Concrete shop floor thickness

[Pat of TN]

Hey guys. I know this is probably a recurring question around the web, but I actually can't find a lot on HM.

I plan on making an extension to my current work... shed. It currently only has a wooden floor, with 2x4 joists on 24" centers and two layers of OSB sheet. Fine for my little 618 lathe, but I don't have the room nor faith in the floor to have any more.

I am looking at purchasing a mill no bigger than a PM-45/932-sized mill-drill, which apparently has a weight of 1100 pounds from the PM site, more likely a PM25 which is only 350 pounds.

I would also like to eventually have a larger lathe alongside the Atlas, something like a PM 10x30 or 11x27, which slightly exceeds 400 pounds.

The extension I would like to build will be 12 foot square, 12 x 12.

Pretty sure I need a concrete floor for machinery of that size along with the Atlas and other storage furniture and such. The question is thickness and specifics of the concrete.

Would a 4" thick slab work for this? I will not purchase larger machinery than mentioned, as for anything larger, I would need to build a better, standalone shop anyway.

Thanks fellers.

 

[Andre]

4" might be enough. My barn is has 4500 PSI (which is highly recommended) 6" slab where my 1800-2k# BP sits on. No cracks or problems in the year it's been sitting there. Keep in mind though, even with my 1/2HP mill (M head BP) I can feel the floor vibrate when taking a cut. And my dad says he can feel it 60 feet back in the barn.

My advise, get a 6" slab. You won't regret it, but this might need a building code, as it could be interpreted as a foundation. But then again, my tree fort is illegal because it's higher than 32" off the ground. Go figure.

 

[ronboley]

A minimal slab is 3-1/2" of concrete over compacted native soil...2000 psi concrete is just about minimum and don't expect the slab to last forever...but better than 2x4's...

A good (proper?) concrete slab on grade consists of 4" thick, 2500 to 3000 psi concrete (a 6-sack mix will usually do it) reinforced with #4 rebar at 18" each way centered in the slab thickness over 4" to 5" of compacted base rock (not uniform size drain rock or pea gravel but "road base" that contains varying size of aggregates that can be compacted). The ground below the base rock should be native or compacted soil that does not contain organic materials...don't put you slab on peat moss...

A "proper" slab like this should support just about anything a home shop on steroids would contain. For really heavy stuff...10,000 lbs or so just go to 5" or 6" of concrete...or if you are in earthquake country and need to anchor heavy or tall equipment down to the slab go thicker....

The main concern is the soil the slab sits on...bad soil, bad slab...

Or so being a structural engineer for the last 30 years has taught me...

Good luck!

 

[Grumpy Gator]

Pat, If you know the footprint of your machines you can always dig a deeper spot in your 12' X 12' slab and put in more steel rebar under where they will go.As long as you have a footer with rebar on all four sides and steel wire in between . You should be fine. Just go for higher mix like 3500 or 4000 . 2500 is standard for slabs.
*******************Just saying*********************Gator********************

 

[Pat of TN]

Hey guys, thanks for the help.

Andre, I see. Although the machines I'm looking at are a lot lighter than your B-Port, that's still surprising to me. I was hoping to get away with a 4" slab, but just off that, I'm leaning much more towards 6". Thanks buddy.

Ronboley, thanks as well. Structural engineer huh, well if that ain't perfect! Hah. A lot of good info in your post. Like I said, I'm looking at maybe 1500-2000 pounds total for all the major machinery, maximum.

The earth beneath where I plan on building this structure is solid. We have owned the land for 14 years, and the area has never been worked or dug. Before that and even up until about six years ago, that part of the land was basically woods, so it hasn't been worked or anything for quite some time.

 

[JimDawson]

My 3500 LB mill is sitting on a 3 1/2 inch floor. I would like it 6 inch thick, but it is what it is. I have not noticed any problems in that area, but running my 9500 LB, hard rubber tired, fork lift over the rest of the floor has taken it's toll. The floor has a few cracks in it. When drilling in the floor, I have never run into any rebar, so I'm not sure that there is any in the floor. The shop existed when I bought the place so I don't know how it was built.

 

[12bolts]

If you know the footprint of your machines you can always dig a deeper spot in your 12' X 12' slab and put in more steel rebar under where they will go.As long as you have a footer with rebar on all four sides and steel wire in between.

I did exactly this for my slab. My shed has a dirt floor, and the couple of areas that I have already concreted for work areas and machinery I just dig a deeper foundation and put a bit more steel in for more substance. I also just leave some starter bars protruding from the edges of the slab to tie into the new slab as I pour it down the track.

Cheers Phil

 

[Andre]

Hey guys, thanks for the help.

Andre, I see. Although the machines I'm looking at are a lot lighter than your B-Port, that's still surprising to me. I was hoping to get away with a 4" slab, but just off that, I'm leaning much more towards 6". Thanks buddy.

NP, the barn is built to store a backhoe, a JD410. Weights around 8 tons, and it sits on a concrete section 12" thick. No cracks and it's been there 15 years. Then off the 12" section we branched out on either side and reduced the thickness to 6" to conserve concrete. And the milling machine sits on one of the wings.

I've been told (I wasn't born when the barn was built) that we threw in bed frames and all kinds of scrap metal we could find to help strengthen the rebar mesh. It's working good so far.

 

[dave2176]

My pickup weighs 4,400 pounds. I bet the front wheels take about 70% of that so about 1,500 pounds per tire. Not seeing any issues on the 4" slab I poured 20+ years ago. I wouldn't think twice about loading it with several more 1,000+ pound machines or even a full size Bridgeport thrown in.

Dave

 

[ody]

I spent an obscene amount of time figuring out the best thickness for the concrete of my slab. In the end the most consistent bit of advice I was seeing was to make sure the ground you are pouring on is solid (all top soil removed) and has a god few inches of hardcore well packed down with a whacker plate. As with most things in life, preparation is key. I went overboard and poured 9inches with A142 reinforcing mesh on well packed (I spent hours with a whacker plate) 3inches of hardcore/MOT .. but I don't ever plan on moving so want it to last.