Technical Thursdays - Elm archive
Thursday 29 January 2015
Dave Bates continues his journey through timber types and this month looks at elm
Nobody is too sure how many species of elm (Ulmus procera) there are worldwide. Botanists cannot even agree on naming elms in the Latin format as devised by Carl Linnaeus. 45 seems to be a consensus figure with some claiming up to 200 named clones, but as I am sitting a short walk from an English elm, which has been hit with Dutch Elm Disease for the third time in as many decades and as is the tree that once accounted for 70% of our hedgerow and parkland trees, this variety will be the subject of this article.
Dutch Elm DiseaseDutch Elm Disease has been with us for over a century but it was not until the late '60s that a particularly virulent strain entered the UK. Spread by elm bark beetles (Scolytus spp.) it has been estimated that by the mid '80s, the disease had killed 30 million of our trees.
The beetles infect the cambium layer - the outer layer that holds the cells that transport water up and photosynthesised 'food' from the leaves - with a fungus which can kill a tree in one season. This has been the single most devastating tree disease we have seen in the UK and although some trees have escaped it and there are areas where infection is being partly controlled, and in other places resistant trees are being introduced, it is unlikely that elms will ever dominate the landscape again.
We have a boundary row on the farm of 26 mature trees and numerous suckers, which have escaped the disease over the years and as mentioned above, one standing alone that has had it three times. On the last two occasions, it simply shed the infected branch and continued living. Worryingly, the small trees it has suckered - they reproduce by suckers - have all contracted it this year.
The history of elmI have an old book of Wayside and Woodland Trees, which I believe was printed in the early 1900s, which says there are - were - three main varieties in the UK: rough barked wych elm (Ulmus scabra), smooth leaved wych elm (Ulmus glabra) and common or English elm, which it names as Ulmus campestris.
No mention is made of Dutch Elm Disease. Indeed, the only threat seems to have been from the caterpillars of the large tortoiseshell butterfly (Vanessa polychloros) eating the leaves just as they do with nettles, they being of the same family. Apparently, the elms of the London parks and squares were 'much infested'. That book was written in gentler times.
Incidentally, U. campestris is now accepted as U. procera and some say the wych elm is the true English elm. Enough botany, I can't deal with it!
Being such a prolific tree and with timber of elm being so versatile, it was used extensively in the old days. Small logs were hollowed and used to transport water - our liquid of life - and at the end of it, for our coffins. In between times, being a timber with an interlocking grain, it was lathe turned for use as wagon stocks - hubs - as well as mallets, ships' rope blocks and windmill hubs fitted with apple or hornbeam teeth. It was used for flooring, beams, ships' keels and chair seats among others and as today, fine burrs were used in fancy furniture.
Felling elm - a storyIn the '70s, I was one of many felling diseased elms all over the county. It was illegal to transport logs with the bark on - and still is - and there was no market for it anyway, so we burnt them on site.
Tree after tree of fine timber cut into rings so we could lift them with a tractor foreloader onto fires started with the branches. Elm is not great burning wood as it makes a fine, dead ash rather than cinders and we had some miserable wet winter days provoking the fires into life. It was a depressing time, felling for no other reason than to dispose of diseased trees in the hope the spread would be arrested. But there were lighter moments.
Tree felling is an occupation with many stories to dine out on. Different trees in varied and sometimes difficult places. We had to fell a huge elm next to a busy river. The tree was directly in front of a new river lock used to control the water depth for the river traffic. It was a straight tree with even branches, so easy to fell in whatever direction we chose.
We only had one choice - directly away from the lock and the river into an open grass field, but it was blowing a real hooley that day in exactly the opposite direction to what we wanted. Our winch tractor was on another job so all we had was a ground winch, which we decided to use as a precaution because the wind would surely drop at some stage. So we secured the winch to a ground anchor, cut the fall, made the main cut and knocked some wedges in. Solid.
