On 2008-07-15 08:24:45 +0100, Rod said:

Steven Campbell wrote:
I put up one of those floating shelves which took 5 screws. It went on to a
brick / plaster external wall.
The rawlplugs said to use 7mm for the hole but I used a 6mm drill knowing
the drill would probably wander slightly.
3 of the Rawlplugs don't seem to be catching at all and the screws just turn
when they should be getting tight.
I tried upping the screws to size 12 but its just the same. I'm
beginning to think I never went into the brick but into the gaps
between the bricks!

I'm not sure if I could get the rawlplugs out without digging into the
wall which I'm reluctant to do as its just been all decorated. Also I
can't move the shelf as its the only wall / height it can be it.

Any ideas on best way to get the screws to take?

Cheers

If you have some polyurethane glue I would think of this (which I have
done quite a few times):

Spray the hole with a bit of water.

Coat the plug with some polyurethane glue.

Push plug in and leave for at least half an hour.

Once set, fix shelf. Full strength might take up to a few hours.

It hasn't happened to me, but you should keep an eye open in case the
glue foams too much and starts to drizzle down the wall.

(This is based on another Fischer system - Fix & Fill IIRC.)

For your specific variant of the problem, you might be able to inject
the polyurethane into the hole, i.e. into the centre of the plug. As it
expands it will probably ooze out and hold the plug fast. But even if
it doesn't, as you put a screw in it will be pushed outwards and help
to fill the hole.

One point here is not to use this as a replacement for what should be a
sound mechanical fixture. Polyurethane is not a good gap filler at all
and not mechanically strong when used in this way. OK, if the plug is
pretty much sound first.

I've used the polyester resin that is used with studs for resin fixings
in this application. Clean hole (important), squirt a little into
hole and push in plug. Leave for a couple of hours and rock solid.

The Ubiquitous and Wonderful Car Body Filler (UWCBF) can be used for
this as well.