I am planning to build a new shop, and would like have the major dust-collection duct runs in/under the floor with risers to key tool locations. My shop will be slab-on-grade construction with radiant heat in the slab.
My Plan: I would lay out the main duct lines (with risers) in trenches under the slab before pouring, probably with a clean-out that runs to daylight. The material would need to be moisture-resistant, so probably Sch 40 or 80 PVC, sized appropriately for my collector. Ducting would transition to flex hose or steel for longer runs inside the shop.
Questions: Will this work? Has anyone done it? Is static buildup an issue? Any issues in transitioning from PVC to steel ducting inside the shop?
Jim Y
Replies
I did the same thing. Under the basement concrete floor I had 4" of gravel. Laid down 4" PVC with 45* bends to a main central trunk line and long sweep 90*'s up. Now I wish I would have used the larger PVC pipes now available at the big boxes for the main trunk line to lower friction losses but am having no problems.
I did use copper wire but I do not think I really needed it. It is in the ground!!
I ran 4" PVC pipe straight up out of the floor to connect my tools to. The metal shut offs at Rockler stick right into them if you wrap a few wraps of electrical tape around them. Pretty sure they are schedule 40.
Chris
This question has got me thinking (a dangerous thing). I really don't know the answer to this but do you really need ducting under the slab? Can the concrete be your "ducting"? If you poured concrete over one of those inflatable bladders (the kind I've seen for pouring new chimney linings) then deflated and removed it after the concrete set, wouldn't the DC system work just as well? Wall smoothness of the resulting tube might be an issue, but just out of curiosity would something like this be feasible?
If you build it he will come.
I think you would have a drag problem.
Also, concrete tends to be damp. I could very easily imagine some nontrivial caking and accumulation issues. I wonder how bad that might smell five years later...
You might also have some issues in securely and neatly making your connections, both for your drops and your cleanouts.My goal is for my work to outlast me. Expect my joinery to get simpler as time goes by.
The top of the concrete 'tube' would most likely crack, acting like a pre-weakened crack-control line.
But how thick is your slab?? Even a 6 inch duct would need at least a 10 thick slab, which you'd may not want to pay for under all the shop, and if you are only doing that in places framing the pour would cost more than the pipe.
Edward
Gotcha. Knew there had to be something (probably a lot of somethings) wrong with the idea. It was just one of those things that made me go "Hmmmm?".If you build it he will come.
I did what Jamie described, a 12" x 12" trench going alongside the walls and one right down the middle, with the duct in it, compressed air and the power to run the machines.
I have a wooden floor over the slab so access is not a problem.C.
Don't do it Jim.
I had considered it for my shop. But there are several drawbacks to embedding it into concrete. First, it will be permanent. Are you sure you know where every piece of machinery will go, and your future tooling needs? Second, you will be forced to make really small radius bends to each tool, severely reducing performance of your blower. Finally, if you ever need to clear a duct, it'd be much harder.
I think it's just me, but efficiency and performance are for my shop, aesthetics reserved for my work. My $.02.
Thanks, all --
I'm still pondering. I appreciate all the ideas/opinions.
Jim
I know a guy who thought about doing that, but he thought he might want to get into the ducts -- maybe to upgrade them, or maybe to run wiring, or maybe to repair them, or something. His solution was to pour the slab with a couple trenches running across the floor. The trenches are maybe a foot by a foot in cross section. He had made steel plates to cover the the tops of the trenches. (There's a little step on the sides of the trenches, so that the steel fits flush with the floor.) He can pick up the plates to get into the trenches. He can place major machines anyplace along any trench. He runs his dust collection and his power through the trenches. The last time I talked to him he was just about to add compressed air.
I have a converted 2 car garage as a shop and have the conventional 'pipes-along-the-ceiling' arrangement. I've often dreamed of having the opportunity to get the pipes beneath the floor if for no other reason to increase the efficiency of the system by eliminating the long vertical run to the trunk.
I, too, have thought about laying the system in a slab (Norm did this in a dream shop set-up on TOH some years back) but don't like the "Permanent" aspect. Who knows what tool will be my next "glotta-have" purchase?
As a compromise, I think having a crawl space and using plated trusses to support the floor solves most all of the problems. It's accessible, changeable, and inexpensive to add to. It also facilitates the running of electrical and compressed air.
You may run into an issue with your radiant floor - were you thinking electric or water? - but there are products that allow either on a wood subfloor. The trusses are very strong and not terribly expensive, they allow the ducting to be threaded through thereby saving "ceiling" height in the crawlspace, and you can close up the on-center spacing to carry tremendous live loads so, even with all the machinery (unless your into very industrial level machines) your floor will not be springy.
Good luck and post some pictures when you're done!
Regard it as just as desirable to build a chicken house as to build a cathedral.
Frank Lloyd Wright
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