Concrete questions for new shop

I am looking at putting up a 24x48 garage/shop. I think I have a metal building supplier selected and it looks like they are around 32-40 weeks out. They are going to provide anchor bolt drawings that I am going to be taking to a local foundation engineer.

I am curious what you all would recommend for a shop. I would like to do a car lift, and eventually have the capacity for 4-6000 lb machines, likely wouldn't go bigger than that. I currently have mostly hobby machines <2000 lbs but eventually would like to upgrade to a hass or something similar.

I was thinking of doing 6" of 4000psi concrete with rebar across the whole floor, but this is just a bit of a guess from what I have read on a few forums. What would you all recommend? Is 6" overkill to go across the whole floor? I appreciate any advise from those of you that have gone through this before.

What are you putting this slab over? That will factor into any sound advice. I would think 6" would be a minimum.

if you have undisturbed non reactive (sand) soil ,you can get away with thinner concrete.......IMHO,if forklifts are to be driven on the floor,then a 12" lift of roadbase,unclassified ,or crusher dust ,which is also unclassified,and not actually dust,under the concrete.....I have just had a 30x50 shed done,and I went for 4" concrete,as at my age ,10 years is probably all Ill be needing.......machines wont hurt ,provided no power hammers etc.......forklifts are the most concentrated (and Destructive) load you get on concrete.....a car hoist is nothing.

I'm in the process of building a 5600 square foot shop. Going with 5" 4500 psi and thicker where the lift will go with 42lb mesh. It will have a good base. I will be storing a RV on it someday and have no concerns.

To be honest I haven't really thought about the base. I was hoping to lean on the structural engineer for that if possible. For those of you with experience on proper base I am all ears though.

Probably not going to be driving forklifts on it, if I get anything that heavy I would be moving it on pipe or machinery movers most likely

I have read that a topping of concrete densifier is a good thing after it is all finished. makes it harder and reduces dust.
Bill D

Bill D said:

I have read that a topping of concrete densifier is a good thing after it is all finished. makes it harder and reduces dust.
Bill D

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I agree but the process to put it down scared off my concrete guy. No one I talked to around here has used it, and it is considerably more difficult to put down than a straight sealer. I ended up going with a product called Impede that is mixed with the concrete.

I'm no engineer. On my home shop (24X36) I did 7" 4500psi with 18"X24" heavily reinforced footings. The slab was reinforced with a rebar grid on 24" centers. It was a monolithic pour and is holding up perfectly after 10 years. I've driven a forklift on it but not regularly. The walls are solid-grouted and reinforced cinder block (heavy).

Just another data point. I'm an amateur but spent a little time researching and talking to people and here's what I rolled with.

I built a 25 x 40 addition.

- poured footers and stem walls
- backfilled
-spent a day with jumping jack compacting soil
- 6" crushed, washed limestone, 3/4" nominal, sometimes called #57s. I prefer this as there's no dust to settle out own the road and create little voids.
- lightly wet the stone and vibratory plate compact in 2 directions.
- apply 10 mil vapor barrier, lap, tape the seams
- #4 rebar @ 16" oc, set on 2" chairs, in a grid pattern, wire-tie every other junction
- pour 4ksi/6 sack mix via pump truck 6" thick to lines snapped on the walls driven by laser level
- paid finishers to get from screed to power trowel to the steel trowel stage.
- late that night I applied curing sealer in sock feet
- saw cut the next morning in 10-12' squares

I hired guys recommended by the local mon & pop redi-mix plant and they were excellent. I did all the prep and ordered the concrete, they just placed and finished and saw cut the next day.

Life has been good ever since, I've been running (rigging with forklift) heavy machinery 5-7k all over and its excellent and rock solid.

Vehicle lift, I would throw the wedge anchors immediately in the garbage and learn to blow + brush a drilled hole multiple times until its clean and no dust comes out after blowing it out with a pipette that reaches the bottom. Install same-sized (likely 3/4") B7 threaded rod and epoxy with something like Sika AnchorFix2. Allow to cure 24 hrs at 70F, adjust for longer cure when lower than that, then you can apply final torque.

One other bit of advice- if you do a tube steel metal building make damn sure the slab is the exact same size as the building and the steel laps slightly over the edge of the concrete. Often its quick and easy to pour an oversized slab and simply bolt the building to it. Absolutely no downside in the construction phase, but you will fight water leaks under the walls forevermore.

