Traditional mass-masonry wall construction (which includes most walls built before 1919) works on the basis that moisture entering a wall is able to escape in the form of water and water vapour as easily as possible. Lime mortars can readily handle the transmission between the inside and outside of a masonry wall, owing to the complex interconnected pore structure of masonry.
Why use Lime?
The use of cement mortars is widely recognised as being detrimental to such buildings and structures as they can drastically alter the way in which a wall handles water and water vapour. Cement mortars tend to have a consistent and ‘closed’ pore structure that traps water. Trapped moisture will expand when frozen, and mortars may ultimately fail, often causing damage to the surrounding masonry in the process.
Lime is important to these solid walls as it lets the walls breathe and allows moisture to dissipate, the building can adapt freely in response to environmental conditions.
The first time you might come across lime work is when you strip off layers of modern paint and old wallpaper. Old crumbly lime may come off by accident or design, revealing stonework, brickwork, wooden laths or other surprises!
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.
Lime allows the building to breathe, it lets moisture in and out, it also moves with the building and is far less brittle
We mostly use Hot Lime/Quick Lime because its most water pervious, if we need it to set for a problem wall we use pozzolans
We like to use Lath and Plaster its very traditional and its a method that has stood the test of time, we use Hemp Render for our ceilings as it is strong and very lightweight
My rule of thumb is at least three weeks in between coats, it must be kept moist for at least a week and allow for carbonation to take place
We use Sand which is specially blended for Lime Mortar work, we often add to the Sand if we need more large aggregate in the mix.
In some cases we blend it ourselves to make the correct Mortar mix for the job.
Add Cement to Lime
Add a chemical such as Febmix
Do not dry Lime out with Heaters
Do not apply in thick quantities
Do not use ordinary building sand for Lime Rendering