Sunday, April 8, 2012

Cast in Place Electrical Outlets

Our search for cast-in-place electrical outlet boxes for the exteriors of the concrete basement walls ended without result.  We've probably all seen those grey PVC or painted aluminum outdoor boxes mounted on the surface of the basement walls.  Ugly.  Oddly enough, there is very little out there to address this issue.  I did find one product by IPX called Kwik-On.  Normally, electricians use 'slab boxes'.  These are similar to the metal boxes used for surface-mounted outlets.  They have no way to secure them to the concrete forms (odd, but true) - I believe the EMT conduit is intended to keep them in place while the concrete is poured.  They are not designed for exterior use, or for walls, and the electrician tapes them all ove to keep the concrete out.  There is also product in Europe where they tie the box to rebar and then cast around it.  The opening is knocked out later.  Availability and cost led us to design our own solution - which was relatively cheap - Materials for each box cost about $7.  Quite good, I would say.

It was just a simple outdoor PVC box mounted to an oiled wooden plate screwed to the box face.  PVC conduit was affixed to the back of the boxes so they could carry wire into into the building from the box.  The wooden plate was delicately mounted to the concrete forms with small nails.  Note:  make the total length a good 1/4" or more shorter than the thickness of your concrete walls - our forms were not well cleaned and the concrete scale on their inside surfaces sometimes interfered with the delicate boxes.  Also, be sure to carefully and thoroughly move the concrete around the boxes to ensure the concrete does not honeycomb around them.

Here are some photos of the process.

The conduit ends in a threaded coupler, sealed with tape for later removal.  Be sure to taper all sides of the wood plate well.  We tapered only the tops and bottoms and found removal after casting could have been a little better with all sides given a decent draft.
The depth and breadth of the depression left by the wood plate is large enough to accommodate the thick, hinged weather-proof PVC cover that will go on this.  Note, we may still apply another finish to the concrete - not likely stne veneer - possibly stucco, hopefully shot-blasting and staining the concrete.

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