Rendering in Brockenhurst, walls that go green

Tapping the wall. Sound render rings hard; render that has parted from the background sounds hollow and drummy. We go over every elevation and mark the hollow areas, since they are always bigger than the crack that prompted the call.

Hacking off and rebuilding. Blown render comes off back to sound masonry. Open joints are repointed, the background is cleaned down and stabilised where it is dusty, then a mesh reinforced basecoat and a finish coat go on. Putting a new system over a hollow wall is throwing money at it.

Choosing a finish for a shaded wall. Two things keep algae off render: how fast the surface dries and how smooth it is. A fine textured through coloured silicone topcoat sheds water and washes down easily. A deep scraped texture on a wall that never sees the sun holds moisture in every groove. On the shaded side we usually recommend the finer finish.

Cleaning down and treating. Green and black staining lifts with a soft wash and a treatment rather than a pressure washer, which drives water into the render and strips the topcoat. Treatments are biocidal products and are regulated as such, so they get used at the stated rate and kept out of the watercourse.

Recoat or clean. If the topcoat comes off on your hand it has chalked and a wash only takes more of it away, so that wall wants recoating. If it wipes clean and the colour under is sound, it is a cleaning job. We say which one you have rather than sell the bigger one.

Lime on period solid walls. A pre-1919 wall has no cavity and was built breathable so moisture soaks in and dries back out through the face. Lime render keeps that open, moves with the wall and patches invisibly. A plastic rich modern system on the same wall leaves the moisture trapped and pushes it through to the inside.

Sand and cement, pebbledash and Tyrolean. Scratch coat, float coat and dash where the elevation carries it, patched to a sample panel where the aggregate can still be had. Dash on a shaded wall greens quickly, which is worth knowing before you choose to keep it.

Beads, bellcast and stop ends. Bellcast at the base to throw water clear, stop beads at reveals and eaves, angle beads on corners, and a movement joint where an elevation is long. On older fabric we hand form the arris instead of using a hard bead.

External wall insulation. Board fixed outside and rendered over, on a render carrier where the background needs it. Good on a modern house, awkward on a designated frontage because it thickens the wall and changes every reveal.

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 cottage tight to the road wants a platform clear of the footway, a large detached house with mature trees against it needs the branches dealt with before the scaffold, and a two storey gable over a lean-to wants the roof below protected. 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.

Algae is not dirt blown onto a wall. It is a living thing that needs three conditions: a surface, moisture and low light. Shaded elevations under trees supply all three for most of the year, which is why the same render can look spotless on the south gable and dark green on the north wall of the same house. Washing it off works, and it comes back on the same timetable, because nothing about the wall has changed.

What changes it is drying time and texture. A finish that sheds water and dries in an hour gives algae less to work with than one holding a film of moisture in a scraped texture. Cutting back overhanging branches helps for nothing, and so does a gutter that is not spilling down one section of wall, which is behind more green stripes than anything else we see. Comparing quotes for a shaded elevation, ask what texture is proposed and how it is meant to be cleaned in five years.

We cover the village, Sway, Boldre and the lanes across to Lyndhurst, broadly SO42, under the New Forest National Park Authority. 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.