? For concrete expert

[naturalgas]

My slab was poured yesterday and finished up and sealed by 7:00 pm. I had closed up and blew heat into garage for 3 hrs .shut off and went to bed by 10. Low temp overnight was around 30. This am temps rising and I put heat on for another hour or so. Closed up. It is sunny and around 40 right now. My ? Is how long before I can walk on slab and set a smaller torpedo in center of slab or do I need to continue heating inside building at all. It is 36x40x12. The contractor who poured it didn't give me any directions as he was in a rush to leave after he tried to scam another $500 out of me. It did not work. He did get me for $60 . Some people really ****. And he has the balls to ask me to put his name out there for referrals . Sorry for rant I just can't stand sleaze bags. I had an uneasy feeling about him and I was right. It does look pretty good though. Any help in how I should treat this for a proper cure would be appreciated. Jim


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[Thumper68]

At those temps I would not worry about heating, give it a few days and then you should be good to go.

 

[lakeroadster]

I'm no expert... but this guy is: Jerzy Z. Zemajtis, Ph.D., PE

http://www.cement.org/for-concrete-.../concrete-construction/curing-in-construction

I have read a lot on this subject, maybe to much, since I am now in wait mode for spring to pour the slab for my pole barn.

 

[joes169]

I'd let it go without heat for a few days, as long as it's insulated and closed up, AND the temp doesn't drop below low twenty's or so. There really is no right answer, it depends alot on what is in the concrete, etc...

Who's going to saw cut the slab?

 

[crf731]

I'm no expert, but we pour concrete in Canada all winter long. Our rule of thumb it to keep it from freezing for a week.

 

[Cyberbear]

There seems to be no set answers to proper concrete curing due to the many variables inherent in each pour. In your location, freezing is a prime factor to consider and you should be able to obtain the answers you need from the company who delivered the concrete. Old rule of thumb used to be 28 days for maximum cure, but you could walk on it in a couple days or so. Many concrete suppliers put in chemicals that help the slab cure properly during very cold weather, as they do for working in hot weather. Unless you have some really big heaters, I doubt they are going to have much effect on a slab your size. Talk to the professionals at the concrete plant, and don't take the contractor too seriously, he's only there to take your money and move to the next job. I put most contractors into the same category as used car salesmen, attorneys and insurance salesmen.

 

[marksland]

Jim - When we poured the slab for my house it was during January with weather/climates similar to what we have now. At the time we closed off all openings and had torpedo heaters blowing into the the basement area for 48 hours continuously.

I just poured a small slab here a couple of weeks ago with pre-mix and it took almost 3 days to set up, granted it was outside without heat but our temps never dipped below 40 at night and it was during the stretch of temps in the 50's/60 during the day.

Who do you have cutting your stress cracks? If you need a good guy let me know, he's out of Hudson and he did my floor.

 

[dbabicky]

You can walk on it the next day for sure and drive on it after a week. If you can't your concrete guy screwed you royally !! ( I would try to keep it from reaching below 32* for a week though)

 

[naturalgas]

Mark, I bet you used Ray . He is the best. He was $800 more so I went with this guy who did a floor for my building inspector neighbor this past summer and it looked great so I used him. I had the garage closed up with tarps and the ceiling is insulated so we could hold heat.the heater I used is good size 150k btu radiant and it was 60 in there when they started at 6:30 am and 70* when they finished at 7: pm. The saw cuts are done also and sealed . So I have a vapor barrier fiber mesh, burnished, sealed floor. It looks great from doorway I just have not gone inside to look at close. It was warm today so I just kept it closed up. I checked it late afternoon and it is warm in there like the concrete is heating inside . Is that possible?


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[brownbagg]

you can walk on it has soon as it will support your weight, that can as early as three hours.

 

[manwithtools]

Curing concrete does give off heat.

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[Thumper68]

Yes concrete cures a chemical reaction which produces heat, I have never worried about heating until over night temps were in the low 20's

 

[csp]

The saw cuts are done also

It had to be set up enough to walk on to do the saw cuts.

