drilling into bejmat / zellige tiles

[Adsibob]

We have a feature wall made of bejmat tiles (which are unglazed zellige tiles, which are hand made clay tiles). Although they are fired in an oven, they do chip relatively easily. Having said that, our tiler did a fantastic job of putting up some 30m2 and they look great. I now want to put up some paintings and need to drill into the wall to install screws etc. If I damage the tile it probably won't matter as the painting will cover that bit of the wall anyway, but I still want to try to avoid damage as the wall is sound proofed, so I rather make my penetrations as small as possible. The tiles are about 14mm to 17mm thick (they are all irregular) and the grout lines are about 2mm thick. I'm thinking that the best option would be to drill into the grout where four corners meet. What drill bit size and raw plug should I be using and what depth hole and screw should I be using? Behind the tile there is plasterboard (this is not a bathroom or kitchen, just a feature wall in a lounge) and then 10mm of a honeycomb board filled with sand (for soundproofing) and then a void filled with mineral wool sound proofing. The paintings we want to hang are about A1 in size and probably weigh around 5kg. I'm hoping one sturdy screw will be enough per painting.

[markc]

I would use a spear point drill bit, drill only, no hammer.  Drill 7mm, brown plug and a 4 or 4.5mm screw will hold your painting easily

[jack]

1 minute ago, markc said:

I would use a spear point drill bit, drill only, no hammer.  Drill 7mm, brown plug and a 4 or 4.5mm screw will hold your painting easily

 

+1

 

I've had to drill through soft-ish brick slips, which probably have similar challenges to the tiles you'll be drilling. Ordinary masonry bits are far too blunt to make any sort of dent without a decent hammer action drill, but the hammer action risks cracking the tiles.

 

Spear point bit and patience are your friends. 

[Adsibob]

2 hours ago, markc said:

I would use a spear point drill bit, drill only, no hammer.  Drill 7mm, brown plug and a 4 or 4.5mm screw will hold your painting easily

Thanks. Do you mean the drill bit should have 7mm diameter, or the depth of the hole should be 7mm deep? If the latter, that seems very shallow. If the former, that seems very wide.

[markc]

11 minutes ago, Adsibob said:

Thanks. Do you mean the drill bit should have 7mm diameter, or the depth of the hole should be 7mm deep? If the latter, that seems very shallow. If the former, that seems very wide.

7mm dia. Drill for brown plugs. Drill depth to suit plug length. If you feel this is too deep then drop down to a 6mm drill on red plugs (or the white ones that come with many light fittings, curtain rails etc). Screws would then be 3.5 or 4mm diameter

[Adsibob]

Thanks for the tips so far. What would be the difference in outcome/experience/skill required between a spear point drill it and something like this:

https://www.screwfix.com/p/erbauer-diamond-tile-drill-bit-6-x-67mm/51908
 

 

[Adsibob]

So finally got around to trying this out with a spearhead drill bit made by “Universal Fit” bought from screwfix. I took it fairly slow but clearly not slow enough as I managed to break the spearhead off at first attempt:

 

I had my DeWalt drill on the greater torque setting of 2 (out of only two options, 1 or 2) and the other setting on 7. Created a lot of heat and only managed a 6mm depth hole before it broke!

[markc]

Looks like it overheated and melted the brazed joint. Spear point drills need to be kept cool either with water or compressed air (water is far better) and run slowly.

 

[dpmiller]

1 or 2 is speed...

[Adsibob]

25 minutes ago, dpmiller said:

1 or 2 is speed...

I thought it was torque? 

[Adsibob]

3 hours ago, markc said:

Looks like it overheated and melted the brazed joint. Spear point drills need to be kept cool either with water or compressed air (water is far better) and run slowly.

 

Yes, managed to keep the others from melting by drilling partly underwater (was drilling holes into ceramic pots). Not sure how I’ll keep it wet enough when I come to drill the tiles. They are also three times as thick as the ceramic pots!!!

[markc]

1 minute ago, Adsibob said:

Yes, managed to keep the others from melting by drilling partly underwater (was drilling holes into ceramic pots). Not sure how I’ll keep it wet enough when I come to drill the tiles. They are also three times as thick as the ceramic pots!!!

Sounds like you need to go for diamond core (or solid for small diameters) bits. Use a piece of ply or timber with a hole to start the diamond bit (they don’t have points or centres) and once started you can keep dipping the bit in water every 10-15 seconds to keep it cool, once you break the hard surface it’s much easier and faster cutting