Once our plumbing groundwork was signed off, we could finally cover it up and give the concrete guy the OK to move ahead. We chose to use a plastic barrier under the concrete, because our hillside is choc full of underground springs; which spring to the surface in random and frequent places, and weep and seep water year-round. The last thing we wanted was damp concrete.
The “concrete guy” recommends putting several inches of sand in between the plastic and concrete, so that when the concrete cures, its massive water content has somewhere to travel before hitting plastic. Otherwise, I guess, if the water all has to go up through the top, this is problematic. So we had sixty yards of sand standing by for this application, and almost all of it was used up in the covering of the plastic.
He is pouring the floors in five different sections; I think mostly because of the limitation of how much he can smooth out at once with just himself and a helper. He has done three so far, and has two more due next week.
The one he did on Friday was dicey. If you live in the area, you know that there was a fatality accident on I-5 in Marysville in the morning, which jugged-up traffic for hours. The concrete truck was delayed in that mess; so I guess by the time it got here, that concrete was pretty “hot”! But they were able to manage ok, it was a smaller section, fortunately not the big one!
The concrete they are using is fiber-reinforced (something along the lines of this company’s technology); rather than the traditional method of embedding welded steel mesh. There are lots of opinions pro and con on this subject; but I can’t find any scientific rationale saying which is better for applications like ours. Some feel that the old school way of using steel mesh has just gotta be stronger, because intuitively, steel mesh is just strong. And of course, old methods die hard.
But proponents of the newer technology point out that steel mesh needs to be placed just-so height-wise within the concrete, or it does not do its job. And even if you set it on “chairs” to keep it at the right height, the weight of the concrete, and the workers slopping around and stepping on it during a pour, can push it down.
The fiber-reinforced concrete is cheaper, both in labor and material savings of not having to put down steel mesh, as well as allowing you to pour a thinner layer of concrete. And theoretically, the fiber strength is more evenly distributed than a steel grid. It is supposed to offer the most stability during the “plastic” stage of concrete- while it’s curing, when cracking is most likely to occur.
And the other part of the debate is that concrete cracking or not cracking is impacted by other variables: initial site prep, stability of the base soil, the concrete mix, and the cure rate of the concrete due to ambient temperature and humidity. So it could be that the reinforcement choice is the least of your worries, if you are building on fill or pouring during a hot, dry week. Anyway, this is what we’re going with because apparently all the pole building builders in the region use this, and the building was expensive enough already. I’ll report back in ten years on whether or not it has cracked!
We are doing smooth floors on one side, and broom finish on the other. So far, so good on the floors, he is doing a nice job! They had to leave one wall un-sided to give the concrete truck the best access to pour concrete into the building. But that is OK to finish now, because the concrete truck can back in the big front door to do the rest. So we just have that, and garage doors and gutters to be installed; plus a few miscellaneous finishing things. We’re hoping it’ll wind down in the next couple of weeks.
We still have power left to deal with, but we’re focusing in finishing out with the builder and plumbing first, then we’ll move onto that venture next. With the days getting longer and warmer, power isn’t an urgent issue just yet!
July 28, 2011 at 2:40 pm
I’d agree with always using a vapor barrier beneath any concrete flatwork poured inside a building. My preference is to use an insulated vapor barrier, such as an A2V reflective insulation (two layers of air cells sandwiched between a reflective aluminum facing down and a white vinyl facing up).
The sand on top of the vapor barrier is a good idea.
I’ve had good personal experience with fibermesh in concrete.
One guarantee about concrete slabs – they will crack. Good expansion joints will at least tend to control where those cracks occur.
The most important thing to getting a good pour, is most certainly what the concrete is poured upon.
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July 29, 2011 at 3:04 am
Pole Barn Guru, thanks for the comments- we are pretty happy with the fact that the concrete does seem to be staying dry despite all the moisture we know we have in our soil and hillside. So I think the barrier was a good call, and I like your idea of doing an insulated one! But we are getting quite a bit of cracking in the floor, I wish the installer would have used more frequent expansion joints. Because it was poured in sections, there are some joints that came with that, but it doesn’t seem like enough. It’s not the end of the world, since we’ll probably make a poopy, oily mess out of the floor over time anyway from use and abuse, so it doesn’t need to be pristine. But, it still is probably the thing we’re most disappointed about with the building. With 20/20 hindsight, I think we would have chosen to have welded wire put in to strengthen it, had we been on top of the builders more. We micromanaged them everywhere else but on this subject, and lo and behold, we should have gotten in their business about this aspect too. Oh well! If that’s the worst thing about the project, then we probably came out ok! 😀
Michelle
July 29, 2011 at 5:21 pm
Michelle ~
Sounds like the vapor barrier is doing its job then 🙂
From experience, I can’t say welded wire would have prevented cracking any better. In one of my own floors, even with 1/2″ rebar tied on a 6″ grid, there are cracks, it is just the nature of concrete.
I’d like to add you to my professional network on LinkedIn, as it appears we have numerous connections in common.
– Mike Momb
July 29, 2011 at 5:23 pm
LOL – I love the way Facebook just adds random comments at times to posts!
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May 13, 2013 at 3:40 am
There is one property well known to concrete. It will crack and there is little if anything to be done about it. I would have suggested a combination of steel mesh or rebar (on chairs of course) AND the fiber reinforced concrete. Many people refer to “expansion joints”. These are joints intentionally (usually) placed between abutting slabs to allow for some expansion and movement of the slab. “Control joints” are slight grooves placed in the slab to promote a pathway for a crack to occur, as we already know concrete cracks. These will usually help keep unsightly, random cracks from occuring as they will follow the control joint. The purpose of wire mesh and/or rebar is not so much to keep a slab from cracking, rather it is primarily intended to keep the cracked concrete from signifcantly separating or settling and lifting, creating a height discrepancy from one section to the other. Hope this explanation helps.
May 13, 2013 at 4:06 am
Roger, thanks for your comments. It has now been over two years, and we have had some cracking. By nature of the fact that the slab was poured in sections, it did have some inherent expansion joints between the sections. But I think not enough, as we still got some random cracks here and there. It’s not the end of the world- as you say, it’s mostly aesthetic. Overall, it’s holding up fine. We have a forklift, so some reasonably heavy loads drive on it, and we’ve had no catastrophic problems at least.