Look before you leap has reared up and bitten me on the bum.
I've finished decorating the bedroom and the sitting room, and bought replacement dimmers (nice brushed chrome ones) to replace the knackered white plastic ones. Unfortunately, I didn't think to check that the backboxes were suitable. So now I have to replace the 16mm backboxes with 25mm ones.
Since both rooms are decorated and carpeted it's not just a question of knocking a bloody great hole in the wall - I have to take a bit of care. However, as long as I'm sensible I don't see any reason to disturb the opening which should mean that whatever mess I make behind won't matter.
However, are there any tips or tricks anyone can offer, or gotchas that I might not have considered? I'm planning to drill some pilot holes to approx. the correct depth and then use a hammer and chisel to remove the rest. Is that a plan?
Sounds OK to me ....Obviously the first problem is getting the old box out but you should manage that if you take your time and ease it out gently after removing any plaster that might be in the knockouts .
I'm with you on drilling out to the required depth then chiselling out the rest .....obviously you'll need to make sure the surrounding decor and flooring is well protected from plaster and brick dust .At least it's only another 9mm.
Stuart P.S. You won't forget to isolate the supply will you ?
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Drill as much out as possible (lots of holes) to the right depth then gently use a sharp masonry chisel to take out the rest would be my advice. But I think you'll be fine as long as you don't go at it like a looney ;->
Dustsheet on the floor obviously, and any residual brick/plaster dust generally hoovers up cleanly even off carpet. Make sure any paintwork that may still be tacky is either not tacky or well protected.
I'd remove the old box by carefully folding it in on itself then cutting with tinsnips etc to avoid damage to the surrounding plaster. Then once it's out carefully slop some 4:1 PVA solution around the hole to try and give some more strength to the plaster and leave to dry for a day or so before commencing drilling. Also, use one of those universal bits and no hammer action. Unless the bricks are so hard you have no choice.
You don't say what type of walls you have. I'm guessing they're not stud cavity walls, as presumably you've had a good look at the existing box.
I'd go with that, having replaced a couple of boxes myself, but I think you'll be *extremely* lucky not to cause some damage to the plaster.
You may also find that the original box has a wirecut nail hammered into the back as a fastening. That may well have rusted into the wall. No easy way to get those out, it's (very careful) brute force and ignorance.
If you have breeze block walls it's relatively easy - if messy - to scratch down to the required depth. If you have one, or know someone who owns one, try a scutching hammer.
If you have brick or other similar hard walls, good luck, I'd look for another type of dimmer. I have bitter memories from many years ago of trying to set in a box where the internal walls were *extremely* hard bricks. The hole in the wall was quite traumatising.......
A lot depends on if you papered round the light switch or painted the wall.
If the former, you have a line that you can work to to prevent damage outside of the light switch body. If the latter, then put some very low tac tape around the switch before you remove it. Get a very thin bladed screw driver and lean it towards the back box body so as to create a small amount of distortion. Once you have done this on all 4 sides, take an old screw driver and pick up on the distorted sides with the blade at
90 % to the back box side and lean it towards the centre of the back box and collapse it towards the middle.
If, as someone said, there is a nail holding it to the wall, then you will have to drill the head of the nail off. Start with a small HSS twist drill (2.5 mm) and get a hole somewhere in the middle. Open this hole up until the head drops off. The nail may be able to be removed after you cut back for the new box. If it wont budge, cut the wall back some more to make a cavity to bury it, then bend it over.
If you look at the back box you should be able to thread some thick fencing wire through the holes at the bent over sides. Do this in an equal way, so that if you pull one side, you can pull opposite at the other side, this is so that the back box will not tilt over as it comes out of the wall and rip off the plaster surrounding the cavity. If you can only get to the top left on one side, go for the bottom right on the other side. etc. The fencing wire should be twisted so that it secure to the back box and have a loop at the other end. Make the twists are longer than you think you will need. They can get pulled open if too much force is put on them if they are too short.
Now find a small piece of wood and wrap it evenly with a clean cloth or rag. You will be holding this against the wall to prevent any damage caused by the pressure from the crow bar that you thread through the loops, one at a time, to pull the box out of the wall. Put the bar through the first loop, going across the box and place the end on the block and pull. Then reverse everything and pull the box out again. Now alternate the pulling so that you gain 1 mm at a time on both sides.
You might have to open the hole in the wall to get it to accept the new back box.
I hope this works for you, it did for me a few years ago.
If you have one, its an ideal job for the multimaster with the stiff scraper blade - run that in around the edges to break the bond and create a little room, and pull the box out. If it has a screw or nail at the back, and it won't pull out, drill it out.
To get the extra depth, stitch drill completely around the outside (a piece of wood the size of the box, drilled in the same pattern as a template will help stop wander if needs be) and as much more as you can be bothered, and then chip the rest out with a small, freshly sharpened cold chisel.
ermm - you didn't mention if you already have cables going into the back box, probably via the knockouts in the side/top.
All the suggestions above seem to not address the problem of getting the back box out without damage to the cables! Bending the side of the box inwards will just trap the cables, and it certainly won't pull straight out of the hole with the cables in place.
Not that I have the answer, but would love to know how for when I eventally get bitten by the same problem. David
Fold the sides in a little way, without flattening them right down to the back of the box, then it's a case of easing the bottom of the box out and down over the cables. Almost impossible to do without at least a bit of damage to the plaster. When I did it, I was left with two or three small patches (upto an inch long and 1/4 to 3/8 at the widest) to make good with filler.
My approach would be to masking tape a dustbin liner under the cut out in a form of hammock to catch the crud. Prise out the old box (drill hole next to the fixings if required to allow it to be pulled free of them if unscrewing etc is not an option). I would then stick a 40mm wide chisel in the sds and plane down the back to depth. Only try this if your drill has a decent speed control!
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