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Plaster is an amazingly versatile material, used for thousands of years to improve buildings of all kinds.
Although plastering is a job that almost anyone can take on, it takes determination and dedication to achieve the level of skill possessed by professionals - like those at Top Notch Walls.
Even so, no matter how skilled the plasterer is, you might notice that your plaster cracks over time. There are several reasons for this, including thermal movement in the walls (expansion and contraction as the materials heat up and cool down), accidental damage, and long-term exposure to moisture.
Surprisingly, it's not only a problem in older buildings, as cracks in plaster walls also occur in new properties as well.
Cracked plaster isn't very appealing, and nobody wants their walls to stay this way. So, what do you do about it?
Well, you basically have two choices: you can either fix it yourself, or you can get an expert to do the job for you! There are times when the decision is taken out of your hands, as the damage is too severe - and you can learn more about this below. But for those cases where it's fine for you to take on the job yourself, we've put together the Top Notch Walls guide on how to fix cracks in plaster walls.
This is important! If your property was constructed prior to the 1940s, your interior walls may be made of plaster and lath. While you can usually fix cracks in the plaster on this type of wall, there may be other issues at play that need specialist attention.
Most modern homes are fitted with plasterboard - at least on non-load-bearing walls - and this only has a thin layer known as skim plaster.
Any walls built from CMUs (concrete masonry units, also called breeze blocks or cinder blocks), brick, or stone will have wet plaster applied, and this can experience cracks of various sizes.
For the most part, no - but it is a possibility; cracks in plaster appear all the time, but you need to understand why this is so you can spot any potentially serious situations.
Before you throw yourself into the task of repairing cracks, it's wise to take a step back and examine the damage. Not all cracks are the same, and it's important to know the difference, or you risk causing further problems. Our post "How To Repair Plaster Walls" maybe interest you. You can check it out.
Here's what you should be looking out for:
It's normal to find hairline cracks in plaster, particularly when it is freshly applied, as the material tends to shrink as it dries or even as a result of the house settling. This issue might be worse if your home is situated by a main road or rail track, as vibrations from passing traffic can crack the plaster. Hairline cracks often appear around door and window frames, as they tend to be the weakest areas.
These appear as very thin lines, no more than 1 or 2mm thick. They can be vertical, horizontal, or diagonal, and you often find several cracks running alongside each other.
Most cracks of this nature can be easily fixed and won't be anything to worry about.
These appear to be slightly worse than hairline cracks, and they take a bit more effort to fix.
Depending on the substrate beneath the plaster, you may be able to see any serious damage yourself. For example, deep cracks are unlikely on plasterboard walls as the plaster is very thin, as explained above.
'Wet' plaster over masonry is more likely to display deep cracking, and this can be a sign of structural damage.
Larger cracks in plaster - anything more than 25mm wide - can be a sign of structural issues, like foundation movement. All buildings shift over time, especially when the foundations are on clay soil, as this expands and shrinks according to the moisture content.
While these cracks can be filled, it's always best to get them checked out by a surveyor - just in case!
Whatever type of cracks you discover, you need to check whether there is any loose plaster around them.
This could be a sign that the plaster has blown (lifted away from the substrate) or that there is an issue with moisture or dampness that needs to be looked into.
Once you have identified the type of cracks you're dealing with, your next step is to get prepared. We also recommend taking a look at our post "How To Fix Plaster Ceiling Cracks" for valuable insights.
Here's a list of items that you might need for the job:
Repairing small cracks is fairly straightforward. If the cracks are hardly visible, you can usually hide them with a fresh coat of paint! For more learnings, you can check out our post "How To Paint New Plaster".
However, if the problem is noticeable and needs a bit more work, you can fix it using a filler.
Cover the immediate area and any furniture with dust sheets. This might seem excessive, but it's better to be safe! Also, make sure you wear safety goggles and a dust mask.
Use the thin blade to carefully score along the cracks to make them wider. Remove any loose plaster and use the vacuum cleaner to get rid of dust.
