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We will undertake lime plastering, rendering, lime repointing and stonework repairs, limewashing and painting with breathable paints.

We also undertake lime plaster and lathwork repairs

Lime plasters, renders and mortars were commonplace in the UK before the mass production and widespread availability of products such as concrete, cement based renders and plasters and chemical paints. Most buildings constructed before c. 1915 incorporate lime mortars and pointing in brick and stonework, lime plasters and limewashes. Lime plastering, rendering and pointing can be found in buildings from high status cathedrals and castles through townhouses to the relatively humble cottages and farms and barns which characterise many rural landscapes.

Our speciality lies in the sympathetic restoration, conversion and maintenance of such traditional buildings.

One of the most important aspects of the conservation and maintenance of older buildings is that materials should be replaced like for like. Modern mass produced materials such as concrete and sand and cement have different physical/mechanical properties to traditional and breathable materials and can cause damage to older buildings.

Historically,‘spring cleaning ’ involved the application of limewash (whitewash), within and outside houses, barns and animal stabling. In many parts of the world, the annual whitewash remains part of the seasonal round, not only because of its cosmetic affects but also because lime is anti-fungal, anti-bacterial and antiseptic. As lime is also breathable, it also balances atmospheric moisture content, creating a healthy living environment. Cement based materials contain many toxic and potentially harmful chemicals linked with cancers and respiratory problems.

As lime is produced at a relatively small scale, it has a lower carbon footprint and lower embodied energy rating (including transport) than cement products. The production of Portland cement is the third highest ranking producer of CO² in the world. Lime production gives off 20% less CO² than cement and lime actually absorbs nearly its own weight in CO² during the curing process (source: greenspec.co.uk).

Lime mortars and plasters are made from solid limestone crushed and burned (traditionally carried out in lime kilns that can still be seen in limestone areas) to form ‘quicklime’. Following this it is put through a process called ‘slaking’, where it is mixed with water to form either lime putty, or dry hydrates. These are then mixed with sand and water to produce lime mortars of different consistencies. After application in the form of plaster, render, mortar or limewash, the lime cures and hardens, returning as close as possible to its natural form. This process is often referred to as the ‘natural lime cycle’.

There are various types of building lime available. The limestones from which these are produced contain different amounts of clay minerals (silica and alumina). The amount of these minerals contained within different limestones affects the hardness and breathability of the mortars produced. The softer the substrate (the surface onto which you are applying the lime), the softer the lime needs to be.

Non hydraulic lime (or fat lime) is the most flexible and breathable of the building limes as it contains few or no clay minerals. For this reason, non hydraulic lime is suitable for use on cob, earth and straw bale buildings as these materials are similarly flexible and breathable. So where cob demands non hydraulic lime, stonework and damp/wet areas close to ground moisture are more suitable for hydraulic limes. Additives, known as pozzolans, are available to mix into non hydraulic lime which will impart to it hydraulic properties and greater strength.

The principal difference between lime putty and Natural Hydraulic Limes (NHLs) is that NHLs set underwater (hence the hydraulic in the name). There are three different types of NHLs based on the percentage of silica and aluimina present.

• NHL2: less than 12% clay minerals
• NHL3.5: up to 15% clay minerals
• NHL5: up to 25% clay minerals; the strongest and most impermeable to water, achieves a set and finish closest to cement.

Bagged hydrated lime which is commonly sold in general builders merchants is not recommended for use with cob. It is best to seek professional advice as to the appropriateness of its use under specific conditions. This material goes out of date 12 months after production and is often left sitting around builders merchants where sand and cement products are more commonly purchased.

Depending on the character and quality of the substrate, the plastering/rendering process involves three or four main phases where the lime is built up in layers:

• Pugging out/scat coat: Pugging out generally only takes place on cob and stone walls where gaps or large holes need to be infilled to create a smooth flowing surface. Depending on the build, new walls and flattish stone/brick walls often require a ‘scat coat’ of lime slurry which provides a key for the following coats.
• Scratch coat: The scratch coat (it is scratched up to provide a key for the topcoat) is the first complete layer of lime to be applied. It helps to iron out any protrusions or indentations in the wall, and creates a smooth surface onto which to apply the topcoat.
• Topcoat: The third layer to be applied is the smooth top coat. For external rendering, this is the final coat. Once this is leather hard, it is rubbed up with a float to iron out any minor bumps and indentations and to create a homogenous surface. For internal work, when this coat has completely dried, it can have a further skim coat applied, or for a more 'rustic' finish, it can be limewashed or painted with breathable paints.
• Skim coat: Internal plastering often includes a fourth coat of lime skim. This is a very thin layer which has a smooth finish similar to modern gypsum. It can also be rubbed up to create a more porous finish. When completely dry, this can be limewashed or painted with breathable paints.

Have a look at some limework in progress by visiting our traditional barn conversion gallery!

Hemp insulating/renovating plaster consists of a lime based binder mixed with chopped hemp. Hemp plasters have great acoustic and thermal insulative properties, and are around twice as breathable as lime. They can be built up to substantial thicknesses (around 2-3 inches is needed to acheive significant insulative qualities) and they dry much faster than lime. Hemp plaster is ideal for rennovating old and draughty buildings as well as new build projects. Hemp plasters can be finished with breathable paints or skimmed with lime, depending on individual requirements.

Tradical Hemcrete products are also available to infill stud walls, as screeds or as in situ cast roofing insulation. These and other natural building products are supplied in Devon by Back To Earth Natural Building Solutions

There are many different brands of eco/breathable paints on the market, either ready mixed or provided as a base colour with added pigments to create a personalised/specific tones and colours. These are environmentally friendly, easy to apply and fume free, these are in general made from natural plant oils. Once mixed, they can generally be applied in two or three coats. Read our breathable paint advice page or see our suppliers page for more information from individual manufacturers.

Lime is very good at its job (and has been for centuries across the world) but it requires a bit of knowledge and understanding. Although some conventional builders⁄plasterers might tell you so, there’s absolutely NO NEED to mix it with cement, and there’s absolutely NO NEED for a ‘base layer’ of chicken wire, or any ‘special coatings’ such as PVA. Such practices make a mockery not only of using a traditional material but also of lime’s inherent breathability and environmentally friendly credentials.

Please feel free get in touch if you need advice (or a price) and⁄or check out our further reading and links list which includes references to a number of helpful books and online resources. Also, Mike Wye and Associates produce very useful free guides and online literature regarding dampness and other problems in old buildings, breathability of lime and natural paints etc. They also run regular plastering courses in Devon.

Because lime is a traditional material, its application outside is dependent on seasonal conditions. Whilst inside plastering and painting can take place all year round, rendering and pointing are best done between frosts (April-September⁄October) and in the dry…

We work predominantly in mid⁄north Devon and Cumbria, but we will travel throughout the north and west.