concrete thickness

[OIIIIIIIO]

Hi,

I searched but didn't quite find what I was looking for...

How thick should I have the garage floor poured? Local dude said 4" is enough...I was thinking of the 4-6" range but definately closer to 6 than 4.

It's 1140 sq ft.

It will need to support a 9900 lb one ton Ford pickup.

I have thoughts/dreams of putting a lift in at some point but not really sure that would ever happen...

Looks like over all I will be using a grade beam on pier set up to allow me to attach a breezeway to both the garage and house...

Thanks for any input!
Patrick

 

[Dan in Pasadena]

You could use 4" with rebar and thicken up in the areas where you will have the lift placed. Personally, I'd just pour it 6" with rebar throughout and never have to think of it again.

 

[jhelrey]

I agree... I would go thicker as well.

 

[346ci]

I'm going to pour mine 6"@5000psi w/ rebar. I plan to have a 10K 2 post lift installed later on.

 

[A_Pmech]

Don't worry about the weight of the pickup. Run-of-the-mill 4" tract home slabs will support that all day long.

Where you should worry is regarding the foundation for your lift. A study of the manufacturer's specifications is a good start.

 

[Daniel Dudley]

The cost of 6'' is 1/3 more than four. Mine is a floating slab, and it got massively over poured to the tune of more than twice the cost. Rebar and mesh on dobies. At the time it seemed like the thing to do, but six inches is really a lot, and really all almost anyone would need. It has been said on other threads, but what you need is a well compacted base. That and six inches of concrete is well overkill. Vapor barrier, do not forget.

 

[Stuart in MN]

Are you planning on a two post or four post lift? The four post style won't require anything special for the floor, but a two post will (at least in the area where it's bolted down.)

 

[folgers]

If you know you're going to put in a two post lift find out what you need for it's base and pour that before the floor. 4 inches of 4,000 lbs. concrete with #4 rebar or wire mesh panels is sufficient for weight you are planning. Put a good compacted sand base under it and a plastic vapor barrier (the plastic under the concrete keeps the water in the concrete to help it cure). A lot of concrete fails not from the weight on top but from frost heaving it up. After you have poured, spay it with a cure & seal or keep it covered with plastic for 30 days to cure it. I would have it sawed every 10 or 12 foot.

If you're not sure about the lift you can saw the concrete out and add a base for it after the fact.

If your house is on a foundation and your garage a floating slab be careful how you join them. You'll need to allow the garage to move.

I've been a mason for 11 years in Illinois.

 

[twostory]

My detached garage is 1,100 sqft. I have a compacted base of 6 inch gravel, vapor barrier, then 5 inches of 4,000psi concrete above that. #4 rebar 2 ft on center. Four years later, it still looks perfect.

I added on this year, 660 sq ft. I have 6 inches of compacted gravel, vapor barrier, 6 inches of concrete, 4000 psi, #4 rebar, 16 inch on center. Slab has not moved/cracked/settled.

The cost of 6 inch versus 5 inches (thickness) is really fairly minor. Since I did all the prep work, the only extra cost is rebar, but I would rather spend a few hundred extra, than regret not doing the rebar. 1 yard of concrete = 1 inch thick (324 sqft)

But I think a good compacted base is critical. Gravel is cheap, make it 6 inches thick (compacted with a vibrating plate) and you should never get frost heaving.

 

[TheGreek]

Hey everyone. Just got on here recently. Glad to find this forum.
I just bought a house and I am definitely going to be putting a 2 post lift in it. I was reading manufactures recommendations and a few I have come across mention 4 inches of 3000psi concrete. Nothing about rebar or wire mesh. Is it standard to use mesh or rebar if its 3000 psi? Its a new house built within the past 3 years so I would hate to cut up the floor if I dont have to. Of course in the sake of safety I would do it. I was going to contact the builder, but in the end what exactly am I looking for? Is there any way to determine if an existing floor would be stable?

 

[38Chevy454]

The cost of 6'' is 1/3 more than four.

