Owners of old houses will be well aware of the unique charm of period properties. But if you have older lime plaster walls or ceilings, they need the right kind of maintenance to ensure your home remains in good condition.
Cracks in lime plaster, blown or crumbling sections are common. These need to be carefully repaired using lime based filler or plaster for larger sections. This is vital to preserve the health of your walls.
Auro 342 – High Grade Lime Filler for Wall repair.
You don't need a specialist lime plasterer for smaller repairs. With the right breathable fillers and an understanding of how lime plaster behaves, you can tackle minor fixes yourself.
What Is Lime Plaster and Why Does It Crack?
Lime plaster is a traditional wall finish made from natural ingredients – lime sand and water. As it sets it undergoes a process called carbonation (absorbing CO₂ from the air). When dry, it remains slightly flexible and vapour open.
This breathability is what makes lime plasters ideal for older homes with solid walls. It helps regulate moisture instead of trapping it. Moisture can pass through lime plaster, helping avoid damp and damage to the structure of your home.
Cracks and defects in lime plaster appear for several reasons:-
- Natural movement in the building.
- Past repairs with incompatible materials.
- General wear after decades or even centuries of use.
Lime plaster can often be repaired rather than replaced, as long as you use compatible materials.
Can You Repair Lime Plaster?
Lime plaster can be repaired, but it's vital to use lime or mineral based products to stabilise the structure. Modern plasters and fillers are not compatible with lime, they're too rigid, lack breathable properties, and tend to fail in a relatively short timeframe due to this.
They can also trap moisture in walls, which can create issues with damp and mould later on. Repairing lime plaster the right way means choosing breathable fillers and plasters that move and breathe in the same way as the original wall.
How to Repair Cracks in Lime Plaster
Cracks are the most common lime plaster repair. How you treat them depends on their size:-
- Hairline cracks – Often just cosmetic. Fill with a fine lime based filler like Auro 342 and smooth flush with the surface.
- Small to medium cracks – Open up gently with a scraper before filling, to allow the lime filler to bond properly.
- Larger cracks – May need multiple applications of lime filler, or in some cases patching with lime plaster.
Always avoid acrylic or gypsum fillers, as they do not bond properly and aren't breathable.
How to Patch Repair Lime Plaster
When sections of plaster are missing, you will need more than just filler. If you'd like to attempt patch repairs:-
- Remove loose or crumbling plaster back to a sound edge.
- Dampen the wall slightly to stop it sucking moisture too quickly from the repair.
Apply lime plaster repair mix or filler in layers, allowing each one to set. - Smooth and blend into the surrounding wall.
For small chased-in sections (like after rewiring), breathable lime fillers are usually sufficient. For larger holes, a finishing coat of lime plaster might be a better option.
Repairing Lime Plaster Ceilings
Ceilings bring their own unique challenges for those wishing to DIY a repair. Many older homes have lath and plaster ceilings, where lime plaster is pressed into timber strips to hold it in place. Over time, plaster can crack or detach from the laths, creating bulges or even falling sections.
- Small cracks can be filled with lime filler.
- Loose plaster may be consolidated using specialist techniques to reattach it to the laths. Depending on your level of skill, you may need to consult a specialist lime plasterer.
- Extensive damage often needs a professional plasterer.
How to Repair Blown or Crumbling Lime Plaster
Blown plaster happens when the bond between plaster and wall breaks down. You will usually hear a hollow sound when you tap it. You will only know the extent of the plaster damage once you've started to attempt a repair, which adds a bit of excitement to the project!
To repair plaster:-
- Remove all loose material until you reach sound plaster.
- Rebuild using lime plaster top coats.
- For badly degraded areas, a full replaster may be the only option.
Crumbling lime plaster should never be skimmed over with gypsum. It will not stick properly and will make moisture issues worse.
Best Fillers and Materials for Lime Plaster Repairs
The most important decision when repairing lime plaster is the filler you choose. It must be breathable, lime-based, and compatible with the existing wall.
Auro 342 Natural High Grade Lime Filler
For cracks, small holes, or surface levelling, Auro 342 is the ideal product. It is a natural, non toxic lime filler made from mineral fillers, calcium hydroxide, and cellulose. It is completely plastic free.
Unlike modern fillers, Auro 342 is vapour permeable, so it will not trap moisture or cause future failures.
It can be used to:-
- Fill hairline cracks and minor defects.
- Smooth and level uneven lime plaster.
- Prepare walls for finishing with lime paints.
Supplied in powder form, it mixes easily with water and remains workable for around 8 hours. When compressed with a trowel, it can create a glassy, polished surface, ideal before painting with breathable finishes.
Other Options
- Lime putty – traditional and breathable, but may shrink back and need reapplying.
- Casein fillers – milk protein based, breathable, but less commonly available.
- Lime plaster finishing coats – best for larger patch repairs or when surfaces need a fresh top coat.
DIY or Professional Lime Plaster Repairs?
When should you call in the professionals? One issue with DIY lime plaster repairs is that once you start to remove blown plaster, you are committed to the job.
- DIY-friendly repairs – hairline cracks, small holes, surface levelling with lime filler.
- Call in a professional – ceiling repairs, blown plaster across large areas, or decorative historic plasterwork.
What looks like a small repair can quickly become a large section of wall needing replaced. Trying to repair extensive damage yourself may lead to bigger problems down the line, and lime plastering is significantly more expensive than gypsum based work. Beware!
Protecting Lime Plaster with Breathable Paint
Once repairs are complete, protect the plaster with breathable paints. Using vinyl emulsion or plastic-based paints will undo all your repair work by trapping moisture again.
Choose natural mineral or lime-based paints such as Earthborn or Auro ranges. These work in harmony with lime plaster and keep walls dry, healthy, and beautiful.
Repairing lime plaster does not have to mean a full replastering job. With the right breathable materials, many cracks and defects can be dealt with quickly and effectively, preserving your walls and saving money.
For heritage properties, this approach keeps you in step with traditional building methods while protecting the long term health of your home.
Need help? Contact Us for advice on your project.
