Top 10 Mistakes Installers Make When Using Glazing Packers (and How to Avoid Them)
Glazing packers may be simple, but using them incorrectly is one of the most common causes of installation failures in uPVC and aluminium windows. From dropped sashes to cracked glass, many problems installers face months later can be traced back to poor packing.
Below are the top 10 mistakes installers make when using glazing packers, based on real-world glazing best practices — and how to avoid them.
1. Not Toe-and-Heeling the Sash Properly
This is the most critical mistake.
When a window is not toe-and-heeled correctly:
- The sash drops over time
- The lock misaligns
- The window rubs on the sill
- The customer calls back within weeks
Fix:
Toe-and-heel at diagonal corners:
- Bottom hinge corner (under glass)
- Top lock corner (side of glass)
This creates a structural triangle that holds the sash in place.
2. Using the Wrong Thickness Packers
Incorrect thickness can cause:
- Frame distortion
- Bowed profiles
- Poor drainage
- Stress on sealed units
Fix:
Use the industry standard colour-coded packers (1mm–10mm) for consistent spacing.
3. Over-Packing the Glass
Over-packing is a serious yet common issue.
It causes:
- Glass compression
- Excess pressure on sealed units
- Difficulty fitting the beads
- Frames bowing outward
Fix:
Only use the packers required for support and alignment.
Never force packers into a tight space.
4. Under-Packing or Uneven Packing
Under-packing causes:
- Dropped units
- Rattling glass
- Movement inside the frame
- Failed locks or hinges
- Air leaks
Fix:
Ensure packers support the full edge of the glass where needed, not just a small corner.
5. Placing Packers in the Wrong Locations
Incorrect placement leads to:
- Blocked drainage channels
- Weight resting on the wrong point
- Sashes sitting unevenly
- Cracked glass due to pressure points
Fix:
Follow proper packing points:
- Setting blocks at the bottom corners
- Toe-and-heel packers diagonally
- Side packers only where needed
Never block drainage holes.
6. Using Improvised Materials (Cardboard, Wood, Metal)
Some installers still use:
- Bits of wood
- Old cardboard
- Scraps of metal
- Silicone blobs
These materials can absorb moisture, compress, or corrode — causing failures.
Fix:
Use only rigid plastic glazing packers designed for the industry.
7. Not Supporting the Glass on Both Bottom Corners
This mistake leads to:
- Uneven weight distribution
- Excess load on one side
- Seal failure
- Dropped glass
Fix:
Always place two bottom setting blocks:
- One under the hinge side
- One under the lock side
These support the entire weight of the glass unit.
8. Forgetting to Check Window Operation After Packing
Many installers snap in the bead and leave — but the sash may catch or be slightly misaligned.
Fix:
After packing:
- Open and close the window multiple times
- Check the lock engages smoothly
- Check equal gaps around the sash
- Look for any slight rub points
Adjust packers immediately if needed.
9. Blocking Drainage Channels With Packers
Incorrect placement can obstruct drainage.
This causes:
- Water retention
- Frame deterioration
- Leaks inside the property
- Mould growth
Fix:
Always ensure packers do not sit in drainage areas.
Check clear pathways after glazing.
10. Mixing Packer Types Incorrectly
Using wedge packers where flat packers are required (or vice versa) leads to:
- Uneven support
- Poor alignment
- Increased stress on the glass
- Difficulty fitting beads
Fix:
Use packers correctly:
- Flat packers: for support and stability
- Wedge packers: for small, precise adjustments
- Bridge packers: over screw heads or fixings
Choose the type based on function, not convenience.
Final Thoughts
Most window installation issues can be avoided simply by using the right packers in the right locations with the right thickness. Proper packing ensures:
- Smooth window operation
- Long-term structural support
- Correct drainage
- No cracking or seal failure
- Fewer call-backs and warranty claims
For installer-grade glazing packers, explore: