Plaster cracks are one of the most common issues homeowners notice inside their property. While some cracks are harmless cosmetic problems, others can indicate movement, poor workmanship, or moisture issues.

Understanding the type of crack you’re dealing with is the first step in deciding whether it’s a simple DIY repair or something more serious.

What Are Plaster Cracks?

Plaster cracks are splits or fractures that appear in internal wall or ceiling finishes. They can range from thin hairline cracks to wider gaps that run across ceilings or down walls.

In most homes, minor cracking is normal over time due to settlement and temperature changes. However, certain patterns or widening cracks may indicate structural movement.

Common Types of Plaster Cracks

1. Hairline Cracks

Very fine cracks (less than 1mm wide).

Usually caused by drying shrinkage or minor settlement.

Severity: Low

Common in: New builds and recently plastered walls

2. Settlement Cracks

Slightly wider cracks that often appear around door frames, windows, or where walls meet ceilings.

Cause: Normal building movement as materials settle.

Severity: Usually low unless widening.

3. Ceiling Cracks

Cracks running across ceilings or along plasterboard joints.

Cause:

• Poor taping and jointing
• Movement in timber joists
• Thermal expansion

If the crack follows a straight line, it’s often along a plasterboard joint.

4. Diagonal Cracks

Cracks running diagonally from windows or doors.

These can sometimes indicate structural movement, especially if they widen over time.

Severity: Moderate to potentially serious (monitor closely).

5. Reoccurring Cracks

Cracks that return after being filled.

This usually suggests:

• Ongoing movement
• Poor repair method
• Underlying structural issue

What Causes Cracks in Plaster?

There are several possible causes:

🏠 Natural Settlement

All buildings move slightly over time. Minor cracking in the first few years is normal.

🌡 Temperature & Moisture Changes

Plaster expands and contracts with changes in temperature and humidity.

🪚 Poor Workmanship

Incorrect plaster mix

Insufficient drying time

Poor plasterboard jointing

💧 Moisture Problems

Leaks, rising damp, or condensation can weaken plaster and cause cracking.

🧱 Structural Movement

Subsidence, foundation movement, or load changes may cause larger cracks.

Are Plaster Cracks Serious?

It depends on:

✔ Width of crack

✔ Pattern of cracking

✔ Whether it’s getting worse

✔ Associated symptoms (sticking doors, sloping floors)

Generally:

• Under 1mm → Cosmetic
• 1–5mm → Monitor
• Over 5mm → Seek professional advice

If cracks widen quickly or appear alongside external brick cracks, further investigation may be needed.

How To Check a Crack Yourself

Here’s a simple monitoring method:

1. Measure the width (use a ruler or crack gauge).
2. Mark the ends lightly with pencil.
3. Take a photo.
4. Check again in 4–8 weeks.

If the crack remains stable, it’s likely cosmetic.

If it widens, spreads, or new cracks appear, further inspection may be required.

How To Repair Plaster Cracks

For Hairline Cracks:

1. Open the crack slightly with a scraper.
2. Remove dust.
3. Apply flexible filler.
4. Sand smooth when dry.
5. Repaint.

For Larger Cracks:

1. Rake out loose material.
2. Apply scrim tape (if needed).
3. Fill with suitable filler in layers.
4. Sand and redecorate.

For Ceiling Joint Cracks:

Often best repaired by:

• Cutting out the loose joint
• Re-taping and jointing properly
• Skimming if necessary

When To Call a Professional

You should seek professional advice if:

• Cracks are wider than 5mm
• They are diagonal and growing
• Doors/windows are sticking
• Floors feel uneven
• Cracks appear externally as well

These signs may indicate structural movement rather than simple plaster shrinkage.

Frequently Asked Questions

Do plaster cracks mean subsidence?

Not usually. Most plaster cracks are cosmetic. Subsidence cracks are typically wider and visible externally as well.

Why do cracks come back after filling?

Movement is still occurring, or flexible filler wasn’t used.

Are cracks normal in new builds?

Yes. New homes commonly develop minor settlement cracks within the first 1–3 years.

Can I paint over a crack?

Painting without filling will not solve the issue — it will likely reappear.

Final Thoughts

Most plaster cracks are minor and part of normal building movement. The key is understanding the difference between cosmetic cracking and structural warning signs.

If in doubt, monitor the crack before carrying out repairs. Stable cracks are rarely serious. Widening cracks should not be ignored.