JimReed

Cutting Concrete Floor for In-Floor Dust Collection-- Nuts?

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I am in the planning stages to convert a large insulated garage into a dedicated workshop. The garage has a poured concrete floor in good condition. My plan is to put down 1.5" board insulation and AdvanTech plywood flooring for a warmer, softer floor.

But before doing so, I had a brainstorm. Or maybe it's a nightmare.

I would love to run a 6" dust collection pipe UNDER THE FLOOR to my tablesaw which will sit in the very middle of the shop. I hate hanging ducts and my thought is that the tablesaw is the one tool that I think will always remain stationary so I can very precisely locate the in-floor duct location.

To do this would require cutting the perfectly good concrete floor with a masonry saw and then excavating a channel approx 10" wide (if I am running under the floor, I thought I would also install electric and air lines while I am at it).

Is this nuts or a good idea?

Will I be risking making the concrete slab unstable or inviting moisture problems? My thought was excavate the trench, put a layer of landscape fabric, then sand, then the piping , then more sand, then a vapor barrier, then the board insulation, then the plywood flooring. I would screw the plywood over the trench so the piping was accessible.

So, what do you think?

Thanks, Jim

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Is resale an issue? People might be bothered by a 10" trench in their garage.

This is not my area of expertise at all, but I'd consider excavating the trench and then starting with concrete on the bottom. That way you have a continuous concrete slab floor, just shaped funny. Remember to check for electrical, gas, etc before excavating.

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I think you are definately leaning more toward nightmare...it is just so hard to repair concrete as versed to drywall. I work in an architecture office, so I have a bit of insight.

The thought though of concealing the piping is not bad though...Is your shop wood frame construction with drywall? Open studs?

you might consider running your piping through your attic space instead...its is a lot easier to repair gyp board if you need to relocate a piece of equipment. If you dig a trench to your saw, Murphy's law will almost certainly kick in and force you to move something, then you are REALLY in a tight spot. and what happens if you want to add more tools to the collection line?

If you really want to hide it, you could even run the piping in the walls themselves, up into the attic, and over the ceiling to your collector. If all of your shop walls are exterior, and you don't want to lose insulation, maybe you could even build a false wall (chase wall) for your air lines and collection piping to live in. This way, if your shop really is large, you might only lose 6" of wall depth where the case is...and add more opportunities for recessed storage, and the like.

Maybe you can post some pictures and a sketch of your space with dimensions and I could help with options...

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Jim, I did something very similar to what you are suggesting but in my case it was to put drain tile in a basement.

If you can avoid cutting the concrete that is the way I would go. If you like swinging a sledge hammer for hours on end then cut away.

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Thanks for all the great advice. To respond to some of the questions. No, I am not worried about resale as I intend to die at this property-- hopefully not too soon! :-)

The ceiling is 12' high so the suggestion to raise the floor is an interesting idea that hadn't occurred to me. Duh! That would provide more room for insulation, wiring throughout the shop, flexibility with running other DC ducting, etc. Would I have to worry about the floor being bouncy with just 3/4" T&G plywood on 16" centers?

The only downside to that approach that occurs to me is that there is a side door and a garage door to the garage so I would have to come up with some method to deal with the raised floor at those two entrances. Hmmm, food for thought!

Keep the ideas coming guys!

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You just answwered on of my questions - how long you intend to be there.

I like Barry's idea for a raised floor. You would have to plan the joists' locations to allow running of DC pipe, but the big benefit here would be that you could run multiple DC pipes, to include not just your TS but also jointer, planer, assembly/sanding table, CMS, etc etc. Running power lines would also be a huge benefit. This would be more easily reconfigured than concrete cutting, if it ever comes to the point that you want to move stuff around. I would think that such a floor would be fairly stable, since it could be almost continuously supported on the existing concrete (with shims/spacers/etc where needed). You could always double up on the flooring if needed.

If you end up still considering cutting into the floor, you should investigate doing more than just the one run. As long as you're cutting it up, go all out. Maybe price out for a concrete cutting company to do it (at least just the cutting), and also maybe get a 'ballpark' estimate on what it would take to either patch the trenches, or just cut up and replace the entire floor. Just for future reference.

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I think it's a good plan but instead of swinging a sledge for hours, while your renting a concrete saw anyway go ahead and rent a 60 lb electric jack hammer easy peasy. when your back filling your trench in stead of sand use pea gravel it is 100% compacted material I wouldN't think you would need the landscape fabric, but it certantly wouldn't hurt anything. When you doing the pour back on the trench if your not the best at finishing concrete it's ok just make sure you clean the slurry off the edges of the existing concrete, and make sure your concrete is a bit low as apposed to too high which you would have to grind down to grade, if the edges are clean and free of slurry and the grade is perfect or sightly low you can use a feather patching product that will make the patch smooth and level to the surrounding concrete. good luck Dave

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If its a newer shop and uses the rebar as the ground spike you need to make sure there is no spike in the oposite corner. If you go to sell a home inspector will not pass the electrical if the ground does not reach the other corner after you cut the rebar.

Don

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Raise the floor!!!

