Simon Ayres, Co-Founder and Managing Director at Lime Green Products, explores the key indicators that can help you to decide whether lime plaster needs repairing or replacing.
Lime plaster is extremely durable. It can last for centuries, flexing with environmental changes as buildings move, regulating moisture and keeping the building dry over time. Many older houses or historical buildings will have lime plaster that’s 100s of years old.
Lime’s qualities – flexibility, breathability, durability and damp-resistance – make it suitable for repair in a wide range of situations. But, when your lime plaster is looking aged and damaged, how do you know if it needs repairing or replacing?
Like-for-like replacement plastering isn’t cheap, so it’s important to make sure it’s the right decision. Skill and knowledge is required to identify problems and determine what measures are suitable. There are ways and means of salvaging and reattaching old ceilings and walls – damage doesn’t always mean replacement.
What are the options?
Older plasters often can’t be replaced to the same standard, so salvaging and repairing the existing material, where possible, is important. Repairing can also often give a more authentic result, which will go on to last for another lifetime or two.
With any refurbishment or renovation of older plaster, it’s important to first consider the existing materials to select a suitable plaster for repair work. This will ensure the materials bond properly and go on to stand the test of time.
Broadly speaking, there are four options to rejuvenate older lime plaster: patch repair, reskim, replace, or repair the key from above.
- Patch repairs
For small aesthetic flaws or cracks, such as those caused by movement, patch repairs can be extremely effective. The important thing is to evaluate whether a smooth and consistent finish can be achieved, without the need to reskim the entire wall or ceiling. There are specific plaster repair systems available for small patch repairs, which are designed to consolidate lime-lath plaster and historical limework.
The need for a fresh top layer of plaster is extremely common. Here, you will need to use a primer to ensure the new materials bond well with the old. You should select a primer that matches the plaster, for example, when using lime plaster, and to retain breathability you will need to ensure the primer isn’t acrylic.
When it comes to replacement, it’s still important to consider the original structure of the wall and if any existing materials can be salvaged to be used as part of the replacement work.
- Repairing the key
Many ceilings of lath and plaster or highly ornate fibrous plaster can still look great, but are slowly detaching from the wooden or hessian supports holding them in place, before eventually crashing to the ground. This has been a problem in theatres, and rules are now in place to survey and repair plasterwork ceilings in public buildings. These can be repaired from above by reinforcing and stabilising the hidden support structure and re-bonding the plasterwork to it.
Possible damage and how to repair
Before carrying out any renovation or refurbishment work, it’s essential to address the issue that caused the plaster to become damaged in the first place, to prevent it from reoccurring. Types of damage may include:
- Impact damage/wear and tear
This type of damage is inevitable, and due to lime’s traditional appearance, it will often carry some wear and tear without need for repair, as it can fit in with the building’s character.
In many cases, impact damage can be solved easily with a patch repair using a matched plaster. However, in some scenarios, such as home upgrades, you may be left with holes in the walls for cabling, for example. This can be difficult to patch and may require an entire top layer of plaster to ensure an even finish.
- Movement of other materials
Damage from other materials is particularly seen in ceilings, as they can become weakened as timbers flex and move or laths go soft or rot over time, for example. In situations where the structural integrity of a ceiling is failing, it is often necessary to replace the materials.
Overpainting – particularly with paints that aren’t breathable – can cause lime plaster to become damaged. Removing these inappropriate paints is often easily done, and can help to recover the wall’s breathability. This will help you to get back to the surface of the lime plaster and assess any damage from there. You can often patch repair any bits of lime plaster at this point, before repainting with a breathable paint or limewash.
Salts can come out of the building’s masonry, and removing them entirely can be extremely difficult. If you notice a white crystal growth on the plaster, and the plaster is noticeably crumbling, the damage is most likely caused by salts.
Salts in the brickwork can crystalise near the surface and move when the wall is drying out. For example, if you’ve got a leaking gutter, salts can begin to move through the wall and damage the plaster inside. If your paint isn’t breathable, you may see it blistering or bubbling as the plaster beneath it crumbles.
Modern gypsum plasters can result in salt being present in masonry and cause degradation in older builders. Lime plaster can avoid the presence of salt in masonry and be less affected than other types of plaster, as it allows moisture and salts to pass through – but a breathable paint or limewash is important.
When repairing salt damage, the first step is to cut off the cause of water – check the external pointing, monitor any leaks and repair guttering work. Then, it’s likely the plaster will need replacing.
For more information or advice when selecting the right solution for your project from Lime Green Products visit https://www.lime-green.co.uk/