A lime-mortar raised bed: 1 to 2.5 and a week under hessian
The raised bed by the kitchen door was my first mortared job, and I chose lime over cement on the advice of a course tutor who said a beginner’s mistakes are easier to take down in lime. The bed is 2.4 metres by 1.2, 450 millimetres high, built from the same local sandstone as the field wall but using the squarer pieces I had been setting aside.
The mortar is a natural hydraulic lime of the middle grade mixed with a sharp, well-graded sand at one part lime to two and a half parts sand, measured by volume with the same bucket. I mix by hand in a barrow, dry first, then adding water a little at a time and turning it over with a shovel for a good ten minutes. The first batch I made far too wet because I was used to seeing cement mortar and wanted it to look the same. It slumped out of the joints and ran down the face of the stones in pale streaks that are still faintly visible on the north side. Lime mortar should be stiff enough to hold its shape when sliced with a trowel and only come alive, becoming workable and slightly sticky, when you beat it with the back of the shovel. That beating, knocking up, is the whole secret and I had never heard of it.
The stone was dampened before laying so it did not suck the water out of the mortar, the joints were kept to between 10 and 15 millimetres, and the mortar was pushed well back from the face as I went. The pointing I did the next day, filling the joints flush and then, once the surface had firmed enough to take a thumbprint without smearing, scrubbing it back with a stiff churn brush to expose the sand and give the slightly open texture lime pointing has.
Curing is the part that cement does not prepare you for. Lime sets slowly by taking in carbon dioxide from the air, and if it dries out too fast in the first week it goes powdery and never gains strength. So the bed spent seven days under damp hessian sacking weighed down with offcuts, misted with a hand sprayer morning and evening, and I checked the forecast every day for frost, since anything below about 5 degrees overnight would have meant covering it with a blanket as well.
Two weekends in total, including the mixing lesson. A year on the mortar has gone a pale biscuit colour, the joints are hard, and the slumped streaks are the only sign that it was a first attempt.