The question many homeowners ask when they spot a crack is simple: can I fix this myself? Sometimes the answer is yes. Sometimes it’s definitely not. And sometimes it’s a bit more complicated. This guide will help you work out which category your crack falls into.
The DIY Repair Checklist
Before you decide to tackle a crack yourself, run through this checklist honestly.
You can probably DIY if:
- The crack is superficial (only in plaster, not in brickwork)
- It’s hairline to 3mm wide
- It’s vertical or random in direction
- It’s stable and not growing
- There’s no damp or moisture involved
- It’s just one isolated crack
- You have basic home maintenance experience
- The wall is easily accessible
You should call a professional if:
- The crack is in brickwork or concrete (not just plaster)
- It’s wider than 5mm
- It’s horizontal or diagonal
- It’s growing or changing
- There’s damp or moisture nearby
- Multiple cracks are appearing
- There’s visible displacement
- Doors or windows are sticking
- You’re not confident or you’re unsure
Crack Type and DIY Suitability
| Crack Type | DIY Suitable? | Why | What to Do |
|---|---|---|---|
| Hairline in plaster | Yes | Purely cosmetic, easy fix | Fill and redecorate |
| Small vertical crack (under 3mm) | Yes | Usually minor settling, straightforward to repair | Fill, sand, paint |
| Vertical crack (3-5mm) | Maybe | Depends if stable and isolated | Monitor first, then fill if stable |
| Horizontal crack | No | Usually indicates movement | Get professional assessment |
| Diagonal/stair-step crack | No | Indicates structural stress | Get professional assessment |
| Crack with damp | No | Needs diagnosis and treatment | Professional assessment essential |
| Growing crack | No | Requires investigation first | Professional assessment needed |
| Crack with displacement | No | Structural issue | Professional assessment needed |
| Multiple cracks | No | Indicates wider problem | Professional assessment needed |
Simple DIY Repairs for Superficial Cracks
If you’ve decided your crack is a candidate for DIY repair, here’s what’s involved.
What You’ll Need
- Crack filler or flexible sealant
- Putty knife or filling knife
- Sandpaper (120 and 240 grit)
- Paintbrush or small roller
- Paint or plaster finish to match existing wall
- Drop sheet or old newspaper
- Safety glasses (optional but sensible)
Basic Steps
Step 1: Clean the crack
Use a putty knife to remove any loose plaster, dust, or debris from the crack. Run it along the crack to clear out anything that will prevent the filler from bonding properly.
Step 2: Apply the filler
Using your putty knife, press the filler firmly into the crack. Work along the entire length, making sure the filler goes deep into the crack rather than just sitting on the surface. You might need more than one application for deeper cracks.
Step 3: Smooth it off
While the filler is still slightly damp, use your putty knife to smooth the surface level with the surrounding wall. This reduces the amount of sanding needed later.
Step 4: Let it dry
Follow the manufacturer’s instructions for drying time. This usually ranges from a few hours to overnight depending on the filler type.
Step 5: Sand it smooth
Once dry, sand the area smooth using 120 grit sandpaper first, then 240 grit for a finer finish. Sand until the repaired area blends with the surrounding wall.
Step 6: Paint or finish
Apply paint or plaster finish to match the surrounding wall. You might need two coats for a seamless result.
Common DIY Mistakes to Avoid
- Not cleaning the crack properly: If you don’t remove dust and loose material, the filler won’t bond well and the repair will fail quickly.
- Using the wrong product: For narrow cracks, use a flexible sealant. For slightly wider cracks, use caulk or flexible filler. For plaster, use plaster filler. Using the wrong product leads to poor results.
- Not filling it deeply enough: Many people fill only the surface. The filler needs to go as deep as the crack for a lasting repair.
- Overfilling then painting over without proper finish: If your filler is slightly raised or uneven, paint won’t hide it well. Take time to sand properly before painting.
- Repairing a growing crack: If a crack is still growing, any DIY repair is temporary. You’ll be filling the same crack repeatedly until you address the underlying cause.
Why Professional Repair Is Different
When a professional repairs a crack, they’re not just filling it. They’re addressing what caused it. That’s the crucial difference.
What professionals do:
- Diagnose the underlying cause
- Determine if the crack is cosmetic or structural
- Assess whether it’s stable or ongoing
- Decide if treatment is needed beyond simple filling
- Use appropriate techniques and materials for the specific situation
- Provide guarantees on their work
- Address any related issues (like damp)
When DIY isn’t enough:
- The crack returns quickly despite being filled
- The crack is in structural materials (brickwork, concrete)
- There are multiple cracks or patterns that suggest movement
- The crack is growing
- There’s moisture or damp involved
Attempting a DIY repair on these types of cracks is false economy. You’ll spend money on filler and materials only to have the problem return or worsen.
Cost Comparison: DIY versus Professional
| Scenario | DIY Cost | Professional Cost | Worth DIY? |
|---|---|---|---|
| Single hairline crack in plaster | £5-15 | £100-200+ | Yes |
| Single small vertical crack (under 3mm) | £10-25 | £150-300 | Yes, if stable |
| Multiple or larger cracks | £20-50 | £200-500 | Usually no |
| Crack with structural concerns | £10-30 (wasted) | £150-400+ | Definitely no |
| Crack with damp issues | £15-40 (wasted) | £300-800+ (including damp treatment) | Definitely no |
The pattern is clear: for simple, superficial, isolated cracks in plaster, DIY can save money. For anything more complex, professional help almost always makes financial sense.
Warning Signs That Professional Help Is Needed
Stop and call a professional immediately if you notice:
During your inspection:
- The crack goes through multiple layers (plaster and brickwork)
- Brickwork is visibly damaged or crumbling
- You find damp or moisture
- There are multiple cracks forming a pattern
- You spot displacement or offset
During attempted repairs:
- The filler keeps cracking or falling out
- The crack reopens within weeks of filling
- You’re not confident with the work
- You realise the crack is deeper or more extensive than you thought
- The repair looks worse than leaving it alone
After repairs:
- The crack reappears in the same place
- New cracks form nearby after you’ve repaired the first one
- Signs of movement continue despite your repair
Insurance and Guarantees
One important consideration: if you attempt DIY repairs and something goes wrong, your home insurance might not cover damage. Professional repairs typically come with guarantees and won’t void your insurance coverage.
Additionally, if you’re planning to sell your home, a surveyor will spot DIY repairs that haven’t addressed underlying issues. This can cause problems during the conveyancing process.
The Decision Tree
Use this simple decision tree to help make your choice:
- Is the crack only in plaster (not in brickwork)? No = Call a professional
- Is it under 3mm wide? No = Call a professional
- Is it vertical or random? No = Call a professional
- Is it stable (hasn’t changed in several months)? No = Call a professional
- Is there damp nearby? No = You might DIY. Yes = Call a professional
- Is it the only crack? No = Call a professional
- Are you confident with basic home maintenance? No = Call a professional
If you’ve answered “yes” to all questions, a DIY repair is reasonable.