repairing wall around back box

[Lindsey Wilkinson]

Hi, I have replaced an electrical back box but was left with a large area to repair. I used mortar to fill in deep holes and have waited 48 hours for it to dry but the mortar in the chasing has a vertcalcrack down it's length how and can I repair this? Help...

 

[CBW]

How large an area? Any photos? How deep is the fill?

 

[JohnD]

Presumably a drying-out shrinkage crack. Include something in your photos to show scale please. Do you recall the proportions of sand:cement you used, and how deep the fill? Did you damp the hole?

 

[Lindsey Wilkinson]

Sorry at work so can't give photo of filled holes but this is prior to filling with mortar (pre mixed sand and cement). It has one crack for length of chasing. I did dampen before but maybe not enough. Does it need packing more around the wires and can I just do that area again? Sorry am a real novice!

 

[CBW]

Might be better with bond and skim?

 

[flameport]

Mortar is the wrong material - plaster should be used.

There are no grommets in the backbox holes, and why are there bits of white tape everywhere?

 

[JohnD]

Mortar is fine to pack round the backbox and hold it firm in the cavity. I find it easier to work with as it is slower to set, and it is stronger. I don't recall having cracking.

But in your pic, you would then need to repair the plaster... with plaster. Preferably picking out the cracked or loose bits first.

 

[Lindsey Wilkinson]

What do I do about the crack? It moves when wires move.

 

[EFLImpudence]

Dig out the loose bit and fill with whatever you are using for the final finish.

 

[Lindsey Wilkinson]

Thanks - Ronseal Smooth Finish Filler for big holes. Do you think it will stick to the mortar ?

 

[EFLImpudence]

Yes.

Scratch the surface of the mortar and vacuum away any bits and dust.

 

[Taylortwocities]

Bonding coat with a bit of cement Would be better than mortar for the fix/fill stage.

but as above
You need grommets in those holes, they’ll reduce the cable movement too.

 

[CBW]

Right hand cable chase probably isn’t deep enough, hence the crack moves when cable does. Might be better clipping the cable.

 

[Lindsey Wilkinson]

Clipping the cable?

 

[Taylortwocities]

Cable clip

Oh yes, and

Grommet