Everything can be hidden, you can make changes of needed, the insulation is a bonus, and it's comfortable.

My previous life was in warehousing. We had a raised mezzanine with a wooden floor and the employees loved it. It was an MDF material with a fancy coating, the stuff would survive a bomb. The little, tiny bit of bounce is nice on the feet. It deadens sound too.

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Its an interesting plan, and its certainly do-able, although it likely won't be a lot of fun (trust me, I've demolished my fair share of concrete). I don't think the rebar ground will be an issue, since typically the ground is only required to be connected to a continuous 20' piece of bar in the slab perimeter. If you decide to go this way, I would suggest installing the vapor barrier in the trench first, then lay in some gravel and compact it. (Nothing fancy, just hand tamping will be fine)

It would be easy enough to fill in and pour concrete back if, at some point down the line you decide you want a solid floor back.

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That's right! A bit of a bounce is comfy. You might need 12" centered joists if you plan on stationary planers or 12" jointers. You could also set heavier tools on a sheet of 3/4" ply cut to the footprint of the tool. But remember, the joists can sit right on the floor, so they don't span anything.

If you shop carefully, you might be able to get a load of the lowest grade oak flooring at a reasonable price. No need to get all crazy finishing it, a basic sanding and a single coat of varniish is fine for a shop floor.

Too bad it's so hard to find removed computer room floors. They were strong, as mainframe and mini-computer stuff was very heavy, and it's so easy to work underneath.

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Raised floor sounds better to me with many benefits including, flexibility and much nicer on legs and back.

I would talk to someone with very specific knowledge before settling on the plan.

16" centers does not sound appropriate for a shop floor with some heavy equipment.

This is where paying for some expertise can be good investment. They could also help steer you to good choice of flooring and if you'd be best served by a sandwich of materials rather than just 3/4 T&G ply. Keep an open mind on materials.

Have fun with your project.

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On access flooing systems I have seen, sometimes it is nice to work with modular sized panels (12"x12" to 16"x16") having modular panels as opposed to 4x8 sheets of T&G would make it much more reconfigurable, being able to only take out smaller panels to run new electrical or DC piping.

Access flooring is also great for forcing air through your shop...a few of the modular panels fitted with air vents at strategic locations can be great for creating a shop HVAC system. You just have to have a heater or A/C to blow into the underfloor area, then with vents in the floor wherever you need them, you can really pinpoint the areas of the shop to control the climate in, changing locations at will...and no ducting needed since the whole under floor area is the duct.

Doors at slab level are not generally an issue, they just usually leave out an area in front of the door, with steps or a ramp as needed up to the raised floor level.

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Access flooring is also great for forcing air through your shop...a few of the modular panels fitted with air vents at strategic locations can be great for creating a shop HVAC system. You just have to have a heater or A/C to blow into the underfloor area, then with vents in the floor wherever you need them, you can really pinpoint the areas of the shop to control the climate in, changing locations at will...and no ducting needed since the whole under floor area is the duct.

We have a system like this at work, in our computer room. The problem is, we run a lot of other stuff besides HVAC under the floor, so the HVAC ended up getting trapped in one small section of the room. If you're going to run, say, 6" DC duct under the floor, then you'll want the floor about 10" high so the HVAC can get past the duct. For a small garage, I wouldn't use under-floor HVAC.

At work we have 2' square panels sitting on a metal framework. We have a few suction cup "floor suckers" that we use to lift the panels. I might consider wooden skins on both sides of rigid insulation, glued into a sandwich. It would be strong, pretty light, and would add insulation.

I'd also consider a small hatch in the middle of the floor, hooked into the DC, so you can just sweep everything into it.

I wish I could put in a raised floor, but the ceiling is too low in my basement shop as it is.

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IF you ask me, it all seems like a lot of work to hide a bit of ductwork. Putting in a DC system can get expensive as it is, now add this to the mix and you are probably going to at least double if not triple the cost. This is just my opinion.

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If you cut the slab you could end up with frost heave problems I know it gets pretty cold there

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Sac +1...hang the stuff. A shop is an evolution...an eclectic, cacoffiny of organized chaos. English....thru the years, you will change things - the tool you thought you'd use 5 times a week gets used 5 times a year - i.e. wood lathe (sorry turners) and you sell it. The tool you thought you'd never have, well now you have TWO of them. DC must adapt and evolve with the tools. Choppin' cement everytime is ...well, in my mind is absolutely foolish because you'll get your shop just right....for now.... and in two years, your tools have changed and your shop layout is different and you'll look at all the work in the floor and all of the flex hoses spread all over the floor because you didn't want to constantly re-engineer the cement or re-work the wooden floor. Then you'll say bad words and you'll think back to this thread ....IMO,don't over-engineer the thing. Hang the pipe, buy really good shoes, change the DC layout easily as often as you need to....and get back to building something asap. Your great grand kids will thank you. ;) Let us know what you decide.

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Tim, you bring up some good points. SHops change. I have all my ductwork done now, and it works great, but there are some things that I am going to change here when I get some time. You may decide one day that you dont like the layout of the shop and want to redo the whole thing. I think about it all the time, though I doubt I will ever change that much, but you never know.

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