Why we specify lime plaster.

Lime plaster is the wall finish you do not notice on day one and cannot stop noticing on day five thousand. It absorbs and releases moisture in cycles, which softens the acoustic register of a room. It develops a patina under sunlight that gypsum cannot reproduce. It can be locally sourced. It does not depreciate.

We specified lime plaster on the soft surfaces of every CPH residence — corridors, bedrooms, the back wall of every kitchen — for those reasons, and one more: we wanted a finish that the residents could maintain themselves, by hand, over the next thirty years. Lime plaster forgives a touch-up. Painted gypsum does not.

The supplier search was straightforward in Europe and difficult in Nairobi. Industrial lime is widely available; building-grade lime suitable for two-coat application is not. We tested seven candidates against four criteria: workability, cure time in Nairobi humidity, colour stability after six months, and cost-per-square-metre at the volumes CPH would consume.

The supplier we selected — names withheld until purchase contract — produces in Naivasha from a quarry we have visited. We have committed to a five-year supply agreement at a fixed price. The cost is approximately 1.4× the gypsum baseline. The thirty-year cost is approximately 0.6×.