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Old 02-03-2013, 08:05 AM   #1
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Cutting channels in concrete wall?


What's the best way to cut channels in vertical concrete walls? Not large channels, just enough to fit 1/2-inch PVC conduit.

Bit of background: My husband and I are working on remodeling our home. It's an old home from the 40s. We're about to start rewiring the house. The wiring is very old, the layout is....let's say, creative.... and it badly needs to be redone.

The house has cinderblock walls that have also been filled with concrete. That includes the interior walls. The original wiring and boxes are embedded in the concrete. No conduit, just straight embedded wiring.

We're just going to completely ditch the old electrical. The old outlet boxes are too close to the floor anyway and need to be raised. Our plan is to cut channels in the wall and embed 1/2-inch PVC conduit to run the new electrical. Yeah, it's going to be a pain. We're thinking about cutting a series of grooves with a diamond masonry blade and chiseling them out. Thoughts?

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Old 02-03-2013, 08:13 AM   #2
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Cutting channels in concrete wall?


Ya, do not do it that way. That would weaken the whole wall.
What do you plan on doing to finish the walls?
Right now you have no insulation in the walls, anyplace there's a small crack air can get in, that walls acting like a heat or cold sink and will transfure outside tempatures to the inside of the home.

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Old 02-03-2013, 08:22 AM   #3
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Cutting channels in concrete wall?


I see that done in Mexico a lot----I don't know about any collateral damage to the strength of the block---But a wet cutting circular saw and a Bosch Clipping hammer would make short work of it---

A standard circular saw can be used with a segmented diamond blade----but the dust will be overwhelming---

An angle grinder with a diamond blade will also work well.
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Old 02-03-2013, 08:37 AM   #4
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Cutting channels in concrete wall?


I didn't think a channel that shallow would weaken the wall. The walls are basically 7-inch-thick concrete, and only single-story height. But granted, I don't know a thing about this kind of wall material. All our previous experience has been drywall.

We could run the new wiring on the surface if it's required to keep the house structurally sound. I just really don't like the aesthetics of it. Do we have any other options?

We're not worried about any additional insulation or finishing on the walls. Cinder block is a very common form of construction with the older homes in this part of the world. Also, the exterior walls are finished and sided, which is rare here. Most of the cinder block homes are simply painted and left as they are. Our heating and cooling bills are significantly cheaper in this 1400 sq. ft. home than they were in our 1100 sq. foot home with modern construction.

Mike: Never thought of an angle grinder. We might have to look into it, provided it won't weaken the walls.

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Old 02-03-2013, 08:43 AM   #5
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Cutting channels in concrete wall?


i wouldn't worry too much about strength if, as you say, the cells are conc filled,,, dustmuzzle has a good shield for circle saws & joe due's got the best shields for grinders - you supply your own dust vac,,, we have mexicans right here in the usa who do it the same way

like joe posted, i would insulate the walls unless its free heat but even touching winter cold walls is a no-no in our house
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Old 02-03-2013, 08:51 AM   #6
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Cutting channels in concrete wall?


One possibility----
Surface mount the conduit----(or Romex)

Inset the boxes into the block---

Glue on foam insulation over the entire wall (except for the conduit)

Then Glue on 1/2" sheet rock (drywall) using enough Tapcon screws to hold the board in place as the glue dries.

Adds a lot to the cost of the project--but gives you some insulation and a nice finished wall--

I've done this successfully more than once.
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Old 02-03-2013, 08:54 AM   #7
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Cutting channels in concrete wall?


Depends on what's exceptable to you.
Not fun but in some cases you can pull new wire as your your pulling out the old wires.
You could add 3/4 blue foam then 3/4" strapping and use a shallow wall box like this.
http://www.amazon.com/Single-Gang-Bo...cal+outlet+box

You would also need to add jamb extentions to all windows and doors.
This would give you a much nicer looking smooth looking wall, and more insulation.
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Old 02-03-2013, 09:03 AM   #8
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Originally Posted by itsreallyconc View Post
i wouldn't worry too much about strength if, as you say, the cells are conc filled,,, dustmuzzle has a good shield for circle saws & joe due's got the best shields for grinders - you supply your own dust vac,,, we have mexicans right here in the usa who do it the same way
Yeah, the walls are concrete. We refer to our house as "The Bunker". You can't even make a scratch on it with a regular electric drill, regardless of the bit you use. And yup, we learned that the hard way. Simply installing curtain rods requires a hammer drill. And let's not get into the joy that was baseboards. On the upside, we never have to worry about trying to find a wall stud.

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Old 02-03-2013, 09:07 AM   #9
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Cutting channels in concrete wall?


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Not fun but in some cases you can pull new wire as your your pulling out the old wires.
Alas, that's the crux of our issue. We'd absolutely love to be able to do it that way. But with the old wiring solidly embedded in concrete, it's not going anywhere.
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Old 02-03-2013, 09:56 AM   #10
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Cutting channels in concrete wall?


I'm going to put up pictures of our house on the projects forum. I'm sure it'll help if you can get a visual of the house. The concrete walls are finished on the inside, as well as finished and sided on the outside, and were when we bought the house. We'll, we made a stupid mistake. When we bought the house, the home inspector said the electrical wiring needed to replaced "in the next couple of years." We knew the walls were concrete filled. We consulted a friend who is a contractor before we bought the house, and he suggested the same thing Joe did: we could use the existing wiring to pull the new wiring into place. Overall, not a major job. So we went ahead and finished most of our other projects first, which at the time seemed to be more "major" projects than pulling some wires. It wasn't until we did our kitchen remodel and attempted to relocate an existing electrical outlet than we realized that the wiring (which everyone involved assumed was run through drilled holes in the wall, which I guess is the usual thing) was actually embedded in concrete. We'd never even heard of such a thing before, so it never occurred to us to check for it.

So we're now trying to redo the electrical while ideally doing as little surface damage to the walls as possible. As it is, we're going to have to remove kitchen cabinets and some of the tile backsplash to do it.

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Old 02-03-2013, 10:03 AM   #11
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Cutting channels in concrete wall?


Don't be to hard on yourself---There is no substitute for experience---You are dealing with an unusual situation that was not in your field of expertise----

How do you think some of the old timers here know so much?

They ran across odd ball situations like yours and had to find a solution----Experience----You are having one with this house---and will be wiser when you are done----
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Old 02-03-2013, 11:37 AM   #12
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Cutting channels in concrete wall?


The trick of a true craftsman is when you screw up you make it look like it was suppost to be that way.
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Old 02-03-2013, 12:14 PM   #13
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Originally Posted by joecaption View Post
The trick of a true craftsman is when you screw up you make it look like it was suppost to be that way.
Well, glad to know that we're not the only ones who've been in a predicament like this.
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Old 02-03-2013, 01:07 PM   #14
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Cutting channels in concrete wall?


Maybe I'm not understanding, but wouldn't surface mounted conduit look better than conduit recessed in rough cut block? The cut's in the block will not look finished by any means, unless you plan to cover the conduit with something??

CHeck out a product like "Wiremold" as well, it's a little smaller and less conspicuous than conduit..........
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Old 02-03-2013, 01:11 PM   #15
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Cutting channels in concrete wall?


We plan to repair the concrete over the pvc conduit, basically embedding it. Or would that not work? Like I said, this is our first-ever experience in dealing with concrete walls.

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