Wood Rot and Stainless Steel

[SHUG]

I have found significant wood rot where the stainless steel rudder fastenings attach to the wooden rudder.
Is it just a matter of rot starting in a confined damp place or is the choice of metal significant? Would bronze or galvanised fittings be better?
I have found articles about wood corroding metals but not vice versa.

 

[TradewindSailor]

You can get electrolysis of the wood, especially with bronze. I doubt if that is happening here though. I rather suspect that the rot is due to water ingress at the fastenings or lack of adequate paint protection under the fitting.

 

[William_H]

I have heard of mild steel damaging (rotting) wood at the bolt hole. I have not heard of stainless steel doing the same although I don't understand the mechanism of the rot so can not comment on SS. I would say regardless you will be stuck with fitting bigger bolts and try to isolate the wood from the bolt perhaps with epoxy. good luck olewill

 

[Poignard]

AD-782 485 - 'Degradation of wood by products of metal corrosion' - Forest Products Laboratory

https://www.google.com/url?q=http:/...ds-cse&usg=AFQjCNH2M5NASnZYc_dwkSDa89DhwzUPBg

 

[vyv_cox]

AD-782 485 - 'Degradation of wood by products of metal corrosion' - Forest Products Laboratory

https://www.google.com/url?q=http:/...ds-cse&usg=AFQjCNH2M5NASnZYc_dwkSDa89DhwzUPBg

It's an interesting article, although it does not specifically mention stainless steels as far as my speed-read can determine. I guess the critical point that arises is whether the stainless steel fittings have deteriorated at all? If there is visible crevice corrosion on the fittings then it might be assumed from the article that this has also damaged the wood. If not then water ingress seems more likely. In either case the message is to keep the water out by using plenty of sealant.

 

[SHUG]

Thanks Vyv and parsifal for pointing the way to a very useful article.
There is some corrosion of the "Stainless" steel and from what I have read elsewhere, the combined process generates acetic acid which causes further deterioration. The indications are that the rudder was painted after the fittings were installed so when water got in it could react with the bare wood.So...the moral of this story is that sealant or paint should be used on the wood before installing metal fittings.
Thanks all.

 

[oldsaltoz]

I suspect you need to re drill the holes 25 mm oversize and fill with a mix of epoxy resin and micro-fibres, allow 24 hours to cure and re-drill to the required size for your bolts.

This will not only seal the timber against further seepage but also give you protection from bolts crushing the timber.

Good luck and fair winds.

 

[GrahamC]

Hi
Many years ago I had a problem with Stainless screws that were holding down the engine bearers on an East German built Folkboat. The engine bearers were oak and I was advised that the wood had rotted round the shank of the screw due to the acid in the oak. The screws were replaced with bronze and problem cured. It is questionable that the Stainless screws may have been of poor quality which would not have helped.
Cost of repair in Oban in 1964 was and I quote "thirty shillings by the Station Clock" Happy days

 

[vyv_cox]

Hi
Many years ago I had a problem with Stainless screws that were holding down the engine bearers on an East German built Folkboat. The engine bearers were oak and I was advised that the wood had rotted round the shank of the screw due to the acid in the oak. The screws were replaced with bronze and problem cured. It is questionable that the Stainless screws may have been of poor quality which would not have helped.
Cost of repair in Oban in 1964 was and I quote "thirty shillings by the Station Clock" Happy days

Oak can be quite a difficult one as I understand it has its own galvanic potential, so maybe the combination of it and stainless steel was just a bad one. Good to know that bronze was the answer, pity tin is so expensive.