On 20/02/2018 09:19, John Rumm wrote:
On 19/02/2018 15:06, wrote:
On 19/02/2018 14:13, Adrian Caspersz wrote:
On 19/02/18 14:04, Vortex13 wrote:
Hello,

I am about to refurbish a 1960's flat.Â* Walls therefore are plaster
on masonry (brick) and I intend to install 8 "new" double sockets so
will need to recess that number of steel back boxes.Â* Not something I
have done for some years.....when I did I used an angle grinder and
it was horribly messy/dusty.

... snipped

FWIW I'm aware of the use of these things in conjunction with an SDS
drill- not tried myself.

https://www.screwfix.com/c/tools/ele...ers/cat6150002
IME the rectangular sinker works OK in soft block (but not in anything
hard) and the rotating thing works OK if the pilot hole is sound (but it
makes a lot of dust).

I'd be very interested in finding an easier way, but what I've been
doing is: draw the outline on the wall, drill a lot of holes to the

The technique that I found works quite well is:

Draw outline on wall around the backbox.

Set a 20mm wide chisel in the SDS, and mark the box depth on it with a
wrap of insulating tape.

Hold the drill perpendicular to the wall, and place the chisel just
outside the line, then sink it to the depth set by the tape. Continue
all round the periphery of the box until you have a channel to the right
depth round the edges.

Swap the chisel for a 40mm bit. Working at an angle about a quarter of
the way across the double socket width (or in the middle of a single),
chisel out and across toward your existing cut. Thus taking out the
edges of the infill. Repeat - moving in toward the centre, until you now
have a box hole that is full depth at the outside edges, and has a
"hump" in the middle.

Now work on the hump - using the die chisel to "plane" off the top of
it. Repeat until its flat enough across the width of the box. Test fit
the box as you go.

Once done, you can in many cases just drill screw holes for the fixing
screws. If there is too much "irregularity", then mix up so (preferably
old) bonding plaster, slap it in the back of the hole, and bed the box
into it.



I've recently bought a very wide SDS chisel so I'll give that a go next
time. We have lime plaster over solid (and I mean SOLID) concrete blocks
from the 1930s. It's a bit of a battle to get the hump flat without
going too deep in places so having a couple of holes drilled to depth
has been a useful guide. Despite this there's always somewhere sticking
up, and it can be hard to find.