What to worry about when getting concrete done

[Capt Crash]

I am getting ready to have a concrete foundation and slab done for a new steel building. I have the engineering and permits. I have talked to some concrete guys and have 3 bids so far. The building is 50x60 and I want 4,000 psi concrete. I want it to be atleast 4 1/2" thick and I will have a deeper area for a 2 post lift. What else should I ask about? What should I have put into the contract? I will include a thickness requirement, and a PSI requirement, and I will state that it needs to pass the inspection, and I will get a copy of his insurance, etc.
What else am I missing?
Thanks
Brian

 

[racecougar]

Slope/flatness spec, substrate requirements (assuming you haven't already done this yourself), preference on taper or step at overhead door openings, preferred finish, reinforcement, location of control joints, etc.

That deeper area for a 2-post lift can generate cracks and isn't called out in the lift manufacturer's instructions. Plan out the location of your lift so that you don't place a control joint under/near a column.

 

[Zeke]

Batch receipts and lien releases.

 

[TurnipTruck]

Ditto on the no sawcut where the two post goes.
Conduit and drain lines.
insulation thickness.
Slab edge details at the doors.

 

[Rst277]

I am getting ready to have a concrete foundation and slab done for a new steel building. I have the engineering and permits. I have talked to some concrete guys and have 3 bids so far. The building is 50x60 and I want 4,000 psi concrete. I want it to be atleast 4 1/2" thick and I will have a deeper area for a 2 post lift. What else should I ask about? What should I have put into the contract? I will include a thickness requirement, and a PSI requirement, and I will state that it needs to pass the inspection, and I will get a copy of his insurance, etc.
What else am I missing?
Thanks
Brian

If you have scanned any of the posts about concrete - don't go with the cheapest guy!
Secondly, be clear, very clear what you want and make sure even though it is in the contract to bring it up in person on the day of the pour to make sure the specs you want happen. There are a ton of posts about slope and finish not being "what I wanted" or "not as expected". I know it will seem like micro managing but if you want "x" slope per foot or whatever, confirm that with the crew. They pour concrete they are not psychics. Use pictures if necessary. They want to do a good job and have a satisfied customer, so tell them what you want - it would be best to be on site in case any issues arise. If you are not there to make the decision they will do it and move on.

 

[RPH]

Agree with both above. I would consider going 6” deep concrete throughout the structure. It’s not that much more in costs and the trucks are coming anyway.

 

[Shiftless]

What special procedures are required when pouring a big slab in sub freezing weather?

 

[Zeke]

What special procedures are required when pouring a big slab in sub freezing weather?

None. Don't. I suppose you could inside a structure. I also suppose you could do somersaults and cover the area with a low tent and heat plus wet blankets.

 

[Mick56]

Take a day off of work and be there during the pour.

 

[bb29510]

there only two ways to screw up concrete, concrete driver, concrete finisher, keep them two away from the water valve and it be ok

 

[pcmeiners]

Plan ahead, do your pour in mild weather, NOT when it is 95 or 25 degrees. Very few crews know how to work in either. I second, no added water. Definitely ask to see other work the contractor has done. If you do not prepare the ground properly do not bother pouring if you expect a good outcome. As mentioned be there on pour day, tell the driver NO water added.

 

[Chaznsc]

Consistent concrete mix and curing.

 

[Firebrick43]

As mentioned above, be there.

As mentioned above, get the batch receipts.

I would recommend one step further, you order the concrete and you spec the mix. Not only the slump so they don't add to much water but pay some for superplasticizers so the labors don't hate you for not adding the water they want.

And you pay for the concrete on delivery so you don't have to worry about any tom foolery if the contractor doesn't pay the mix plant.

If pouring in cold weather they will likely want to add an accelerator. Chloride based ones are cheaper but will cause corrosion in any steel in contact more than standard concrete. Even if more expensive get a non chloride based accelerator.

 

[BombShelter]

4500 psi with rebar (no mesh or wire), 4"+ (depending on ground conditions) of compacted class 5, concrete sealer, worker's comp certificate. What equipment is used for surface finish and how are they supporting the rebar, some guys try to lift it while pouring and then it sinks to the bottom.

Depending on ground conditions, some companies will water down the area for a few days to help the soil and rocks sink

What the warranty or guarantee covers.

Up here for normal garages we always had a course of block to get everything above grade and meet code, is this included in the pricing?

That's an interesting comment about paying the concrete supplier, I have heard about plants putting a lien on the homeowner's project so basically you have to double pay for the concrete if the contractor is a flake. At that point they usually haven't paid for the month (or more) and are really behind.

Good luck, sounds like fun!

