Rendering Cob Walls
Cob walls need a render that moves and breathes with them, cement render on cob almost always leads to trapped moisture and structural damage over time. We apply traditional lime renders suited to earth-built walls, preserving both the strength and the character of the original structure.
What Is Cob Wall Rendering?
Cob is a traditional building material made from a mix of subsoil, straw and water, historically used across the South West and parts of the Home Counties for load-bearing walls. Because cob is an earth-based material, it requires a render system specifically compatible with it, lime render, applied in a way that protects the wall from direct weather exposure while still allowing moisture within the cob to evaporate outward, rather than a modern render designed for brick or block construction.
Why It Matters
Cob relies entirely on being able to dry out after wet weather; if it can't, the wall softens, loses structural integrity, and can eventually fail. Cement render, applied to cob in the belief it offers better weatherproofing, does the opposite, it seals moisture inside the wall, where it has no way to escape except by continuing to soften the cob from within. This is one of the most serious and expensive mistakes we see on cob properties, and one of the hardest to reverse once significant damage has occurred.
Lime Heritage Restorations proudly serves clients across London and the Home Counties, including Chelsea, Kensington & Notting Hill, Richmond upon Thames, Wimbledon, Hampstead & Highgate, and Greenwich.
In addition to our work across the capital, we regularly work further afield, delivering heritage restoration and full house refurbishment in Surrey, Kent, and Hertfordshire.
Whether you're restoring a listed building or undertaking a complete heritage refurbishment, we bring expert craftsmanship, breathable materials, and conservation-sensitive finishes to every project we take on.
What to Know Before You Start.
Lime render specifically suited to earth-based walls, along with traditional aggregates and, where structural repair to the cob itself is needed, compatible earth-based repair mixes rather than modern cement-stabilised alternatives.
Cob walls on listed properties are almost always considered a significant part of the building's special interest, and render work, even seemingly minor repairs, typically requires listed building consent. Given how serious the consequences of an incompatible render can be, we'd always recommend a proper survey before any work proceeds, consent or not.
Cob render work is typically slower than standard rendering, since lime render on cob is built up in multiple coats with proper drying time between each, a single wall elevation can take several weeks from start to finish, and rushing this is one of the most common causes of failure.
Cob is a specialist material that a general renderer, even a competent lime renderer, may not have direct experience with, the render system and detailing at wall heads and bases differs from standard masonry. Our approach is specifically suited to cob's particular moisture behaviour, not a generic lime render applied to a different wall type. Our team's cob and lime render work is fully insured, and we guarantee workmanship against defect, though we're also upfront that cob rendering, done correctly, is a slower process than standard rendering, and rushing it to meet an artificial deadline is not something we'll do even under pressure.
Frequently asked questions
Cob has a distinctive appearance, no visible bricks or blocks, often slightly irregular or rounded wall lines, and typically found in older properties across the South West and some Home Counties areas. We can confirm during a site survey if you're unsure.
It requires care and time rather than being inherently expensive, the priority is not damaging sound cob during removal, which is why this isn't a job for a standard renderer unfamiliar with the material.
In most cases yes, provided the underlying structural cob hasn't failed entirely, we assess the extent of damage and advise honestly on whether repair is viable or more extensive rebuilding is needed.
Yes, using breathable insulation materials and methods compatible with cob's moisture behaviour, standard modern insulation systems are generally not appropriate and can cause the same trapped-moisture problems as cement render.
Lime render and limewash can be tinted using traditional earth or mineral pigments, so a colour finish is possible while remaining fully breathable and appropriate for the cob substrate.
