Concrete slab for work shop

I am going to be building a new workshop in the future. It will be a place that will house my F150, a few garden tractors and possibly an A or B John Deere tractor along with all my tools. It will be approximately 30'x30'. My question is, will 4 inches be thick enough for this building?

4000 pound with 3/8th rebar 12 to 16 inches on center and I'd throw in some fiber mesh cheap cost..fibers will wear smooth and I think you'll be fine...thicken edges and cut control joints.

Here is how I would look at it. To go to six inches of concrete will cost you about $500 on a 30x30 slab. So how many years are you going to be using this shop/shed????? Lets assume just ten years. You talking about "saving" $50 a year.

The math 30ft x 30 ft. x .33 ft.(4inches)= 11 cubic yards of concrete. 30 ft. x 30 ft. x .5 ft. (six inches) = 16 yards of concrete. Concrete is right around $100 a cubic yard around here.

Here is my personal experience. I know of barn floors and corn crib floors that are only four inches thick. Every single one of them I know of are cracked all to heck. Now I know that the concrete used would have been a lower grade than say 5000 lbs. mix but four inches is not going to carry much load without cracking.

I would go six inches thick, 1/2 rebar every foot, 5000 lbs. mix and fiberglass fiber in the mix too. This slab would be maybe $750-1000 more than a 3000 lbs. mix four inch thick slab. I know the slab poured like I state will not crack easily. I would not want to bet the four inch one would not.

I echo JDSeller's advice. When I built last it was roughly your dimensions and I added a 12' x 24' pad outside so I can roll projects in and out when the weather is nice or I don't want to do a job inside the shop. So, I suggest you consider a nice large pad too.

The keys to keeping your concrete floor from cracking is to have a very good solid compacted base to pour the concrete on in the first place if the base isn't solid
it'll crack no matter how thick you pour the concrete and #2 is to have it poured right with the correct slump.Concrete finishers always want it too wet because then its easier to
put down.In 25 years working in the concrete industry I can say for sure 95% of non inspected concrete is put down out of spec in some way or the other.You can hire an independent
inspector to oversee the pour for not much $$$ and they can save you a lot of money and a lot of headaches.They'll check the compaction of the slab and check the concrete
to make sure its in spec and the concrete supplier and the finisher will do you a whole lot better job if they know the concrete will be inspected and test cylinders made.
There is a whole lot to know about concrete mixes,additives and such that anyone not in the industry has no idea about.Think we had about 300 different mixes in the computer when I retired.

Go six inches thick in the middle and under the entrance. You can thin it out to four inches along the side walls, since that space will likely not be driven on. Compact the base well, use rebar or mesh and you should be good.

My concrete guy went full 6 inches on my 30x40. He used no forms. Outside walls and a board at doors. Wire and a continuous pour. Next day he cut joints. Hasn't cracked. You run a risk of cracking and settling if you don't do a continuous pour and no forms down the middle. Established level with 16p nails in each post and used rotating laser to establish grade at a few points in middle during the pour.

My concrete guy makes his living finishing concrete. He finished my job my noon on a Saturday. He had 2 other guys to help. Motorized trolling.

I put 2" Styrofoam under my workshop floor. No cracks in floor and shop is easier to heat.

Don't forget the insulation and tubing for the radiant heat. Pretty much everyone who doesn't have it wishes that they did.

I second or third the outside slab too. Shop is full so I never see the slab in there. ALL the work gets done outside on the slab.Sure am glad we poured it!!

I had your BCI guys build my shop back in 2005. Excellent job. I figured 5" slab, 5 bag mix, #3 rebar on 18" centers, well packed select fill (combination sand and clay.......used around here for skyscrapers) pad.

You can say what you want, but unless the ground under the building remains uniform, you'll wind up with nothing to support your well thought out, prepared, building pad and slab. Around here the soil is Houston Black Clay, referred to, by a local Registered Civil Engineer as "unfit for roadways and dwellings".

The last place I worked was built with steel H piers to bedrock....like 30' deep to get to it, with roughly a 10" slab floor. That was '84. In the early 90's the floor was cut open to lay some utilities to a new program that was commencing. Kid you not, I could have easily crawled between the slab and what was the "prepared pad" upon which the floor concrete was poured when the building was built. Just a big mess. Course the foundation was self supporting such that working in the building, no one had a clue what had happened beneath the floor......no indications.

Back to my shop: While the soil moisture was constant, I had zero cracking for the first 10 years on my floating slab (shop was "pole barn theme") but then the droughts came and the clay shrank and shifted (separating my house by 4" on one wing; buckled Texas State highways), and that was with nothing more than the weight of a P/U on it. The corners sank about 5" no more than 25' from the center of the building. The rebar did it's job and kept the chunks from separating. Then, the last 2 years, when we got plenty of rain, the soil puffed back up and the building righted itself.

So unless you are on stable soil, all bets are off unless you spend a ton of money on supporting reinforced concrete beams suitable enough to contain the slab with half the supporting soil missing.

Yes if you can live with minor cracks. My guy said they all crack somewhere eventually. advised steel screen and fiber additive. I am 12 years of happy with four inches.[insert joke here} Made it thicker where the lift bolted down and around the walls. If I had to do it again I would put U bolts around the floor to pull frames and such, and to chain things up to keep them from walking off.

6 bag mix with water reducer 5 inches thick. Wire mesh or rebar 1 and 3/4 inches up from the bottom. 4 inches of gravel on dry ground that you have driven something heavier than your pickup truck on the area to see how solid the ground is (pump or not pump).
I've poured a couple million square feet of warehouse slabs that have racks 20 feet high or so and have heavy forklifts running on the the floor constantly from blueprints that an engineer spec'ed sometimes 4 inches of 4,000 lb mix on dirt or gravel, all the time with wire mesh, once with rebar.
If your ground is dry and stays dry (and doesn't pump) after the building is up the 4,000 lb mix with water reducer 5 inches thick with wire mesh (placed up 1 3rd from the bottom) you can sleep at night.
The joints need to be cut the same day the slab is poured.

You may also want to use a vapor barrier and fiberglass rebar as it will not rust! 8)

Thanks for all the info. We have a pretty dry climate here so I am thinking I can get by with a well prepared base and fiber reinforced concrete as well as plenty rebar. I am thinking 4" will do the job.

Rebar is high tensile strength and rust is just on the surface. Besides in a small way it helps hold the crete.