Choosing the right Lime Plaster
Lime Plastering Guide – Based on background
We manufacture and supply a variety of ready-mixed performance plasters, supplied wet and ready to use or in premixed powdered form. Our Lime plasters are convenient to use, coming premixed to suit your application needs, we also sell ancillary products to support your application. So how do you choose the right Lime Plaster for the job you’re undertaking? There are several different build ups of lime plaster based on the background:
Plastering onto exposed stone or brick internal walls
There are generally two options:
The first and most historic method uses Coarse Stuff and Fine stuff – Coarse Stuff and Fine Stuff are manufactured by Womersleys from mature lime putty and selected. Both products are completely breathable, meaning moisture isn’t trapped in the walls, they have natural elasticity, which allows for absorption of minor building movement, and they are supplied as ready to use wet mixes.
Coarse stuff is manufactured with a blend of hair and fibres to give it strength and reinforcement within the dubbing out and scratch coats. If you are plastering onto timber laths, then coarse stuff with extra hair is the ideal product for providing secure nibs and strength around the laths. Often customers prefer soft goat hair in the final float coat, to prevent hairs protruding through the topcoat.
The coarse undercoats are then traditionally finished with Fine stuff, a rich lime putty topcoat plaster made with fine moist silver sand and mature lime putty, this and is often applied at 2-3mm thickness.
Manufactured from Natural Hydraulic lime to create high performance coatings for internal walls, again ensuring breathability so moisture isn’t trapped. Duro basecoat lime plaster is a natural, elastic and salt resistant undercoat, that can be built out at 12mm per pass, leaving 4-5 days between coats.
The undercoats are then finished with Solo One Coat lime plaster, which is supplied premixed ready to just add water. It can be finished to a smooth or a slightly textured finish.
Insulating and plastering the internal face of exposed stone or brick external walls
Older buildings were typically built using materials to hand, with solid walls of stone or brick bound with a lime mortar. They were often built without a cavity and certainly no insulation. The lack of insulation and poor thermal properties of the materials used means they retain very little heat. There is therefore a desire to insulate these walls but using modern polyurethane insulation damages old buildings.
Any insulation applied must be vapour permeable or ‘breathable’, or your walls will become saturated. We manufacture and supply a number of insulation products for older buildings please see our how do you choose insulation guide. The guide looks at five insulation options and how they can be plastered:
2. Wood fibre boards – which can be plastered and finished with Solo lime plaster. This is applied in two 5 mm layers, with an alkaline resistant mesh pushed into first coat. The second coat is trowelled up to provide a finish or Fine Stuff can be applied instead as the second coat to get a smoother appearance.
5. Sheep wool insulation (Cosy Wool) – Covered with Celenit render carrying boards. which can be plastered and finished with Solo lime plaster. This is applied in two 5 mm layers, with an alkaline resistant mesh pushed into first coat. The second coat is trowelled up to provide a finish or Fine Stuff can be applied instead as the second coat to get a smoother appearance.
Skimming Over Old Plaster
Sometimes old plasters are too smooth or too "thirsty" to achieve a good finish when skimming with lime plaster.
Solo Primer - Helps control the high levels of suction and provides a gritty key for the plaster to stick to, but unlike PVA it is as breathable and durable as lime. Once primed you can skim over the primer using Solo lime plaster. Also suitable for use on gypsum plaster, tiles and nonglossy paints.
St Astier Eco 50 Renovation plaster - The St Astier Natural Hydraulic Lime Eco renovation plaster is suitable for coating of gypsum plasters and composite backgrounds (plasterboard, gypsum plaster, timber or concrete). Providing a unifying coat ready to receive a finishing coat of fine stuff.
Skimming Over Render Carrying Boards or Gypsum Boards
These can be plastered and finished with Solo lime plaster. This is applied in two 5 mm layers, with an alkaline resistant mesh pushed into first coat. The second coat is trowelled up to provide a finish or Fine Stuff can be applied instead as the second coat to get a smoother appearance.
Appropriate floats for lime plastering and ancillary products to consider
Usually lime plasters are finished with a steel trowel but textured finishes can be achieved using different sponges: The Orange medium sponge float gives a tight close-grained finish whereas the Grey coarse sponge float leaves a more sandpaper finish. Wooden and poly floats can also leave a nice finish, a little more closed in than the medium sponge. Some customers use a felt float which leaves a similar finish to the Orange float. A combination of using a wet coarse sponge followed by poly float or medium sponge is often the best way to produce a fine textured finish.
Ancillary Products to consider: