What mortar mix to fit backbox

[veedee]

After chiseling out my kitchen wall to fit a backbox, i have been left with crumbly breeze block.

So there is no way i can get a secure fixing here with plugs and screws

Therefore, I plan to sand and cement the backbox in place.

However, could i get confirmation on the ideal sand/cement mix for this please? e.g. 3 to 1, 4 to 1 etc

 

[crystal ball]

I used to use bonding in that situation, also slightly punch out the knockouts to give key

 

[veedee]

Thank you.

Unfortunately, i only have some sand and cement. No bonding.

In this instance what sand and cement mix is appropriate?

 

[JohnD]

my preference is to start with at least one screw.

in crumbly breeze, the hole may get quite wide, and loose for a plug. Clean out dust with a vac or water jet, and inject no-more-nails or cheaper adhesive into the screw hole, starting at the back so there is no air bubble. Press your plasplug into it to it is surrounded by adhesive, which is surrounded by wall, and allow to set.

When you drive the screw, the hardened adhesive cannot expand, because the wall holds it, so the plug and screw are firmly held.

butter the back of the box with soft sand and cement mortar so the box has something that will squash flat to back onto. Poke more soft mortar under the bottom of the box, round the sides, and over the top so it falls into any remaining gap. Smooth off so it is slightly below your intended finished plaster level. It will hold the plug firm and is much stronger than plaster. Ensure it is fully hard before screwing on your sockets and switches as the faceplate screws will try to pull the box out.

 

[footprints]

You only need a weak mix to hold a back box remember that many are fixed with bonding or plaster.
Even 1 to 6 will hold it in, remember one day some poor sod may want to get it out!

 

[securespark]

Ensure it is fully hard before screwing

Oooh, Matron!!

Being serious for a moment, I use bonding too and never had any issues. Holds firm and easier to get the box out in the future if required.

 

[dontbelieveawordofit]

personally.....to answer the op, id stick the back of the box overnight with a blob of gripfill .
then 4-1 sand and cement the following day.
prefered is bonding coat though as stated.

 

[Taylortwocities]

prefered is bonding coat though as stated.

Yes. I like to use bonding with a bit of cement thrown in. It then sets rock hard in an hour. When its gone off you can drill a couple of extra fixings through theback.

 

[veedee]

What is the forums take on this sparkys method?

Skip to 3m 35s

1. He wets substrate area.
2. Places the backbox in the hole
3. Then uses insta stik (i.e. Low foaming, expandable foam).

Claims that he's never had an issue before

 

[securespark]

I wouldn't.
As an aside, I worked with a builder in the nineties who fixed uPVC windows and doors with that stuff. No screws, just gunk!
As for gunking the DL box in, that could be messy (messier than usual) if you had to change the box.
I also disagree with running the cables outside of zones.
Where possible on LAP walls, I used to screw the boxes sideways into the timbers.

 

[Taylortwocities]

I agree. No excuse for running the cable outside zones. Good tip on the CEF drywall boxes though.

What looked really odd is his height of the sockets that in that old house. Its possible the owners might be in wheelchairs…