Should You Worry About Cracks in Your Plaster Walls?

Crack in Wall

All houses, old and new alike, will experience cracks in walls at some point. In most instances, small cracks are perfectly normal and nothing to be too concerned about; however, with our helpful guide, we will help you recognise when these plaster cracks are concerning.

Summary

What Causes Plaster Cracks?
Different Types Of Cracks
When Do Cracks in Walls Become Serious?
Are Cracks in Walls a Sign Of Subsidence?
Repairing Minor Cracks in Walls
Does Building Insurance Cover Cracks?
What To Do If You’re Worried About Cracks In Your Walls

What Causes Plaster Cracks?

Plaster cracks are small fractures within plastered walls. While they may sound concerning, most plaster cracks are extremely common and normal.

For most properties, slight cracks occur as the plaster dries and shrinks. New builds and properties that have undergone recent extensions are expected to experience cracks in walls as their foundations settle. It may come as a surprise, but stabilising can take approximately one to three years. During this time, the building or extensions’ weight will cause the plaster to move and, in some places, crack.

Humidity, temperature changes and moisture levels will also cause similar cracks within a plastered wall. Any fluctuations in conditions will cause the plaster to expand and contract, causing the building’s overall structure to swell and sink. As a result, hairline cracks can occur and grow over time into more noticeable cracks. These hairline cracks can also be expected as newly plastered walls dry out.

If you are experiencing some minimal cracking and none of the above applies, there still could be no reason to worry. Houses located on busy roads can experience slight cracking through the vibration the building experiences from the sheer volume of traffic going past. And, if you’re in a quiet spot, but updated old window frames to uPVC double glazing, you may see cracks appear around here. Windows that are not supported by a lintel, common with timber frames, often have plaster cracks around the opening.

In most cases, plaster cracks are minor issues requiring simple cosmetic attention and a plaster skim for a flawless wall. If your cracks are more substantial, it is always best to play on the safe side and investigate further.

Different Types Of Cracks

All cracks are different and, as we’ve said, some are completely normal. A reliable way of assessing which cracks are cause for concern is by taking into account their size, including their length, width and depth. The Building Research Establishment (BRE) has released a report guiding the Assessment of Cracks in Houses, which highlights six grades of crack severity by their width. This scale does not account for other features of subsidence, but it is a good initial indicator of whether or not there is cause for concern.

Severity	Size (Width)	BRE Equivalent	Action
No Cause for Concern	Hairline	0	No action particularly necessary.
Minimal	Around 1mm	1	Easily fixed by redecorating.
Small	1mm to 5mm	2	Easily fixed with filler. Exterior cracks may need repointing.
Moderate	5mm to 15mm	3	May need professional attention.
Serious	15mm to 25mm	4	Often caused by structural damage. Seek expert advice.
Very Severe	Over 25mm	5	Serious structural damage. Major repair work is needed, including unpinning and rebuilding.

Vertical Cracks

Vertical cracks in plastered walls, especially in new properties, are common and appear as the plaster dries out and settles. Hold off filing and repainting them as soon as they form. Doing so means more could appear that you will have to address. You are much better at waiting until your plaster has dried out further and then taking action. However, if these cracks progress to more than 25mm, a more severe issue could need immediate attention.

Diagonal Cracks

You cannot ignore diagonal cracks in your wall, similar to a set of stairs going up or down. They usually result from structural movement and, consequently, can be extremely serious. Contact an expert for assessment, as these cracks often signal hidden issues.

Hairline diagonal cracks in the upper sections of a wall typically suggest the settling of a house. As temperatures vary, especially in older homes, structural adjustments may occur, leading to minor shifts and cracks as the building accommodates these changes.

Dry Shrinkage

Dry shrinkage refers to the cracking that occurs in concrete due to the loss of moisture during the curing process. As water evaporates, the volume of the concrete decreases, leading to cracks.

Popping

Popping is a type of cracking that results from the sudden release of pressure within the concrete. It often happens when entrapped air or water vapour tries to escape, causing a localised explosion-like effect.

