How to fix cracks in plaster

Cracks in plaster on walls and ceilings sometimes seem to appear out of nowhere!

Whether you're a homeowner or a renter, discovering these cracks can be worrying. However, small cracks in plaster can be a common occurrence and can vary in size and depth, but with the right tools  and techniques, you can often easily say goodbye to these unsightly imperfections and restore your walls and ceilings. 

Keep reading to learn when to take action, how to fix cracks in plaster and the best tools to do it with - or when it may be time to consult a professional!

Jump to:

• When to worry about cracks in plaster
• Contacting a professional to fix cracks in plaster
• Prepare your tools and workspace
• How to fix cracks in plaster

When to worry about cracks in plaster

Before we get started on explaining how to fix cracks in plaster, let’s first work out whether you’ll need a professional to give it some serious attention instead.

Try not to worry too much about small or hairline cracks as most are not a sign that there is anything serious going on in your home structurally. However, understanding the signs of potential structural issues and how to tell which kinds of cracks you need to be concerned with can save you from the problem developing and eventual costly repairs and inconvenience.

If you are renting your property, your landlord or housing provider should be informed if you notice any cracks appearing in your home that could indicate there is a problem. If you’re a Places for People customer in a managed property, you can report a repair.

Here are some key indicators of when you should act against cracks in plaster:

Width of the crack in plaster

Any crack from 1 to 5 mm wide isn’t usually a cause for concern. However, if the crack exceeds this width, it's time to investigate further. While narrower cracks aren’t typically a sign of a bigger issue and are most often easy to fix yourself, wider ones may signify underlying problems such as dampness and moisture in your walls, or movement in the property itself. Read more of our tips on how to prevent condensation and mould at home.

A crack reaching around 25 mm in width, or wider, could be a strong indication of structural issues, such as subsidence or water ingress, requiring prompt professional intervention. Ignoring cracks like this could mean that the issue gets worse over time.

Cracks over door frames or mirroring external brickwork

Cracks appearing above your door frames are potential red flags and can hint at possible foundation issues or structural movement within your home. They shouldn’t be ignored and seeking expert assessment is strongly advised in such cases to address the root cause promptly.

Diagonal cracks, especially those mirroring the brickwork external to your home, demand immediate attention as they often signal shifting foundations, posing a risk to the structural integrity of your property.

Consult a qualified structural engineer and get them to evaluate the extent of any damage the cracks may have caused or potentially cause, then organise for any necessary repairs.

Contacting a professional to fix cracks in plaster

Understanding the appropriate point of contact—be it your landlord, property management company, or recognising when it falls under your repair responsibilities as a Places for People tenant—is important before addressing the issue yourself or arranging professional assistance.

If you’re a Places for People Customer and you believe the crack could be an indicator of structural damage, please report a repair as soon as possible.

If you are the owner of the property, it will be your responsibility to arrange for repairs, unless you are living in a new-build home that is still under warranty.

To contact a professional, we recommend contacting a reputable website to find a suitable tradesperson such as Checkatrade, TrustMark or Trust a Trader. If the crack isn’t a threat to your home’s structural integrity, keep reading for a step-by-step guide on fixing hairline cracks in plaster.

Prepare your tools and workspace

Now you’ve established whether the cracks in your home’s plaster can be manageably fixed, the next step is to ensure you have all the tools and materials needed to complete the job:

• Old curtains, bedding or plastic floor protector sheets
• Utility knife
• Chisel filler knife
• Plasterboard tape
• Filling compound and any PPE that is stated as required by the manufacturer.  
• Mixing tray (unless you are using a ready-mixed filling compound)
• Sandpaper
• Scissors
• Vacuum cleaner or brush and pan

Gather your tools and ensure you cover nearby surfaces. Move any furniture out of the way, especially if the crack is on the ceiling. Consider using a step ladder if necessary and take all the required safety precautions before using it.

How to fix cracks in plaster

Follow these simple steps to fix minor or hairline cracks in plaster:

• Use a utility knife to carefully score the crack, then carefully remove any loose plaster and widen the crack as needed. Vacuum away any small pieces of plaster and dust.
• Cut a piece of plasterboard tape to the length of the crack using scissors. Set it aside for later use.

• Next, in a tray, mix the filling compound according to the instructions on the packaging. Then, add a small amount of the mixed compound to your filler knife and spread it over the crack. Make sure to apply a thin layer that covers both the gap itself and the sides of the crack.

• Take the piece of plasterboard tape and position it over the crack, ensuring it covers the entire length. Smooth out any bumps with your filler knife, being careful not to rip the tape.
• Then, spread another layer of filling compound over the crack with your knife, before allowing it to dry completely.
• Once the compound is dry, sand the area until it's flat and even with the surface.
• Finally, you may want to paint over the area to match the rest of the surface, so if you’re wanting to add a new lick, check out our home painting tricks and hacks to guide you through the process and help you avoid the most common painting fails.