This is not really true. Yes you have more concrete material cost, but the labor and forming costs are essentially the same for 4 or 6 inch.

On my garage I have 5 inches of 4000 psi, with mesh in the slab and rebar in the footers. The cost increase for 4000 psi vs 3500 psi is only a few dollars per yard, and going 5 inches vs 4 inches thick was only about 4 extra yards. So my upgrade to 5 inch 4000 psi on 1248 sq ft was about $500.

 

[Daniel Dudley]

This is not really true. Yes you have more concrete material cost, but the labor and forming costs are essentially the same for 4 or 6 inch.

On my garage I have 5 inches of 4000 psi, with mesh in the slab and rebar in the footers. The cost increase for 4000 psi vs 3500 psi is only a few dollars per yard, and going 5 inches vs 4 inches thick was only about 4 extra yards. So my upgrade to 5 inch 4000 psi on 1248 sq ft was about $500.

Yeah, it's not much, and I would not even hesitate to go to 6'' for myself. But 500.00 is 500.00. My slab is 14 - 16'' around the edges, and averages 9 in the center. This is because the excavator made a grade error. I have a lot of steel and mesh in there, and I don't regret it, but the cost of the extra concrete was almost double. I paid a kid 80 bucks to help me screed it, and did the pour myself.

Personally, I won't pour 4'' for myself, unless it is a sidewalk, but that's just me.

You may never be able to tell the difference between 4 and 6'', but I have jack hammered plenty of the stuff, and let me tell you that there is a big difference when you break it apart. There is a bigger difference if there is mesh and rebar, a HUGE difference. I can also tell you that 3000 psi concrete properly cured is way stronger than 5000 psi concrete improperly cured, so keep it wet and let it reach full strength. PSI is what holds the anchors in BTW.

Nobody ever regrets pouring too much concrete, or using too much rebar. There is no such thing as too much really, but there is such a thing as not enough.

 

[Wanna Ride]

Four inch is more than sufficient.

Most of the guys on here will **** in their gut, put their hands on their hips and tell you that you just HAVE to have 6" of concrete or you're not a real man, and your garage is going to cave in when you walk on it. When the truth of the matter is, most of them don't know the correct way to twist a bull float, because all they did while their slab was poured, was bring out lemonade to the concrete finishers, and get in their way.

Hats off to the guys who really built their garage, home, street-rod, or whatever else themselves, instead of just getting papercuts from writing checks to contractors. But I guess they have their place too, because if it wasn't for them, then the contractors wouldn't have as much residential work.

A four inch slab will be more than sufficient for the garage, if properly compacted, and reinforced. My 40x30 is on a four inch slab and I've built everything from streetrods, to motorcycles to mud-boggers, and 10,000 pound pulling-trucks w/44's on it. Don't listen to the naysayers, half of them live in their mother's basement anyway.

Good luck, and let us know it comes out!

 

[Shocker]

I think most people said that 4" is fine if done correctly. But several folks are pushing for the 6" if you are installing a 2 post lift.

Personally, I spent the extra $$$ on the 6" with wire mesh and rebar. Looks great, no cracks or shifting of any kind. I felt is was worth the extra cost (which was minimal) to go the extra mile on the foundation.

Mine is 5000 psi, 12" compacted gravel, 18" perimeter with 2" stem wall.

I don't live in my mom's basement.

Oh, and I am an engineer.

 

[rickycobra]

Do six inches and remove any and all doubt now and in the future.

 

[brownbagg]

If you do rebar, you will need six inches due to rebar clearance which is 1 1/2 inches top and bottom four would be pushing it with #4 bar. If all you want is wire then 4 inches is fine. Or cut the different and do five

 

[WNYflyer]

A true 4" thick 4000 psi slab properly installed is more than adequate to take the load from your truck.

But if it was me since you are talking a new slab............

