Traditional Lime Plastering & Rendering
Lime plaster is type of plaster composed of hydrated lime (slaked lime), sand and water. Lime plaster is similar to Lime mortar, the main difference is based on use rather than composition. Traditional lime plaster also contains horse hair for reinforcement.
Improvement in the slow curing time of lime plaster, especially in cold and/or wet conditions was done in Roman times by adding volcanic ash (activated aluminium silicates) to produce hydraulic lime and hydraulic cement.
Today, cheaper power station fly ash or other waste products are used to make hydraulic lime plaster or cement instead of volcanic ash.
Lime plaster is sold as 'bagged' powder or hydrated lime; or is available as lime putty. Lime putty is generally considered to be more suitable for pure lime application.
Lime renders are mixed and composed of a sand / lime mix on site, however pre mixed bagged Lime Renders are available but one should remember it was nearly always mixed on site.
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.
Lime Renders and lime plasters can be applied to a variety of backgrounds including earth (which should nearly always be rendered), stone and brick. Lime 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.
Plastering & Dry Lining
Gypsum Plastering and Dry Lining>
In recent years, the construction sector has witnessed a number of new trends, technology advancements and innovations across applications, all aimed at making construction faster and delivering higher performance.
However, very few would have imagined that the substitute for the generations old method of sand cement surface plastering will be an even older method of plastering i.e. gypsum plastering. Gypsum has proved to be a miraculous material aiding interior construction. Gypsum surface plaster is one form that has caught the attention on the sector and is growing in popularity.
Gypsum what is it?>
Gypsum is a light weight material which is formed as the result of evaporating sea water in massive prehistoric basins. In terms of its chemical composition, it is Calcium Sulphate Di-hydrate (CaSO4.2H2O) and inherently contains 21% water by molecular weight. Gypsum products have been used for centuries in the construction space and are the material of choice because of gypsum’s unique properties.
It has excellent insulation properties both thermal and acoustic and can offer very good passive fire protection, moisture resistance, impact resistance and vapour control when used in combination with the right systems.
What is Gypsum Plaster?>
Gypsum is a light weight material which is formed as the result of evaporating sea water in massive prehistoric basins.It has excellent insulation properties both thermal and acoustic and can offer very good passive fire protection, moisture resistance, impact resistance and vapour control.
Plastering and Dry Lining Information
When a wall is constructed with brick or block, they are finished with a coat of plaster which is called internal plastering.
Backing coat which is the underlying coat that sits on the substrate can be one of several plasters designed for a particular use.On this is placed a skimming coat again which can be of several types. Some interesting plasters are x-ray plasters which are very heavy and lightweight plasters such as board or multi finish.
Dry lining is technically the covering of a background surface with a plaster substitute; Masonry, block work and generally brickwork are unacceptable as a finish not only for aesthetic reasons but also because they generally are not as true as a plastered finish.
Dry lining is the fitting of plasterboard or a board material akin to plasterboard to any surface in lieu of a hard plaster.
Dry lining doesn’t require anywhere near the amount of water that traditional plastering needs and to some degree less technical expertise to fit than plaster. Plasterboards are produced by leading manufacturers in huge factories and in great volume. Plasterboard is available in various lengths, widths and thicknesses.
When dry lining and fixing plasterboard to timber or metal this is referred to as ‘tacking’ if using nails, or ‘screwing’ when screw fixings are used.
Screws will always support the plasterboard better than clout nails and we recommend whenever possible to follow this recommendation.
Dry lining to timber or metal is reasonably straightforward providing you follow a few basic principles.
Always choose the most suitable plasterboard or board for the job in hand. If you’re dry lining a wet area, maybe a bathroom consider the extra value moisture resistant plasterboard will give you. Moisture resistant plasterboard is normally green.Moisture resistant plasterboard however will not stand being submersed in water for long periods and the core is like any other board making unbound or cut edges susceptible to water penetration.
Lafarge produce an aqua board and Knauf an ‘Aquapanel’ plasterboard, both of which are extremely water resistant. The Lafarge aqua board can even be used in external lining applications.
The plasterboards are then skimmed with a board finish gypsum plaster and trowelled flat to provide a smooth finish for decoration