Environmentally benign preservative for (English) oak?

Alan Sloan alansloan at maccas.globalnet.co.uk
Sat Dec 19 08:10:08 EST 1998


Preservative?  Why bother ?.

Oak in England at least is high in natural oils with a tight cell structure.
It won't take any preservative in and likewise it does not absorb a lot of
water.  If presevative is used just treat end grain. If it is properly
jointed and detailed, and  the roofing is tight it will stand several
hundred years.

The key is to keep water out.  A DPC is usually essential, though it is
possible to build on posts set in the ground.   A wide eaves can provide dry
storage or covered walking space around the building, if you want to keep
the structure dry.

Frame structure or log cabin?

Avoid using sapwood, very definitely for anything exposed to the weather.
If possible, work with the grain if you need curved timber, and check your
soil.  This is because soil quality has a lot to do with the quality of the
finished timber.  Work the greenwood with joints which accept the inevitable
shrinkage...there are traditional techniques which are really well worked
out, but if you want to innovate then you should understand the principles.
Look at Stave Church detaining in Norway, there pine buildings preserved for
7 hundred years without  artificial biocides.  Polish techniques are also
well proven, and incredibly exicting visually.  Again, these are techniques
that took hundreds of years to develop...even the way the end of a shake is
carved has a bearing on performance.

Now, if you have small oak stock, why bother to square it up?  A post in the
round performs perfectly in a structural sense.  By sawing you waste time
and strength, and expose the torn sap cells to weather and insects.
Let me know if I can be of any more help.

alan

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