Possibly stupid question about small concrete slab work

[EddieWalker]

It does not necessarily crack!
Depends on how many, and where, expansion joints are.

Yes it does. You might not notice it if it was poured without any extra water, but for every gallon of water used to mix the concrete, you have that volume going away when it cures, which means the concrete will crack. If done well, the cracks are so fine that they are just about impossible to see. If there is a lot of water used, the cracks can be massive. Rebar or wire holds the concrete together when it cracks so you don't see the cracks. Most cracks happen within a week of the pour. After that, if it cracks, it's probably going to be years later and a result of the soil underneath not being compacted properly.

 

[jwstewar]

Monica and I did a poor last year two sections. 1 was 6x12 for feed storage in the barn and the other was 12x22. We had the concrete delivered. The feed storage area turned out OK - actually pretty darn nice for being in a barn. The other area in the tack and milk room leaves a lot to be desired. The tack room is OK, but the milk room area where we really wanted it to be the nicest turned out the worst - still not terrible, but certainly not like we wanted. We had it fiber reinforced and did no rebar. Unfortunately it all got away from us before we had a chance to put expansion joints in. I really expected it to crack last year, so far I have not seen a single crack in any of this concrete. It was a pretty tight mixture. He had to add a little water in because at one point it would barely slide down the chute.

 

[4570Man]

I've never mixed a pour of that size because locally it was cheaper in a ready mix truck. Even it the truck couldn't make it in I moved concrete with the tractor.

 

[s219]

For something that is so simple, pouring and finishing a slab can be very hard work.

I had a crew do the 20x20 slab for my barn. They had 5 people and they all kept busy. Did a trowel finish that came out beautiful. We had a concrete truck for that job, obviously.

I did the 32"x10' skirt in front of the barn sliding doors all by myself. Broke it into three sections. Used sacks (about 22 of them) and mixed in my wheel barrow. Did a brushed finish. Came out great, but it was a hot humid day, it took about 2X longer than I expected, and I seriously felt like I risked my health for that project. It kicked my butt hard. Didn't help that I banged my head twice -- had the bright idea to hang a tarp from my tractor bucket to give some shade, which it did quite nicely, but don't you know I walked into the edge of the raised bucket not once but twice. I guess it didn't knock enough sense into me the first time. So I was sore that evening and had a nice egg on my head for a couple days.

Finally, when working on the 10x10 patio behind my house, I had two guys do the work and I was the "go-fer" that kept them fed with sacks of concrete, water, fiber pouches, etc. We used a mixer for that. Took about 75 sacks if I remember right. The mixer helped immensely. But all three of us hustled for sure. That one was going to be topped with blue stone so we didn't fuss about a finish at all, just leveled it off with a board and I did a quick trowel.

Anyhow, I give this kind of work a heck of a lot of respect. An experienced crew makes it look easy, but it is HARD work. I think very carefully about doing slabs myself.

 

[SammyNole]

Oh wow! I'm sorry that I have neglected so many helpful posts. I have been away from a computer all day and honestly didn't expect to receive so many replies! Thanks to everyone who shared some thoughts.

To answer a few questions: I live in Northwest Florida, but I planned on doing the work this winter, so it would possibly be more doable(?) due to temperature, etc. I planned on leveling grade and preparing the site(s) myself, tamping ground, and laying some gravel substrate for all slabs, and I would probably want to try to do rebar as well for durability. The "workforce" would be my wife and myself, both 37, and the time frame would be over weekends. The main reason why I am thinking about trying to do this myself is that I live "in the country", about 45 miles from a reasonable sized city, and EVERYTHING that I have priced to have done has been double what I would pay if I lived in town, because almost all service providers are located in town and don't want to drive out, or if they are willing to do so will have weeks of delays to make it out.

I had planned on doing 4" slabs, with one 12'x12', one 20'x10', and one 24'x12'. For the larger slabs I would do sections, say two 10'x10's or two 12'x12's with an expansion joint. After reading some of these replies, though, I just don't know if it is something that I would be willing to try to tackle. At least maybe not the larger slabs, anyway. Someone did bring up a good point about the high cost of personal labor, so I will have to re-evaluate I suppose!

 

[jaxs]

Oh wow! I'm sorry that I have neglected so many helpful posts. I have been away from a computer all day and honestly didn't expect to receive so many replies! Thanks to everyone who shared some thoughts.

To answer a few questions: I live in Northwest Florida, but I planned on doing the work this winter, so it would possibly be more doable(?) due to temperature, etc. I planned on leveling grade and preparing the site(s) myself, tamping ground, and laying some gravel substrate for all slabs, Someone did bring up a good point about the high cost of personal labor, so I will have to re-evaluate I suppose!

