QUESTION

I am a tile contractor in Georgia with four employees. I need to drill a hole in a 3”x9” frosted glass with backing. The glass is cracking well after I have drilled the hole.

The very experienced glass guy said he will not install his glass over glass tile because it cracks. He said he’s done experiments where he has drilled holes, left the tile overnight, and come back to a cracked tile. If I succeed in drilling a hole without cracking, am I setting the homeowner up for a crack later?

Would you advise bisecting the tile and carving out the hole to release that tension? What’s the best play here?

ANSWER

Thank you for reaching out with this question. It’s a good one, and a fairly common concern when working with glass tile.

What you’re describing is consistent with what many installers and glass fabricators have experienced. Glass is inherently brittle and sensitive to stress, heat, and vibration. When a hole is drilled, even if it looks successful initially, internal stresses within the tile can cause delayed cracking hours or even days later. Factors such as tile composition, backing type, edge contact, and the thermal expansion characteristics of the substrate and setting material can all contribute to this delayed failure.

A key thing to understand is that glass is a poor conductor of heat. As you’re drilling, the area under the bit heats up while the surrounding glass stays cool, which creates thermal stress that can lead to cracking. To help manage this, use plenty of water to keep the drill area cool throughout the process.

When drilling glass, technique and tooling both matter:

• Avoid “rocking” the drill in a circular motion as is sometimes done with ceramic or porcelain—this can cause microchips around the edges of the hole.


• Start the hole by holding the drill at a slight angle, then slowly bring it up to 90° once the bit has a grip. Keep a steady, consistent speed and pressure.


• Not all diamond hole saws are created equal. A less-aggressive diamond pattern will help you drill more smoothly and reduce chipping.


• Once the hole is complete, polish the edges on both sides of the glass. Drilling or cutting glass leaves behind microchips—tiny fractures at the edge that can spread over time. Think of a small rock chip in a windshield: it may stay stable for months, then suddenly turn into a large crack with vibration or temperature change. Polishing removes these microchips and significantly lowers the chance of delayed cracking

Even with careful technique, drilling through installed glass tile eliminates the possibility of polishing the edges. If at all possible, holes for hardware or penetrations should be pre-drilled before installation by the tile or glass fabricator. If modification is unavoidable, your idea of bisecting the tile and carving around the penetration to relieve tension is a smart approach—but may not be acceptable to the homeowner.

It’s also worth noting that even with every precaution, glass under stress from hardware such as shower door hinges can still fail. I’ve personally followed every step listed here and still had to replace cracked tiles under hinge points. For that reason, I would encourage pre-drilling and planning hole locations during the installation process whenever possible.