To Pour or Not to Pour ......Slab

Jawgarage · Dec 8, 2016

For those following my other posts you will see that my foundation is in and has passed inspection and that we can now backfill. We also are now into the time of the year that the temps here in NJ are now getting into that normal 30-50's days and 20-30's at night. My trusses and lumber are being delivered in Two weeks.

So do I pour the slab now or not? Do we simply backfill and lay gravel substrate and compact then pour slab in Spring? Hate to wait but dint want to screw it all up.

Richard Cranium · Dec 8, 2016

You could use heat blankets

readhead · Dec 8, 2016

Pour now. Concrete can be placed year around. When you are framing it is much easier to work on the slab than dirt.

lakeroadster · Dec 8, 2016

I waited until spring.. contractors in my area would not sign on the dotted line to follow 306 Guide to Cold Weather Concreting: http://civilwares.free.fr/ACI/MCP04/3061_90.pdf

Trust, but Verify!

Here's what I specified... and they wouldn't agree to:

The concrete shall only be poured if the ground temperature is above freezing. The concrete shall not be placed on a frozen sub base or frozen concrete forms

Contractor shall take whatever means is necessary to ensure that the concrete does not freeze and shall maintain a surface temperature of 50 F. for the initial 2 days (reference Chapter 7 of ACI 306). Recording devices shall be supplied (placed on the slab - under the insulating blankets) by the contractor and used both inside the barn (minimum of 2) and around the perimeter (one on each side) of the slab to ensure this. Recording device results will be reviewed by the contractor and owner on a twice daily basis. Blankets shall not be removed for 7 days if the temperature forecast shows temperatures below 50 F.

flan · Dec 8, 2016

My garage is 100% minus the slab. That said I'm waiting til spring. The 3/4 process is nice and solid I built on that without issue since it's nice and level and I can park whatever I want in there now so I'm in no hurry. No point risking it with cold New England winters.

pcmeiners · Dec 8, 2016

Not thrilled with pouring this late, I am in NYC, we are way over due for a nasty cold front. As Richard advises, heat blanket will make it OK, left on for awhile, if you can get them for a couple weeks that should do it. The ground presently is very warm, a definite plus. Watch your concrete guy, he will want to finish the concrete while it is too wet, don't let him add extra water. Think your biggest threat is not the weather but the concrete guy, if he "finishes" too early, adds water, does not have blankets or takes them off early there will be issues.

readhead · Dec 8, 2016

Lake makes the obvious important point. Make sure the concrete guys are familiar with cold weather requirements. Also important is that you are familiar also so you know if they are doing the correct job. The first important step is to cover the dirt with blankets as soon as slab prep is done so the ground does not freeze. Also be aware that pouring in the cold may increase the price. Some guys don't add anything around here because work slows down but that may not be the case where you are.

rmack898 · Dec 8, 2016

If you have a good concrete guy he will know what to do and work around the weather.
The temps are supposed to drop on the Jersey Cape this weekend, but I'm sure there will be a 3 or 4 day weather window to pour a slab in the coming weeks.

wssix99 · Dec 9, 2016

Jawgarage said:
So do I pour the slab now or not?

I'd hold off until you are in a position to control the temperature and keep things from freezing. If you want to move things along this winter, you can do it once you get the shell up.

We did this, tarped the windows/doors and built a temporary plywood shelf on the wall to hold a gas heater to keep the temperature up.

The other thing you'd have to worry about is the temperature of the ground. You'd need to heat the space for a while before pouring to ensure you aren't pouring the concrete on top of frozen ground.

Northislander · Dec 9, 2016

IMHO do a decent job of compacting and leveling your substrate and work off that to build the garage working off this for the winter is going to help to compact and settle the fill. Pour when the weather is better

duwem · Dec 9, 2016

The did mine a week ago. Day later put insulation blankets down. This morning the slab was still warm under the blankets (19F outside). They took the blankets off today.

Jawgarage · Dec 9, 2016

duwem said:
The did mine a week ago. Day later put insulation blankets down. This morning the slab was still warm under the blankets (19F outside). They took the blankets off today.

Thanks for all the advice everyone.

I spoke with the Mason today....he knows his stuff and has the blankets and is going to use them. Coming Monday to prepare the ground and lay the gravel. Will calculate the cement needed and order for a mid-week pour. I have the ability to run a large tarp from the wall of the existing garage to the outer block wall of the new addition and drape the sides too. I was thinking of doing that and running my kerosene jet heater from inside the existing garage and blowing into the new garage once the slab is poured. Even if it does not stay hot, it will keep the freeze out easily.