 

[Zeke]

In CA the driver will present a "preliminary lien notice." This states that if the concrete is not paid for, they can lien the job. They can send this by mail even up to 20 days after the load has been delivered. Usually it comes out with the truck and one gets mailed. If the owner is not there doesn't matter. He is informed as to who owes the money and how to secure a release. Well, that's pretty easy as you don't pay for the work up front. So when the contractor pays, he can show you the release. You can follow up if you wish.

 

[jkuro]

As said above DON'T pour in cold freezing weather. Allow the concrete to cure the full 28 days before exposing it to freezing temps.

 

[Coach James]

I had a slab poured a few years ago~40x50. When I was getting bids, one of the questions I asked each guy was how they would set up to get the right slope and verify it was correct after pouring. One guy said he had been doing it long enough, he could do it by looking at it. I didn't hire him.

 

[WarDamnEagle]

Lots of good advice already given. Not sure how you pour concrete in Colorado in the winter. I don't think it's a major issue if the temperature dips below freezing for a few hours but it can't be prolonged, sub freezing temps.

Nobody talked about keeping the concrete wet after it has set and finished. You need to water cure for at least 1 week, preferably 2. That moisture will help minimize shrinkage cracks.

 

[Capt Crash]

Thanks for the replies. I will absolutely take the day off and be there for the pour. Also this will not be done right now. I am planning on the end of March or early April so it should be above freezing by then. I will ask for a price difference on the 6" slab instead of 4 1/2". I will put in the conduit for the wiring, and a couple of spares just in case. There wont be any water, or plumbing.
The building will be in a low spot so everything under the slab will be built up, and compacted with a lot of gravel/ road base. There will be insulation under and around the slab/ foundation and plastic underneath.
What would you recommend for a slope and finish? My thought was have the slab to be flat with a taper to the doors. This will not be for daily drivers, and I don't anticipate having snowing vehicles inside. I am planning on a smooth finish and I am undecided on painting/ finishing the floors.
Thanks everyone.
Brian

 

[Dig Doug]

I think flat or slope is dependent upon usage and weather

I would want to go flat surface throughout the building interior with a 1/2 step or a slight slope at each roll up door & slope the entry drive approach out away to avoid build up


I would think about adding a few 3inch drain lines or a section of track drain in each bay that get wet use during winter and slope the drain line out away from the the building under the slab, like a storm drain line

although I don’t live in snow /heavy rain country, and if the truck is in / out every day and the bay gets wet that can be a pain to constantly de water / dry out.

 

[karoc]

I would also ask about someone with hook for lifting the wire mesh up off the ground or lift the rebar.

 

[The Bean]

Be sure to put a surveillance camera up so you can monitor the work..

 

[WarDamnEagle]

My 40x40 red iron shop has flat floors with a slight taper in front of the two 12x14 roll-up doors. The finish is a slick machine finish (burnished maybe?) and spills clean up very well with little to no staining. I didn't build the shop, it came with the property when we purchased it. Whoever did build it did a fantastic job on the concrete. There are two saw cuts; one down the middle in each direction which cuts the slab into four 20x20 sections. I was considering having an epoxy flake finish installed but after living with the floor for a couple of years I have decided that I don't need it. I have had polyaspartic flake systems in two previous garages so I'm well aware of the advantages/disadvantages. The only improvement I have made to the floors was pouring Sikaflex self leveling sealant in the saw cuts so they aren't dirt traps.

I installed a 10k Rotary lift a year ago and was happy to find 6+ inches of concrete. I'm guessing you will find the cost difference between 4.5" and 6" to be fairly minimal. It might be helpful to only go 5.5" given that is a normal 2x6 width but that's a question for the contractors. Rotary specifies 4.5" min but it's always nice to have a bit more than minimum.

Again, keep the slab wet with either wet burlap or a sprinkler for a week or more after it's poured. Most people skip that very important step. Good luck with the building. My 40x40 is nice (and I'm working on a 20x40 lean-to expansion) but 50x60 would be fantastic.

 

[NUTTSGT]

Shop/garage area for working, I want FLAT. No slope.

I'd want a smooth finish, easier to clean, push a broom and mop if need be.

 

[67CarGuy]

Some good points and discussion here, and we've been here before.
Check out this thread for all your concrete questions!

 

[luvtheheat]

Add a UFER near the eventual electric sub-panel.

 

[jonesg]

when the concrete truck came he adjusted the slurry a couple of times to get the flow the way he wanted it, he's the expert not me.
i didn't want a smooth dance floor finish but its flat and no cracks in 6 months, not a huge job 10x13.

