Restoration projects can be no small feat, with any number of problems lying below the surface. Rising damp is a common problem, causing cracking and decay on plaster and render.
Lime-based renders are incredibly permeable, meaning vapour is able to easily pass through the porous material – making the building breathable. Ideal for regulating humidity, lime renders can hold excess moisture in humid conditions without becoming noticeably saturated, which will evaporate slowly as the temperature drops.
If painting over lime renders, a vapour permeable formula should be used, however, a wide array of coloured render options are available to offer a simple solution.
Lime-based alternatives are designed to withstand light changes in settlement. As the ground moves over time, cracking is less evident and will help maintain the structure and stability of the wall. Mesh reinforcement can be added to give the system an adequate ability to withstand impact. Unmeshed render can crack if the coat is too thick, so mesh should be considered to absorb and contain tensions without transmitting them to the finishing plaster and counteract any stress.
The difference between weather proof and water proof, lime-based renders protect the external surface of the building without sealing it. Not only is this kind of render resistant to harsh climates including ice, frost and heat, it is also resistant to the salts in sulphate resistant binders.
A formula perfected over time
The Romans used lime effectively for many major engineering projects such as bridges, domes, suspended floors and heated floor slabs. The earliest known use of lime is 4000 years ago, with the formula being built on and developed over time.
Lime-based renders are recommended for restoration and conservation projects as they have the ability to adhere to any former brickwork, stonework or medium dense blockwork. With no need for a board, lime render is perfect for use on listed buildings, where planners want to keep the renovation as original as possible to preserve heritage.
If you are rendering over an original surface, check the substrate is structurally sound with no hollows or gaps, free of any existing plaster, clean and dry. It’s important you consult a professional to be made aware of the load bearing capacity of the surface.
Hand application has the added benefit of allowing the renderer to work close to the substrate, checking for any cracks, but this process can be slow and labour intensive on larger scale projects, especially since lime renders are usually applied in two or three coats. They are suitable for mechanical application with a spray machine, which effectively covers large surface areas in a shorter time frame, with the same professional finish.