There is a good deal of lead being used on my oak frame extension. I heard that lead should not be in direct contact with oak as the oak produces acids and corrides the lead. On my building they seem to have nailed the lead to the oak in quite a few places and ignored the plans that show a membrance. Any advice on how serious a problem this really is? There does not seem to be a lot of info on the subject. Thanks.
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Lime
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It will depend on the water content and humidity of the situation where the lead and oak are in contact.
Long-term I'd consider the corrosion risk to be quite high.
Long-term I'd consider the corrosion risk to be quite high.
biffvernon
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I expect the lead is there to keep the oak underneath it dry.
There are some rather unusual situations such as:
but I doubt it will be a problem for you.
There are some rather unusual situations such as:
http://www.buildingconservation.com/articles/roof/leadroof.htm
but I doubt it will be a problem for you.
I would hazard a guess and say that exterior lead in direct contact with green oak may only last 80 or 100 years instead of the average 200 to 250 years it may last if in contact with masonary tiles or walls. If lead can be isolated from corrosive reactive materials and kept well patinated with purpose made oils, the life of lead will extend into millenia and not decades or centuries.
I would not worry too much, it will outlast you :wink:
Middi
I would not worry too much, it will outlast you :wink:
Middi
biffvernon
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It might be wise to use one code heavier in vulnerable locations than Bodge the Builder suggests if you want it to be good for your great grand children.
Since posting have got further info which may be useful to others. It's not the issue df condensation it's tannic acid from green oak and other hard woods that is the problem. Not sure how great a problem it is and how quickly it occurs but it's in the literature and guidance notes for lead and conservation practice so ought to be followed.
The building reg notes state:
All Lead flashings and sheets to green oak frame to be coated with bitumen paint on the side facing oak and to be separate from oak with a breather membrane or DPC to protect the lead from corrosive tannic acid from the green oak.
I will be getting them to do it retrospectively.
The building reg notes state:
All Lead flashings and sheets to green oak frame to be coated with bitumen paint on the side facing oak and to be separate from oak with a breather membrane or DPC to protect the lead from corrosive tannic acid from the green oak.
I will be getting them to do it retrospectively.
Lime
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The moisture enables the acid to leach out of the wood, otherwise if dry it remains locked in the wood.Alex F said:
Painting the underside of lead is totally against good lead working practice.
It will mean that the lead will stick to the wood and prevent necessary movement required by the lead when moving in heat, cold etc.
The biggest form of short-term failure with leadwork is splits and cracks caused by lead adhering the material it covers.
Lime
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I hope so.MdB said:
However some types of underfelt becomes sticky under lead too and/or the bitumen can travel through it.
tobydog
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Just when I thought I had enough to worry about with the old part of the house! :roll: Our new extension is oak clad and the flashings above the door and one window are lead and, as far as I can tell, are in direct contact with the boards above. Whilst the oak was not totally green, it was partially air dried. The tannines have been coming out for about 2 years now so I'll have a look at the weekend for any staining. I'll add it to the list!
I think the intention is to use felt in addition but I have merely quoted the notes I was supplied by the architect.
My impression is, many in practice, do apply lead directly to oak and probably in many cases it is not a problem. I suppose it depends how long one is aiming for the building to last. Personally I like the thought of doing the job so that in theory future generations will not have to replace the work although perhaps in practice a future owner will knock down and rebuilt anyway!
My impression is, many in practice, do apply lead directly to oak and probably in many cases it is not a problem. I suppose it depends how long one is aiming for the building to last. Personally I like the thought of doing the job so that in theory future generations will not have to replace the work although perhaps in practice a future owner will knock down and rebuilt anyway!
Andrew Bodenham
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AlexF,
There are two issues here. Firstly there is a technical question about the effect of oak in contact with lead. I don't know enough about that to comment, but I'd be guided by your architect. Lead manufacturers (e.g. Calder) have useful info on their websites.