 

[bb29510]

go buy you a cheap soaker hose and a roll of plastic, as soon as they finish where you can walk on it lay the hose on the slab and cover with plastic, every day turn the water on for a while to keep the slab wet for 28 days. in the old days we would have the form six inches high and when they got done, we cover with hay and then flood it like a pond, kept it underwater for 28 days

 

[Acuratechva]

All the notes guys brought up are great, one thing for me.
Be on the spot and make sure its the thickness you want, even if all you're doing is sticking a stick. Dont trust those **** suckers, especially to make sure its uniform thickness across such wide plane. Center in my experience tends to be the thinnest and that is the important part for lift and quipment.

 

[Wiz02]

In addition to the drain and ufer recommendations, how about radiant heating or sewer lines. I am glad that I added a sewer line, regret not adding radiant heat.

 

[C-S-H]

I have the engineering and permits

If you have the engineering approved, why you do not know how thick the slab is or what the slab and reinforcement should look like in the vicinity of the 2-post lift?

 

[Beemer]

Compacted gravel layer and vapor barrier under the slab is a good thing, standard in commercial work here. Good for both support and moisture control.
Cure the slab for atleast 7 days. You don't want it to dry out prematurely; think of mud in the desert. Ask about or look into the various curing methods.

 

[ConCretin]

I am getting ready to have a concrete foundation and slab done for a new steel building. I have the engineering and permits. I have talked to some concrete guys and have 3 bids so far. The building is 50x60 and I want 4,000 psi concrete. I want it to be atleast 4 1/2" thick and I will have a deeper area for a 2 post lift. What else should I ask about? What should I have put into the contract? I will include a thickness requirement, and a PSI requirement, and I will state that it needs to pass the inspection, and I will get a copy of his insurance, etc.
What else am I missing?

Honestly, it's more about picking the right guy than it is about the contract. I understand your desire to get the contract wording correct but the reality is that it's virtually impossible to monetize and recover damages related to a failed placement. Give my Guide to Floor Slabs a look for some thoughts on a successful slab placement.

With that said, if I had to pick one thing that determines the success or failure of a slab placement, it would be water. Mix water in the concrete must be minimized, bleed water must be managed, water must never be added to the surface and mix water must be preserved through proper curing. If you get the water part right, you are well along the way to a successful slab placement. It's hard to write all this into a contract but a truly competent concrete guy will understand it. Ya gotta find that guy.

 

[andyvh1959]

Back in mid Oct 2019 I had the slab poured for my shop here in Green Bay WI. It was a cold wet October, not freezing. Though just two weeks later we had the coldest, near sub-zero November on record. Pour was onto 2" pink styrofoam atop 6mil plastic, atop 8" of packed recycled asphalt grindings which had been down for over a month, atop packed sandy soil. Not one crack or fail that I have been able to see since I built the shop that fall, had it weather enclosed by mid-December.

I just told the flat work contractor what I planned for the shop. No paperwork given with the concrete delivered.

 

[pcmeiners]

. "I will put in the conduit for the wiring, and a couple of spares just in case"

Place the conduit below the concrete.


"I just told the flat work contractor what I planned for the shop. No paperwork given with the concrete delivered."

You were lucky .

 

[bb29510]

Compacted gravel layer and vapor barrier under the slab is a good thing, standard in commercial work here. Good for both support and moisture control.
Cure the slab for atleast 7 days. You don't want it to dry out prematurely; think of mud in the desert. Ask about or look into the various curing methods.

add a point, without vapor barrier, the soil will **** the water out of the bottom of the concrete white th etop is still wet, can we say cracks, you want it to set unformity and slow.. quick setting causes cracks.

 

[GrayFlattop]

Make certain that the gravel is well compacted with a plate compactor. If you have the time to wet the gravel down and do it a second time - do it.

Even if you aren’t sure how you are going to heat it, put some oxygen barrier PEX in the slab - stubbing it up where you think your heat source will be. If you never use it, you’re only out a few hundred and a few hours. If you do decide to install a boiler (or an appropriately designed tankless heater, you will be SO happy. Radiant floor heat is the most comfortable you’ll ever work on. Snow that melts off your cars will be gone in a day. You will be very happy.

Install perimeter insulation before backfill.

 

[GrayFlattop]

Once you have your choices for concrete contractor down-to a few, go and look at their recent work. If you get a chance to talk to previous customers, see what they have to say.

 

[rayra]

What special procedures are required when pouring a big slab in sub freezing weather?

You don't for a residential project.

 

[CraigStu]

I don't know how it is done, maybe the keep it wet for 28 days? I had a garage bay added on at 2 other houses. First the finish was nice. Second it sucked. Slightly rough which was fine as a no slip but it dusted like crazy. hated it and HAD to paint it. Our current house the garage and the basement are very smooth like WarDamnEagle describes. For me that finish is worth it's weight in gold. I will never need to do anything to it. The larger you build the more important that is.