How to Fit Coving: Plaster and Polystyrene Installation

The Classic Ceiling Finish

Coving covers that awkward junction between wall and ceiling, hiding cracks and adding character to a room. Cutting internal and external mitres takes practice, but once you've got it, it's satisfying work.

Types of Coving

Plaster coving:

• Traditional, solid appearance
• Heavy - needs good adhesive
• Can be painted any colour
• Cuts with fine-toothed saw

Polystyrene coving:

• Lightweight, easy to handle
• Good for DIY
• Cheaper option
• Cuts easily with sharp knife

Polyurethane coving:

• Durable, lightweight
• Mid-price option
• Flexible enough to follow slight curves

Tools and Materials

• Mitre box sized for coving (or large mitre saw)
• Fine-toothed saw (or sharp knife for polystyrene)
• Coving adhesive
• Scraper and filling knife
• Sandpaper
• Pencil and tape measure
• Spirit level
• Clean cloths

Preparation

1. Clean walls and ceiling along fixing line
2. Remove loose paint or wallpaper
3. Seal dusty or porous surfaces with PVA solution
4. Mark guidelines for top and bottom of coving

Understanding Coving Mitres

This is where people get confused. Coving sits at 45° between wall and ceiling, so cutting it requires specific technique:

The key principle:

• Coving goes in the mitre box upside down and backwards
• The wall edge sits against the base of the mitre box
• The ceiling edge sits against the fence

Internal corners:

• For left piece: place coving with ceiling edge against fence, cut from left down to right
• For right piece: same position, cut from right down to left

External corners:

• Opposite cuts to internal
• Usually need to fine-tune with sandpaper

Step-by-Step Fitting

1. Plan your layout
   • Start from the most visible corner
   • Work around the room
   • Try to end in least visible spot
2. Cut internal corner pieces first
   • Test fit dry before adhesive
   • Adjust cuts as needed
3. Apply adhesive
   • Butter both back edges with coving adhesive
   • Don't skimp - it needs to grip
4. Press into place
   • Position carefully on guidelines
   • Press firmly along entire length
   • Support heavy pieces while adhesive grabs (pins help)
5. Clean off squeeze-out
   • Run finger along joints to smooth
   • Clean excess immediately with damp cloth

Joining Lengths

Where pieces meet on a straight run:

• Cut both ends at 45° to form a scarf joint
• Apply adhesive to both cut faces
• Butt together and fill any gap
• Scarf joints are less visible than butt joints

Problem Solving

Gaps at corners:

• Fill with coving adhesive or decorators caulk
• Smooth with wet finger
• Sand when dry

Coving pulling away:

• Support with pins until adhesive cures
• Check surface was clean and sealed
• May need to remove and refix properly

External corners don't meet:

• Walls are rarely perfectly square
• Test fit and adjust mitre angle
• Fill and sand remaining gaps

Finishing

1. Fill all joints and gaps
2. Sand smooth when dry
3. Apply second fill if needed
4. Prime bare surfaces
5. Paint to match ceiling (usually)

Tips from Experience

• Buy 10% extra for mistakes
• Cut a test piece to check your mitre setup
• Internal corners are easier than external
• Temperature matters - cold adhesive doesn't grip well
• Don't rush - let adhesive cure before painting

The Bottom Line

Coving fitting is about patience and understanding the mitre cuts. Once you crack the "upside down and backwards" concept, it becomes straightforward. Good adhesive, clean surfaces, and taking time to fill and finish properly make professional results achievable.

A fine-toothed saw from our hand tools range makes cleaner cuts in plaster coving.