Hole size for masonry screws into Victorian brickwork?

[PaulUszak]

I'm looking to install a key safe onto the side of a house built circa 1900. The manufacturer suggests a 5 mm hole for a 6 mm masonry screw. That seems a general guide, and I know that these types of fixings are sensitive to hole sizes.

The house is made of bricks so hard that they ring when you whack them with a hammer. They might be engineering bricks. I'm concerned that the key safe provider is thinking of modern houses made of modern (effectively mud) bricks. What would the appropriate hole size be so I don't mess up?

 

[Burnerman]

Why not use 6mm plastic plugs? If the wall is soft, go for a 5mm hole first before increasing to 6mm.
John

 

[foxhole]

The construction has little bearing on the hole size.

You said
That seems a general guide, and I know that these types of fixings are sensitive to hole sizes.
Care to explain?

 

[catlad]

Start off small and widen if necessary with 0.5 mm increments, I would also splay the screws slightly.

 

[PaulUszak]

Why not use 6mm plastic plugs? If the wall is soft...
John

Firstly, "...house is made of bricks so hard that they ring when you whack them with a hammer..."

Secondly, there is no choice. You have to use the supplied masonry screws in order to maintain the Police accreditation and manufacturer's warranty.

 

[PaulUszak]

Start off small and widen if necessary with 0.5 mm increments, I would also splay the screws slightly.

I don't understand how this might work. How would I know when it's necessary to widen without having driven the screws in? If they go in, fine. But if they don't and there is a problem, then the substrate might be messed up or the screw sheared off. Then it might be necessary to widen the hole by several millimetres and use larger screws. I've never used masonry screws, but I'm under the impression they are a one shot type of fixing.

I'm also not sure how you widen a hole in 0.5 mm increments. Doesn't that just cause the drill bit to screw itself into the hole?

 

[PaulUszak]

The construction has little bearing on the hole size.

Well they're not like a fibre /plastic plug /expanding bolt that expands. That allows some latitude in the hole diameter and the fixing still works (albeit perhaps with varying effectiveness). With a non expanding threaded screw going into non yielding brick they can only be a little overlap for the screw to work effectively. I would have though that it would be extremely difficult to drive home a 5 mm masonry screw into a 6 mm hole in a solid steel plate. I think that the house is made of steel bricks. Therefore the construction must matter?

 

[Burnerman]

Why not use 6mm plastic plugs? If the wall is soft...
John

Firstly, "...house is made of bricks so hard that they ring when you whack them with a hammer..."

Secondly, there is no choice. You have to use the supplied masonry screws in order to maintain the Police accreditation and manufacturer's warranty.

Ok, I was unaware of any Police accreditation requirements.
Why not do a test drilling, 5mm, in the area which will be covered by the key safe? It doesn't matter how hard the bricks are, a quality SDS drill and bit will get through. Test that drilling with a spare screw.
John

 

[foxhole]

The construction has little bearing on the hole size.

Well they're not like a fibre /plastic plug /expanding bolt that expands. That allows some latitude in the hole diameter and the fixing still works (albeit perhaps with varying effectiveness). With a non expanding threaded screw going into non yielding brick they can only be a little overlap for the screw to work effectively. I would have though that it would be extremely difficult to drive home a 5 mm masonry screw into a 6 mm hole in a solid steel plate. I think that the house is made of steel bricks. Therefore the construction must matter?

No, its a simple job.
No chance of snapping a masonry screw, they should be hardened.