Anatomy of a Partition

A partition, a division. A single space becomes two.

What we see of this separation is the surface; a skin of whitewash tens of microns thick, stretched taut from ceiling to floor. Beneath this, unseen, is a 3mm skim of plaster on two layers of plasterboard, their tapered edges taped together. A familiar material: in the UK alone 270 million square meters of the board are produced and used each year.

So common, in fact, that we forget that plaster is rock. Gypsum was commercially mined for centuries in Montmartre, hence Plaster of Paris. Naturally occurring hydrated calcium sulphate, it takes the form of a lattice of interconnected crystals. The embedded water molecules form hydrogen bonds between crystals. It is the relative weakness of these bonds that allows the crystals to move past each other, and this results in an extremely soft mineral.

Bake gypsum at 150ºC and the water is driven off, leaving a more brittle hemi-hydrite, which can then be ground to a fine powder. Add water to this powder and the process reverses: the mineral rehydrates; the crystals reform. Instant stone. Except that, even with a fine powder, the water does not penetrate every molecule immediately. At the beginning of the process we have surplus calcium sulphate on the one hand, and surplus water on the other. For the next twenty minutes the plaster takes the form of a thick colloidal suspension. It is malleable, can fill any gaps, smooth over any imperfections. As the water penetrates the powder, the plaster cures and the liquid hardens, enabling it to be polished to a flat, even substrate.

Beneath the skim is plasterboard. Reconstituted rock in a sleeve of card, it is light enough to be carried by one man, and soft enough to screw through without pre-drilling. And yet it supports its own weight, and maintains a flat surface. Combined with a scaffold of carcassing softwood, it is easy and cheap to assemble. Few joinery skills are exhibited in the softwood frame: a header, a sole plate, studs at 600mm centres. Simple right angle cuts and screws forced in at an angle. Noggins forming a haphazard line across the centre, keeping the studs a constant distance apart. All of this hidden from view.

But the wall is more than just a handy support for the paint finish. The combination of liquid and solid plaster effectively seals this room from the other, preventing the transmission of airborne heat, sound and smell. The mass of the reconstituted rock acts as effective sound dampener – the four layers of board reduce sound by 50dB, or a factor of 32. Unsealed, the plaster will breathe, helping to moderate fluctuations in air moisture content. Plaster is not only a good fire retardant, but apply sufficient heat, and, once again, water is driven out of the gypsum crystals. This reaction is strongly endothermic and so cools and helps contain the fire.

Considering architecture as merely surface denies it richness. The details of even the simplest intervention change the way in which the space feels and responds. This is not new technology: plaster was first used as a render some 900 years ago in Anatolia, plasterboard a hundred years ago in America. But we should not take it for granted