- Pick out a two post lift from a top quality vendor and call them and talk to the tech people and tell them to send/e-mail you the REAL and SPECIFIC foundation/slab requirements (thickness, strength, size, reinforcing, contraction/expansion joint restrictions) for that lift. Do not use generic info from the manufacturer's web site. Do this for a 4 post lift also.

- With this info you may be able to set up your new slab to accept a future lift. It will cost you more $$ ( for a 2 post lift) over a standard/generic 4" slab. It maybe worth it to you and also you will be making a educated decision on what to do.

- Personally I would do as a minimum a 5" slab assuming no lift requirements and to allow for some variance in the quality of the crew doing the work.

- And as others have already said a properly compacted base will make all the difference in the world in how your slab holds up. I would use a minimum of 6" (adjust upwards depending on your grades/elevation) of compacted DOT subbase material (state road base stone).

 

[Wanna Ride]

I don't live in my mom's basement.

Oh, and I am an engineer.

Well, ok... if you thought that was directed to you.

 

[Justanoldguy]

Pretty rare for anything thicker than 4" for garage floors here in NZ.
Overkill if you must, but generally the money is better spent on more tools.

 

[e-tek]

Pretty rare for anything thicker than 4" for garage floors here in NZ.
Overkill if you must, but generally the money is better spent on more tools.

Exactly. Even Mom's basement is 4".

 

[mtwaterguy]

Four inch is more than sufficient.

Good luck, and let us know it comes out!

Here I fixed it for you. No sense sounding like a smart *** new guy that's only been here for a couple of months.

 

[Strouty]

I'm going to pour mine 6"@5000psi w/ rebar. I plan to have a 10K 2 post lift installed later on.

you may not want to go with 5000, it can be too brittle. Especially when installing a lift. I would only go with 3500 or 4000. Talk to some people, but warehouses usually use the higher PSI due to super concentration of weight.

 

[38D]

I have a full 8"...might as well go for overkill

 

[Wanna Ride]

Here I fixed it for you. No sense sounding like a smart *** new guy that's only been here for a couple of months.

I didn't ask you to "fix" it for me, but thanks for the censorship. Let me think... yep. That came out exactly as I intended it to. I was merely stating my thoughts, no need to chastise me for speaking the truth. I'm sure there's many others that feel the exact same way as I do about it.

Why is it that when someone asks a question or for advice, and there's always several different opinions stated that if you don't agree with them, you MUST be wrong? I know for a FACT what my slab consists of, because I poured it. I didn't pay someone else to pour it, I did it. And I also know for a fact that it is crack-free, and it's had many heavy jobs performed on it.

It's the same discussion on many issues, like tools and their country of origin. Some guys swear that unless you paid $120 for a hammer that has Snap-On emblazoned on it, it's going to break when you take it out of it's packaging. I enjoy this board, and also like to contribute to it, but in all honesty I think some of the members act like you have to be in an elite tool club or they turn their noses up at you. And the fact of that matter, is I'd bet many of those guys don't have much else to pay for. Now don't everybody get your ******* in a wad, I didn't say ALL of those guys, I only said "many".

It's like the recent posts from someone asking for opinions on lighting arrangements in his garage... A few people offered valid concerns and opinions, and then there was some others that did everything but tell him he was making grave mistakes for not using a totally different type of overhead door, or he had three times more light than he will need, or not half as much as he'll need. And then others suggested he add lights where he clearly said were not options. Truth be known, half of the people that nmmade suggestions probably don't even own a garage, and because they spend all of their income on overpriced tools (but cool tools none-the-less), will maybe never own anything more than a condo, with one reserved parking space in a parking lot.

There... I said that too. Ban me if you think it's going to fix the root problem.


And I stand firm on my response to the original post. 4" slab is more than sufficient, speaking from first-hand experience. If you know which lift you are going to go with, then find out what the manufacturer recommends in the effected installation area. We'd love to see some build pics!

