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|lime plasters and renders
This page offers general advice about repairing lath and lime plaster studwork and ceilings. For more information about lime and its uses, see our lime plastering and rendering page, our lime mortar/repointing and stonework repairs page and our limewashing and breathable eco-paints paints page.
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Most buildings built in both town and the countryside before c.1919 incorporated lime in their construction, for mortar, plaster, render and decoration. During early 1900’s, harder cement-based materials crept in and by the mid 20th century, traditional lime mortars had largely disappeared. As a consequence, the majority of two generations of construction professionals have lost the specialist skills and knowledge required to understand and use lime in building.
Lime is moisture permeable, or breathable, and is an important element within most traditionally constructed walls, allowing moisture to pass in and out, thus keeping walls dry.
Although many damp problems are due to poor external maintenance, these can be exacerbated by the application of impermeable cement-based renders and plasters. See our insulation page for more about breathability and the main causes of damp in older buildings.
When older buildings have been re-rendered or plastered with impermeable materials, once water gets in, it can become trapped within walls. Its easiest route of escape is often through internal plasterwork, especially where cracks and other faults already exist.
From the outside, the sand and cement rendered mid 19th century townhouse pictured to the left illustrates some common damp problems mainly associated with leaking cast iron guttering and downpipes. Damp had penetrated stone walls some 2ft in thickness and created significant problems inside the building. With a bit (actually quite a lot!) of TLC, internal repairs to studwork and stone walls as well as new gutters and lime dashed and limewashed render, the building is now dry inside and out (see picture below right).
Lime plasters, renders, pointing and paintwork allow walls to breathe; they are durable yet porous, and any moisture content present is allowed to escape into the atmosphere without harm to the structure of the building.
Lime is technically and historically appropriate to many older buildings and authenticity is key when repairing or restoring them. Contrary to what modern builders might tell you, used appropriately and sympathetically, lime lends itself extremely well to repairs and can help solve problems with damp.
When restoring any old house, whether it be a Victorian townhouse or a 17th century country cottage or farmhouse, one the first times you might come across limework is when stripping off layers of modern paints and old wallpaper. Old crumbly lime may come off by accident or design, revealing stonework, brickwork, wooden laths or other surprises!
Whilst the experience might seem overwhelming, these patches are relatively easy to repair with lime if the right methods and materials are used.
The golden rule here is patience; ripping off large areas of lime or pulling down lath ceilings is rarely necessary and may be extremely expensive and time consuming to put right!!
Whether you intend to do the work yourself or you hope to employ a specialist, do some research and make sure you have all the facts to hand. Our lime plastering and lime pointing pages contain more information, and our links page provides access to building conservation organisations and has lists of useful books.
We would recommend “The Old House Handbook: A Practical Guide to Care and Repair” (by Roger Hunt and Marianne Suhr in conjunction with the Society for the Protection of Ancient Buildings (SPAB)).
SPAB website homeowner FAQs
Mike Wye provides useful fact sheets and a free downloadable practical guide to lime and other traditional materials.
To undertake lime plaster repairs, make sure that you understand the materials and how to apply them before you start. If in doubt contact us or your local lime specialist. This section and other pages of this website provide only general advice and should not be used as practical guides.
Basic plaster repairs require up to three coasts of coarse lime plaster and a final coat of lime skim. This of coarse depends upon what you are plastering onto, and if it is a patch repair, the depth of the existing plaster. There a two basic rules to be followed here. Each layer needs to provide an adequate key (i.e. rough scratched surface) for the next and needs to be wetted down before the application of plaster. Secondly, for patch repairs, make sure that the depth of plaster applied allows for the final coat (whether this is to be coarse lime or lime skimming plaster) to be flush with the existing plaster. Our lime page further explains the layering method.
Before the availability of modern sheet materials, lathwork was the cheap and easy alternative to building brick and stone walls. Consequently lath and lime studwork often forms interior room divisions as well as window and door headers. Laths can get broken due to decades of wear and tear or more proactive activities such as inserting or renewing windows, skylights and doorways or electrical rewiring.
To plaster onto lathwork it is essential that it is stable and firm, so wobbly and broken laths may need to be replaced or strengthened. Laths are available from online suppliers (see our links page-or talk to your local woodsman!) To replace lathwork take the plaster back to the nearest stud or joist and replace the lath if it is broken. It is best to use a cordless driver as the percussion from hammering in nails might result in more damage. Usually one coat of coarse lime is required, onto to wetted down laths. This is followed by a coat of lime skim when the base coat has cured. Make sure to leave room on top of the coarse coat for the lime skim to be flush with the existing skim coat!
Lath and lime ceilings are extremely strong and durable and only rarely to they need to be completely pulled down. Whilst small patches or cracks can be repaired easily, replacing a lath and lime ceiling can be prohibitively expensive so please think twice!!
Cracks or patches of loose plaster in ceilings are often a result of water leaks or movement in the joists of the floor of the room above. Lifting floorboards in the room above may reveal the root of the problem. One way of consolidating cracks is to pour a thin layer of plaster of Paris or a mixture of wet coarse lime/ lime grout mix onto the ceiling from above. Otherwise repairs can be made as described for lath and lime studwork.
If you are in the unenviable position of having no ceiling or are lacking internal studwork and have found that re-lathing is prohibitively expensive, then there are various relatively cheap and environmentally friendly alternatives to gypsum plasterboard on the market. Products such as reed board and reed matting link to Mike Wye Natural products page) when plastered with lime do retain some of the aesthetic qualities of a lath ceiling. Reed board, reed matting and clayboards are also suitable for internal stud walls. Many of these alternatives are available from online retailers, so use our suppliers/links page or browse the web to find out more.
Because lime is breathable, to retain its permeability it requires breathable paints. Modern emulsions and masonry paints incorporate plastics derived from the petroleum industry and are impermeable much like cement and gypsum products. Traditional limewashes can be used internally and externally, but will not cover modern paints. Today breathable paints are also available for internal decoration, some of which will cover both new limework as well as existing paintwork and gypsum plasters. See our paint page for more information and links.>
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.
|links and suppliers
For queries regarding limework in Devon contact Glyn at email@example.com
or telephone: 01884 829584