Discoloured Cracks

Discoloured cracks are structural cracks characterised by a change in colour along the crack lines. This type of cracking can be caused by various factors, including chemical reactions, impurities in materials, or environmental exposure.

Grinning

Grinning occurs when cracks at the surface of concrete reveal the underlying coarse aggregates. It gives the appearance of a “grin” due to the exposure of the larger aggregate particles.

Expansion Cracks

Expansion cracks result from the swelling or expansion of certain materials within the concrete, leading to internal pressure and subsequent cracking. Common causes include the reaction of aggregates with alkalis in the cement.

Lack of Hardness Cracks

These cracks refer to the formation of cracks in the concrete due to inadequate strength or hardness. This can be a consequence of improper curing, poor mix design, or insufficient compaction.

Debonding

Debonding occurs when the bond between the concrete and an adjoining material, such as a reinforcement or overlay, is compromised. This can lead to cracks and separation between the layers.

Window Sill Cracks

Window sill cracks specifically refer to cracks that form in the vicinity of window sills. These cracks can result from various factors, including differential settlement, thermal expansion and contraction, or structural issues in the support system.

Structural Cracks

Structural cracks are fractures that occur in a material or building component, compromising its integrity and potentially affecting its load-bearing capacity. These cracks are caused by various factors, including structural overloading, settlement, foundation issues, material defects, seismic activity, or inadequate design. Structural cracks are a serious concern as they can lead to safety hazards and may require thorough evaluation and repair to ensure the stability of the structure.

Spider Cracks

Spider cracks, also known as craze cracks or hairline cracks, refer to fine, interconnected fractures on the surface of a material, such as paint, coatings, or certain types of polymers. These cracks resemble a spider web, hence the name.

The primary cause of spider cracks is usually attributed to the expansion and contraction of the underlying material due to temperature variations, ageing, or exposure to environmental stressors. These cracks are often cosmetic and don’t necessarily compromise the structural integrity of the material but can affect its appearance.

When Do Cracks in Walls Become Serious?

As a rule of thumb, small cracks are nothing to be concerned about. However, larger cracks that are over 5mm should be taken more seriously. Cracks become serious when they start to exceed 25mm, these are the cracks to worry about.

The main characteristics that suggest a crack is much more serious are the following:

Wide cracks over 3mm
Cracks travelling diagonally across a wall
Jagged cracks that run along a wall
Cracks around door and window frames
Cracks showing glimpses of daylight through

If you have any cracks that tick any of these boxes, you are right to be concerned. With the right professional advice, you can address them before permanent damage occurs.

Are Cracks a Sign of Subsidence?

Where a property has more significant cracking, this may be a sign of more serious structural problems. The most common of these issues are subsidence and compromised foundations. These larger cracks can be caused by a range of factors that result in the subsidence of a property, including:

Damage to drains surrounding a property and any underground leaks, destabilising the ground below the property
Excessive rainfall and flooding
Periods of drought and extremely dry periods
Poor and shallow foundations
The root system of nearby trees can interfere with a building’s foundations and, sometimes, they can take too much moisture out of the ground directly below a property, unsettling the soil a house is built upon
Mining in the local area’s history
Extreme lintel failure surrounding windows and doors

Where these factors are in play, it is recommended to monitor any cracks in walls that are visible, checking for signs of growth and deterioration.

How to Identify Subsidence Cracks

If you notice any of these features in the cracks in your walls, your property may have subsidence.

The crack is wider than 3mm (the thickness of a £1 coin)
The crack is diagonal, following a stair-step pattern along your brickwork
The crack is wider at the top than at the bottom
The crack is visible on both sides of the wall
There are more cracks appearing suddenly
There are other signs of movement, such as sloping floors, creasing wallpaper, stuck doors or windows and gaps between skirting and walls

These signal that the earth underneath your home is shifting significantly, and you need to call a subsidence repair professional.

Why Are There Cracks in My New Plaster?

Cracks in new plaster can be quite common and can result from a variety of factors.

