Installing receps in block walls

[cwsnsons]

I would appreciate some suggestions on installing receps and switches in a dwelling "basement" that is to be used for living space. The interior walls are stud/drywall construction. However, the outside block walls are not studded out, just bare. The owners do not want to run conduit on the surface, rather they want me to run the wires inside the blocks (which I think is OK - NM-B). But I am not sure what is the best way to bring out the wire and mount the devices/covers. Has anyone done this before or have suggestions? Any input would be appreciated.

Chris

 

[iwire]

Re: Installing receps in block walls

Give them a high quote or charge by the hour.

I have never done this with NM, most times EMT as the blocks are installed.

Before I made the hole for the box I would make sure you can fish down to that spot.

Once you are sure you can fish down to your desired location you will need to make a hole for a "Mud Box" that is the only name I know for these boxes that are made to be cemented in place.

I would suggest an small angle grinder with a cement cutting wheel to make the hole, expect a lot of dust and wear a dust mask.

Or drill a series of 1/4" holes and chisel the hole out.

Now get you wire in the box and mix some cement and "mud it" in.

Good luck I have tried to "mud in" boxes before and I was poor at it.

 

[a.wayne3@verizon.net]

Re: Installing receps in block walls

It is pretty easy actually,first determine location of the receptacle or switch.Then outline a pvc old work box with a marker,using a small chisel place it inside the outline on a diagonal
at each corner punching through the block.This blows the block inwards from the corners.Then finish tapping the remaining block along the line.
If done right you now have a clean cut that is angled on the inside of the block allowing the ears of the old work box to grab the block.Then if the top cell is poured sleeve the nm in carflex/sealtite and strap it to the block or chisel enough block away to embed it in the block itself.I hope this helps !!!!!

 

[Guest]

Re: Installing receps in block walls

rather they want me to run the wires inside the blocks (which I think is OK - NM-B).

I would be concerned about dampness if the basement block walls are below grade. NM may not be the best choice, and may be prohibited due to moisture. I wonder if you could use UF? Probably not! Just brainstorming here. Don't pay me no nevermind!

../Wayne

 

[iwire]

Re: Installing receps in block walls

Originally posted by awwt:
I would be concerned about dampness if the basement block walls are below grade. NM may not be the best choice, and may be prohibited due to moisture.

334.10(A) Type NM. Type NM cable shall be permitted as follows:

334.10(A)(2)To be installed or fished in air voids in masonry block or tile walls

 

[bthielen]

Re: Installing receps in block walls

awwt,

I think you bring up a good point about the moisture. It seems that no matter how well a basement is protected against incoming moisture, the coolness due to the below ground level still encourages a high relative humidity, especially during summer months. We installed drain tile and sump pumps in my house when we remodeled and I still had to put in a dehumidifier to control water vapor in my basement. It got so bad mold could grow freely on anything organic such as leather. Ah, don't ask what the leather was for!

Bob

 

[Guest]

Re: Installing receps in block walls

iwire said:

quote:
--------------------------------------------------------------------------------
334.10(A) Type NM. Type NM cable shall be permitted as follows:

You left out the part that NM is for dry locations only. If the wire is below grade my position is that it's not going to be dry. Your milage may vary. Happy trails!

../Wayne

[ September 06, 2003, 02:42 AM: Message edited by: awwt ]

 

[iwire]

Re: Installing receps in block walls

Great picture Wayne , this is another one of those areas of the code you will not like as it the AHJs call.

In my area most all panels are in the basement and all the branch circuits are NM including any basement wiring.

In this area all foundations are required to be waterproofed on the outside.

Bob

 

[torint]

Re: Installing receps in block walls

The installation would look much neater and less expensive to stud/drywall the basement and do the job corectly. Personally, I would not get involved in the fishing in cinder block thing. I've done it before in commercial settings (once). Res settings look much neater with drywall. Just my opinion

 

[macmikeman]

Re: Installing receps in block walls

new neat trick I stumbled onto for cutting out block walls.
Try using a roto zip with the ceramic tile bit. It works good but requires a few passes to get thru the 1-1/2" depth of the outer wall of the block. Also you have to untwist and remove the guard to get in close. A 4" makita grinder with a diamond blade is also excellent but doesn't get the corners well unless you over saw the outline of the box.
dust mask and goggles required.

 

[cwsnsons]

Re: Installing receps in block walls

Thanks to All;

The walls in this "basement" are all above grade, except the lower half of the front and a small portion of the two side walls. The house is on a low hill. So the walls are not likely to get much direct moisture from outside. The owners are coating the exterior and interior of the walls with "Drylock". I was some concerned about the condensation issue that some pointed out. Will it make a difference that this basement will be heated/cooled space with a drop ceiling.

The idea of a 4" grinder to cut the holes was mentioned here as well. What about that roto-zip idea? Anyone else tried that?

As far as the NM-B issue, I wouldn't be opposed to using UF. It's not really that bad to work with, once you develop the technique. Wondered about the possibility of putting the cable in some of that flexible NMT ("Spiroduct"?).

Does anyone know a trade or manufacturer name for the "mud box" Iwire referred to?

Again, I really appreciate the input.

Chris

PS how do you get the "post bar" at the bottom of your messages to display "from: such n such a state, etc"?

 

[ryan_618]

Re: Installing receps in block walls

Originally posted by cwsnsons:

Does anyone know a trade or manufacturer name for the "mud box" Iwire referred to?

