Filling Large Gap Around Socket Back Box

[novaf4]

I would appreciate advice on the best type of product to use to fill around a socket back box in my brick and plaster wall of my bedroom. There is a gap between the back of the box and the brick wall which is about 1cm deep x 40cm wide x 11cm high, as well as 40cm deep gaps at both sides and top and bottom. I also need to use something effective for skimming the top coat that won't crack. The wall will eventually be painted (not wallpapered). From my failed online research my shortlist is Sand & Cement Mortar or Bonding Plaster or Thistle One Coat Plaster but I've never used plaster before and am worried that it will need building up in 13mm amounts and may take forever the dry. I need something that dries as quickly as possible as I'm running out of time for the whole decorating job. I could also do with some advice on how to fill around the hole that the wiring comes through as I'd rather not fill up the hole and get stuff all over the cables unless that's acceptable or unavoidable.

I initially used pretty cheap Deep Gap Filler from Screwfix for the bottom void but it didn't dry after 2 days!. I had to (easily) scrape it all out.

In case anyone wonders the photo is a bit of an optical illusion as the box is almost flush to the wall; just slightly set back. The front plate will be a nice flush fit one. The job was a nightmare having had to deal with an awful attempt by a previous owner so i had to start with an oversized hole widthways and had to bash out the depth for a deeper box. I also had to raise the box so that the plugs clear the skirting. It's been an awful day so please don't bash me too much if you don't think it's a very good job!

Thanks.

 

[Tigercubrider]

You can get small bags of quick set mortar in wickes, I have used it for similar jobs
Don't forget to fit a grommet where that cable meets the box

 

[novaf4]

Thanks. Could I do the whole job in one hit with this stuff? How long do you think it will take to set?

 

[magicmushroom666]

I'd do the very top surface with a skim of some sort of filler that will be easier to sand and make good.

 

[Tigercubrider]

It sets in about 30 mins but needs 12 hours proper drying
If you have some wooden tamping tools then you could mix up a batch, use a palette knife to load it in and then tamp it into the gaps.
Leave enough room for a layer of filler on the outside

 

[sparkwright]

Tigercubrider is spot on. That stuff IS very easy to use, it starts to go hard after a few hours.

You should be able to do this in one hit, although you will need to do a final finish with plaster or filler.

Make sure you push the mix well into the gaps, it needs to right the way back, or as near as you possibly can, otherwise you risk it cracking and falling out later.

If you run out of mix, mix up more and just shove it in.

Be sure to clean the wall before it fully sets.

Keep the mix just below the surface level, when set apply plaster or filler.

 

[sparkwright]

He got there first.

Don't forget the grommet.

 

[sparkwright]

It would pay to wet the bare brick and plaster before applying the mix - it will stick better.

 

[novaf4]

I'm relieved to read your replies - thank you all so much. I will grab some of this stuff tomorrow at Wicks, shove it into all gaps and fill up the void just below the surface where I'll use filler. I'll also grab a grommet whilst I'm at the shops. One thing - whilst filling up the gaps what do I do about the cable hole and the part of the cables coming out of it? Just cover it all with the stuff too?

 

[Tigercubrider]

Shove a bit of masking tape over the holes from the inside.
Too much getting in is a pain as it impedes the function of the box
But a little gripping the edge of the hole helps hold it all together

 

[opps]

I agree with all of the advice you have been given so far, but would suggest spraying water into the areas to be filled. It will help reduce the level of suction.

In cases where the hole has to be filled, sanded and painted in one day, I use two pack filler. The deeper the hole, the fastest it sets. Given the amount of sanding/refilling/sanding/etc it is much more labour intensive than using quick set mortar or plaster though.

 

[novaf4]

Just thought I'd end the thread with a successfull conclusion to the job. I masked up the holes of the back box on the inside as well as the crucually the little tabs on each side that incoporate the screw holes. The of these helfully moves up and down to allow for small corrections to the angle of the front socket plate so I made sure nothing was going to end up jamming that by using some extra strong Gorilla tape over the outside of that part which had an irregular shaped hole. I also masked off the whole front of the back box as I knew otherwise I'd end up with mortor on the inside. I then used the Quick Set Mortor from Wickes. I applied it in 6 separate batches so I had just enough to work with before it began to cure. Down the back first, then the sides, then over the top and then along the bottom. I found the best method was to get a load on my finger and jam it in using my fingers. I was great stuff to use. The next day I cut back parts of it with a knife where it wasn't supposed to be and used No Nonsense filler powder which I mixed with water. This was quite tricky as the back box actually was tipped back at a slight angle along the top. I used various size scrapers to help simulate the back boxes' surface level and another scraper to push the filler on and up to the correct level on the surrounding wall. I had to wait 24hours for this to dry. Today I've added another layer of the same filler in the same fashion as it needed building up even more. I'm very pleased with the results. Sanding it back tomorrow where I'm going to use a peice of wood long enough to reach the adjacent correct wall levels, wrapped in sandpaper so the correct level can be achieved. I've done this before to good effect. Finally I'll be ready for painting. Cheers to all!

 

[sparkwright]

Let's have a picture then .

 

[novaf4]

 

[sparkwright]

Very very nice. Very well done, you can be proud of that (even if you did forget about the grommet).