Drying and Curing: Plaster goes through a drying and curing process as it sets. During this time, the plaster loses moisture and can shrink slightly. This shrinkage can lead to cracks forming on the surface. These are typically small, hairline cracks and are generally considered normal. They can often be fixed with a simple patching and repainting.
Improper Mixing: If the plaster was not mixed properly, it might not have a consistent texture and composition, leading to areas that dry and cure differently. This can result in uneven shrinkage and cracking.
Inadequate Base Preparation: Plaster needs a solid and clean base to adhere to. If the surface underneath wasn’t properly prepared, it can lead to poor adhesion, which in turn can cause cracks as the plaster separates from the substrate.
Application Technique: Inexperienced plasterers might apply the plaster unevenly or too thickly in some areas. This can lead to uneven drying and an increased likelihood of cracks forming.
Rapid Drying: If the plaster dries too quickly, whether due to high temperatures, direct sunlight, or drafts, it can develop cracks as the outer layer hardens before the inner layers have a chance to properly cure.
Structural Movement: Cracks can also form due to movement in the underlying structure. If your building settles, shifts, or experiences any structural changes, the plaster on the surface can crack as a result.
Temperature and Humidity Changes: Fluctuations in temperature and humidity can cause materials to expand and contract. This movement can lead to cracks in plaster over time, especially if the plaster and the substrate have different rates of expansion and contraction.
Low-Quality Materials: The quality of the plaster and other materials used can play a role in crack formation. Using subpar plaster or additives can affect the overall durability and longevity of the plaster.
Vibration and Impact: If the area where the plaster is applied experiences regular vibrations or impacts (such as heavy machinery or slamming doors), this can lead to cracks over time.
Insufficient Priming: Applying a primer before plastering helps create a better bond between the plaster and the surface. Without proper priming, cracks can develop due to poor adhesion.

It’s important to assess the severity and pattern of the cracks. Hairline cracks are usually not a major concern and can be fixed with simple solutions like patching and repainting. However, if the cracks are large, deep, or widespread, it might indicate more significant issues that require professional assessment and repair. If you’re uncertain about the cause or how to address the cracks, it’s advisable to consult with a professional.

The Shrinkage of Plaster

Plaster can exhibit various types of cracks due to its inherent property of shrinkage during the drying and curing process. Shrinkage cracks can compromise both the appearance and structural integrity of plastered surfaces. Understanding the different types of shrinkage-related cracks can provide valuable insights into their prevention and repair.

Dry Shrinkage: As plaster dries and loses moisture, it undergoes a reduction in volume, resulting in dry shrinkage cracks. These cracks are typically small, fine lines that appear on the surface of the plaster. Dry shrinkage cracks are often considered normal and are mainly a cosmetic issue. They can be addressed through patching, sanding, and repainting.
De-Bonding: Improper adhesion between the plaster and the substrate can lead to de-bonding cracks. When the bond between the plaster and the underlying surface weakens or fails, cracks can develop as the plaster separates from the substrate. This type of cracking is often caused by inadequate surface preparation, insufficient priming, or the use of low-quality bonding agents.
Structural Cracks: Plaster can also crack due to movements in the building’s structure. Structural cracks often follow a pattern that reflects the movement, settling, or shifting of the building. These cracks can be more concerning, as they may indicate underlying issues with the building’s foundation or structural integrity. Addressing structural cracks often requires both repairing the plaster and investigating and rectifying the underlying structural problems.
Grinning: Grinning refers to the appearance of cracks along the edges of plastered surfaces, often near the corners of walls or ceilings. This occurs because these edges have less mass and are more prone to movement and stress during the drying process. Grinning can be mitigated by using proper corner beads, reinforcing mesh, and ensuring consistent plaster thickness.
Lack of Hardness: Plaster needs to achieve a certain level of hardness during the curing process to resist cracking. If the plaster is applied too thickly or the mix ratio of plaster to water is incorrect, it might not achieve the necessary hardness. Soft or weak areas in the plaster can develop cracks as they are more susceptible to deformation and stress.
Popping: Popping occurs when air bubbles trapped within the plaster expand and burst during the drying process, leading to the formation of small craters or depressions on the surface. These depressions can later develop into cracks as the plaster dries further. Proper mixing techniques, such as using a mechanical mixer and allowing the plaster mix to rest before application, can help reduce the occurrence of popping.
Expansion of Plastering: While not a type of shrinkage-related crack, it’s worth mentioning that plaster can also expand as it absorbs moisture from the air. This can lead to cracks forming if the expansion is not uniform across the surface. Proper curing and maintenance, such as controlling humidity levels, can help prevent this type of cracking.

