Laying concrete 4' at a time?

[BioHazard]

My barn and attached carport have a gravel floor, which I would absolutely love to make concrete. Unfortunately the $3000+ that would cost could be much better used in many other places.

The cost of concrete these days is ridiculous, I have a giant pile of crushed 3/4" gravel I can use, and I can get sand for $15/yard. If I got a small mixer, and used a recipe of 1 part cement, 2 parts sand, and 3 parts gravel, I can make my own concrete for less than $14/yard.

There is no way in hell I could lay a nice 30x40 slab by myself and with a small mixer. However, if I poured it in sections 4'x4'x4", each section would only take a little over 5 cubic feet of concrete. That wouldn't be too hard to mix or finish, and would have plenty of "expansion joints".

Does anyone think this is a bad idea? Frost heave is not really an issue here, especially in the barn. I've already got a great packed gravel underlayment. Should each section be joined to the other with rebar? Should I lay rebar in each 4' square?

I figure it won't come out as nice as a professional one peice slab, but it should cost me >$300. Even if I put racedeck or something on top it would be less than having it poured. I wanted to buy a 3.5 cu/ft mixer anyway for some other projects...mixing concrete by hand is for illegal immigrants.

 

[1chicken]

I'd say go for it! I did my barn floor with crush-n-run at first, but my skid loader tore it up every time I moved it... I ended up tilling portland into it and gave it a good misting over the next few days... Hard as a rock now! Its by no means pretty, but works great. If you do 4' squares, I'd drill the forms and run rebar through it with bends on both sides as well as wire and tie it all together. Take your time and it could look great.
Another way would be to lay wire over the whole floor, and slot your forms so the wire runs through it, you'll only have a little flow through under the wire to knock off before setting up the next section. pretty easy once you get the forms made up.

 

[dodriven]

I would try to make the sections at least 8x8, but since the ground is well prepared it shouldn't be an issue.

Just make sure you keep the grade consistent so that you don't have water runoff issues.

 

[red]

Two years ago my brother's neighbor wanted to pour a slab in his backyard. Didn't want to pay for a pumper (no access for concrete truck). Well 70+ 80lb bags and two cement mixers plus 5 neighbors and 6-7 hrs of serious work the slab was poured. A few cases of beer help deaden the pain! Kept telling the owner that he was nuts cause he picked up all the cement with his Explorer. Pointed out it would have been cheaper to pay for delivery then the money he spent on gas!

If can't talk your neighbors into helping you I would break it up into 8 sections of 10x15 with at least one helper! Any way you slice it that is a lot of concrete to mix by hand!

 

[bimmer1980]

not quite sure how you get $14 per yard for the concrete.... that would be some pretty weak concrete. Your ratio is correct, but unless you are getting the portland cement for free, there is no way that it will be only $14 per yard. Using your mix ratio, you will need about 4.5 bags of 94# bags of portland cement to make one cubic yard. 4.5 times about $10 per bag is about $45. Plus the cost of sand and the rock. and your time to mix it and place it..... And you have to worry about it starting to set up while you are still mixing.

Ready mix concrete really isn't that expensive. Save your money and do it 5 to 7 yads of concrete at a time. that's enough to really get a decent slab and not incurr delivery charges from the concrete place.

 

[slopecarver]

Big question here, do you value your time or the surface finish more? Would your time be better spent making money to pay for a professionally poured slab? If you can I'd suggest renting a large mixer to pour larger sections at once, I did foundation work for gravestones last summer and we used a 2 yard trailer mixer to mix up batches, that baby makes work easy(er)!

on a side note here is a neat concept for a mixer, if you could find something smaller where you could mix your own that would be perfect for your application. Known as a continuous mixer or on demand mixer.

 

[premierplayer]

save your $, hire a pro

a monolithic pour has many advantages

2 cents

check your math, 4x4x.33=5.28 cf
not even one section per 3.5 cf mixer full? it's gonna be a l-o-n-g day

 

[jct]

not quite sure how you get $14 per yard for the concrete.... that would be some pretty weak concrete. Your ratio is correct, but unless you are getting the portland cement for free, there is no way that it will be only $14 per yard. Using your mix ratio, you will need about 4.5 bags of 94# bags of portland cement to make one cubic yard. 4.5 times about $10 per bag is about $45. Plus the cost of sand and the rock. and your time to mix it and place it..... And you have to worry about it starting to set up while you are still mixing.

Ready mix concrete really isn't that expensive. Save your money and do it 5 to 7 yads of concrete at a time. that's enough to really get a decent slab and not incurr delivery charges from the concrete place.

Brad is right, your math is wrong. Do it right.

 

[Kevin54]

I've went the route of the sand and gravels mix, cement, mixer, and wheelbarrow after wheelbarrow of hauling. Bottom line....it is not worth it. Unless it is a small area or a short sidewalk, and if you don't have a few other people, you can't keep it mixed fast enough to not have problems. Too many inconsistencies. Too little of water in this batch, too much cement in that batch, too much water toss in a little more cement. Then you have inconsistencies in the curing.
Best to get it mixed all at once. poured all at once, and curing all at once. Do it once, do it right.