JDMopar · Dec 9, 2016

Check the forecast before you commit to pour. It's gonna be down to zero in your part of the country in a few days. That will need one helluva heated blanket! :shocking:

matt_i · Dec 9, 2016

I didn't see near zero for Cape May, NJ 10 day forecast. Lowest I saw was lower 20s overnight.

I would still pay attention to curing despite the cold.

Jawgarage · Dec 10, 2016

matt_i said:
I didn't see near zero for Cape May, NJ 10 day forecast. Lowest I saw was lower 20s overnight.

I would still pay attention to curing despite the cold.

We will keep a close eye on things. Right now the coldest they are calling for in the next 10 days is around 27 degrees where I am. I think the blankets and my tarping with heat will keep the cement content..... :bowdown:

Streetbu · Dec 10, 2016

Any good concrete guy can do it with out any issues. That being said, I'd wait until spring. It will give the the dirt a freeze/thaw cycle to style and mitigate any potential for settling and therefore cracking of the floor. It won't guarantee that it won't crack or settle, but it will help.

lakeroadster · Dec 10, 2016

Let's see a bunch of photos of the prep, pour and post pour activities :thumbup:

What did they do for compaction and did you get it tested? The Sub-Grade Compaction Thread

Jazz1 · Dec 10, 2016

I poured in December when I built. Insulated blankets on top for a few days. Temps dropped to -20C at night. There were no issues. I had contractor prepare site and pour. He knew what he was doing. I built the rest of the garage over the next two weekends

RWorth · Dec 10, 2016

The floor is forever, I would build the garage, then pour the slab when you can heat it. I poured mine in the late fall, and first summer I realized there wasn't enough expansion of an expansion joint and it cracked my foundation. I should have poured warm.

Pouring a slab wouldn't be an issue because it can expand infinitely, but I wouldn't pour the floor inside a foundation if it were me.

joes169 · Dec 10, 2016

With lows in the upper 20's, I wouldn't be concerned. Slow curing under blankets in Winter is still superior to rapid evaporation under a Summer sun IMPO.

Be sure to read up on "Carbonation" of concrete in relation to unvented heaters and fresh concrete before running a torpedo heater in an enclosure......

wssix99 · Dec 11, 2016

joes169 said:
Be sure to read up on "Carbonation" of concrete in relation to unvented heaters and fresh concrete before running a torpedo heater in an enclosure......

I don't think this is anything to worry about. There is CO2 in the air we breathe every minute of the day and for CO2 to get to such a concentration to greatly change the chemical reactions/uptake of carbon by the concrete, one would die of asphyxiation the minute someone entered the enclosure.

Jawgarage · Dec 11, 2016

I agree.....if I go this route and use the torpedo heater with the tarping, the tarps are not going to be airtight ......not even close. In short I will attach the tarp to the current exterior 30' garage wall which we are extending from. I will take the tarp all the way across the new 24' slab and attach it on the 45 degree angle to the new exterior cement block wall anchor bolts. Since the tarp will be 60' long, I will then have plenty to allow the tarp to simply hang down and sort of drape the sides forming a sort of enclosure. I would weight down those two sides as well. So you can see that there would be lots of air exchange going on. Again, my goal would be, in addition to the masonry blankets, to allow the tarp to keep the cold air from settling onto the slab, and the heater to help keep the air circulating above 40 degrees as a minimum. Lets see where we go this week with the weather.......now rain tomorrow which will delay the prep work.....and then 30's in daytime for Thur & Fri with Teens at night. We may simply prep this week and wait for the artic blast to pass and then pour next week.......

joes169 · Dec 12, 2016

wssix99 said:
I don't think this is anything to worry about.

It really doesn't matter what you "think". This is simple elementary "Concrete 101", and has been common knowledge within the industy for decades. Perhaps you should spend a little time educating yourself on the topic before pretending to be the expert yourself...........

