Thanks. You were right about the coach screws and it wasn't the problem I thought it would be. In fact, they were just right. The washers were a bad idea and I abandoned them. I'd bought a chain to hang the mirror from. I thought it would let me adjust things a bit to get it dead centre and be easier to hang. But I hadn't thought it through. The D-Rings started to twist towards the centre (of course) and it didn't look healthy. I'd drilled a small exploratory hole but that doesn't matter too much so I just measured exactly where the D-rings were and put the bolts there and hooked them over it (no washers!). I'm pretty pleased I got it right. The spirit level has the bubble juuuuust off-centre, so not bad for a first attempt.
Wasn't perfect though. The first hole went in fine but the second one hit a LOT of resistance and I actually got out what looked to be actual stone chippings (not dust). I don't know how that's possible but the resistance did lead to me making the hole a little wider than I planned and there's a very small amount of play in the second bolt. But it seems okay. I'll stop dreading a sudden crash in a couple of months.
It's not an SDS drill. I nearly bought one of those but there seemed to be a big leap in price with the drill bits and I didn't know much about it at the time. I regret that now, but it's a pretty big Fat Stanley drill all the same and seems pretty good? I did what you suggested though and started with a 2mm hole for checking, then I did a 7mm and then finally the 10mm. Too late for the vacuum. I have to go over it all with that, now!
Thanks a lot for all the replies (both). I've learned a lot from this and think I'll be doing a lot more DIY in future! Not least because Screwfix would only sell me the plugs in a pack of 50 so I've got a lot to use up!
Wasn't perfect though. The first hole went in fine but the second one hit a LOT of resistance and I actually got out what looked to be actual stone chippings (not dust). I don't know how that's possible but the resistance did lead to me making the hole a little wider than I planned and there's a very small amount of play in the second bolt. But it seems okay. I'll stop dreading a sudden crash in a couple of months.
It's not an SDS drill. I nearly bought one of those but there seemed to be a big leap in price with the drill bits and I didn't know much about it at the time. I regret that now, but it's a pretty big Fat Stanley drill all the same and seems pretty good? I did what you suggested though and started with a 2mm hole for checking, then I did a 7mm and then finally the 10mm. Too late for the vacuum. I have to go over it all with that, now!
Thanks a lot for all the replies (both). I've learned a lot from this and think I'll be doing a lot more DIY in future! Not least because Screwfix would only sell me the plugs in a pack of 50 so I've got a lot to use up!