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Cutting a hole in a wall for a new electrical panel.

Updating Old House Wiring:

Adding A Sub-Panel - Part 1 - Cutting A Hole In A Plaster Wall

Cutting Plaster Is A Common Task In Old House Remodeling

 
In This Article:

An existing stud is removed from a plaster-and-lath wall, a rectangular hole is laid out, the wood lath is cut away and the final hole is cut in the wallboard.

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Skill Level:
2-3 (Basic to Intermediate)
Time Taken:
About An Hour
Author:
, Editor
Project Date:
March 2006
 
 
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Starting Point:
Small hole cut in wall to allow electrical wire to be fished into wall cavity from below.

I cut this 8-inch-square hole about two years earlier.

While remodeling the first-floor rooms below, we ran a 6-3G cable from the basement up to this second-floor hallway. By cutting a large hole I was able to reach into the wall cavity and grab the cable while the homeowner pushed the cable from below.

 

 

 

Sub-Panel Location:

 

After removing the plaster and lath from the old apartment kitchen, the access hole (red arrow) could be seen from behind.

The 6-3G sub-feed cable can be seen coiled up just below the hole.

Old house interior wall with plaster and lath removed, showing location of future electrical sub-panel.
 

 

In this old house the space between studs is only 14 inches.
A Problem:

The spacing between the old studs was only about 14 inches, and the new panel requires almost 14-1/2 inches.

 

 

We removed the stud near the door opening.

Old stud removed and new stud installed nearby.
 

 

Fastening new studs with deck screws.

To compensate for the reduced structure, we added another stud to the double-studs at the door opening.

 

 

Also, since the old studs were wider than new studs (almost 3-7/8" wide) we added a layer of 3/8" plywood to the new triple-stud, and all the other new 2x4 framing that had to align with the old framing.

The location of the old stud is visible as a whitish streak on the wood lath.

Wider space between studs after one old stud was removed.
 

 

Cutting plaster and lath to make large hole in wall.

Cutting short lath boards can be tricky. The boards will wiggle and vibrate and cause the plaster to crack.

To keep the lath from moving, We clamped a piece of 1x3 lumber to the back side of the wall. This board was rather curved, and we placed the "crown" toward the wall. This held better than a straight board.

We started cutting like it was a plunge cut.  Our goal was to only cut through the lath.

We used a short wood-cutting blade. A long blade is sometimes better for starting plunge cuts because it can be held at a lower angle against the wall. But long blades also flop around a lot while starting the cut.

 

 

Other Plaster Cutting Methods:

Typically I'll use a carbide-coated plaster-cutting blade to cut both plaster and wood lath at the same time. However, a plaster-cutting blade cuts really slow through wood.

Normally, once the blade breaks through the wall surface I will rest the foot of the reciprocating saw against the lath, to minimize the amount of flexing of the lath.

The wall in these photos had a layer of paneling over the plaster, and then a layer of ½" drywall. (The previous remodeler was too cheap or too lazy to simply yank the paneling from the walls before adding drywall.) Consequently, cutting with a plaster blade was painfully slow.

 

The other side of the opening needed to be flush with the stud.

For this cut we used a long wood-cutting blade... one that was kinda old and getting dull.

We started with this tricky plunge cut that was against the stud.

Using reciprocating saw to cut old plaster and wood lath to make opening in wall.
 

 

Cutting technique where long Sawzall blade is flexed so it can cut flush against a wall stud.

The key to cutting an opening that is flush with a stud is to flex the blade like this.

The blade needs to be pushed firmly against the stud, so the front part of the blade rides against the stud while the reciprocating saw moves the blade back and forth.

Of course the blade needs to be mounted upside down in the reciprocating saw, and the saw needs to be held as close to the wall as possible.

 

 

We only cut part way through the wall... just enough to cut the wood but not deep enough to engage the plaster.

Old plaster contains sand, which dulls the blade immediately.

Removing old wood lath after cutting part way through the wall with reciprocating saw.
 

 

Cutting old plaster with a carbide-coated reciprocating saw blade.

I put a carbide plaster-cutting blade in the reciprocating saw and cut out the plaster/drywall from the front side.

 

 

The completed hole.

We still needed to grind down some high spots along the edges of the hole.

Hole in wall for electrical panel.
 

 

 
 
 
 
 
 
 
 
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Blocks of 2x4 and 1x4 to fill in opening so electrical panel can be fastened.

To create the 14-1/2" wide opening in the framing, we fastened some blocks of wood to the nearby studs.

 

 

We mounted the new sub-panel to the framing with 1-1/4" Simpson Strong-Drive screws.

But... we couldn't use the normal mounting holes. The plaster/lath and drywall multi-layer surface was so thick, the mounting screws would've just bit into plaster.

So we drilled four new holes farther back, so the screws would hit the wood framing.

Fastening small electrical breaker panel to wall studs with short screws.
 

 

Continue To Part 2 - Changes At The Main Panel

 

HammerZone's Recommended Electrical Tools
 
 

 

More Info:
Tools Used:
  • Basic Carpentry Tools
  • Cordless Drill/Driver
  • Reciprocating Saw
  • Carbide-Coated Plaster-Cutting Blade
Materials Used:
  • 2x4 Scraps
  • 1x4 Scraps
  • Deck Screws
  • Simpson Strong-Drive 1¼" Screws
 
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