Contractor advised against 5" flat work?

[97CV]

Just had a contractor out here this AM.

D&S Masonry in MI.

I told him I wanted a lift put it and we talked rebar, he replied "That's all we do" , which I liked.

I asked him about 4" or 5" and he stood by his 4/rebar flat work.


Does this sound strange to anyone else that a contractor turned down a more expensive project?

Yes I am putting a lift in, but I am not going to be running a city maintenance garage either.

Is 4" ok?

He states his mix is 4000PSI too.

 

[SunsetsAndFriends]

I just had a garage floor poured. I had them pour it 4 1/2".

Normally I would do it myself but I didn't have enough people to come help, so I hired it out. This is only the second time I've hired someone else to do any work for me. I will not do it again.

That being said, I would get 4-5 estimates from flatwork contractors in the Yellow Pages. It costs a lot of money to place an add in the phone book. Likely anyone in there is going to be around a while. I would also make a list of exactly what you want. Photocopy it. Give it to each contractor and say "Can you do this and how much?" This way you will be able to compare each bid next to the other, line by line.

4000 psi strength is the standard compressive strength. You can get concrete specified to 5000 PSI. It'll cost more and not needed. I would ask for a 6 bag mix, which means 6 bags of portland cement per cubic yard. It'll be more durable. As for thickness, in terms of labor, the cost shouldn't increase that much but material cost will.

If it were me, I would be sure they use 3/8" or 1/2" rebar, not wire mesh. I would also be sure that whatever thickness you ask for, that you be sure they give you the full thickness. Some contractors say 4" but then put a hump in the gravel base, so that the thickness thins to 3 1/4" or 3 1/2" but they charge for 4". Then over 10 jobs, they've made extra cash. It happens. I would watch the site prep and then measure for myself.

Lastly, if you want 5", then get it. Remember, you're the boss. Tell them what you want. Tell them exactly what you expect. Tell them you want it in writing, including warranty. Be firm and clear. Otherwise, you might be unhappy.

 

[Rookie2]

Check with your lift company, what is their requirement ? are they installing it ? i'm sure if it falls over (two post) no insurance co. in the world will cover you !

compact the substrate,compact, compact, compact ! I prep'd my 40x60 x 5" myself and paid a local finisher to pour it, 6x6 wire with fiber (i have radiant heat) . add saw cutting to your bids and have it done asap. I have one about 24" crack that i caused from over heating .
have an extra form for a sidewalk etc. ready because around here they order extra rather than being short 1/4 yard.

 

[97CV]

I am meeting Max Jack's requirements.

I have to get up to the city, but despite what they say I'm going 42" footings even if they require less for building code.

Also, when I do install the lift I will never take it up. I just can't be convinced torquing down the same bolts over and over is a good idea, and besides, the lift will be a nice bump guard and offer some small protection to my 300C. I'm leaving the car between the lift posts as its home.

 

[97CV]

Oh, and thank you guys for nice in depth posts. I'm really digging the advice and information.

 

[JCByrd24]

A solid 4" is probably fine and not worth the extra cost to make the whole thing 5" but getting exactly 4" is the problem. I ended up with 3.5". There are a lot of factors that go in to the finished depth and if it's not done right along the way you'll end up with less in places. You could go for 4" but ensure that in the area of your lift the gravel is low and not high and make sure the prep is nice and even everywhere, especially where the lift is. Personally that's what I would do, leave the gravel low for around 3' radius around the lift pads shooting for 5-5.5" at the pad itself and gradually tapered to 4" nominal.

 

[Gerald O]

I went with 6" and rebar since I'm putting in a lift or two. It's easier and cheaper to do it right the first time than to have to tear the slab up and replace or thicken it later because it was inadequate.

 

[ConCretin]

I'd take it as confirmation that you picked the right guy that he eschewed your suggestion of a more expensive 5" slab.

Adding depth to a slab is not usually cost effective. A 4" slab is more than adequate if it is placed on a proper base but a 5 or 6" slab won't stand up to one that is improperly prepared.

4000 psi mix is about right for a slab on grade. The compressive strength is overkill but the higher water cement ratio will give you a more durable surface.

