Concrete floor joint sealing: a practical guide

Types of joint

• Saw-cut or contraction joints that control where the slab cracks.
• Construction joints between separate pours.
• Isolation and expansion joints round columns, walls and between slabs.
• Deck joints in multi-storey car parks, often with traffic and water to deal with.

Choosing the filler

Internal floors with hard-wheeled forklift traffic usually need a semi-rigid filler, often epoxy or polyurea, that supports the joint edges. Joints that move more, and external slabs, need a flexible sealant such as polyurethane. Forecourts and bunds may need a fuel or chemical resistant product. The slab designer or the floor contractor's specification should say which.

Signs a floor needs work

• Joint edges breaking up (arris damage).
• Empty or debonded joints collecting dirt.
• Water standing in or getting through deck joints.
• Vehicles or trucks jolting over joints.

Planning the job

Floor joint work often has to fit round a working site: nights, weekends, or a section at a time. Give metres of joint, joint width, the floor's use and when the area can be closed when you post. Read about concrete and floor joint sealing or post a floor joint job.

Quick answers

When should new slab joints be filled?

Semi-rigid fillers are normally installed once the slab has done most of its early shrinkage. Follow the floor designer's or manufacturer's guidance.

Can damaged joint edges be repaired?

Yes. Broken arrises are usually cut back and rebuilt with a repair mortar or resin before the joint is refilled.