What to expect when re-rendering a cob cottage

A re-render on a cob cottage is one of the longest jobs we do, and one of the most satisfying. It is also the one most often misunderstood — both by owners and, sometimes, by builders. Here is roughly how a typical Somerset job runs from first survey to final limewash.

1. Survey and assessment (week zero)

We visit, look at the wall, look at the inside as well as the outside, take some photographs, and if necessary cut a small inspection patch through any modern render to see what is behind it. The question we are answering is not just "does the render need replacing" but "is the cob still sound under there, and if not, how unsound." Most cob cottages we are called to have had a cement render added in the 1960s or 70s; the question is how much damage that has done.

2. Stripping the failed render (weeks 1–2)

Cementitious render comes off by hand. Slowly. Quill picks and chisels around door and window reveals; lump hammers and bolsters on plain elevations. The cob underneath is fragile and will tear away with the render if you are careless. Where the render is bonded so firmly that removal would do more harm than good, we leave that patch in place and address it later.

This stage almost always reveals worse damage than was visible from outside. Voids, slumped sections, areas where the cob has lost cohesion entirely. We photograph everything and price the remedial work as a clear variation if the original quote did not cover it.

3. Drying (weeks 2–6)

This is the part owners find hardest. Once stripped, the wall must be allowed to dry out. The water that was trapped behind the cement render has to leave the wall before any new lime work goes on, or it will simply be trapped again. We cover the wall in breathable hessian, often double-layered, and wait. Depending on saturation and the time of year this can be two to six weeks. There is no shortcut.

4. Structural cob repair (weeks 4–8, overlapping)

While the wall dries, we mix fresh cob for the repair. The subsoil is matched to the original by sieving and feel — most Somerset cob is a sandy clay subsoil with around 15–25% clay, mixed with chopped barley straw and water. We rebuild lost sections in lifts of 300–400mm, allowing each lift to firm up before the next. Smaller patches are repaired with pre-made cob blocks, stitched in with a lime grout.

5. Lime render — base coat (weeks 8–10)

Onto the prepared cob goes the first coat of hot-mixed lime render, well-haired with goat or horse hair, applied 12–18mm thick, scratched off with a comb for key. This coat is the structural one — it ties the surface together and provides a substrate for the floated coat. It is then kept damp under hessian for at least a week and shaded from sun and wind throughout.

6. Float coat (weeks 10–12)

The second coat is thinner — 8–12mm — and finer-grained. We float it with a wooden float when it has reached the right firmness, and it is again kept damp and shaded for the following week. On some buildings this is the finish coat. On others we add a third, finer coat.

7. Limewash (weeks 12–14)

Once the render has begun to carbonate (usually two to three weeks after the final coat), we apply limewash. Three to five coats, mixed with earth pigments to match the surrounding cottages — Somerset whites, soft creams, occasional warm pinks and ochres. Each coat is brushed on, allowed to dry to a chalky bloom, then the next coat goes over.

What it costs and how long it really takes

A typical front elevation of a two-up two-down cob cottage in Somerset works out at roughly £8,000–£14,000 depending on cob repair work needed, with the whole programme running 10–14 weeks on site. A whole cottage might be £30,000–£50,000 over a season.

It is not cheap and it is not fast. It is the only way that genuinely works, and the building will repay you for the next two hundred years.