As we began to winch the tree over, the wind began gusting up to gale force - the older I get, the stronger it was! - and the winch sheer pins broke with a pop. The winch design was such that when these 'overload' pins sheered, the winch simply locked solid and would not unwind. So we put a new set of pins in and tried again with the same result. Twice more we did this and now had no spare pins. It happened that our round saw files were the same diameter and although these were hard and brittle, not soft as the real pins should be, we were young and invincible so we snapped the file into bits and inserted these. We achieved the same result, but still the winch remained locked with the tree leaning as we wanted it, but only just.
We had cut the tree perfectly, the timber was sound, the hinge was parallel and thick enough, the wedges were holding and the winch was well anchored. We just had to wait for the wind to drop. Unfortunately, our efforts had upset a local boat owner who thought we might demolish the lock, so called the river authorities.
Mid-afternoon a new Land Rover with a new winch rolled into the field with a very efficient driver who explained his concerns over the lock and the cost - more than our annual income and probably not covered by insurance - but no problem, with his new winch, he would simply pull it over. We told him there was no way he could anchor his vehicle to get a pull and in any case, when the wind dropped, our tree would fall into the field as we planned. Not satisfied, he came up with a master plan: at 90° to our taut cable, he hooked his winch cable onto ours, drove backwards until there was just one wrap on cable on the winch drum, then using the controls in the cab, proceeded to wind his cable in. It was something like pulling a giant bow string.
Drawing our cable into a V, slowly the tree leaned further into the field but held by the wind as it was, refused to fall. Tighter he pulled and narrower became the V in our cable and more the tree leaned. Just then the wind decided to fight back with a tremendous gust. We had hilarious discussions afterwards on the 0-60mph acceleration of a Land Rover in a wet grass field but that was nowhere near as funny as seeing the driver clamber out shaking like a leaf with his new vehicle now directly under our winch cable and his cable bundled up under the chassis but still hooked over the roof into ours above. Our jokes about his skid marks were not well received and we ended up on our knees slapping the ground with mirth. And the tree? The following morning it was laying in the field waiting for us to finish the job.
The timberElm is a slightly hard, coarse timber to mill and, to my nose, has an unpleasant dung-like smell. English elm is our darkest brown timber but has pale sapwood and can have straight or wavy grain, solid burr or cat's paw burr patches, but I don't recall seeing much in the way of ripple, as can be the case with many other trees.
The variation in the grain/figure can vary hugely within a tree, even within a plank. The planks dry very slowly with little splitting - except around burrs - but they usually buckle and warp quite dramatically. The key is to close stick the planks and put a lot of weight on top, especially if they have been cut to 50mm for chair seats or turned platters. For these, burry bits would look nice but plain or swirling grain is more reliable. The same applies with kilning the planks: use lots of weight to keep it flat.
Turning characteristicsLike the milling, elm is slightly tough to turn and takes the edge off the tools more quickly than most temperate timbers. Although it has a coarse texture, the hardness of the timber usually means it is firm enough to cut well with little end grain tearing of bowls and faceplate work. For spindle work, it cuts easily and firmly because with all spindle work, you will always - or should - be cutting with the grain.
Because Dutch Elm Disease kills the tree by effectively strangling the water supply, it does not affect the characteristics of the timber. However, although elm can remain durable for many years underground and in contact with water, dead trees left standing or piled in the yard after felling do go corky after four or five years and this timber can be a devil to cut cleanly. Burrs can vary from tight and sound to open with fissures, but usually cut well. They are, however, inclined to move and buckle, leaving an almost leathery texture on the piece, especially if they were not fully dry when turned. The effect is very attractive and tactile.
AbrasivesNot much to say on these except that the dust can be unpleasant. When sanding burry pieces or those with voids, it is often better to resist power sanding and use a hand block so that the abrasive does not sink in and round over the leading edge of any holes or voids.
FinishingI am not a great experimenter with finishing products. As elm is a coarse timber, until now, I have only ever used a finishing oil, usually three coats or more left overnight to dry between coats. For the burr clock, however, I used one of the newish hard wax oils. This is a finish I like more each time I use it.
No doubt quicker drying cellulose or acrylic-based products could be used, but I would be cautious about using a quick setting finish on any open burrs, as it is likely there will be globs setting in the voids. Soft wax will increase the shine but with enough coats of oil, the residual shine can be buffed to a satin finish, which suits this timber well.