Pouring a monolithic slab in two parts in two days – ok/bad?
mikeysp
| Posted in General Questions on
Hi. I am in zone 4a and pouring a 28×80 monolithic slab.
I am thinking of doing it myself, but that is too much for my skill set. I wondered if I put an 80ft keyway, I could do two 14×80 slabs in two days.
Is this poor practice or problematic?
I will have 2ea 1/2″ rebar in footer and 8’x20′ welded wire panels with 6″ squares in the field, as well as 3/4″ pex for radiant heat.
Thank you for your advice.
-Mike
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Replies
Mike,
Sure you can pour the slab in two rounds. But if it's beyond y0ur skillset, I'm not sure it makes much difference whether you pour a big or small slab. Both are way too big for one guy. You'll need a crew - and if you don't have much experience finishing slabs, you need to hire someone who does.
A lot of additional work flows from poorly finished slabs. Framing, floor finishes, trim - everything becomes more complicated, or compromised. It's worth getting it right.
Malcolm, Thank you. I was not sure if the "cold" joint line down the middle meant something bad.
I was weighing options. I can muster up a good size crew. Screeding 14 feet seems doable; whereas, a 28ft span seems overwheming. I have done a 12x18 slab before with two men and it turned out good. I plan to find someone who knows what they are doing to foreman at a minimum. I will likely bite the bullet on this and have an experienced crew handle it; but, I am looking at options to keep costs down. If an 8 man crew spends a day at my property, that could be rather spendy, but I may have no other option that makes sense. I am going to prep everything, so I am hoping that will save me some money.
You can pour slabs in sections, you just need to pin them together with rebar so that they stay in alignment. This is how concrete road surfaces are done.
Malcolm is right too, if you have your slab not flat or not level everything else becomes a problem since you're constantly having to try to compensate for the uneven slab. I'd hire a crew for this. It's relatively easy to do DIY pads for things like generators or support columns, but a large slab is tricky and takes some skill. I'd contract this out to a crew, which will do a better job and also go much faster. Concrete guys go fast, partly because they have to -- the concrete doesn't wait for anyone -- but also because they do it all the time so they have experience.
Finishing concrete is a bit like finishing drywall. Crews that constantly work with the material get a "feel" for it that lets them go faster AND do a better job.
Bill
Bill, I am convinced I will need to pay the piper and get a pro crew. Thank you. I want a DEAD FLAT slab too. I have noticed some slabs have high and low spots while others so flat it appears to the naked eye a machined surface. I am hoping for the latter.
The way I see it words mean things. A monolithic slab by definition has no parts it is one piece.
If the word monolithic is a code requirement then it needs to happen in one day.
There is nothing wrong with a 2 part slab if the two are well connected. Generally it is easier to pour one slab than to get enough rebar sticking thru the forms to connect the slabs.
Walta
Walter,
Monolithic Slabs are simply slabs with integral footings. The term is used to distinguish them from Floating Slabs, and Suspended Slabs.
Gents, thank you. I have made the decision to hire a concrete contractor for this one piece of my build. I want a DEAD FLAT concrete surface.
Mike,
Good decision. You've got literally hundreds of other opportunities to save money during the build by doing the work y0urself. Nice smooth slab underfoot for decades to come!
Watch the crew finish that slab to learn how they do it, and to marvel at their skill. This will help you to get a better finish the next time you do a small slab, and will make you appreciate the money you spent hiring a pro to do the large slab :-)
Bill
Mike,
I agree with others. Let a crew do it. That's a big slab for non pros if you want it dead flat.
Ask them for a power trowel finish. Just watch out that they don't push the concrete around in the first couple rounds of troweling. Ie creating low and high spots, usually around the forms.
The keyway is easy, but if you want a one piece, (I would prefer this, but that's just my aesthetic preference) I think some crews set up screed references, like the keyway, with wood and then pull them out after the initial screed
Jamie,
On wider pours I leave screed reference points for the finishers. A chunk of 2"x8" with a 2"x4" nailed upright at the correct height. It sits on the foam or poly and they can take it out when they have reached it. The finisher's preference, which works too, is to drive rebar into the fill and tap it to the right height, then hammer it down once they reach it.