Understanding the various factors that contribute to the shrinkage and cracking of plaster is essential for both preventing their occurrence and effectively addressing them when they do appear.

Repairing Minor Cracks in Walls

Depending on where your cracks are categorised on the BRE scale, they may only require little to no action. However, others cannot be ignored. Consult a professional engineer for an expert opinion on severe and potentially dangerous cracks.

Cracks over 5mm need repairing and filling; you should always seek professional attention. All contractors will have their preferred method of repairing cracks based on their prior experience and general industry know-how. In most cases, it depends on the type of wall under repair.

For drywall cracks, a popular approach is to re-tape the joint. Firstly, a plasterer will scrape away any loose tape and crumbled drywall materials before sanding the surface. A drywall compound will then be added to fill the crack with new tape, repeating this process for a few coats to achieve a flawless finish.

Small plaster cracks can be filled with a putty or polycarbonate filler. Use a palette knife to press filler into the crack, before smoothing over the excess with the edge of the knife. Leave to dry and sand it smooth before painting.

However, if the plaster is crumbling away, feels powdery has pockets of air behind, or more cracks keep appearing, it may be time to re-plaster the whole wall.

The Crack Stitching Method

Crack stitching is a popular method with masonry walls as it provides a permanent solution to structural cracks. Stainless steel helical bars are inserted in slots within the mortar joints, helping to reinstate structural integrity.

Equipment Required to Repair Cracks

You need some typical hardware equipment and specialist materials to repair cracks in plaster walls, including:

A Stanley knife
A filler knife
A chisel
Drywall tape
Drywall joint compound
A tray to mix joint compound
Sandpaper
Scissors
A vacuum cleaner

How to Repair a Crack

1. Score the crack

Using the Stanley knife, score over the crack and remove loose plaster.

2. Vacuum to remove dust

Vacuum the crack to remove loose materials and dust.

3. Cut drywall tape to length

Cut a piece of drywall tape to the length of the crack and then keep it for later.

4. Mix joint compound

Following the instructions on the packet, mix the drywall joint compound on the tray.

5. Spread the joint compound over and in the crack

Use the filler knife to apply the joint compound over the crack. It should be a thin, even layer.

6. Cover the crack with drywall tape

Place the drywall tape over the crack. Smooth out any air bubbles or bumps.

7. Apply another layer of compound

Smooth a top layer of compound over the tape and allow it to dry.

8. Sand to finish

Sand the area smooth. Take care to prevent ripping or removing the tape.

Fixing Different Types of Cracks

Other cracks are tougher to handle, often requiring specialist repairs. However, you can tackle some yourself.

Cracks in the Corners of Plaster Walls

Corner cracks are hard to reach and repair, although you can follow a similar method to a traditional fix. Use additional pieces of drywall tape, one for either side of the corner crack.

Recurring Cracks in Plaster Walls

Often recurring cracks are worrying but harmless issues. However, you should always consult a specialist to identify whether structural problems are the culprit.

Cracks in Plaster Walls Before Painting

Failing to fix plaster cracks before painting will cause recurrences and impact your finish. If you have minor shrinkage cracks, you can simply fill them. Any peeling plaster, either in cracks or patches, should be tackled by an expert.

Hairline Cracks

You can fix hairline cracks simply with a filler.

Larger Cracks

Large or deep cracks are often signs of structural issues, so you should consult a specialist to diagnose underlying problems. If they identify any, you must resolve them before repairing the cracks.

You can apply a mix of sand and cement to the crack to fill in the hole. It should be one part cement to four parts sand.

Plaster vs. Drywall Repair

You can apply drywall (plasterboard) or plaster to your walls to prepare them for decorating, depending on your home’s structure. Installing drywall is a shorter, more affordable process, as you can simply attach the panels to wall studs and then skim over them. Therefore, you can repair cracks in this plaster by replacing a single plasterboard.