 

[My Custom S]

I am also a PE (Professional Engineer) and a 4" thick concrete slab is more than sufficient for a general purpose garage. I have poured two slabs (one 12 years ago and one 6 years ago) and they both have stood up fine. I used approximately 4" tamped #57 stone with a 6-mil vapor barrier and then 3000-psi concrete with fiber and #4 rebar at the corners. Don't forget to put in control joints about every 20-feet because the slab will develop minor cracks due to curing, so you mind as well control them. If you have the extra money you won't hurt anything by pouring a thicker slab, but the money could be better spent somewhere else. That's my two cents...

 

[Wanna Ride]

I am also a PE (Professional Engineer) and a 4" thick concrete slab is more than sufficient for a general purpose garage. I have poured two slabs (one 12 years ago and one 6 years ago) and they both have stood up fine. I used approximately 4" tamped #57 stone with a 6-mil vapor barrier and then 3000-psi concrete with fiber and #4 rebar at the corners. Don't forget to put in control joints about every 20-feet because the slab will develop minor cracks due to curing, so you mind as well control them. If you have the extra money you won't hurt anything by pouring a thicker slab, but the money could be better spent somewhere else. That's my two cents...

Ahhh... the refreshing voice of logic. Thank you!

 

[checkthisout]

I poured mine to 6" in the bays with the 14' tall doors because of the potentional that I may park a motorhome or sometimes work on large, heavy equipment. The rest is 4"

It's 5000 PSI per code for "walking surfaces and areas exposed to weather".

I laid a row of re-bar across each garage entrance but simply used wire mesh everywhere else.

No cracks yet! 6" will better bridge any settling that may occur under the slab and gives you options for hoist placement in the future.

 

[Jack90210]

The same guys that will tell you that using synthetic oil in your compressor is a waste of money are probably the same ones that will tell you that nothing shy of 8" with rebar will do.

I am also a PE (Professional Engineer) and a 4" thick concrete slab is more than sufficient for a general purpose garage. I have poured two slabs (one 12 years ago and one 6 years ago) and they both have stood up fine. I used approximately 4" tamped #57 stone with a 6-mil vapor barrier and then 3000-psi concrete with fiber and #4 rebar at the corners. Don't forget to put in control joints about every 20-feet because the slab will develop minor cracks due to curing, so you mind as well control them. If you have the extra money you won't hurt anything by pouring a thicker slab, but the money could be better spent somewhere else. That's my two cents...

Great first post, and only made better by the fact that you waited 3.5 years to say hello.

 

[bill9860]

5" 4000 psi in my 26w x 28L, with mesh & no rebar. had 8" poured in vicinity of lift only because I wasn't sure what I would be doing. Ended up w/ Mohawk A7. Mohawk rep said 5" would have been fine throughout.

 

[Wanna Ride]

This has me curious... how many members have a lift that use it professionally, as opposed to who has one just for their own vehicles?

How much can a guy expect to pay for one that's sufficient for their own vehicles (ie- not used many times a day, every day)?

I never realized how many individuals have them in their home garage, and now I'm contemplating maybe saving up for one.

 

[bill9860]

for new, probably $2,600 installed w/ tax

 

[Goobzilla]

This has me curious... how many members have a lift that use it professionally, as opposed to who has one just for their own vehicles?

How much can a guy expect to pay for one that's sufficient for their own vehicles (ie- not used many times a day, every day)?

I never realized how many individuals have them in their home garage, and now I'm contemplating maybe saving up for one.

Depends on what you want I'd say from $1500 to $10K, but that's a whole nother can of worms.

 

[CreekRat]

Not exactly on topic but just for comparison I've got a guy coming out next week to pour a slab for me. It's a small building, 15' x 19', 4" slab with a vapor barrier, for $995.

It's been worse than pulling teeth to get someone out to do this job. More than a year of dead-ends to get to this point. I think I've got a winner this time, I hope so anyway because I can keep him busy for a while if he's good.