Not exactly concrete but you can see what insufficient pavement strength and a compromised base will get you...



I was transporting this 18x30 Monarch 612 and had about 4 feet to go....But you can see the effect of transporting a ~7k load with a ~7k capacity forklift...the front tires bear the sum of those loads just like the fulcrum on a playground see-saw.

Your engineer will be the boss, but 6 inch with 5 bar would be the rule in Montana with a outside foundation for the steel posts, 6 sack or 4000lbs cement. ...Phil

Base prep is very important. It will vary by location due to local soil conditions and materials available. When we did mine my excavation contractor cut out all the top soil over the entire footprint. Back filled the entire pad with limestone crusher run (stone dust) to level. Up front that was at least 6 inches, in the back that would be over 16 inches to make grade. This was packed in place and rained on until is was nice and solid. When it was time to pour a couple of months later we brought in a truckload of #57 limestone so the concrete crew had something do final adjustments on the grade. We did a frost footing with insulation board down 16 inches and poured up to it. So the edges of the slab are 12 inches with overall thickness no less than 6 inches.

I built a slightly bigger garage/shop fifteen years ago. Have been very happy with it. Key points for me-

hire a local soil engineer and listen to him- do not cheap out on concrete, rebar or prep (including piles if you’re on crappy clay soil like me)

put in pipes for radiant in floor heat- cheap to put in pre pour even if you don’t wind up using

absolutely make it strong enough to drive a loaded forklift- if you don’t you’ll be swearing and paying up every time you move a machine in or out

finally- high solids professional epoxy floor coating at least thirty days after concrete pour and before anything goes in.

Have fun with your project!

L7

Forgot overhead lifting- rolling gantries are a pain in a full shop- suggest one or two fixed overhead I beams framed into walls and ceiling.

Tell your concrete finisher you want a burned finish. They will power trowel until the surface will reflect the lettering on a one gallon jug. Surface will be so smooth and easy to sweep. If you get snow on it you may slip on your butt too.

teemfan93 said:

I am looking at putting up a 24x48 garage/shop. I think I have a metal building supplier selected and it looks like they are around 32-40 weeks out. They are going to provide anchor bolt drawings that I am going to be taking to a local foundation engineer.

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Your paying for an engineer, have them doo the interior slab as well.

teemfan93,
Always go with what the soils engineer says to a point... 6 inches would be fine with a suitable subgrade to park equipment on.. Grade beams for the lift would probably be OK to.. As fur the anchor bolts.. well is a spread footing and a column called for ? Spread footing would be below the frost line and the column with the anchor bolts at grade ? Lot's of variables.
As for machine placements and such. You want to ISOLATE the machine from the slab. This stops cracking and damage to the steel building itself. Ask about isolation pads. They are cheap and easy to install ( really just a modified concrete placement excersize than anything else ) Just some things to think of.
Another thing that I find handy is to install 'hard points' in the slab. Think of a I beam with a plate on top sunk into the slab protruding at grade level. You can weld a ring on the flat for moving,jacking what ever.
While your at it maybe a base for a swivel crane ? Try and think of your shop building itself as a tool rather than just a tool house.
Hope this gives you some food for thought
stay safe
Calvin B

After having many problems on my property with concrete cracking, my shop has a 8" thick slab with lots of rebar. No cracks yet after 3 years. Anything less than 6" here is guaranteed to crack badly. The footings also have rebar and are 12" thick.

Concrete is cheap, most of the cost is labor and delivery. Go as thick as you can!

Scruffy887 said:

. . . If you get snow on it you may slip on your butt too.

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Or oil, or coolant, or water...

I consider 4500 psi concrete the minimum for a shop floor. With a proper sub grade you don't need it for the floor strength, you need it for the durability of the top surface. Dropped pieces of steel won't chip the floor nearly as much as with weaker concrete.

A few friends and myself built my entire shop including concrete from scratch. When I was costing out the concrete it occurred to me how incredibly cheap the product itself is. Go thick because it's kinda stupid not to. The difference between a 4" and an 8" slab is maybe $1000 in your building.

I poured the slab inside my main door 30" thick tapering back over 6 feet down to 8" thick. It supports a pair of 3000 lb doors and constant forklift traffic. I just wanted my doors to stay a bit straighter over time. Not very expensive.