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Knob and Tube Light Switch Rewiring

I have hired an electrician to completely update the wiring of out 100 year old home. He has completed most of the work and started rewiring the wall switches today. He found that the boxes are mounted in concrete behind the switch and destroyed one of the switches when trying to remove it to access the box. Now he is saying the only way to get the switches rewired is to cut holes in our plaster walls above each switch. I have 2 main questions:

1. Is there any other way to rewire these outlets? Hopefully, someone has run across this issue before.

2. If we do have to cut holes, is there a particular way plaster walls should be cut and how are holes in plaster walls generally repaired? Will it cause cracks up the walls to cut into it?

I hope someone can help us figure this issue out so we will know how best to proceed with this rewiring project. Thanks in advance for any advice you can offer!

Re: Knob and Tube Light Switch Rewiring

You will need advice from an electrician for question # 1.
As for cutting holes in the plaster you can use this tool. A Pneumatic Die Grinder like Grainger's 1/4 inch # 5ZL15 with a Cylindrical Burr Bit # 1Z285.This set up will cut nice neat holes in plaster with no damage from vibration plus you can cut down to the wood lath with no damage to the lath than use a smaller bit to cut the lath as required.
Cost for tool and bits $ 75.00.
Contact a plaster contractor or person that deals with Conventional plaster for repairs.
If you can't find a good plaster call the local Historical Foundation for info on who they know for plaster restoration.

Re: Knob and Tube Light Switch Rewiring

A clean round hole should not cause cracks. Cracks tend to start at corners with sharp, defined angles. Rounded corners are not as prone to cracking, the rounder the better. In fact, the first step in repairing a crack is to drill a stop hole at each end of the crack.

As an amateur, I have found it far easier to repair holes in lath and plaster walls than in sheetrock.

Re: Knob and Tube Light Switch Rewiring

Emily, there are plastic "old work" boxes that might help.

First I would loosen the cable connectors and drop the old box into the wall, then slide a new "old work" box into place and extend the ears to hold it in place.

If the old box is cemented in place removing the old box may require considerable effort. If so consider using a plastic box extender which slips into the old box and gives the electrician a new box, in the old box.

Re: Knob and Tube Light Switch Rewiring

A small hole above the switch box or receptacle box is the most common way to remove the old boxes, you cut along the stud to remove the nails or nailing fin off the old box, then a retrofit box with tabs or wings can be used, either metal or pvc. This is the most cost effective way to rewire, I have always plastered up the holes during a complete rewire, then the customer can finish coat the wall and sand ,prime and paint, but most electricians now will leave this to the homeowner or have them hire a plasterer to re-finish the wall,most work now is bid by the job,so the faster you get to the next job the more money you make. Good Luck!

Re: Knob and Tube Light Switch Rewiring

Had to do this earlier this year. It was very frustrating at the time but I learned a lot. Tried the grinder but it didn't work. Ended up cutting it out and then replastering. If you look at it now you would never know that any work was ever done to it.

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