How best to stabilise rotted oak?

[Penners]

I've been helping friends to expose an original ogee mullion window in their timber-frame C17th house. The window has been imprisoned under concrete render for goodness-knows how long - I reckon more than 50 years, at the very least.

The oak members of the window are very well preserved internally, where they weren't covered with concrete. But externally they are badly rotted and have suffered from (now extinct) infestation by woodworm and DWB. Some of the finer parts of the mouldings are so delicate that they crumble to dust when they're lightly touched (see my pictures below).

The CO has given them permission to plant a new, secondary window-frame externally on the timber frame, to protect the old window. The glazing bars of the new frame will align with the old one, so as to minimise any visual change to it.

The CO doesn't want the old window to be hacked about with repairs (I and my friends completely agree with him). With regret we have to accept that some parts of the mouldings are beyond conservation, but these represent a minority of the window. We would rather conserve what remains of it in as good a condition as possible, leaving the rotted parts to speak for themselves - but to be stabilised as much as possible to prevent any further deterioration and, as I said, protected for the future by the external secondary window.

Ideally, we'd like to treat the most delicate parts of the wood with something that will impregnate and bind its crumbling structure together. I think that the remainder can then be stabilised with wax.

Does anyone have any thoughts or suggestions on how to conserve the crumbling wood? Obviously the treatment must be "friendly" to the wood, and not become the source of further problems.

Any ideas would be very welcome.

 

[worms]

Perhaps you could phone the conservators at a suitable local museum and ask for advice?

 

[biffvernon]

http://www.donhead.com/conservation_of_timber_buildings.htm (The book)

http://www.birmingham.ac.uk/schools/iaa/departments/ironbridge/news/2011/timber-conservation.aspx (Pleasant film, nice music)

http://www.wealddown.co.uk/Other-Courses/Masters-Programmes/ (You need 18 months and loads of money but they give you a bit of paper at the end)

http://www.ihbc.org.uk/context_archive/95/mccaig/iain.htm (More practical and an introduction to the philosophy of Araldite)

http://www.tonygraham.co.uk/house_repair/Historic_Timber_Resin_Repair.pdf (As above but more so)

http://www.buildingconservation.com/articles/rooftimber/rooftimber.htm (Good reading with reference to resin repairs)

http://www.benring.co.uk/our-products.html (Advertisement for BENCON 20 EPOXY CONSOLIDANT)

 

[MatthewC]

I don't like to advertise major companies, but there is one who sells things that do "what it says on the tin". They sell "Wet Rot Wood Hardener" which says (on the tin!) that it is "designed to soak deep into the fibres of decayed wood. When dry the special resins harden, strengthening and reinforcing the softened wood... Can be used on any softened, decayed or rotting wood, inside or outside..."

I have used this previously on the softwood window frames of a fairly modern house with apparently good results. I don't know if it is suitable for an old building or how well it works on oak, but it might be worth a try.

Matthew

 

[middi]

No easy way around this problem Penners, simply becauuse these fine detailed window bars if exposed to the elements the still remaining details will be lost to wind and rain and, worst of all, not much can be used to stabilise the outer surface without compromising the breatheability factor of the still sound wood.
A compromise has to be reached if that window has to remain in situ
1) repair with great skill and effort the outer surface --Not practical or useful from a conservation point of view in this instance as this will involve replicating those fine detailled bars or replacing the whole window lights, the original will be lost for ever.
2) lightly and carefully clean the existing by using a combination of vacuum an commpressed air then cover with warm melted ( thinned down) bee's wax as this will stabilise the crambling exterios frass on the wood.
3) The stabilised window has to be protected from the direct weather elements to save it as existing and there is no other choise but to have a secondary window arrangement to protect it.

(I suspect you knew all the above)

this example is the sad side of conservation, the time will come when one has to acept that an acient artwork cannot perform the function for wich it was originally intended and has to be protected by concealing it beyond a "facade", museum style.

Middi

 

[Penners]

Many thanks for replying, chaps.

worms - thank you. I am still in conversation with the CO about the problem. He claims no particular expertise, though, so if this route doesn't look promising I might do as you suggest.

Biff - some very useful stuff, there. Thank you. I have emailed Benring about their Bencon 20 product. Have you ever used it? Do you know whether it has a sufficiently low viscosity to soak into the wood? The course at Birmingham looks fascinating. Do you know what town was featured when the class went on their field trip to snoop at real, live windows (of which there were some lovely examples)? I wondered whether it might be Chester.

Matthew - yes, I have considered that product, thank you. I'm just a bit concerned about its long-term affect on the wood. I might talk to the CO about it.