 

[James-W]

I am certainly not an expert in concrete work, nor am I an authority on lifts. But it seems to me that if you put in a two post lift you would need thicker concrete where the lift is mounted. My reasoning is, if you have a two post lift there can be an awful lot of weight on one end of the lift. For that reason I tend to think you would want a rather thick slab of concrete, at least where the two post lift is mounted. On the other hand, if you put in a four post lift, then all the weight is just downward and four inches of concrete would no doubt be OK.

 

[Gerald O]

Adding depth to a slab is not usually cost effective. A 4" slab is more than adequate if it is placed on a proper base but a 5 or 6" slab won't stand up to one that is improperly prepared.

Unless the building is quite large, the added cost for an inch or two more of concrete in the slab is trivial. There is no reason to expect that 4" slabs are going to be placed on better bases than 5" or 6" slabs. That said, a 6" slab is most certainly going to be far stronger than a 4" slab, all other things bein equal. Further, it is possible to get more steel into a thicker slab and have it positioned where it can do more good. I'll wager that most professional shops aren't cutting corners by specifying "minimum" 4" slabs under their lifts.

 

[tininjin]

Just dig footings where the lift is going, go down another 4"-6" in the soil and add some more rebar.

 

[Justanoldguy]

Just dig a deeper hole where the posts go.
No need to thicken the whole slab under the hoist.

 

[SunsetsAndFriends]

Verify the footing needed for the lift and either pour the footing for the lift first and then pour the floor around it or thicken the slab as tininjin said and pour the footing contiguous with the slab.

 

[ConCretin]

Unless the building is quite large, the added cost for an inch or two more of concrete in the slab is trivial. There is no reason to expect that 4" slabs are going to be placed on better bases than 5" or 6" slabs. That said, a 6" slab is most certainly going to be far stronger than a 4" slab, all other things bein equal. Further, it is possible to get more steel into a thicker slab and have it positioned where it can do more good. I'll wager that most professional shops aren't cutting corners by specifying "minimum" 4" slabs under their lifts.

You missed my point. It's the sub grade that determines the load bearing capacity of a slab. That's where the priority should be. Adding an inch of concrete and rebar will do very little in comparison. Slabs are too thin for rebar to make them act like a beam - they just 'bend' and crack.

The OP can spend the money on more concrete if he wants but it's not doing him much good. I'd just thicken the slab under the lift posts and call it a day.

And by the way, you'd lose that wager. A 4" slab is very commonly used in professional shops and a great many other applications for the reasons i mentioned. It's not cutting corners.

 

[mygarageone]

What I find interesting . The concrator is trying to not over build and save the op money.
And yet the contractors opinion is questioned , which is fine.
But many times because a contractor is doing the right thing being as honest as he can be , he may very well lose the job because he will be viewed as in competent.
I have experienced this because I wouldn't over sell something , yet some contractor came in and convinced the home owner they needed more than what I offered , the other contractor implied , my proposal would'nt meet the customers needs . When all was said and done , the home owner paid for something he didn't need. More is not always better !

 

[mygarageone]

You missed my point. It's the sub grade that determines the load bearing capacity of a slab. That's where the priority should be. Adding an inch of concrete and rebar will do very little in comparison. Slabs are too thin for rebar to make them act like a beam - they just 'bend' and crack.

The OP can spend the money on more concrete if he wants but it's not doing him much good. I'd just thicken the slab under the lift posts and call it a day.

And by the way, you'd lose that wager. A 4" slab is very commonly used in professional shops and a great many other applications for the reasons i mentioned. It's not cutting corners.

I totally agree , having been in commercial construction for 40 + yrs , the only time I see over 4" concrete is in commercial garages were heavy equip will be worked on .
I have yet to see a Menards , lowes , Home Depot or a walmart with thickened floors and they run heavy fork lifts on this stuff.

Thicken the slab were the lift is going and be done with it .

 

[97CV]

Ok so I see the 4" is ok, I am all over Max Jacks specs.

I just had a place come out. They actually gave me hard numbers which I have really needed.

32x26 with 42" footings, 6 bag mix at 4000PSI, wire mesh and all the permit and site prep done...

$10,700.

I have yet to hear back from D&S. I would like to see their numbers too.

I have not discounted any one yet, I'm just going to keep bringing guys out. If all 5 or so are the same then I need to face facts that I can not afford this project and will pursue a smaller structure.

I am already willing to demo my old, run my own electrical and gas and do all the structure building myself with help. I have two material quotes from Menards and Lowes for $6K and $9K respectively.