 

[gpflepsen]

I've seen floors damaged from too aggressive of heating for the cure. The surface dries out and flakes due to combinations of drying and/or unvented heating, known as carbonation.

These typically happened when it is far below freezing, when concreting down near 0 degrees F. There is very little moisture in the air and drying happens pretty fast.

I'd lay off the heat. The structure is closed and there really is little chance of freezing your slab.

 

[purplezr2]

Measure the surface temp of the concrete.

When they poured mine it was 28 degrees overnight, they covered it in blankets for the night, the next morning it was 60 degrees on the surface of the concrete due to the heat from curing.

 

[naturalgas]

Measure the surface temp of the concrete.

When they poured mine it was 28 degrees overnight, they covered it in blankets for the night, the next morning it was 60 degrees on the surface of the concrete due to the heat from curing.

I knew I bought that laser temp gauge for something . I forgot I had it. Thanks for the reminder. Jim


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[bczygan]

Keep it moist.

 

[nolimits76]

I think you are overly worried. A few things to note...

1. If the saw cuts are already done, you can walk on the slab.

2. Most concrete sets up enough to walk on it within 3-4 hours. That said, a good rule of thumb is to wait 24 hours.

3. Technically, concrete doesn't fully cure for 28 days. Being fully cured, means it is also now at full strength.

4. If you actually take test cylinders and test them, you will see that many times you reach full mix design strength well ahead of the 28 days. Recently my crew did some pours and lab results confirmed full strength (4000psi) within 3 days.

5. Although I don't see it commonly being done in the residential construction, it is common practice to test slump, concrete temp, air, etc. when pouring concrete and to take a minimum (3) test cylinders for each number of days you want to test concrete strength. So if you want to test at the 3 day, 7 day, 14 day, 21 day and 28 day mark you would have 5 tests x 3 cylinders for 15 cylinders total.

6. The advantage to taking extra cylinders and testing earlier (3 days, 7 days, etc) is that you can generally start working on the slab once it reaches 70% of strength. So if you have a 4,000psi mix and 70% requirement, then if you reach 2800psi in 3 days you can start erecting steel, etc. safely.

7. At the temps you noted, you can cover if you want. The heaters are overkill. At the end of the day, the slab is covered by your permanent structure and it already has protection. While temps may be 30* outside, it will be warmer inside a closed in structure.

 

[NUTTSGT]

I was on my floor within the week doing stuff in the garage, well working on the garage itself. As long as it doesn't get too cold, I wouldn't worry about the heat.

Now, if it was me, I'd be putting the O/H door up after the third day (72 hours) being careful with the tracks on the floor. With the tarp down and the floor exposed, I'd run the heater just for that extra heat so it doesn't see a big drop in a colder temp.

 

[naturalgas]

Checked slab with my laser temp gauge this morning 29 degrees outside and the slab was 49 degrees no heat for 24 hrs just keeping it closed up. I have a 3 to 4 week wait for overhead doors. Both are off size. A 18x10 carriage style front and a 6x8 smaller door on side. I really have no reason to walk on it other than to fully admire it, so I am resisting the temptation to walk on it. I had it sealed so I don't think I would want to wet it to keep it damp. Jim


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[pcmeiners]

A couple layer of plastic will help insulate and keep surface from drying too fast. With the plastic, the curing process, and the ground temp below the slab being high from mild temps, I would not worry too much.

 

[NUTTSGT]

Checked slab with my laser temp gauge this morning 29 degrees outside and the slab was 49 degrees no heat for 24 hrs just keeping it closed up. I have a 3 to 4 week wait for overhead doors. Both are off size. A 18x10 carriage style front and a 6x8 smaller door on side. I really have no reason to walk on it other than to fully admire it, so I am resisting the temptation to walk on it. I had it sealed so I don't think I would want to wet it to keep it damp. Jim


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It's great that you are getting the doors in the size you want but that ***** having to wait that long for them....especially since it's getting cold out.