Middi - all good advice, thank you. I've never used warmed beeswax - does it become very liquid, or can it be smeared on like butter and then shaped to suit? Fortunately the prospect of further damage from wind and rain can now be averted with the new, secondary window on the outside. And much of the inside face of the window is still very sound timber. Do you feel that applying some sort of low-viscosity resin to the outer faces would still be a bad plan, given that the inner faces would remain breathable? I should add that the wood is now thoroughly dry (although I haven't taken a moisture-content reading on it).

 

[AMc]

Have you given SPAB a ring?

With wax could you spread it on then heat it with a hair drier to liquify it in situ and help to control it penetrating?

 

[MdB]

Two layers of glass + sunlight + wax = greenhouse = big puddle at the bottom?

I would also thought old wood + wax would burn really rather nicely if there was ever a fire.

 

[Penners]

AMc - thanks for the idea. I'm not a member of SPAB - would that matter, do you know? As to the beeswax, I'm not sure how spreadable it would be, unheated. I may have to carry out some experiments, if we go that route.

Or maybe we need something more spreadable, like "I Can't Believe It's Not Beeswax". :roll:

Two layers of glass + sunlight + wax = greenhouse = big puddle at the bottom?

A good point, MdB, thank you. Actually it'll only be one layer of glass (regs have been waived), but it's still a point worth considering.

Middi - any experience of beeswax in this context, please?

 

[AMc]

AMc - thanks for the idea. I'm not a member of SPAB - would that matter, do you know?

It seems not though it might be polite to make a contribution or to join if you feel their work is important or their advice is worth the membership fee ?
http://www.spab.org.uk/advice/

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[skier-hughes]

They gave me loads of advice before I joined, had hardly any in the last 4 years, but I feel the few pounds is well worth it.

 

[middi]

Beeswax and oak timbers.

The best source of beeswax is is the natural stuff that can be obtained from beekeepers, a number of beekepers advertise their honey product and wax as a by-product. ( usually not too far from a local area where one lives

Spreading it on badly frassed timber is quite simple, make sure the timber is clean and dry and DO NOT USE wirebrush or any other harsh bristles scrubbers ( hence the use of a vacuum clean in conjunction with some lightly pressurised air to ONLY remove dusted frass).

Place the stiff wax " lump(s)" in an old paint tin ( or your best small boiling saucer- makes no difference-) and place the saucer on - ideally- one of those small portable one ring camping cooking stoves next to the window to be treated. Warm the wax close to melting point and turn the flame as low as you can get it and keep the tin/saucer on it. Once the wax becomes liquified use a soft, thin brstle brush to spread it on the wood area , keep the brush in the pot and return to the stove as soon as the temp drops and the wax starts to bind and solidify then repeat the process untill the whole of the desired area has been treated. This will fill all the cavities of the frass and stabilise further deterioration with no ill effect to any rmaining wood or frass. A " plasticky" finish with a good, transparent, outline of the wood detail is the end result. This process has been used by myself on badly frassed wall studs ( internally), bressumers, door frames. and floor beams. Admittedly all internal work protected by thr elements.
If future carbon dating of the timbers to be treated is not an issue then ( CAREFULL !!!) use of white spirit added to the wax and melted will speed thing along considerably from an application point of view, also the wax will remain quite malleable after is has cooled.

Middi

 

[middi]

.... sorry Penners cannot comment on resins. Never used them on oak.

Middi

 

[Penners]

Many thanks again, Middi. That's a very useful set of instructions. Thinking about MdB's concerns above, I've checked the melting point of beeswax, which is listed as 62 to 64 degrees C. I think that reassures me about any risk of melting due to sunshine through the outer window.

AMc - thanks. I shall definitely give SPAB a call. I'm confident about Middi's wise counsel, but it won't do any harm to see what SPAB have to say about this.

 

[MdB]

As always, can you post some before and after shots please? I've never seen this sort of thing done so I'm interested in the results.

 

[Penners]

Certainly, MdB, so long as you don't hold your breath! I'm not sure when I'll get round to the job.

 

[Keithj]

That's useful information to store away. The only slight snag is that I'm allergic to beeswax (one of the very few triggers, but that's life).

 

[biffvernon]

Beeswax would stop the wood looking dusty but can't add much strength. A drying oil like linseed would add a tiny bit of strength to crumbly wood (though it might make it look darker). If you want strength you could paint it with (purists look away now) Cascamite!

(Ducks)

 

[88v8]

I used Ronseal wood hardener resin 30 years ago on some fairly rotten wood. Repainting for the first time this year I saw that there is still good bonding and the wood around the repair is still sound. It's very liquid and will penetrate. Repeat coats will develop a little strength as well. Then if you wish you could fill it up to profile with a stainable filler.

Wouldn't use beeswax unless the window is north-facing. When the sun gets on it, it will melt......

Ivor

 

[Penners]

Cascamite

I remember using Cascamite when I were lad, building a boat with my father.

Biff, if you were doing the job I've outlined above, is that what you would use?