Exterior wall rendering, Wall Coatings and rendering walls

Renders and rendering on external walls, a complete guide: By Guy Alexander Bell, BSc.(hons), Surveyor. Are you looking to have your rendered walls repaired, or perhaps you are surfing the web looking for a reliable builder or contractor to repair your render or pebble-dashed house? Get a quote today!

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We have many years experience with invisible render repairs, crack repairs, subsidence and settlement cracks, cracked tyrolean, render and pebbledash, render exterior wallcoatings and so on………..

To get a quote or free estimate from one of our exterior wall rendering teams, please contact us and we would be only too happy to help and advise

anyway…………

Well, your search is over! We have been repairing and making good render walls since 1986, and been the most prominent and world famous website related to exterior walls since 1999. We have been copied many times but no one comes close to our unrivalled service and quality of workmanship!

We repair render, tyrolean and pebble-dash, as well as smooth stucco and flat rendered walls, however we don’t leave bare render, we always protect it with a smooth or textured exterior resin based masonry coating. This means that once you have had your house re-rendered and wall coated, you don’t have to call us back for at least the next 15 years!

If you have arrived at this page and you are simply looking to get a quote for property rendering, painting, pebble-dash or coatings on exterior walls, please CALL US NOW ON 0800 970 4928 to request further information.

THE COMPLETE GUIDE TO EXTERIOR WALL RENDERING, By Guy Alexander Bell. Bsc.(hons). Surveyor.

Lime and Plaster Render for External Walls

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Lime renders were traditionally applied to give protection to walls built of poor quality rubble stone or porous brick or to walls in exposed locations facing driving winds. They help by acting like a sponge, absorbing rainfall then allowing it to evaporate rather than soak into the wall.

Most cottages and houses built of rubble stone would have been rendered originally and they tend to suffer from penetrating damp if the lime render is removed or replaced with a cement rich render.

There is a very wide range of types of lime rendering. Rubble walls of many vernacular buildings were often treated with just a single coat of render, amounting to not much more than a very full, flush pointing. Such a render is thicker in the hollows and very thin over the stone faces.

There was no attempt to create a flat surface so the undulations of the wall and even some of the stones themselves were not concealed. For a smarter finish or on more prestigious buildings the aim would be for a more uniform render achieved by applying a scratch coat to fill the hollows and take up some of the unevenness followed by one or two more coats which were worked to a flatter surface.

Sometimes joint lines were ruled into the damp top coat to create the illusion of ashlar stone, but a common finish for many houses and cottages was a rough-cast where the final coat consisted of a mortar slurry containing coarse grit applied by throwing from a special trowel. For interiors a fairly smooth surface could be obtained using a coarse render mix, but for top quality internal plastering the final coat would be richer in lime and polished up to a smooth, close finish.

Renders and plasters can be applied to a variety of backgrounds including earth (which should nearly always be rendered), stone and brick. Plaster is also applied to wooden laths for ceilings and internal partitions.

By carefully selecting appropriate aggregates it is possible to match existing renders and successfully repair failed patches without the need for complete re-rendering. Hollow or detached plaster can sometimes be consolidated and saved and further advice should be sought before replacing it, especially if it is very old.

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Preparing a wall to be re-rendered

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For stone and brick any hollow or decayed render should be hacked off and any loose pointing should be raked out and replaced prior to rendering. Brush the wall to remove loose material. Do not rake out pointing to provide a key.

Do not use plastering bead on corners as this will give a modern appearance. Do not use chicken wire or metal lath to form a key as it can cause stress in the render due to differential thermal movements and can lead to large-scale failure, especially when it rusts.

For plastering onto existing wooden laths check that they are firmly fixed and free of lumps of old plaster. New laths should ideally be riven oak or chestnut. Sawn laths are inferior as they are smoother and weaker than those split along the natural grain of the wood. Laths should be fixed so that the distance between them is approximately 8-10mm. This allows the right amount of space for the plaster to be pushed between the laths and flop over to form a key. Do not apply preservative treatments to either old or new laths as they can introduce harmful salts into the plasterwork.

Metal lath is sometimes used internally instead of timber laths as it is quicker to fix and cheaper, but it is harder to plaster onto as it is slippery and the sharp edges may cut into and weaken the plaster key. Plenty of hair in the mix is essential.

For masonry, thoroughly wet the wall with clean water using a hose-pipe or sprayer. The more porous the background the more water will be required. Allow the water to soak in a bit then spray again, and repeat until the surface layers of the wall are thoroughly damp. When the render is applied the wall should be damp but without water glistening on the surface. Timber laths should be thoroughly dampened before plastering.

Mixing plaster and render

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A basic lime render or plaster can be made using the same ingredients and mixed in the same way as a pointing mortar. A coarse sand can still give a smooth finish suitable for most vernacular buildings although the mix should be slightly richer in lime than a standard pointing mix, say one part of lime to two-and-a-half or three parts of sand.

Do not be tempted to use a soft, fine sand – you will just end up with lot of cracks. The mix will need to be slightly wetter than for pointing but it should be slightly stiffer than its modern cement or gypsum counterpart.

Once you start plastering you will soon discover whether your mix is the right consistency: too thick and it will be virtually impossible to apply it smoothly and get it to stick to the wall; too thin and it will go on beautifully then slump, sag or drop off.

Whether you mix your own or buy ready mixed lime render or plaster it is a good idea to ensure that the lime putty used is at least three months old. This will ensure that the lime is thoroughly slaked. If the lime is younger than this any unslaked particles in the mix may slake some time after plastering causing a small eruption or ‘lime blow’. Many practitioners advocate the use of six month old putty for plastering, but few suppliers stock it.

When plastering onto lath it is essential to add hair to the mix to help in forming a key of plaster between the laths. Whilst it is not essential to use a haired mix for other backgrounds it can help to reduce shrinkage. Hair should be added to the mix just before use. Do not add hair to coarse stuff that is to be stored for more than about six weeks as the hair may rot if left in damp lime mortar for a long time.

The hair should be gradually teased into the mix so that it is well distributed and does not form clumps (often referred to as dead mice). As a rule add 4 Kg of hair per cubic metre of mortar for work on laths. For the second coat halve the quantity of hair.

To check whether there is sufficient hair in the mix, scoop a dollop of mix into a gauging trowel, tap the underside of the trowel smartly against a hard edge so that the blob flattens and the surplus mortar falls off the edge of the trowel. There should be a fringe of hair at 1-2mm intervals around the edge of the trowel.

CONTACT US NOW FOR FREE PRICES AND QUOTES FOR RENDERING AND WALL COATINGS ON 0800 970 4928

NPA makes sure that when they do a job on your house, all repairs needed to the exterior walls, such as fixing cracks and loose or hollow render, must be made good. Our teams are so skilled that if we have to repair a patch of render, once our exterior wall coating system is on top of the render, you will NOT see where the repair was, guaranteed!

CONTACT US NOW FOR FREE PRICES AND QUOTES FOR RENDERING AND WALL COATINGS ON 0800 970 4928