I'm shocked at the poor customer service of the vast majority of residential contractors I've tried to work with. Some would give a decent bid but weeks would go by before the would return my calls. Others try to hit a home run on my project by quoting +100% above even a high quote. Times are tough for all of us; I don't want to stop anyone from making a living but no one is going to make it all back on my job alone.

 

[Wanna Ride]

Did the $995 include material, or is that just labor?

 

[mkbrower]

First off I'm no engineer and my thinking may be off and if so, I would appreciate it if someone would point me to references with the right information. With that being said, my thinking is that 4000 psi concrete means that one square inch cubed concrete will support 4000 lbs plus 25% if properly supported and cured to 28 days. That means, by my thinking, that a 12X12X4 inch concrete slab would contain 544 cubed inches of concrete and would support a whopping 2 million, three hundred and four thousand pounds not including the 25% fudge factor.

My thinking is that a very compact and strong base, proper mix and curing is much more important than thicker concrete or rebar. If you live in an area that has loose sandy soil than rebar and wire mesh will help prevent cracking but will not increase the compression strength.

Again, this has always been my thinking when it comes to concrete.

Mark

 

[ForceFed70]

I'm pretty sure that the PSI doesn't add up when looking at thickness. It's 4000PSI before the concrete starts to crumble... doesn't matter how thick it is.

 

[Daedalus]

I'm pretty sure that the PSI doesn't add up when looking at thickness. It's 4000PSI before the concrete starts to crumble... doesn't matter how thick it is.

Exactly correct. 4000 PSI is the compressive load rating over area, not volume. Concrete is weak under tension. The thickness of the slab is to keep bending and tension to an acceptably small level.

"Better is the enemy of good enough."

 

[mkbrower]

I don't think that is correct, it doesn't make any sense. A 1 inch thick slab composed of 4000 psi concrete will not have the same compression strength as a 6 inch slab of 4000 psi concrete whether it is 1 square foot or 1600 square foot. I will agree that surface area has a huge effect on tensile strength of concrete. That is why I believe expansion joints are important.

I was able to find the ASTM reference for testing the strength of concrete. A 4X8 cylinder of concrete is compressed to destruction and the strength is determined by dividing destruction pressure by surface area of the cylinder. Anyhow, sounds like determining concrete strength is pretty complex.

Mark

 

[Daedalus]

I don't think that is correct, it doesn't make any sense.

To who?

I was able to find the ASTM reference for testing the strength of concrete.

Probably the same ASTM procedures I used in the concrete structures test lab at my internship while getting an engineering degree.

Strength is rated is PSI -- "pounds per square inch". The only surface area that matters is the one being stressed. If you have a 1x1x1 solid cube sitting on a surface, and you balance a 10 lb flat/smooth weight on it, both top and bottom surfaces of the cube feel 1PSI (they have to be equal). If you then put the weight on a similar block of 1x1x10, where 10 is the height of the block, both top and bottom surfaces feel the same 10PSI. The compression force is the same magnitude and direction at any point within the solid. With small samples there are "edge effects" that can cause errors in the test results, but reality and theory align very well overall.

 

[TheGreek]

Don't worry about the weight of the pickup. Run-of-the-mill 4" tract home slabs will support that all day long.

Where you should worry is regarding the foundation for your lift. A study of the manufacturer's specifications is a good start.

I am working on installing a 2 post lift in my home garage in the near future. We just moved in and the house was built 2 years ago. As of now the only information I have is that the builder said it has a minimum of 4 inches of 3000 psi concrete.

I called Bendpak and looked at Rotary lift's website to get an idea of concrete requirements. 4 inches seems to be the norm. I asked if that was reinforced and they said no. Reinforcement is not necessary.

This is a quote from Rotary lift.

On all Two post models; If anchors do not tighten to specified torque, replace concrete under each column base with a 4’ X 4’ X 6” thick 3,000psi minimum concrete pad keyed under and flush with top of existing floor.

Its the first time I have read a way to determine if the floor will be capable of supporting a lift.

This is the webpage.
http://www.rotarylift.com/uploadedFiles/FAQ1.pdf