Glass bonding – Troubleshooting

When Glass Bonding Goes Wrong…

The adhesive won’t stick; the glass bond is coming clean off the glass:

• Check surface preparation
• Joint design – If your glass bond is a butt joint, this can be problematic as this introduces peel or cleavage stress into the joint. Try to redesign the joint to minimize the peel stress.  You can also build up a fillet or meniscus of adhesive around the joint which can reduce the peel stress.
• Check with the glass manufacturer if there is some layer of something on the glass, process additive, or “self-cleaning” property of the glass which may be affecting the adhesion.

Bonded Joint has Crazy-Paving effect…
This crazed effect is caused by air getting into the joint before the adhesive is cured. The solution is to take the joint apart, clean up and start again. Make sure when the joint is assembled, it is firmly clamped during cure and not disturbed.

Glass Has Cracked…
This may be due to temperature changes and differential thermal expansion and contraction between substrates. Switch to a softer, more flexible adhesive (something with a lower Shore D value or Shore A, which is softer).

UV Adhesive isn’t Curing…
Colored or UV-blocking glass can be a problem as not enough UV light of the correct wavelength is getting through the glass to cure the adhesive. To bond UV blocked glass, switch to a visible light cure UV adhesive which will cure between 400 and 420nm wavelength instead.

Disassembling Joints and removing cured adhesive
Obviously, you have to be extremely careful not to break the glass. Heating the joint up to above the service temperature of the adhesive will soften the adhesive and make it a lot easier to disassemble. Other options include soaking the joint in methylene chloride (don’t do this if any plastic components are on your assembly).

For further help bonding glass, please contact Permabond.