Well sometimes the internet isn’t completely full of crap. Found a fifty pound bag of silica sand, threw a couple of cupfuls in the hole in the wall, turned water down to a trickle, ran the bit in, did that two or three times then it finally started cutting. Found anytime it seemed like feed speed was dropping off, bring it back out and some sand in the hole, some more in the bit itself. With the trickle of water when the sand did start to come out it would pack a little around the core bit and act as a dam to keep more slurry in the hole. Went 5 inches or better repacking the hole with sand about every inch, finally got thru the rock then speed picked up drastically once it was cutting part rock, part mortar. Probably had a rock in the wall 10-12 inches in diameter and of course that’s where I decided to drill.