I believe Raco makes them and they are also known as a masonry box

 

[hbendillo]

Re: Installing receps in block walls

If this space is going to be used as a living space, I suggest they install drywall over the block using a shallow "hat" channel stud. I think these studs come in 1.5" depths which gives you space to mount an outlet box and install wiring.

 

[Guest]

Re: Installing receps in block walls

A masonary box is like a plastic box made out of metal. Most metal boxes have the ears turned outside the box. If you set them in mud then you cannot screw your device into the box. On a masonary box the ears where you fasten the device turn in to the box. This way you can turn your screws when you fasten your receptacles and switches. The ears run full length to give your device yokes a better place to land. Also, the masonary boxes aren't full of holes so they don't fill up with chum.

Follow these links for some pictures and Raco model #'s:
http://www.foxelectricsupply.com/content/products/ProductDetail.asp?qsCatID=24606&qsProductNo=690

http://www.foxelectricsupply.com/content/products/ProductCatalog.asp?qshCatId=24606

Raco is owned by Hubbell so you might find them under the Hubbell brand too.

../Wayne C.

RACO by Hubbell Masonary Box #690

Image property of: http://www.foxelectricsupply.com

[ September 11, 2003, 01:29 PM: Message edited by: awwt ]

 

[cwsnsons]

Re: Installing receps in block walls

OK, Iwire, now that I have the boxes, what about "mudding" them in? I know you said you felt you were poor at it. Anyone else developed a technique that seemed to work for you? One question I have specifically is, how much larger than the box do you make the hole so your mud has some thickness to it so it will hold up over the years. I don't want these people to come back in 5 years complaining about a bunch of loose boxes. I went through the house yesterday with one of the owners and counted 14 boxes according to present plans. I might try this out on a loose block to see how it goes. (I thought doing electrical work was volts & amps, here I am turning into a mason!)

Also the boxes Wayne showed (Thanks) look like they don't have integral "romex" clamps, so NM-B or other connectors will need to be installed. Do you think AHJ will have any problem with that? Actually, I'm planning on having him come out on a "consultation" permit once I get this a little clearer; I'd rather pay up front than have him reject the job when a little "good faith" communication could solve any potential problems.

[ September 19, 2003, 11:24 AM: Message edited by: cwsnsons ]

 

[iwire]

Re: Installing receps in block walls

Originally posted by cwsnsons:
OK, Iwire, now that I have the boxes, what about "mudding" them in? I know you said you felt you were poor at it. Anyone else developed a technique that seemed to work for you?

Yes I asked my apprentice to do it and he did it fine.

Most times I work with them the masons do it.

It seems about a 1/2" space is enough, but your idea to experiment on a loose block seems like a good one.

Bob

 

[genel]

Re: Installing receps in block walls

I have embedded boxes in stone walls with ordinary (Type S) mortar. The joints I used were half an inch or so. How well it will adhere to the box is dependent on the coating of the box. (Try buttering the box sides and the block with mortar before placing the boxes.)

If you want to keep the joints as small as possible, consider some epoxy grout that is made for tile grout.

[ September 19, 2003, 04:45 PM: Message edited by: genel ]

 

[hbiss]

Re: Installing receps in block walls

If you are concerned about moisture in the wall enough to use UF, keep in mind that mud boxes are not suitable for damp locations either.

Mud boxes are normally used with conduit and installed as the wall is built. The conduit helps hold the box in place as does wedging pieces of block in the void against the box sides and mortar. You won't be able to do this and will have to rely on cutting an oversize hole and packing around the box with mortar and hoping it will hold. You could try hydraulic cement which expands when it sets up. Either way you are going to see the patch job because the plate isn't going to cover.

Another potential problem is fishing the cable in the block with the connector attached. That's what you will have to do and you better hope that the voids line up and you have the space to get the connector through. Willing to bet that you will have several holes cut that you won't be able to get the cable to.

How do you plan on entering the wall at the top?

By the way, Drylock "paint" won't do much at all except make the wall look better.

 

[Guest]

Re: Installing receps in block walls

Even if Drylock were a perfect membrane cutting mud boxes into the wall will violate the membrane. If the membrane is perfect the water will seek the path of least resistance-- and that will be the mud box. Look up hydrauger to see how water finds its way out of an unstable slope. If you punch a hole in a wet, unstable slope it does not matter too much where you punch the hole-- the water will find the hole-- you don't have to find the water with the hole. If you put a hole in a damp wall, the water will find it. Your mud box will become the hydrauger no matter how good your membrane is.

PS: I'm still bothered by the concept of running NM or UF in hollow block walls-- and bothered by hollow block walls used as a structure. But I'm on the left coast and in earthquake country.

 

[macmikeman]

Re: Installing receps in block walls

I have a good way to mud in the boxes that I have used over the years. My former employer when I served my apprenticeship showed me this one. Mix 50% cement with 50% plaster of paris. add water and work real quick. It sets up in about 8 minutes. You can drill it at 15 minutes. stuff newspaper in the hole below the box level first to contain the mud behind the box, and just trowel in a couple of large scoops. Use a stick or something to knock the mix off the uf you have run down to the opening so you dont have a cable embedded in mortar. Run the cable into the box and shove the box back into the hole. Wet sponge off the excess. Done. you will need a chisel to ever move that box again.