Rendering in Tarrant Monkton, cob and flint walls

Tapping and reading the wall. A hammer handle tells you where the render has blown. The wall thickness at a window reveal tells you what it is. Anything much over 450mm with soft edges is likely cob, and cob is the one background where the wrong render does structural harm rather than cosmetic harm.

Taking cement off. Most of the failures we see on old cottages here are a hard cement render applied decades ago. It cracks, water gets behind it, and because the cement will not let that water back out the wall behind stays wet. On cob that means the earth softens; on flint and brick it means frost damage and salts. Removing it is careful hand work, not a breaker.

Lime render. Applied in coats onto a dampened background: a hair reinforced scratch coat left with a good key, a float coat ruled out, and a finish coat or a limewash over it. Soft, breathable and slightly flexible, so it takes the movement instead of passing it to the wall. Kept damp and protected while it carbonates, which is why the scaffold stays sheeted.

Flint and brick repair before rendering. There is no point rendering onto loose material. Open joints get raked and repointed in a lime mortar first, and anything spalled is cut out, so the background is sound before a coat goes on.

Sand and cement, pebbledash and Tyrolean. Ordinary and correct on the twentieth century houses in the village. Scratch coat, float coat, and dash or Tyrolean where the elevation already carries it, matched by sample panel where the aggregate can still be had.

Silicone thin coat and monocouche. Both good systems on a modern cavity wall: a stabilising primer where the background is dusty, a mesh reinforced basecoat, then a through coloured topcoat that needs no painting. Neither belongs on cob or on a solid period wall, and we will say so rather than take the order.

Beads, bellcast and stop ends. On modern work a bellcast bead throws water clear at the base, stop beads finish reveals and angle beads keep corners true. On cob we usually form the arris and the drip by hand, because a hard metal bead in a soft wall gives the render something to crack against.

External wall insulation. On a modern house, board fixed outside and rendered over, on a render carrier where needed, lifts the thermal performance without losing a room. On a breathable solid wall it takes a specialist build up, and on a protected frontage it usually is not the answer at all.

Cracks, delamination and algae. A straight hairline crack is shrinkage. A stepped or widening crack is movement behind the render. Green on a shaded elevation lifts with a gentle clean down and a treatment, never a pressure washer on lime.

No rate per square metre, because the square metres are the easy part; what is already on the wall decides the price.

Getting to it. A thatched cottage tight to the lane needs a platform that keeps clear of the eaves, a farmhouse with open ground takes a straightforward scaffold, and a converted barn with a tall gable needs one that reaches the apex. A bungalow gable comes off a tower, a three storey elevation wants a scaffold, and the platform has to stand for the whole system rather than a day. The work at height rules are why it is a priced line rather than something folded into a rate.

What is already on the wall. Rendering over sound brick is one job. Hacking off blown sand and cement, or a pebbledash that has parted from the background, is another, and it is the part nobody can see from the road. We tap the whole elevation before quoting, because the hollow areas set the hours.

The system, and what the wall behind it needs. Silicone thin coat over insulation, monocouche through-coloured, or traditional sand and cement all price differently and behave differently. On a solid wall that has to breathe, a plastic-rich modern system traps moisture and moves the problem inside, so the right system is a wall decision rather than a colour decision.

Comparing quotes? Ask which system is being quoted and how many coats, whether the old render is being hacked off or overlaid, whether beads, bellcast and stop ends are included, whether the scaffold is in the price, and what happens to the existing sills and pipework. Two quotes for the same job are usually two different jobs.

A cob wall is chalk, earth, straw and water, built thick, standing on a stone or brick plinth and traditionally kept dry by a good hat and good boots: a generous roof overhang above and a plinth below. It is not waterproof and was never meant to be. Rain wets the outer face, and the wall dries back out through that same face when the weather turns. Everything about how it survives depends on that drying.

A cement render stops it. Water still gets in, through a crack, around a window, up from a raised path, but it can no longer get out, so it sits in the earth and softens it. By the time the render is bulging the damage is already done, and it is a rebuild rather than a repair. The historic building guidance on cement and traditional masonry is blunt about it. So if your cottage has a hard grey render that rings dead when you tap it, get it looked at while it is only a render problem.

We cover the Tarrant valley villages, Tarrant Keyneston, Tarrant Hinton and the lanes towards Blandford, broadly DT11, under Dorset Council. You are dealing with Bournemouth Roofing & Building, the trading name of Bournemouth Roofing & Building Ltd, registered in England and Wales, company number 15471719, which you can look up in a minute. Thomas Hannen's business, and he is the one who comes out to price the job, not a salesman. A verified customer's 10 out of 10 on Checkatrade. The visit and the written quote are both free.