Drilling through 600mm stone walls - sealing the holes?

[Mark and Jen]

I have a number of places in my stone walls where I need to drill from inside to outside in order to run cables for Internet, Starlink, etc.

I’m up to speed on the importance of using lime mortar (as I have a lot of pointing and rendering to do in the attached barn) but when it comes to filling around these holes that I will make for these cables…. Can I just use a regular silicon sealant the way I would in a modern house. Will that tiny bit of sealant really matter? To give you an idea-I am drilling a 22mm hole in order to feed and 18mm cable. (actually, the cable isn’t that size-but the fitting on the end is) so I’m only going to be left with a few millimetre gap around the cable where it exits the wall either side. Quick squirt of any exterior sealant, surely?

 

[Lacan07]

I have a number of places in my stone walls where I need to drill from inside to outside in order to run cables for Internet, Starlink, etc.

I’m up to speed on the importance of using lime mortar (as I have a lot of pointing and rendering to do in the attached barn) but when it comes to filling around these holes that I will make for these cables…. Can I just use a regular silicon sealant the way I would in a modern house. Will that tiny bit of sealant really matter? To give you an idea-I am drilling a 22mm hole in order to feed and 18mm cable. (actually, the cable isn’t that size-but the fitting on the end is) so I’m only going to be left with a few millimetre gap around the cable where it exits the wall either side. Quick squirt of any exterior sealant, surely?

I don't see a problem with that personally and I've done it myself a few times. I find filling tiny gaps with lime mortar impossible anyway. Others may have different opinions, there are alternative materials.

 

[aockenden]

There are alternative options, but no, sealing a couple small holes with non breathable modern sealants / caulking isn’t going to cause any massive issues and won’t stop the entire house from breathing/

 

[Cubist]

Dumb question if I may - Do you know/understand the structure and nature of the materials used in these 600mm walls?

Typical construction of such thick walls consists of inner and outer skins of large stones and/or brick with a core of any old infill rubbish that may consist of small stone rubble, earth - in fact anything that came to the builders hand.

Drilling long small diameter. anything less that 100mm, holes through such walls can be extremely problematic due to the collapse of the infill material when the drill is withdrawn. There is though a technique that must be followed if you are not to run the risk of complete failure every time and ending up with lots of redundant holes

This requires that when the drill head breaks through to the other side of the wall the drill must not be withdrawn. Leaving the drill bit in situ, unlock the chuck and set aside the boring machine, use insulation tape to form a cap over the end of the cable or conduit you intend to use and then tape the capped end to the drill bit head. Use this to gently but firmly push the drill bit out of the hole - you will need someone on the other side of the wall to hold the drive end of the bit and gently resist the pressure from the other side so that theres no chance that the taped cap is pulled off as it transits through the hole and thus allowing debris to fall into the path of the cable/conduit - Do not be tempted to pull the cable/conduit through using the drill bit.

 

[Flyfisher]

I entirely concur with the risk of internal collapse - been there, done it with a section of our house that has a 'rubble wall' and in my case made worse by the wall containing a far bit of flint, which a typical hammer drill bit won't touch, it just vibrates it until the whole flint works itself loose and the result is a bit like the exit wound of a bullet - but I digress.

My solution is similar to Cubist but as well as leaving the drill bit in situ, I tend to use some 20mm conduit to push the drill bit through the wall, then cut off the conduit flush with both sides of the wall before pushing through the cable. In this case, if there's an 18mm connector to pass through as well then 20mm conduit might be a bit tight (but easy to verify), in which case try overflow pipe (21.5mm) or perhaps 22mm pipe - basically, anything suitable lying around in 'the stores'. You do have a 'stores' somewhere in the house, surely? No self-respecting PPUKer would throw away odd lengths of pipe (or anything actually!) after a DIY job

 

[Cubist]

Oops, I forgot to mention...

If the drill bit is of the 'bladed' type, as they often are for small diameter masonry drills, then you may need to rotate this counter-clockwise as the cable or conduit pushes it out. Careful though, this action needs to be carefully coordinated by the 'cable pusher' NOT the guy handling/turning the drill bit.