The Company offers a specialist lime plastering service for external and internal projects. We also offer a painting service for the lime plaster finishes which ranges from using hydraulic powder based lime washes through to organic breathable paints imported from Germany. Lime plastering is an essential part of maintaining a breathing house wheather new or old. The lime allows the walls to breathe and move absorbing man made chemicals and moisture released from our bodies. In essense modern finishes prevent a house from breathing and as a result they sweat. Lime is the opposite to this, absorbing and releasing moisture naturally. Importantly, lime plastering is finished with breathable non-synthetic paints, the application of such paints enables the plaster finish to remain porous whilst not realising VOCs and other chemical compounds.
Many older houses have had their lime plaster removed and replaced with hard cement based renders which do not move or breathe. It is a common site to see older houses with significant cracking in the cement based render where the under lying cob or stone/brick walls have moved but the cement render has not. Once cracking has taken place it is common for moisture to get between the cement based render and the wall leading to frost induced freezing and thawing leading to blown plaster. The cement based renders often lead to over drying of upper walls, where the mortor looses its pliability and bonding strength, as well as, extra dampness in the lower part of the wall where mositure has sunk or risen to and cannot escape through the plaster.
The use of lime plasters address these problems and externally two types of application can be carried out
Hydraulic Lime Based Render.
Hydraulic lime cures through exposure to moisture but remains breathable. For external plastering we apply a plaster with a value of NH 3.5 this will allow the walls to breath and move but will also provide excellent protection in poor weather districts, I.e in the south west. Application involves a dobbing out coat where loose mortar is removed and replaced with a lime and sand mix. This is followed by a adhesion / scat scoat applied with a tumbler machine, this coat is brushed in to form a back ground over stone and brick for the plaster to stick to. The next coat is the plaster base coat with hair, which is usually cut horse hair mixed to two kilos to one tonne of plaster. Once this coat is semi cured the final finish coat is applied and floated. This coat is hairless and can be finished to suit building look, i.e. formal, informal or cottage style.
Lime Putty Based Render.
Lime putty cures through exposure to air, it goes hard through carbonisation, this is the uptake of CO2. It is used for external plastering but is much less flexible to apply externally than Hydraulic as it needs a much longer curing time. The lime putty based render will need a minium of three months curing before any frosts otherwise the plaster will be damaged. The application sequence is the same as hydraulic lime except sometimes an extra coat is applied between the hair coat and the finishing coat.
Internal lime plastering is lime putty based as it can be applied to a frost free zone and does not need to give the extra protection to the building externally.
The lime plaster can be applied on a solid background of either cob brick straw or stone. For solid backgrounds the method is similar to external plastering. The wall is prepared, re-pointed if necessary, and a scat coat for adhesion applied. A hair coat is then applied and allowed to dry sufficiently to form a non cracked hard background. This is achieved by slow curing and a number of floating applications to ‘push up’ the plaster. Once this coat has achieved the desired state a second no hair coat is applied, this is a thinner coat and again is ‘pushed up’ and formed into a suitable background for the final coat. The final coat is applied whilst the mid coat is still green, meaning it is not fully cured. The finish coat is usually a fine sand and lim coat which finishes well with a trowel or a sponge. If required a very fine pure lime based coat can be applied to give a mirrored formal finish.
Lathe or Reed Backgrounds
For ceilings and stud walls timber lathes or reed bundles can be used to provide a key background for the plaster. The timber lathes are usually 35mm wide by 8mm thick and vary in length. The lathes are fixed with nails or screws and are staggered every twelve to break the joint lines. The reed is fixed in very small bundles, again by nails or screws and staggered to break the joint lines. The timber can very from pine to oak, it is common practice to use air dried sawn oak. The lathes are fixed approx. 10-15 mm apart allowing for a plug of plaster to push between the lathes. Once the lathes or reed is fixed in place the application of the lime is the same as for solid backgrounds, except for the scat coat, which is not needed.
Externally a hydraulic paint is usually applied, for a putty based external render a putty based lime wash would be used.
Internally again hydraulic or putty based lime washes are used as well as a range of breathable emulsions.
Limebase Products Limited - http://www.limebase.co.uk
Mike Wye & Associates Ltd - http://www.mikewye.co.uk
AURO Natural Eco Paint - http://www.auro.co.uk