Clinging Film 2

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Clinging Film 2

Postby Stanford Peverill » Thu Mar 30, 2017 9:49 pm

I wrote in these columns last year - June 6th 2015 about my intentions to store lengths of 30 mm x 30 mm x 1500 mm ash square section in wrapped industrial clingfilm. The stock was literally from the tree and wrapped the same day. They had been planed to the dimensions required and stored in the roof space of my workshop, wrapped in packs of three. Regularly checking their condition I decided to use them today on a steam bending project. Being anxious that all their 'moisture life' had been lost and they would be covered in fungus and other gremlins, they were gingerly removed from the film, fettled, cut to the desired dimension and put into the steamer. After a couple of hours or so they became intimate with a stainless steel backing strip and wrapped around the former. Wonder of wonders the 'bend' went brilliantly. I have always been anxious of storing green wood for some considerable time but using the Clingfilm method as a way to retain the natural moisture appeared to work for me. There might of being other variable at play here such as the volume of heat but nevertheless I would be really interested in other readers experience but I will wrap other new stock in industrial clingfilm again.
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Re: Clinging Film 2

Postby monkeeboy » Sat Apr 01, 2017 11:00 am

Did you use a moisture meter on them?
How do you actually know for sure that they were still green?
And was there any sign of mould?

Why does the wood need to be green when being steam bent?
The steam adds moisture and the heat softens the lignin, so why does it matter if the wood is still green or not?
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Re: Clinging Film 2

Postby Stanford Peverill » Sat Apr 01, 2017 7:58 pm

Hiya Monkeeyboy No I didn't use a moisture meter. I watched my supplier cut them into section from the newly felled ash tree so they were very much 'in the green' and packed with plenty of lignin. This, I understand, is the 'glue' that hold the cell walls together. The heat softens this in the steaming process and makes bending possible. In the process of kiln drying, however, this important substance is driven out of the timber and it is very difficult if not impossible to steam bend kiln dried stock. There was no sign of mould, which was surprising. My conclusions are that steam bending is a dark art but very interesting, exciting and very seductive one.
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Re: Clinging Film 2

Postby monkeeboy » Sun Apr 02, 2017 1:40 pm

I'm not entirely sure that the lignin is lost as wood dries.
The lignin is a solid matter in the wood and would not evaporate with the sap.

But it does seem to be commonly accepted that green wood is easier to steam bend.
I'm not convinced that your cling-film wrapped ash was still green though, or stayed as green as it was at first.
If it was stored for any length of time in a contained environment, with the sap in it, then surely it would have started to go even slightly mouldy?
There's no way of preventing microbes/fungal spores from landing on any object except in a completely hermetically sealed environment.
I imagine that the ash actually dried out very slowly, although not to the same degree as a kiln dried piece.
Maybe it came to some sort of equilibrium that suited the steam bending process.

I have stored green wood, mainly ash, in a shipping container that has very little ventilation.
The temperature in the container varies massively from sub-zero in winter to 40+ in summer (with the doors closed).
I've been repeatedly surprised as to how green some wood stored in there stayed despite these conditions and I put it down to lack of air flow, not temperature.
And if the wood is very fresh (especially if felled when the sap is up) then it is likely to go mouldy.
The lack of mould on your wood does suggest a lack of moisture, but I could be wrong!
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