Diary of an Eco-Builder

The walls came tumbling down this week. Not, thankfully, the walls of our timber frame (which are yet to rise), but the old brick walls that form the boundary at the front of our site.

The walls came tumbling down this week. Not, thankfully, the walls of our timber frame (which are yet to rise), but the old brick walls that form the boundary at the front of our site. It was a pity to lose them, but they were leaning precariously and various DIY bodges over the years had not done their structural integrity any favours. We want to rebuild them to last another century, so non-stop Jonny, our current site hero, knuckled down to the task of reclaiming them, brick by brick.

Most of the wall had been built with traditional lime mortar, a soft binder that is relatively easy to scrape off, but some sections had been made with the cheap and cheerful modern alternative - cement. These had set so hard that it was impossible to remove the cement without ruining the bricks in the process.

The ubiquitous use of cement is a hidden eco-disaster, because the life expectancy of any masonry building is far shorter than the solid materials it is constructed from: buildings fall apart before bricks crumble. Reusing bricks, time and again, would cut the huge environmental cost of the three billion new bricks manufactured in the UK every year.

Until the beginning of the 20th century, lime mortar was used to build everything from houses to gothic cathedrals. Cement, invented in the early 19th century, eventually triumphed because of its structural rigidity, especially in the versatile form of concrete, a cement and rock mixture that can be poured to make any shape you desire. The death knell of English lime kilns came in the Second World War, when huge cement works were built to construct our Cubist beach defences. After the war, their output was diverted to reconstruction (in some unfortunate places only minor modifications to the beach model were required), rapidly wiping out the market for lime mortar.

But rigidity is not everything. Lime mortar may not bond as tightly as cement, but this gives it a flexibility that enables walls to cope with pressure and movement without cracking. Unlike cement, lime mortar is porous and allows walls to breathe: any dampness inside a wall can pass through the mortar rather than being forced through the bricks, damaging them in the process.

In the same way, a wall rendered with lime will let moisture escape, whereas the same wall rendered with cement will encourage moisture build-up inside your house.

Lime may not be quite as brilliantly green as its small, round homonym, but it beats cement on all counts. Although lime and cement are both made from the same raw material - limestone - cement is fired at a much higher temperature, and although in both cases the chemical reaction involved gives off lots of carbon dioxide, lime mortar reabsorbs the gas when it is setting (or "going off" as a brickie would say).

Lime mortar and lime render are widely used in restoration work but there's great scope for their revival in new buildings. If you have a wall or house to build, get advice from one of the specialist suppliers about which of lime to use. Try the Old House Store ( www.oldhouse store.co.uk), the Cornish Lime Company ( www.cornishlime.co.uk), Lime Technology ( www.limetechnology.co.uk) or the Lime Centre ( www.thelimecentre.co.uk), where you can attend courses in using lime. Bear in mind that it's nasty stuff to prepare, so get health and safety advice, too.