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I would like to build several lamp posts for my backyard. To cut costs I am considering dadoing a channel down the middle of a 4x4 for the wiring, and covering up the dado with "ornamental" wood tacked to all four sides. Does anyone have any experience creating lamp posts such as this or see a down side that I am missing? I cannot fine any plans or ideas on the web for such a project.

Any guidance or help would be appreciated!

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    Most pressure treated wood is only pressure treated to a particular depth, so you may need to effectively re-treat the area where you cut the dado. If you're going through all that work, might be just as easy/effective to manufacture the whole post from pieces, or build it all around something like metal conduit. – BrownRedHawk Jun 21 '16 at 19:13
  • @BrownRedHawk is talking about using an "end grain preservative"; basically Ensele is the main brand. – Ben Welborn Jun 21 '16 at 20:37
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    Treated lumber will likely twist and check quite a bit. It's going to be hard to trim it nicely due to that. – DA01 Jun 22 '16 at 5:07
  • What type of wire are you using? For outdoor/wet location, you'll want either UF or THWN in PVC conduit. UFB is flat and better for running in a notch. You'll also want to make sure that there's enough room for ventilation around the wire- conduit would guarantee that (when using the right size for the wire). – Nick Apr 17 '18 at 13:27
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It may be easier to make a post out of two 2x4's where you can use a router to cut in a V groove down the center of the face of each piece. The two V grooves facing each other would make a channel down the middle of the post.

You may want to consider the use of a PVC conduit in the channel to eliminate the possibility of rusting.

An easier procedure than cutting a the V groove would be to build your lamp posts out of four 2x4s like shown below (end view). This would result in a nice sturdy post that was 5" square with a 2" square hole down the center for the conduit. And if this was constructed from pressure treated lumber before it fully dried it will likely hold its shape as it dried out.

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  • I would need to use pressure treated wood or cedar to prohibit rot and weathering. The issue with 2x4 pressure treated as everyone knows (or should) is the incredible warping that happens to the lumber as it dries. Not sure 2x4s would work for the best finished product. However I do like the idea of creating a center channel and running conduit through it. – Ode Jun 22 '16 at 16:53
  • @OdeeOdum - Yeah, some pressure treated 2x4s do warp and twist when they dry out.....but it has been my experience that if they are fastened onto some type of assembly that holds them into a fixed position there is a lot less free warp and twist that occurs. I've used them as the horizontal members on yard fences and not had much problem with the ones I installed when they were still wet/damp. The left over ones in a pile in the side of the garage are twisted. – Michael Karas Jun 23 '16 at 5:25
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Your plan should work fine. I didn't expect that you'd channel the wood to the center of the post, so I don't have concerns about dramatically reducing the effectiveness of the pressure treatment.

I'd channel 3/4" x 3/4" and be sure to avoid damaging the wires when you trim the post. Optionally, create a wider channel in the face and lay in a strip of 1/8" aluminum stock as a protective cap under the trim.

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I'm assuming the meaning of "down the middle" was to create a channel in the cross-sectional center of the 4x4, which would be a "protected" location. If you're intending to channel near one surface of the 4x4, consider that NM wire needs protection if closer than 1.25" to the surface in order to reduce the risk of somebody adding a nail or screw to your circuit.

Also remember that this is considered a "wet" location, and you should use a cable rated for wet environment, NMW or the like.

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I am currently doing that exact project. My plan is to convert my existing fixtures to Low Voltage (12 volt via 300 Watt transformer) and using standard ES26 low voltage LED replacement bulbs. I have experimented ripping a 4 x 4 in half and then a 1/4" wide by 1/8' deep dado down the center of just one of the halves to create a channel to run the low voltage cable through. I will piece the two halves back together using biscuit joints and Gorilla glue, clamp pieces together until dry then through bolt using countersunk #10 screws.

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The approach posted by Michael Karas with several 2x4 arranged to create a channel down the middle makes sense in terms of the structural post for your project. Fastening several smaller pieces of pressure treated lumber together should alleviate the extreme warp/twist you can get with using a single larger post, and by not machining the channel, you're preserving the integrity of the pressure treatment process. I did want to post a separate answer though to address some additional points:

First, this should go without saying, but if the post is in contact with the ground, it should be constructed from ground-contact rated pressure treated lumber, not lumber meant for above-ground use.

Second, based on this quote from your question:

and covering up the dado with "ornamental" wood tacked to all four sides

The typical approach to trim a rough post would be to build a sleeve-like box with your trim wood, and install it semi-floating - slide it down over the post and tack it on to the post along one side only. The sleeve should be built to fit loose on the post, not to the exact dimensions of the post. This prevents warp/twist/checking/shrinkage in the post from causing your trim joints to pop or misalign down the road - the post can move (somewhat) freely inside the trim "box" without disturbing it. Your light fixture or other trim on the top of your lamp post would be attached to the trim sleeve, not directly to the post.

That approach is superior to the literal explanation you gave in your question, of tacking trim to each side of the post, which pretty much guarantees that you'll end up with an ugly trim job down the road as the post moves/shrinks differently than the trim wood.

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