How to Fill Cracks and Holes in Walls

Why Cracks and Holes Appear

Walls develop imperfections for many reasons. Understanding the cause helps you choose the right repair method.

• Settlement cracks appear as buildings naturally shift over time, especially common in older South London properties
• Nail and screw holes from picture hooks, shelves and fittings
• Impact damage from furniture, door handles or everyday knocks
• Plaster shrinkage as lime plaster in period homes dries out seasonally
• Structural movement which may need investigation before filling

Choosing the Right Filler

Ready-Mixed Filler

Best for small holes and hairline cracks. It comes in a tub ready to use and is easy to apply with a filling knife. It dries fairly quickly and sands to a smooth finish.

Use for: Nail holes, small dents, hairline cracks up to 2mm wide.

Powder Filler

You mix this with water to the desired consistency. It is more economical for larger areas and gives you control over the thickness. It sets harder than ready-mixed filler.

Use for: Deeper holes, wider cracks, areas that need multiple coats.

Flexible Filler (Caulk)

A sealant-like filler applied from a tube or cartridge gun. It stays slightly flexible after drying, which makes it ideal for areas that move.

Use for: Cracks between walls and door frames, gaps along skirting boards, corners where walls meet ceilings.

Two-Part Filler

Mixes a filler compound with a hardener. It sets extremely hard and is virtually unshrinkable. More difficult to sand.

Use for: Deep holes, damaged corners, areas that need structural strength.

Step-by-Step Guide

For Small Holes and Cracks

1. Clean the area — remove any loose material, dust or flaking paint
2. Dampen the hole slightly with a wet finger or brush (this helps the filler bond)
3. Apply filler using a flexible filling knife, pressing firmly into the hole
4. Overfill slightly as most fillers shrink a little as they dry
5. Smooth the surface with the knife, feathering the edges
6. Let it dry completely (check the product instructions for drying time)
7. Sand smooth with 120-grit sandpaper, then finish with 180-grit
8. Wipe dust away with a damp cloth before painting

For Larger Holes

Holes bigger than about 5cm may need a different approach:

1. Cut back any loose plaster to a firm edge
2. Apply filler in layers no more than 5mm deep, letting each layer dry before adding the next
3. For very large holes, consider using a plaster repair patch (a self-adhesive mesh) over the hole before filling
4. Sand and finish as above

When a Crack Needs Investigation

Not all cracks are cosmetic. Seek professional advice if you notice:

• Cracks wider than 5mm
• Cracks that keep reopening after filling
• Diagonal cracks running from window or door corners
• Cracks visible on both sides of a wall
• Cracks accompanied by bulging or bowing plaster

These may indicate structural movement that needs proper assessment before cosmetic repair.

Professional Wall Repairs in South London

For extensive crack repair, replastering or making walls ready for decorating, our handyman team has the experience to get walls smooth and paint-ready. Combined with our painting and decorating service, we can take a damaged wall from cracked to freshly painted. We work across Battersea, Streatham, Wimbledon, Tooting and all of South London.