Then you’ll need to consider whether to use a smaller gauge screw or drill a larger pilot hole if it’s in wood. In masonry you always have the option to re-drill the hole one size bigger (drilling through the existing wall plug) and use a bigger plug, red up to brown for example. General Tips Let me know what you’re fixing up and clarify the shank diameter of the screw and I’ll be much more specific, I promise! I definitely agree with you re the larger screws, I’ve got nothing over a 10g x 100mm in my box for sure. Bolts or frame fixings for me at and above that. I don’t have too much problem getting the bigger gauges in, as I use a pretty powerful drill driver, but yes, you can’t stop and they need lots of ‘feed’ or you’ll get into trouble. You’d struggle getting them in by hand I do agree. See what they have at the store screw/length wise, stainless steel is best of course. You could even consider structural timber screws, if you can get a wall plug big enough for them. They are long, have flanged heads and designed for outdoor use, just a thought (Have a look at what I mean at screwfix…). It depends more on the diameter or gauge of the screws shank really. You might find that a large plug like a 70mm one is designed for a really large diameter screw (5 or 6mm plus).

Any mirror that needs more than this should be hung on a pair of hooks in my opinion (gives better leveling too). Difficult without knowing the weight of the mirror, but I’d have through that an 80mm slotted, square hook would be fine with a regular brown 7mm plug, making sure that you push the plug into the masonry itself and through the plasterworks. How deep does a wall plug need to be? I talked about this a lot on another post, here’s the link: How to Properly Use Wall Plugs

Screw Gauge, Metric, Size, Clearance Holes, Pilot Holes & Wall Plugs

I think with it being ‘only’ 500mm high, I’d be tempted to get long outdoor screws, preferably with a hex head and then use regular wall plugs as deep as I could get into the masonry. Drill holes very slowly and carefully (SDS etc)and blow out the dust (seems worse on vertical holes as the bit doesn’t clear as well as horizontal holes). Don’t worry too much about hitting mortar, obviously if it’s three out of four holes maybe! As long as it’s only the odd one, it should still hold well. Any really bad holes you could resin fill maybe and push the screw into it (seen this done with outdoor ‘no-nails’ type stuff in a pinch, he left the screw a couple of turns proud and nipped it up after 24hrs… big dodgy but what can you do sometimes!).

Yes, the leverage could be considerable. Especially if someone falls or pulls on it etc. I’m assuming it’s outside so whatever you choose obviously needs to be suitable for prolonged outdoor use.Can I first ask what you are fastening to the wall? It’s just that plastic wall plugs of the size you’d need for a screw that size are not in common use. Sure you can buy ‘sets’ of big screws that come with a large plastic plug (sink/washbasin screws to name one) but usually if you’re hanging something heavy on a masonry wall you’d use a ‘rawlbolt’ style expanding bolt; either a hex head and washer or a nut and washer.