 

[BioHazard]

not quite sure how you get $14 per yard for the concrete....

You're right, I was off, it's about $42/yard, or $8.21 per 4'x4' section. Still way cheaper than even buying 80# bags of premix. I consider the gravel I have already free and the sand to be near free. Portland is $8.25/bag locally.

And you have to worry about it starting to set up while you are still mixing.

That's the whole point of doing it a little bit at a time. 4x4 is less than two full mixers.

Ready mix concrete really isn't that expensive.

At $100+/yard, I'll have to disagree. Plus if I have them deliver that much, I'll need to hire help to smooth it all out.

save your $, hire a pro

I'm not sure I could come up with a bigger oxymoron than that.

not even one section per 3.5 cf mixer full? it's gonna be a l-o-n-g day

Didn't say I was going to do it all in one day. Again, that's the point of breaking it up...so I can finish it at my leasure. Might only do one section a week...or month! Whenever I get around to it. Some people pay money to work out at a gym, I prefer to spend money on materials and "work out" by building something...

 

[BioHazard]

Just make sure you keep the grade consistent so that you don't have water runoff issues.

I think there's a better idea in there...if each section was spaced apart a little, and the gap filled with grout, then I'd have built in drain lines that I could slope to the outside. Sort of like a giant tile job.

 

[lilredex]

I did something similar, but went even further.....made my own mixer to do it with.

Sections of approximately 4 X 8 Ft. were poured over a summer to widen a single drive into a double, and worked mainly alone. I just kept moving the form along and poured right against the last section. It is important to measure your materials (cement, sand, stone, water) so you get consistent results.

That was thirty years back and it is still going strong.......would do it again if I were thirty years younger, had much more energy back then.

A neighbour down the road decided to pour a driveway and brought in a concrete truck. Looks like it was a much bigger job than he anticipated or his help called in sick. You can see that he had to really hustle to get it all positioned before it set up on him, did not get a chance to properly finish it and looks rather rough........but at least it is concrete. Would have helped if I had seen it sooner!!

 

[tncatadjuster]

I think there's a better idea in there...if each section was spaced apart a little, and the gap filled with grout, then I'd have built in drain lines that I could slope to the outside. Sort of like a giant tile job.

Thats brilliant. I would place dowels of rebar at appropriate places, it would be good to tie them together. Forms notched and bars on risers.

 

[WVBrady]

...on a side note here is a neat concept for a mixer, if you could find something smaller where you could mix your own that would be perfect for your application. Known as a continuous mixer or on demand mixer.

I would not recommend this. I used one of those in my old garage. Even after I asked the driver to make it as dry as it would come out of the chute, it still had a lot of water in it. I had the concrete sloped to a center drain (covered with plastic), and the bleed water made a small lake in the middle. I also found that the meter shorted us on volume. It turned out that the driver was a former student of mine, so he showed me the chart to convert the meter reading to cu.yds, so I know that the meter was at fault. To top it off, I later found that their concrete would not meet the requirements for the department of highways. When I built my new garage, I used the ready mix trucks and there was almost no bleed water and the amount used came out almost exactly what I had calculated.

 

[Spareparts]

If that is what you want to do then do it, but do it a little larger area at a time, 80 sq ft at
4" is a yard, if you are using 2X4's for forms then it will be more square feet. Put plastic on top of the gravel to keep water from wicking down to give you more time to finish. We put the mixer right at the form and stocked piled the sand and gravel close to the mixer, three hours we mixed and finished 1 1/2 yrds at a time. That would be about 7 days to do your pour, but you will need 1 other person to help.

 

[BioHazard]

Yeah...I'm just kind of thinking outloud here. I want to buy the mixer anyway for other projects, so I'll play around with it first and see how much I should do. And yeah, I'll be using 2x4 forms, so actually my calculations are a bit high for 3.5" thick...

 

[rockchucker]

I have helped pour, witnessed and worked around concrete for years. When you have the right tools and the right materials the pour comes out excellent. Usually if you try to half-*** it then that is your End product.

Personally I would save the time and headache and get someone who knows what they are doing for long lasting durability and looks of the pour.


Just my .o2 though.

 

[BioHazard]

I totally agree my floor would never look as good as a professional floor. But then my 12" thick pro floor in the main shop looks like ****.

But, however it comes out, I think it will be 1000 times better than the gravel.

I guess we'll see how I feel after I lay the concrete pad in my compressor shed.

 

[waltmcq]

the only ***** I can think of is, rolling stuff around could be a problem with joints every 4'. Me I'd get 4 or 5 colors of dye. You could make some cool patterns with 4' squares.

 

[kizer]

Just remember if you start this project your either going to be moving stuff around all the time or not using your slab until its done. To me its a toss up. Its going to cost your either way.

Time/inconvenience=$