If it's only a small area, mix the filler in the plastic pot according to the manufacturer's instructions. Dampen the area thoroughly - a plant sprayer or damp sponge will do the trick, but don't overdo it; it should not be soaking wet.
Apply the filler using the filler knife, making sure to press it in firmly so it reaches the base of the groove. It's okay to make it slightly thicker over the crack, but always remove excess filler from either side using a blade or a damp sponge. Once you have applied a final coat, you can use a squeegee to smooth things down. If you don't have one of these, then a putty knife or trowel will do the trick.
Allow the filler to dry fully before sanding it lightly to get a smooth and level surface. Use a medium-grade sandpaper first, followed by a finer one.
Oddly enough, this process is often easier than repairing small cracks, as you don't need to scrape them out to make them worse in the first place!
Brush the entire area to remove loose debris and dust, then clean up with a vacuum cleaner. Use the narrow brush fitting on the vacuum cleaner and run it across the damaged area.
Apply a suitable primer to help the filler bond with the surface and existing plaster, and leave it for about 24 hours to dry.
You can then use a ready-mix patching plaster or filler, or you might want to purchase a powder-based filler that you need to mix with water.
Apply this using a trowel, putty knife, or plasterer's float, making sure to press it firmly into place to ensure that the fissures are completely filled.
Allow this to dry completely and sand lightly with a fine-grit sandpaper. You can also check out our post "How Long Does Plastering Take To Dry" for more additional insights.
If your surveyor (or building professional) has checked the property and is happy that there are no structural issues, then you can go ahead with your repairs.
A large crack takes a little more effort to repair than fixing minor cracks, and you'll probably need to use a plaster mix rather than a filler. Big cracks are more likely to be found on masonry walls, so the following instructions relate to this.
One method we have come across is to stuff the fissure with newspaper or card (and, in some cases, pasta!). However, this is not ideal and should be avoided at all costs, as it provides no structural support and can lead to moisture absorption. Depending on the severity of the crack, you may want to use a caulking gun and suitable caulking material, then plaster over the top of this.
Before you do so, it's necessary to clean out the fissure, removing any stubborn debris with a chisel. Brush and vacuum the area, as with the smaller cracks, and apply a suitable primer.
Mix the plaster according to the instructions, and apply the first coat. Clean off any excess with a wet sponge and leave it to dry for ten minutes, then scratch the surface with a trowel blade in a criss-cross pattern.
Apply the second coat once the scratch coat has cured (about 24 hours) and leave it to dry completely before sanding. It may be necessary to use multiple layers to get the desired result. In fact, it's better to apply several thin layers as this provides a stronger finish over the repaired area.
Occasionally, you'll find that the plasterboard (or drywall) has split, causing the skim plaster to crack. This is most likely a result of accidental damage, either from someone falling against the wall or furniture bumping into it while being moved.
When this happens, you can repair the crack using drywall tape (also mesh tape or jointing tape) and by applying a thin coat of plaster over the top, or you may want to replace the damaged board.
You can either replace the whole board or cut out the damaged area with a drywall knife and replace only a small section. It's an option, but it can get very dusty and messy.
At Top Notch Walls, we're often asked the question, are cracks in plaster walls normal?
The honest answer is that cracks can appear in any plaster wall for a variety of reasons. In the majority of cases, it's reasonable to assume that you can sort out the problem yourself. The trick is to know when it's time to contact a professional plasterer.
The above guide gives a general overview of what to expect and which tools and materials you might need, and most plaster repair jobs - particularly minor ones - are straightforward.
But with bigger cracks, you might feel out of your depth. There's also the possibility of structural damage or the spectre of leaking walls and roofs to consider. It's no use repairing plaster walls if there's a major issue with the structure, as you'll be storing up trouble for the future!
Repeated cracking is often a sign that something isn't right.
When you need help and advice about cracks in plaster walls or any other issues regarding plastering, contact Top Notch Walls.
