Comparing maintenance needs of render finishes

The finishes side by side

Sand-and-cement render is often painted. The paint is what weathers, so the job is washing it and, every so often, applying a new coating once the colour has faded or the surface has started to chalk. The render underneath lasts as long as water is kept out of it.

Monocouche is coloured all the way through, so it never needs paint to keep its colour, and a chip shows the same colour underneath. Its scraped texture can hold dirt, and it does not take kindly to being patched. If it fades badly, it can be given a new coating made for render; K Rend lists its Colour Enhance for existing scraped and unscraped renders.

Silicone thin coats are water-repellent and, in K Rend's Silicone TC for example, contain a biocide to help resist moulds and algae. They stay cleaner than plain cement surfaces, but the coat is thin, so knocks show and repairs are hard to hide.

Monocouche rendering ↗

Lime and pebbledash

Lime render is softer and more open than cement. SPAB recommends finishing it with limewash, which wears back over time and is renewed, and advises against ordinary modern masonry paints and clear water repellents, because they can trap moisture. On a wall that had cement render before, SPAB also notes that salts can come through the new lime and that some remedial re-rendering after a couple of years may be required.

Pebbledash needs little attention while it is sound. It collects dirt in the stones and can be washed down; the Mineral Products Association data sheet for cement renders suggests washing rendered walls with water at mains pressure through a fine jet, after any cracks are repaired. Once dash starts to sound hollow, maintenance turns into repair or removal.

Cleaning without damage

Most render only needs washing. Green and black growth on shaded walls can be treated with a cleaner the manufacturer approves for that finish, then rinsed. K Rend's instructions for its Colour Enhance coating, for instance, tell the installer to treat fungal or algal growth before coating. Keep to the gentle end of washing: the MPA data sheet describes mains-pressure water through a fine jet, and Womersley's warns against pressure spraying its natural hydraulic lime paints.

Before choosing a monocouche or silicone finish for a shaded or tree-lined elevation, ask about the product's resistance to algae. Before cleaning any finish, check whether the maker has particular advice, because the wrong cleaner can mark a coloured render.

The checks that protect every finish

Most render damage starts with water from somewhere else, so the routine is the same for every finish. Each autumn, clear the gutters and check that they are not overflowing onto the wall. Check downpipe joints and brackets. Look at window sills to make sure they still throw water clear with a drip. Look at the base of each wall: render should stop above the damp-proof course, and paths or soil should not have built up against it. RICS's consumer guide on bridged DPCs uses a path two bricks, about 150mm, below the DPC as its example.

Then look at the render itself. Tap it at reachable height and note any new hollow areas. Look for cracks at window corners and along the base. Small problems found early are local repairs; left for years, they become re-renders.

Frames, sealant and new fixings

The sealant joint where render meets a window or door frame is a small part of the wall that does a lot of work. Check it when you check the sills: if it has split, shrunk away from the frame or gone hard, water can run in behind the render at the reveal. Renewing it is a small job compared with the render repair that follows a long-term leak.

New fixings are the other common source of damage. Every screw for a light, a bracket or a cable clip makes a hole in the render. Drill cleanly, use a fixing long enough to reach the masonry, and seal around it. On a wall with external insulation behind the render, use only fixings designed for that system.

Recoating and repairs

When a painted or faded render is recoated, the order is: repair, clean, dry, coat. K Rend's coatings, as an example, go on in two coats and should not be applied below 5°C or above 30°C. Repairs should match the original build-up and material; a cement patch on lime render, or a resin filler in a monocouche, will stand out and fail at its edges.

Patches rarely match exactly. On a through-coloured or silicone wall, the honest choices are a patch that shows a little, or a coating over the whole elevation to even it out.

A worked example

Consider a hypothetical house with a monocouche front, a painted sand-and-cement rear and a silicone-finished extension. Each autumn the owner clears the gutters and checks the sills and the base of the walls. Every few years the rear is repainted. The north-facing side of the extension goes green after a few winters and is treated with an approved cleaner. After fifteen years the front has faded unevenly, and a coating made for monocouche is applied. The timings are illustrative, not predictions for any real house.

Keeping the record

Keep the product names, colour references and any care guidance in one place, with photographs of each wall when the work was finished. When a repair is made, add a note of where and with what. The next person to work on the wall then starts from facts rather than guesses. If the house is sold, pass the file on with the deeds; a buyer's surveyor will want to know what the walls are finished in, and whether any part of them has insulation behind the render. For other rendering services, see the Middlesbrough rendering homepage.