The second issue, and perhaps the more important, is that your builder has chosen to ignore construction details provided by the architect, presumably because he/she didn't understand the importance of the detail, didn't have the necessary materials or was doing that bit on Friday afternoon and simply couldn't be bothered. Makes you wonder which other details they've decided to ignore. If I was you I'd be informing him in writing of the defect and inviting him to put it right in a timely fashion and at his expense. It's been my observation that tradespeople, regrettably, will often take the path of least resistance, and do need supervision to keep them up to standard. I hope you get it all sorted out ok.
There are two issues here. Firstly there is a technical question about the effect of oak in contact with lead. I don't know enough about that to comment, but I'd be guided by your architect. Lead manufacturers (e.g. Calder) have useful info on their websites.
The second issue, and perhaps the more important, is that your builder has chosen to ignore construction details provided by the architect, presumably because he/she didn't understand the importance of the detail, didn't have the necessary materials or was doing that bit on Friday afternoon and simply couldn't be bothered. Makes you wonder which other details they've decided to ignore. If I was you I'd be informing him in writing of the defect and inviting him to put it right in a timely fashion and at his expense. It's been my observation that tradespeople, regrettably, will often take the path of least resistance, and do need supervision to keep them up to standard. I hope you get it all sorted out ok.
Keithj
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Oh!
There's a lot of lead in our repaired building, with oak butting right up to it. It's thick stuff, mind.
There are tannin stains on it, where the green oak has "bled" onto it. I was intending to rub that off come the spring, but maybe I'll go and take a look to see if it's eroded the lead at all.
There's a lot of lead in our repaired building, with oak butting right up to it. It's thick stuff, mind.
There are tannin stains on it, where the green oak has "bled" onto it. I was intending to rub that off come the spring, but maybe I'll go and take a look to see if it's eroded the lead at all.
biffvernon
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I'm not claiming to be expert on this but the tannins in oak only become mobile tannic acid and get onto the lead when the oak gets wet, and the point of the lead is stop it getting wet. Hence the stuff about condensation as this is a way it can get wet that one didn't think about.
It is vital that the timber is seperated from the lead so that the metal can move, with thermal expansion / contraction; if it is in contact then the lead will quickly settle on to the irregularities of the timber and, being unable to slide over the surface will soon start to crack.
Isolation from corrosion is a lesser and secondary item.
See Calders site (as mentioned above) - underlay
"Underlays are used to isolate lead sheet from its substrate. They allow expansion and contraction with changes in temperature by reducing drag between the two materials. An effective underlay will also support the lead sheet and level out substrate imperfections such as nail heads or knots. Our underlay additionally protects the lead sheet from condensation and corrosive attack, is free of any substance that can degrade lead and is not adversely affected by in-situ welding."
Good luck - check that your lead worker is aquainted with the 'Lead Development Association' - they publish excellent manuals.
Isolation from corrosion is a lesser and secondary item.
See Calders site (as mentioned above) - underlay
"Underlays are used to isolate lead sheet from its substrate. They allow expansion and contraction with changes in temperature by reducing drag between the two materials. An effective underlay will also support the lead sheet and level out substrate imperfections such as nail heads or knots. Our underlay additionally protects the lead sheet from condensation and corrosive attack, is free of any substance that can degrade lead and is not adversely affected by in-situ welding."
Good luck - check that your lead worker is aquainted with the 'Lead Development Association' - they publish excellent manuals.
Lime
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Yes, the underlays are completely different from roof underfelt that I have seen used too often in the past.stephenh said:
There is a polyester based underfelt available and also building paper may be used but not if it is likely to get damp.
I'd use the polyester for preference.
Have a look at how to use the underlays in these two pdf downloads:
(You can check that it is being used properly when installed and quote verbatim from them if necessary.
)http://www.britishlead.co.uk/downloads/underlays.pdf
http://www.britishlead.co.uk/downloads/BLM%20Building%20Paper%20Download.pdf
biffvernon
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Lime said:
There's nothing like using traditional materials.