Going rate for concrete

[JSUPreston]

Well, after the deluge of 2009, my shop in Montgomery, AL got flooded again. I'm obviously a lot better off than people that had 2 feet of water in houses that are not in flood plains, but I'm still a little frustrated.

Anyway, I've done the math and I believe if I were to add another 2" total height to my shop floor, that should take care of most of my issues with the shop and allow me to divert the water elsewhere. Due to having to raise part of my shop floor 10" and part of it just 2", I figure I need about 8 cubic yards. Obviously more than I can or care to do by myself. Any ideas how much this might cost me if a truck can come and pour? I have no issues with getting the truck right to the spot, and I can form up everything myself before they come.

Thank you for all the help.

[Tom Slick]

2 years ago I paid $140/yd with a pumper. It was probably $120/yd for the concrete only. If you need 8 yards order 9. When you need that extra .5 yard it will cost $300 to send another truck out.

do your homework on how to pour over an existing slab. IIRC there are issues with doing it correctly.

[gjat]

$140 seems a bit expensive, unless that includes installation.

Check on a on-site mixer truck or batch truck, where they mix it right there and you only pay for what you use. You buy the entire load of ready-mix. Depending on the slump, usually only 9 yards comes on a truck.

[Tom Slick]

The concrete pump charged about $20/yd, that's where the $140/yd came from. A pump makes life much easier for any job over a couple of yards.

[stormdog74]

do your homework on how to pour over an existing slab. IIRC there are issues with doing it correctly.

I have heard the same thing - definitely ask questions about it.

[gjat]

That still seems pretty high. I pay much less than that for special high-strength concrete.

If you over-pour your slab, what is going to be the form for your sides in the interior wall? That seems problematic if you're going to pour concrete 2" to 10" above the existing studs.

The second consideration is the bond between the new and old concrete. Is your floor painted or have any kind of flooring? If not, a good cleaning and having the floor damp before pouring should be good enough for a cold joint. You still would probably have to have expansion joints as the bond won't be as good as a single pour without a lot of extra work, especially at the 2" thickness. 10" is extremely thick. You could land small aircraft on 10" slabs. It's not going to crack from movement of the slab below.

[jking]

You may find that depending on your location, the price varies quite a bit. I ordered a yard and a half last fall to pour a stoop on the side of our house. IIRC, the concrete was around $150~$160. That was a 4000psi driveway mix with really nothing special added. If you're pouring a 2" topping, you might want to consider using a topping mix. You did mention you have some that will require 10", a topping mix might not work the best for that, though. Not knowing what you really have going on, you might think about whether you can fill some of the 10" area. You could use foam insulation board or sand. You will want to clean the existing floor thoroughly (maybe an acid etch). On thin topping slabs, it is recommended to apply a bonding agent to the existing slab. I can't remember if 2" would be thin enough to warrant that; bonding agents are expensive.

If your existing wall framing sits directly at slab level (no curb wall), you probably want to use PT lumber or treated plywood to form the slab edge next to the wall framing. This is assuming you have wood framed walls.

Get quotes from several Redi-Mix suppliers, I found enough of a price difference that it was worth shopping around. I'd also encourage you to talk to the suppliers about what you are doing. See if you can get some recommendations on what type of mix to use. A good Redi-Mix supplier should be able to help you out with this.

[JSUPreston]

Thanks for the input so far. Good questions, and so I'll clear up things a little, and muddy the waters some more.

The shop is 20'x20' cement block. Existing floor has 2 levels - why I don't know. The side which has a regular exterior door is 8" lower than the side that used to be a garage. Rough estimates have each area being about 9.5'x 19.5'. Using online calculators, several said that I would need about 7.5 yards, so I went ahead and rounded up to 8.

If I do this, I'm going to completely gut the building, taking it down to the shell, roof and lights. I'll replace both doors, so I was going to allow the slab to slope down in front of the garage opening so that I could have a small ramp. The only wood I will be leaving that concrete will contact is 4 4"x4" pressure treated posts that are dead center of the shop. The way the roof was originally framed, this post is load bearing. I don't like it, but short of a completely new roof frame, not sure that it can be changed. LarryG from here has actually run a couple of estimates, and we're not sure that if we changed the roof framing that the walls would support it.

Unfortunate side of this will be that even at my modest height (5'8"), it can get a little tight at the back of the building, since the roof slopes downhill front to back.

One thought I've had is possibly putting in a floor drain if I pour a new slab, but it would most likely get clogged with saw dust/debris. I'll have to research pouring a slab over existing.

BTW: The online calculator at Quickcrete estimated that I would need over 230 80lb bags to do the job. That is around 8 1/2 tons and would cost over $1300 at the local Lowe's. I'd rather have someone come with a truck and pour it for me at that cost. If nothing else, I wouldn't kill myself moving around that much weight.

[JSUPreston]

One thing I forgot that someone else mentioned. I'm not opposed to putting in some fill to raise up the lower slab the 8". Could I make use of busted up slabs that I sometimes see on craigslist? Would I be better off filling with sand or gravel?

[crokett]

I would use gravel as the fill and not chunks of concrete. I'd be worried about them settling. Or at least I'd put down a layer of gravel then put the chunks of concrete over that. If you do use busted up concrete as a fill, you need to vibrate/agitate the pour very well to make sure it flows in between the chunks and there are no voids.

[gjat]

I'm basing my comments on experience installing concrete foundations for structures and some sidewalk work.

No, don't use a loose fill, it doesn't do anything.

You probably can keep the post in the concrete. I would treat with a roof cement and wrap it if you don't want to jack the roof up and put a steel spacer under it. That would allow you to remove it if you ever had the need.

Have you considered building up the floor with wood? More comfortable on your feet, you could possible run duct underneath...

[JSUPreston]

Have you considered building up the floor with wood? More comfortable on your feet, you could possible run duct underneath...

My boss actually recommended that to me this morning. I did that to the low side a few years ago to bring it somewhat level with the high side. I guess I could make use of that substructure and add PT 2x3's on top of everything, shimming it as needed to make things level and add 3/4 pt ply for a new floor. His concern is with as much concrete as I could be looking at that it might blow out the walls, putting me in a much worse situation than I am in now!

At that point, I could put drains in the original slab and punch a hole on the low side of the shop so that when water comes in again, it could flow out easier.

I'm going to have to do some price figuring to see what works out the best...especially since this is technically a "rental." (SWMBO's parents own it and have promised it to her in the will.)

Ideally, I'd love to level the building and build a new shop in its place. Not gonna happen for a LONG time.

[Hellrazor]

http://www.casilioconcrete.com/order.php

There is a cost calculator for MY area.

[chopnhack]

As far as bonding the two layers of concrete together, you may want to drill on regular spacing 2'x2', perhaps and dowel in some short stubs of rebar. Epoxy them in place and then tie some 6x6 mesh to the stubs. It would be difficult to walk on while doing the pour, but it would never separate

[iceman61]

I've looked at several jobs that involved pouring more slab thickness over existing & every concrete sub-contractor I've ever dealt in my line of business with has told me the same thing. It needs to be 4" nominal thickness for it to hold up over an existing slab. 2" over existing is asking for trouble especially in a shop invironment.