Wood in Traditional Building 2: Poplar and Pine
Everyone will be familiar with the beautiful poplar trees that make valleys in Burgundy and elsewhere so charming to the eye. Poplar produces straight-grained timber of prodigious length. The wood is soft and easy to cut, and it holds nails very well. It resists splitting firmly because is has an interwoven grain, so it is tricky to plane well; better to use a power plane. But poplar is in any case best kept for rough work.
It has two big disadvantages; it can to warp severely as it dries, so great care must be taken in stacking; and insects just love it. Poplar should never be used unless it is treated or painted, or else the woodworm will have a field day. However, it is reasonably resistant to rot, and as long as it is used with care, is a useful timber. It is cheap and plentiful, light and easy to handle.
Unfortunately, poplar is usually grown individually, in long thin avenues, or as windbreaks along the edges of fields, and more rarely in plantations. Its presence in the beautiful valleys of central France is a great asset visually. However, this causes a problem when it is cut for timber.
Trees that grow alone are subject to pressure from the wind, and so they tend to build up tension within the trunks to withstand the prevailing wind, otherwise they would break. Even where the wind is usually moderate, a big tree in leaf is like a huge sail, and anyone who has handled a sailing-boat knows how much power there is in the breeze. All this pressure has to be handled by the trunk of the tree, so it develops powerful internal connections and stresses to counter the effect of the wind as it grows.
This is all fine and dandy while the tree is alive, but when it is cut and converted, these stresses are released, almost like a spring, and the wood tends to warp. This is why forest-grown timber is always better for building and finishing than timber from solitary trees; poplar is by no means alone in this, it’s just that it’s less common to find forest-grown poplar. It pays to ask your sawmill where they source their timber.
Poplar is very light
Poplar is also prone to warping for another reason: it is a very light timber. Denser woods like oak and pine have more woody material, but poplar has more water when alive. This means that microscopically, it has more cavities. As the wood dries, these change shape and the timber contracts, as is well known. This also can lead to warping. In poplar, because there is relatively speaking more void than cellulose, this effect is amplified. Warping in poplar is therefore a problem, and it must be seasoned very carefully to minimise this.
Poplar is often used for the main timbers in working buildings such as barns. It can look, to the inexperienced eye, a little like oak, especially when it has been there a century or so. But there is an easy test; push your fingernail into a solid part of the wood along the grain; if it goes in, the timber is probably poplar. There is no reason to fear the presence of poplar as a structural timber, but a buyer should thoroughly check all the timbers for evidence of insect attack, and if necessary take the steps required to eradicate it. In most cases the owner should be able to do the work himself, but if not, a specialist should be engaged.
Poplar is easy to cut and holds nails well, but can be hard to plane because of cross grain. It can be pretty enough when left unpainted. Curiously, although poplar is much softer than some pines, it is still regarded as a hardwood.
Pine (sapin) is a generic title given by the timber trade to the wood from a number of species. They are known as softwoods. Most of the pine in use in the UK is spruce, known as ‘whitewood’ and a good deal of spruce is found in France; however, Douglas Fir, Scots Pine, Larch and other species are also found, more commonly than in the UK because of France’s vast natural reserves of mature pine forest. The most sought-after type fund in France is “pin de Landes”, which is Douglas Fir by another name. It is strong, quite resistant and straight. (Most commercial ‘redwood’ sold in the UK is actually Douglas Fir.)
In the Morvan and other mountainous areas, other pines are found, going under the generic name of “sapin”. A good deal of this is again Douglas Fir, and is excellent timber. In my area of France, over the last twenty years, there has been a big shift away from poplar as a general-purpose timber, towards Douglas. I think this is partly due to large amounts of commercially-grown timber in plantations established fifty years or so ago reaching maturity and becoming available, but also because Douglas is a far superior structural timber, and unlike poplar, Douglas planes easily and can be a beautiful timber just with a coat of varnish. It has a noticeable difference in colour between the sap and heartwoods, which isn’t always desirable, but often adds to the charm. Douglas is easily available ex sawmill in big sections and good lengths.
Most of the pine species are easy to work and hold nails well. They make good structural timbers. In particular pine is available in long straight lengths which are ideal for beams, and it is a fraction of the cost of oak. Pine, particularly plantation pine, is not prone to warp unless it has been badly stored.
Pine is often used for tongue-and-groove flooring, but please beware; it splinters easily into needle-sharp shards. Children running around barefoot are particularly at risk and I can assure you that removing an inch-long splinter from a screaming child’s foot is quite enough to ruin your day! For this reason I prefer oak or beech for flooring.
Pines range from those which are prone to rot and very subject to insect attack, such as spruce, to those which very resistant to both, such as larch, pitch-pine or long-leaf pine. Douglas Fir and yellow pine fall somewhere in between. Identifying all of these is a skilled job; the inexperienced are advised to ask the merchant’s view, and treat any timbers likely to be exposed to attack with xylophene in any case. It’s cheap insurance.
Originally published at Rod Fleming’s World.