Should I Repair or Replace Lime Plaster?

Lime plaster is extremely hard-wearing. It can last for hundreds of years, flexing as buildings move, regulating moisture and ensuring the building remains dry over time. Many older houses or historical buildings include lime plaster that is centuries old.

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Lime’s qualities, such as flexibility, breathability, durability and damp resistance, allow it to be repaired in a wide range of situations. But, when your lime plaster begins to appear aged and damaged, should you repair it or replace it?

Simon Ayres, Co-Founder and Managing Director at Lime Green Products, shares the key indicators that can help you to decide whether repairing or replacing is the best option for you, sharing the techniques for doing so successfully.

Replacing plaster can be expensive, so it’s important to ensure you make the right decision. Identifying problems and determining which method is suitable requires skill and knowledge. However, there are methods of salvaging and reattaching old ceilings and walls, so damage doesn’t necessarily mean replacement.

What are the options?

It’s difficult to replace older plasters to the same standard they once were, so, wherever possible, salvaging and repairing the existing material is key. Repairing can also provide a more authentic result, which can last for another lifetime or two.

When refurbishing any existing plaster, it’s important to evaluate the materials and choose a complementary plaster for repair work. This is important to ensure the materials bond properly and stand the test of time.

For most renovation projects, there are four options to breathe new life into older lime plaster: patch repair, reskim, replace or repair the key from above.

1. Patch repairs
For small, aesthetic cracks caused by movement, patch repairs can be particularly effective. It’s important to evaluate whether a smooth and consistent finish can be attained, without the necessity to reskim the entire wall or ceiling. Specific plaster repair systems are available for small patchwork repairs, created to consolidate lime-lath plaster and historical limework.

2. Reskimming
It’s not uncommon to need a fresh top layer of plaster. In this process, it’s important to use a primer to ensure the new materials bond well with the old. Be sure to select a primer that matches the plaster. For example, when using lime plaster, consider using a primer that isn’t acrylic to retain breathability.

3. Replacement
For replacement, it’s still important to review the original structure of the wall to determine if any existing materials can be salvaged and rejuvenated in the remedial work.

4. Repairing the key
Ceilings made from lath and plaster or highly ornate fibrous plaster can still be aesthetically pleasing, but they may be slowly detaching from the wooden or hessian supports holding them in place. The material can then eventually come loose and fall to the ground. This has been a common problem in theatres. There are now rules in place to survey and repair plasterwork ceilings in public buildings. The material can be repaired from above, by stabilising the hidden support structure and re-bonding the plasterwork.

Possible damage and how to repair

Before undertaking any renovation or refurbishment work, you will need to address the issue that caused the damage in the first place, to prevent the possibility of the same issue reoccurring. Types of damage may include:

Impact damage/wear and tear

Lime’s traditional appearance means it can often carry some small blemishes without the need for repair, as it can add to the character of the building.

Generally, impact damage can be solved simply with patch repair, using a matched plaster. However, in some circumstances, such as home renovations, you may be left with holes in the walls for cabling, for example. This can be difficult to patch, and an additional layer of plaster may be needed to create a consistent finish.

Movement of other materials

Damage caused by the movement of other materials is particularly common in ceilings, as they can weaken as timbers flex or laths rot over time. Where the structural robustness of a ceiling is decreasing, it is likely you will need to replace the materials.

Overpainting

Overpainting, particularly with non-breathable paints, can cause damage to lime plaster. Removing the incompatible paints is often simple, and can salvage the wall’s breathability. You can then reach the surface of the lime plaster and inspect any damage from there, making repairs where necessary. You can then repaint with a breathable paint or limewash.

Salts

If there is a white crystal growth on the lime plaster, and it’s noticeably crumbling, this damage is most likely to be caused by salts.

Salts in the masonry or brickwork can crystalise and move when the wall dries out. For example, a leaking gutter can allow salts to move through the wall and spoil the plaster inside. If you use a paint which is non-breathable, it may begin to blister or bubble as the plaster underneath crumbles.

Modern gypsum plasters can allow the presence of salt in masonry, which will cause degradation in older buildings. Lime can help to prevent the presence of salt in masonry and is less affected than other types of plaster, as it allows moisture and salts to pass through.

When repairing salt damage, it’s important to cut off the cause of water. Check the external pointing, monitor any leaks and repair any guttering work. With salt damage, it’s likely the plaster will need replacing.

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