Make trip and fall hazards safe first
Loose slabs, rotten decking and slippery surfaces can cause serious injury. Stop using elevated or structurally soft decking until it has been assessed.
MOST LIKELY CAUSES
Start with movement, support and drainage
Weak or unsuitable mix
The joint material lacks strength or compatibility.
Shallow joint depth
There is not enough material to resist weathering.
Slab movement
Loose paving repeatedly cracks the joints.
Frost and water damage
Saturated joints break down in cold weather.
Symptom variations Match the movement, cracking or surface condition. ⌄
- Joint material turns to powder
- Cracks reopen quickly
- Weeds grow in gaps
- Ants remove sand
- Loose pieces collect after rain
Quick checks Safe checks before lifting slabs or boards. ⌄
- Check whether slabs move.
- Measure joint depth.
- Inspect drainage and ponding.
- Remove a small section to assess the material.
- Check how widespread the failure is.
Important:
Fix the support, drainage or structural cause before replacing surface materials.
Step 1 — Remove failed pointing fully Make the smallest safe correction and retest. ⌄
Clear loose material to a sound depth.
Step 2 — Repair movement first Make the smallest safe correction and retest. ⌄
Reset any loose slabs before repointing.
Step 3 — Repoint in suitable conditions Make the smallest safe correction and retest. ⌄
Use the correct product and follow curing requirements.
Why the problem happens How support, water and movement affect paving and decking. ⌄
Pointing cannot survive if the slabs beneath it move or if the joint is too shallow.
Advanced checks Further diagnosis for persistent outdoor surface faults. ⌄
- Identify paving type.
- Check joint width.
- Assess rigid versus flexible jointing.
- Review bedding method.
- Inspect edge restraints.
Tools and information needed Useful items for accurate checks. ⌄
- Joint rake
- Stiff brush
- Trowel
- Mixing bucket
- Knee protection
Parts or materials that may help Common paving and decking materials linked to this fault. ⌄
- Jointing compound
- Mortar materials
- Primer where specified
- Replacement bedding
- Edge restraint
When to call a professional Conditions that should end basic DIY diagnosis. ⌄
- Most of the patio is loose.
- Historic stone needs specialist materials.
- Drainage is poor.
- Large areas need raking out.
- Previous repairs keep failing.
Frequently asked questions Common paving and decking questions. ⌄
Can I point over the old material?
No. Loose and failed material should be removed first.
Why does it crack again?
The slabs may still be moving.
Can I use ordinary sand and cement?
Only where compatible with the paving and construction.