Alternatively, if you have plaster walls, you should carefully repair them rather than replace them if possible. You may need specialist assistance for large cracks and holes.

Treating Damp

Damp mould is infectious and can spread across your walls, meaning that you should quickly treat it to prevent health risks or damaging other furniture.

You should always ventilate your rooms to remove water and condensation. Then, if mould and dampness occur, you can treat them with over-the-counter solutions or bring in specialists for larger jobs.

Does Building Insurance Cover Cracks?

Buildings insurance should cover cracks that appear due to subsidence. But, it is worth remembering that most providers will expect an excess fee. Going through your insurance company often encourages your provider to monitor your property’s cracks with regular assessments, allowing them to advise a suggested course of action.

If cracks occur through other causes, including thermal variations, lintel failure near doors and windows and natural settlement, insurers will see them as an issue with maintenance. As building insurance policies do not include general wear and tear, you will not be covered.

For more extensive details on what cracks are covered, explore your policy document or contact your insurance provider directly.

Should I be Worried About Cracks in Render?

The presence of cracks in render can be a cause for concern, as it may indicate underlying issues or pose structural problems. Hairline cracks, which are common and often result from settling or temperature changes, may not be a major worry. However, wider or deeper cracks could signify structural movement or other significant issues.

Various factors contribute to cracks in render, including settling during the initial years of construction, temperature fluctuations causing expansion and contraction, substrate problems, and potential structural issues. Identifying the specific cause is crucial for determining the severity of the situation.

Cracks in render can also facilitate moisture ingress, creating a pathway for dampness, mould, and related problems. Regular maintenance and inspections are essential to catch cracks early and prevent them from escalating into more serious issues.

If significant or recurring cracks are observed, seeking professional advice from a building expert or structural engineer is advisable. Their assessment can help pinpoint the cause of the cracks and guide appropriate solutions. Repairing the render may be necessary, but addressing the underlying issue is equally important to ensure the long-term integrity of the building.

What To Do If You’re Worried About Cracks In Your Walls

If you are worried about cracks in your wall, the best thing to do is to gain an expert’s opinion. For homeowners, we recommend choosing a professional plasterer and engineer in your local area to arrange an assessment. However, if you are in rental property, contact your landlord as soon as possible; freeholders are responsible in the case of leaseholder arrangements.

Whether you’re concerned about internal cracks or external cracks, our expert plasterers at AB Drylining are qualified to help you achieve a smooth, crack-free appearance once more. We offer plastering andrenderingservices across Wiltshire and the South West, including Bristol, Swindon, Bath and the West Midlands. Give us a call on 01225 941006 or send us an online enquiry and our team will be happy to help you.

FAQ

When should I be worried about cracks in walls?

If cracks in your property are over 5 mm in width, get an expert’s opinion on how best to proceed. Any diagonal cracks will require urgent attention.

What are the characteristics of structural cracks?

Structural cracks often form diagonally, in a jagged nature across a wall. When they occur, seek a professional’s advice as soon as possible.

What are the different types of ground movement that affect cracks?

Four different types of ground movement can cause cracks in a property:

Compaction – downward movement from the soil being compressed under the weight of the property (within ten years of being built)
Landslip – downward movement on sloping ground
Heave – upward movement resulting from soil expanding
Subsidence – the ground beneath a building sinking and pulling on the property’s foundations

Will claiming for plaster cracks affect my insurance?

Often claims on subsidence will result in a higher premium the next time you renew. A no-claims bonus can also be affected.

Can I fix hairline cracks on plaster with paint?

Covering hairline cracks with plaster will leave a poor finish and risk them reappearing. You should fill them in before painting.

Can you fix plaster cracks with caulk?

You can fix plaster cracks with caulk, although it will leave an uneven surface as the caulk will sink into the crack, producing an indent.

Why do plaster cracks keep recurring?

Typically, movement in the foundations causes cracks. In rare cases, recurring cracks can signal a structural issue.