Drilling hole from inside out without blowing the face of brick work

[Fallout]

Whats the best way of doing this? Take of hammer for the last 50mm or so?

 

[Madrab]

Presuming you can't drill from the outside, I start with a smaller diameter drill and create a guide. Then measuring the depth and mark the drill and when getting to the last 20mill or so back off on the pressure on the drill.

With some stone work it can't be avoided, sandstone can be bad, that and older render, it just blows out for fun. A smaller drill to start, I find, minimises that.

 

[Roddy Young]

If you are able to, drill a smaller diameter hole right through the wall from the inside. Then go outside and drill half way through with the larger drill. Finally drill with the larger drill from the inside. Hopefully they should line up OK.

 

[YorkshireMidge]

When it comes to long drills for going through walls, smaller pilot hole is relative. The smallest diameter I have in my selection of long drills is still 10mm and that does cause a bit of spalling if I'm forced to drill right through from the inside. I'm with @Madrab on his method for trying to minimise it as you can usually work out the wall thickness pretty accurately through an open window (I think ours is around 300mm incl the dry lining).

 

[cdbe]

If it was that critical I'd have a few goes till I felt a bed in the outer skin.

 

[opps]

I recently had to do just that, the difference being that the wall was rendered on the exterior. I put some tape on the drill bit to indicate the depth. The bricks were fairly hard. I just eased off on the force as I reached the end. I was impressed how little blowout there was. In part, I suspect that it may have been down to the fact that I was using a four flute drill bit.

eg https://www.tooled-up.com/dewalt-elite-xlr-sds-plus-4-cutter-head-drill-bit/prod/251584/