Yep,you sound more than capiable of handling all the grade and prep but dragging and trowling might be something to hire out. The answer lie's in what you and you wife can earn per hour in spare time doing what you know best. If and electrician can earn $80 per hour wireing a neighbor's barn,why shouldn't he hire a $35 concrete supervisor and a couple of $20 helpers? An added bonus in hireing pros is they will bring a mixer 3 times larger than anything a homeowner can afford.
I must tell you a funny that IMO holds a lot wisdom. I was once interviewing a candidate for part time handman work and asked he knew how to paint. His reply"I always thought I did,then I watched someone that actually does know how". He got the job. I held back thinking real pros would offer advice but I'll go ahead and make a couple of often overlooked but extremely important points. Concrete that flows out and is easy to spread has far too much water in it. The result is diminished strength. Want proof? When you see someone using a shovel to help concrete slide down the chute,look around and you will see an observer making sure he get's what he paid for. Farthar proof? Work crews on large commercial pours don't help concrete down the chute without reason. That reason is that every load is being tested and if one fails a bunch of concrete has to be taken out.
The second point is that concrete can be both over worked and under worked. Do you know where the two cross? Me neither in most cases. Several elements determine how and how much to work. If you watch many pours you sometimes see some of the crew go sit/stand around for up to 20 minutes then go back to work. The concrete wasn't ready and like the wine saying "we trowel no concrete til it's time". That's not a primer on concrete but many jobs turn out sub-standard because of those two things. The damage(like spalling) often doesn't become appearant until months/years later.

 

[Egon]

The home done slab is still very possible. Just break it down to areas that can be done comfortably by yourself in a reasonable amount of time. Just make sure all internal joints are keyed and connected by rebar.

 

[tomplum]

With that much area, take pride in the prep you do and have it poured. You're not going to be saving much cash in the end. Take the exact dimensions and run it through a concrete calculator. A 12 yard truck of concrete is cheap in the long run. Pumping isn't cost prohibitive either if it needs to be done. If there's a house around, chances are a concrete truck has been there before and will find the place again.

 

[EddieWalker]

Given that you and your wife are both young, you plan on doing it when the temps are cool, then you might as well give the 12x12 pad a try. It's not rocket science, and the basics are pretty simple. Try not to over think it, and realize that once you start, you cannot quit until it's done.

The dryer you mix it, the stronger it is and the less cracking you will have. The wetter you mix it, the easier it spreads and levels. Most crews will try to mix it really wet so they can spread it easier. They get away with it all the time because even when mixed too wet, it's usually plenty strong for most things in a house, and the areas that need the extra strength, like where the load bearing walls are, is a lot thicker.

Do not use wire, it's impossible to walk on it and keep it in the middle of the pad. Rebar is more money and more work, but it's spaced far enough apart that you can walk between it and not kick it off the chairs. It needs to be held up off of the ground with something. Plastic chairs are the most common thing used for this. Normal spacing of rebar is 24 inches for most applications. I'm adding to my porch right now and I'm going with 16 inches because of concerns with tying it to a pool I'm building and the existing porch. Overkill never hurt anything except my pocket book, and for this project, it's only $20 more in rebar.

Staging is a big deal. I looked at a concrete calculator and it said you need 130 60 pound sacks for a 4 inch 12x12 pad. I would buy 150 because it's very hard to get that pad perfectly flat, and not need more. Have your mixer and wheelbarrow right next to the pad. Pour into the pad as long as you can from the mixer, then use the wheelbarrow after that. When I buy a lot of concrete sacks, I put them on my trailer by the pallet. I can carry two pallets at a time, and I position the trailer right next to the mixer. The closer the better!!!!!

Get a scree board longer then your forms. Find a perfectly straight 2x6 and cut it down to 14ft. You want it to be able to rest on the forms at both sides. When screeing the concrete, I like to roll it, and also sort of slide it side to side while pulling it back. When you find a low spot, fill it right away, and go over that area again. With just the two of you, troweling with a hand trowel what you scree right away will help with the finish work, but also use a pole trowel as often as possible. Pros go over the concrete for hours after it's poured. It will start to harden on you, and having a 3x3 foot piece of plywood to kneel on will alloy you to work the middle area if you need to.

Watch youtube videos if any of this doesn't make sense to you.

Get everything in position the day before you start.

Start mixing first thing in the morning with nothing else to do the rest of the day. It wont take all day, but when you are done, you will be DONE!!!!

 

[/pine]

Something that is often neglected in DIY mix/pour projects is "air entraining" the mix...Granted it is more important where freeze/thaw cycles are more profound but air entraining any concrete will make the pour more durable etc...

Because of the hydration process of Portland cement...a certain amount of water will remain within the concrete after the 21 day curing process...this water can freeze and cause issues...

http://www.concreteconstruction.net...ntrained-concrete-and-why-you-should-use-it_o

Air entrainment - Wikipedia