernon]

Do nothing. Just sit on the bench and enjoy the view. If the oak wants to warp there is absolutely nothing you can do that will have any effect. Just hope that neighbouring slats warp in the same direction or you will need a cushion. (It probably won't warp.)

 

[michael]

Thanks all. Reading your comments, I’m now tempted to leave the wood untreated and open to the elements. With all the slats bolted in place to the bench ends it would be difficult to get into the end grain anyway. I’m not too worried about a bit of black discolouration where the iron is in contact with the wood but I would like to avoid black mould from forming. Is untreated oak susceptible to this?

 

[biffvernon]

No. What happens is there is a reaction between the tannins in the oak and the iron, which produces a blue/black stain. It can look dramatic at first but the stain is water soluble and so will wash out and fade eventually. Just sit on the bench and admire the view.

 

[FamilyWiggs]

I'm with Biff - sit and admire the view; the weight may help stop the timber warping!

Provided the slats have a chance to dry out regulalry, I don't think you need worry. If the oak slats last less than 100 years, then you have a case to take them back to the timber yard. :wink: