I had to put up a drilled mirror last night. It's metric of course, but the holes are exactly 1.5" in from each edge, which made measuring the holes from the centre line difficult.
So I did the first hole (top right hole and put the mirror in place. Then holding it and checking it was vertical, I marked through the other holes. Removed mirror and drilled other holes. I used a 3mm pilot drill to try to start the hole in the right place and then 6mm masonry.
Put the plugs in but a couple of the holes are half the hole diameter out. :( . Of course, with a drilled mirror, and the washers used, there's absolutely no margin for error - how on earth are you supposed to drill holes in masonary with complete accuracy?
If you use plastic plugs there is enough flexibility to have margin for error. Or glue the mirror and then epoxy the covering caps on to pretend you screwed it.
Anyway - one option may be to overdrill the incorrect holes to about 10mm, plug with dowell so it's tight with a drop of glue, then put mirro screws into that.
This is a mirror - which implies the use of mirror screws with dome caps, which then look dreadful if they're inserted at even a slight angle. Although the flexibility of plastic plugs might be sufficient to let you insert a screw off-angle and hold the mirror up, it's not a good way to do it for neatness
What I'd do is first of all to drill the holes accurately: mark them from the mirror, not by measuring. Then drill them with an SDS drill and copious surplus power rather than struggling with a weak hammer drill that will follow mortar courses. Use a very low power to start the hole though, so that it doesn't wander initially.
With a hole that's off centre, then first check that the hole is big enough to allow the screw to go into it, and perpendicular, without needing to put it in off-angle. If the hole isn't, then drill it bigger (up to about 1/2" - anything more and you're better re-drilling another, maybe smaller). Don't be tempted to polyfilla it up and try again, that's too soft and it wil lead the drill back into the old hole. If you _must_ do this, at least use a fairly hard mortar mix.
Now your problem is an oversized, but well placed, hole. Use a plug in hee, but make it either carved wood, or else use a resin or putty plugging compound. The old asbestos fibre Rawlplug compound was one solution, nowadays Fisher sell (Screwfix) some papery disks that you wet before use and then poke down the hole. Bit pricey for regular use, but they're great for getting you out of a jam. If it's high load, then of course there's polyester resin kits.
After marking through the holes (small circle) and removing the mirror, draw a large (1" or so) cross over the spot. Then if the drill wanders during those crucial first few revolutions, you can spot it and drag it back on line.
While doing it I did think something like that would be ideal! Drill holes about an inch in diameter and fill them with a sausage of some plasticky type of stuff that you could just screw into.
I also learned that brick dust is a bu**er to get off grout, even if the grout has been in place for a week. I thought it would just vacuum up, but it didn't. Mrs R was still cleaning it at 11PM - that's teach her for making me do stuff during the week. :)
You can improve success rate by centre punching as if drilling metal, but it will take longer. Remove a circle of plaster (about 1" diameter - just enough to see clearly) and mark the hole position on the brick face. Centre punch the mark using either a proper centre punch or a 6" nail. Now using your smallest bit (1/8") drill the hole directly into the brick / block. Open up the hole to take a plug and fix the mirror to this hole. Use the same technique (centre punch / drill) to mark each hole in turn directly into brick. When all holes are correctly drilled put a plug and screw into each hole (without mirror) and make good the plaster with Polyfilla.
If this still doesn't work, drill oversize holes and insert solid wooden plugs to take the screws.
Does anyone else have the problem that Sod's law says that wherever you place the mirror one screw will be on a brick / mortar interface and is therefore guaranteed to be out of alignment?
Guaranteed to happen with everything that needs a secure fixing - especially rads. Luckily with those you can use a rawlbolt which will grip between the two courses. But overkill for a mirror. ;-) What's needed is a mortar finder that works through plaster - like a stud finder. Only more accurate. ;-)
Start with a very small drill, not the size required. Use low power until the drill is at least 1/2 inch into the brick (not the plaster).
Small drills break easily, take extra care.
If the holes line up, fine, drill out with the right size. If not do not be tempted to fill with polyfiller and redrill. Poly filler is so soft the drill will wander to it. The best thing is to drill oversize, so that the required hole will be in the oversize, then fill with polyfiller and redrill.
I've found sometimes it's useful to make a quick template out of thick metal with holes in the right place and of the right width for a drill bit, and then drill small pilot holes - then take the template off and enlarge to the right size using a different bit.
(At some point maybe I'll get my act together and make some sort of pivoting adjustable template so I can set holes at different spacings.)
Wherever I can I use permanent brackets for things, though - it's a lot easier to drill the wall, make a bracket to fit the holes, then add the attachment points so that the thing being attached sits square (the only problem with that route being that it's hard to make things sit completely flush with the wall, but that's not always an issue)
If I'm doing light masonry drilling then I use my left hand to hold a little piece of folded card underneath the drill bit to catch all the dust. For heavier drilling where I need both hands, the spouse holds the vacuum cleaner pipe just underneath the drilling. Both techniques work well. You can get fancy attachments for drills to suck the dust, but they are expensive. As you say, sometimes the brick dust can be a pain to clean off some surfaces.
Similar problems with my house walls which are made of stone. The inner walls are more accurately described as rubble with a "mortar" consisting of clay. Some of the rocks are sandstone and others are granite. Pot luck when drilling what you hit. Generally, when fixing up wooden battens to the walls I attempt to drill twice as many holes as I need as half will fail due to hitting "nothing" ie big soft lump of crumbly clay, or solid granite.
I've found that using my DeWalt SDS drill that you can be very accurate with drilling, largely because of the varispeed function, eg dill starts off very slowly and gradually increasing the speed. That is when the hammer action automatically cuts in. Only one thing that still bugs me is that you can't see through the plaster and you can still hit the edge of a brick and it goes off line into the mortar. I suppose the only way then is to move the object and drill somewhere near-by and Pollyfill the original hole/s.. Wavey Dave
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