I’m building a 40 ft X 40 ft pole barn. I want a concrete floor. So I need to hire a concrete contractor to do it.
I have seen some pretty crappy concrete jobs. I’ve also heard after-the-fact horror stories about concrete contractors cutting corners. What do I need to know to ensure the concrete contractor is doing a good/quality job? I talked to one of my coworkers, and he talked about witnessing a slump test, specifying strength (PSI), specifying the type of rebar or mesh, temperature and time of day, etc.
I don’t know anything about this stuff. So I guess I’m looking for factual advice on what to do to ensure the job is done correctly and no corners are being cut.
Does your jurisdiction require an inspection after concrete? Mine did. That doesn’t help going in but you could accompany the inspector on the inspection and see if he/she thinks it’s all right.
Slump test: a standard cone is filled with concrete in three stages, and packed with a metal rod. When the cone is lifted, the concrete should slump evenly, without collapsing or falling to the side; for a floor, the target should be a slump of 5 inches, and no more than 7 inches. Up to nine inches is acceptable if the concrete will be poured and struck off by hand, or in very hot weather.
Strength (in PSI): This is really more of a finishability constraint in a floor; finishability is enhanced by using more cement in the mix, which results in greater strength. Floor designers typically specify 4000 psi, or a cement content of at least 560 pounds per cubic yard. For a good finish, it is important to have enough fine aggregate (sand), cement, and water to form a smooth mortar that rises to the top of the slab. However, large aggregate is also needed to prevent shrinkage and provide a solid base.
Reinforcement: For the floor you describe, mesh will probably be OK, but if you’re planning to drive heavy equipment on the floor, you’ll need rebar. Reinforcing mesh should be suspended in the middle of the slab’s height with little concrete dobies, but it can also be laid over a winding bead of concrete poured before the main pour. The sides should be formed with wooden boards set in place with plenty of stakes.
Adjustment for environmental factors is complicated, but if the contractor talks about it without prompting, it’s a good sign.
A good concrete floor will not be the product of the lowest bidder: all of the standards described above add to the cost in labor and materials. It’s worth it to have a strong floor that doesn’t crack before the year is out.
I called the concrete plant directly when I did my 50x80 barn and they referred me 2 crews; one to come level the dirt floor and wire up the rebar and set the dobies and another crew for pour day. The pour day crew supervised the pumping and spreading and then stayed into the evening running whirlybirds and trowels. We did a brush finish on the front apron and cut crack seams in the morning with a skilsaw, waited 2 months and epoxy coated it. There was no contractor and no inspectors, just 2 crew chiefs. Job came out great. We park tractors on it.
Good stuff, here. If you’re having the dirt work done as well, make sure that it’s back-filled with proper material and compacted properly. Poor compaction can be the cause of settlement, which means doors and windows don’t close properly, or they stick, and your slab can crack. Since this is an interior slab, you likely wouldn’t have any reason to have rock salt on the floor, but it’s worth mention that you don’t want to do that for at least a year after the slab is placed, as it can cause spalling. As mentioned, unless there will be heavy traffic you probably only need the hog wire mesh. If you have footers, they may put rebar in them and attach the mesh to it. You don’t want metal showing once the concrete is in place, as it will rust.
Not without a compaction test. If you see someone out there with a sled or an elephant’s foot, you can probably assume that it will be adequate. Compacted soil has a whole other look, of course, than non-compacted. Were it my slab, I would have a pretty constant personal presence to monitor the job. It’s important that the mesh is on the dobies, for instance; it does no good whatsoever for the mesh to be lying on the dirt. I think if you pick a reputable company, you’ll be okay. That said, I was QC manager for a $22M aircraft facility, which had very close tolerances, and the concrete company was routinely trying to fuck us with poor workmanship.
With a slab that size, I’m assuming whoever does your placement will do it in sections to make it easier to screed, so it should be easier to keep an eye on things. I would ask them for a scope/schedule of work before anything starts, so you have something to check progress against.
Are you getting a permit? Do you have structural plans drawn up by a licensed engineer? If so, the plans should call out the specs about what concrete to use, rebar, footings, etc.
You would normally have a pre-pour inspection, and possibly a Special Inspection during the pour to verify the concrete is the correct type, that the pour is done correctly and that the seismic hold downs are properly placed.
I hope you’re not just pouring a slab and then planning to build on top of it. You’ll want a foundation and footings wherever there are going to be bearing walls. How are you determining those things?
I’m hiring a professional to build the pole barn. (He’s been building pole barns full-time for 15 years.) He will be doing everything except the concrete. After the poles and base boards are up - but before the walls and roof are up – I am going to have a concrete contractor come in and pour the floor. The pole barn builder said he would do all the prep work for the concrete, which includes leveling, compaction, and gravel.
Are you quite sure you don’t want to put the barn up first - using the barn guy’s generic canned drawings and plans - and permit the barn, which, if it’s like mine will be mounted on 6 or 8 3’ deep 24" diameter concrete pilings…and then pour the floor inside and match it to the baseboards? Maybe your version of a “pole barn” is different from mine.
Don’t forget to plan for getting water out when it floods or you wash it down. Drains? Slope? Gutters?
Throw a few plastic U bends into the floor before it hardens, in case you want additional water, power, air, phones, etc. coming up through the floor later. Saves a lot of drilling and patching.
The good epoxy floor coating is U-Coat-It. Get it online. it’s pricier than the stuff at Home Depot but worlds better and it’s easy to use. I’ve used it on 3 different projects. You roll a diluted primer coat onto a clean WET floor and it bonds and looks like hell. Then you go over it later with a denser coat of the same stuff and bammo…Paint for Life. You can throw chips in it if you like and clearcoat it for more money. I never did. Pay attention to how long you wait before using it on raw concrete in your climate. It’s different everywhere.
Who is going to design the foundation/footings and set the forms? It’s not rocket science, but it’s more than just pouring a slab. You should have a foundation around the perimeter and footings for any load bearing posts inside the foundation perimeter.
As part of setting the poles, does he set concrete footings?
Looking to build a workshop’garage on our property and will be hiring a contractor to pour a floor as well. Anyone have a rough idea what a floor like the OP described should cost? Hard to know if you aren’t getting cheated if you don’t have a rough idea of what it should cost.
I asked the pole barn contractor about this. He said the total cost for a concrete floor is usually somewhere between $3.10 and $3.25 per ft[sup]2[/sup]. That price includes concrete, mesh, labor, etc. I suspect the price for a concrete floor will vary depending on location, so your cost may be higher or lower.
The pole barn guy recommended control joints on a 10’ X 12’ or 12’ X 12’ grid. I guess I would have to specify what I want when I talk to the concrete contractor.