 

[James-W]

I would hesitate building something smaller than what you feel you need. When I built my new garage I built it as large as the city would allow, which is 24 X 36 and no more than 18 ½ tall at the roof peak. While the new garage is certainly much better than the little one car garage I had previously, there have been many times when I wished it were bigger. I would have built it larger if I could have, but unfortunately I had to stick with what the city would allow.

My opinion is, if you need to wait awhile before you can build the new garage, then do that rather than build something now that you will be sorry you built later on. It is far easier to build a larger structure all at one time rather than build a smaller garage now and try to add on to what you have later on down the road. Yes, it can be done, but I think you would be happier doing it all at one time. Those are just my thoughts on the subject, others may disagree.

 

[97CV]

Waiting won't fix a lot, this is based on the payments we can afford.

We'd be paying the same per month, now or later.

 

[James-W]

I don’t understand. If you wait and save up some money, you could pay a portion of the cost outright and then borrow the rest. Let’s just say the total cost of the garage is $18,000 and you saved up $7,000 for the project. Now you only have to borrow $11,000 so the cost of the payments should be quite a bit less than if you were to borrow the whole amount.

 

[radrush]

What I find interesting . The contractor is trying to not over build and save the op money.

Oh please! The contractor is trying to finagle a job. These guys will say anything to get a job.

Anyhow, if the mix is 4000psi, it doesn't matter if it's 4" or 5" thick. If the subgrade is right you won't be able to punch thought it. A 4" or 5" slab-on-grade isn't reinforced or designed to bridge subgrade imperfections.

The only real reason to thicken a slab is if bigger rebar is needed then the extra inch (or inches) of concrete is needed for proper rebar cover.

 

[radrush]

By the way, the second reason they use a 4ksi mix is because concrete cures to required strengths in 28 days. A 4ksi mix will achieve approximately 70% of its required strength in 7 days, 2800 to 3000 PSI, assuming it's properly cured. That strength, 3000psi, is sufficient for you to drive a standard family vehicle on.

 

[Dugan]

My family concrete company charged 5.50$/sq ft.

I just did some math, not 100% on it but I came up with 9777$ for the 1777.6 sq ft with a 24" wide footing at 42" deep with a 4" slab. Im sure youll only be doing a 12" wide footing but that gives you a price range.

 

[NZ0J]

The devil is in the details.

#1. A properly cured 3500psi mix is way better than a 4000psi mix that isn't cured properly.

Did you ask them what their plan is for curing the slab after it's finished?

I can assure you that the ONLY reason they use this 6-bag 4ksi mix is because it sets up faster than a 3000psi mix and thus can go home earlier.

High amounts of cement in the mix = more shrinkage cracks.

Curing is super important.

#2 Wire mesh is never used in concrete. Mesh is for fencing. Welded wire fabric in FLAT sheets on the other hand is used in concrete. But are they going to use 6 x 6 - W1.4 x W1.4 which cast .30 cents per square foot or are they going to use 4 x 4 - W4 x W4 which cost .80 cents per square foot?

Ask them what concrete company they use and/or for the mix ID. Then call the concrete company and ask for the mix design information. Post the mix design info so we can review it.

I have sold more 4000 for floors than I can ever remember, and not one of them was because of set time. If someone told me they wanted to use something less than 4000 in a floor, I would really doubt their abilities and knowledge as a contractor. Also, I wouldn't consider 4000 a high cementitious mix, I've had people use higher bag mixes than that before on floors without any problems with shrinkage cracking.

Also, look at his location. Things need to be done a little differently in colder climates. A 3000 or 3500 mix may be fine for a floor in Georgia, but in places like where he lives, I'd highly recommend 4000 at a minimum.

 

[brownbagg]

it doesn't cost any more in labor for flat work on 4 or 5 thickness, just he extra concrete. I would go six just because you only do this once and one day you might one to pull something heavy in. it not that much more , couple hundred dollars

 

[Justanoldguy]

it doesn't cost any more in labor for flat work on 4 or 5 thickness, just he extra concrete. I would go six just because you only do this once and one day you might one to pull something heavy in. it not that much more , couple hundred dollars

Of course, the 6" is 50% more concrete than the 4" so 50% dearer.
To a lot of garage guys, the money is better going into tools and car parts.

 

[1grnlwn]

6" slab 8" under posts, rebar on 1' centers.