Jawgarage said:
I agree.....if I go this route and use the torpedo heater with the tarping, the tarps are not going to be airtight ......not even close. In short I will attach the tarp to the current exterior 30' garage wall which we are extending from. I will take the tarp all the way across the new 24' slab and attach it on the 45 degree angle to the new exterior cement block wall anchor bolts. Since the tarp will be 60' long, I will then have plenty to allow the tarp to simply hang down and sort of drape the sides forming a sort of enclosure. I would weight down those two sides as well. So you can see that there would be lots of air exchange going on. Again, my goal would be, in addition to the masonry blankets, to allow the tarp to keep the cold air from settling onto the slab, and the heater to help keep the air circulating above 40 degrees as a minimum. Lets see where we go this week with the weather.......now rain tomorrow which will delay the prep work.....and then 30's in daytime for Thur & Fri with Teens at night. We may simply prep this week and wait for the artic blast to pass and then pour next week.......

Thanks, but you don't need to explain this to me. I do this or a living, and as a matter o fact, I spent most o last week inside of a heated enclosure laying veneer stone. I understand how they leak fresh air in, even when you're attempting to make them air tight, I also know from decades of first hand experience that CO2 is heavier than air, and will settle to the surface.

THat said, best of luck with your project. Just keep in mind, what your about to spend your hard-earned money "should" last you a lifetime, minimum. There's no realistic sense in trying to save a few weeks, or months for that matter, and end up with a floor that is problematic for the rest of the time that you own the property..........

Jawgarage · Dec 12, 2016

joes169 said:
It really doesn't matter what you "think". This is simple elementary "Concrete 101", and has been common knowledge within the industy for decades. Perhaps you should spend a little time educating yourself on the topic before pretending to be the expert yourself...........

Thanks, but you don't need to explain this to me. I do this or a living, and as a matter o fact, I spent most o last week inside of a heated enclosure laying veneer stone. I understand how they leak fresh air in, even when you're attempting to make them air tight, I also know from decades of first hand experience that CO2 is heavier than air, and will settle to the surface.

THat said, best of luck with your project. Just keep in mind, what your about to spend your hard-earned money "should" last you a lifetime, minimum. There's no realistic sense in trying to save a few weeks, or months for that matter, and end up with a floor that is problematic for the rest of the time that you own the property..........

Joes169.......I have trouble following sarcasm so really cant tell what your suggestion for the one asking for advice is ....me.

So you are saying that since you do this for a living and do work inside heated enclosures like you are now that it is OK......correct? Or that its OK to get the just get the job done and let someone else worry about failure later? Or?

Im not looking for a poor job here and in fact thats why we are doing 6" gravel, 6" slab, 4500# mix, wire reinforced, 10mil vapor barrier, with 4 piers three foot deep on footings ( 1 for the girder support and 4 for the automotive lift posts), then pouring above 40 degrees and using blankets along with an "enclosure" with heat for two days. Is there something more to do other than wait for a warmer stretch?

wssix99 · Dec 12, 2016

joes169 said:
It really doesn't matter what you "think". This is simple elementary "Concrete 101", and has been common knowledge within the industy for decades. Perhaps you should spend a little time educating yourself on the topic before pretending to be the expert yourself...........

The assertion that a torpedo heater will carbonize concrete in a room is far-fetched, so I shared a thought rather than citing references that don't exist. If you want to make these kinds of representations before the Garage Journal Moderators put you the "Expert Merit Badge" on your avitar, you'll need to share some sources of fact with us.

joes169 said:
I also know from decades of first hand experience that CO2 is heavier than air, and will settle to the surface.

How do you explain the survival of mammals on this planet, then? By this rationale, all CO2 would separate from the air in Earth's atmosphere, sink to the ground and suffocate us all. By this rationale, the CO2 we exhale would also fall to the ground and suffocate rabbits and other ground-dwelling creatures.

I hope you don't give advice to customers based on this line of thought.

wssix99 · Dec 12, 2016

Jawgarage said:
we are doing 6" gravel, 6" slab, 4500# mix, wire reinforced, 10mil vapor barrier

All good.

Jawgarage said:
with 4 piers three foot deep on footings ( 1 for the girder support and 4 for the automotive lift posts)

My math has 1 + 4 = 5 piers.

Jawgarage said:
4 for the automotive lift posts)

Can we have some more time to convince you not to put in piers for the lift posts? This will encourage your floor to crack. (That is one of the reasons why your lift instructions do not direct you to do such a thing.) As the concrete cures, the cement shrinks and the slab generally pulls away from the walls towards the center of the room. These piers will anchor the slab to the ground, parts will still shrink, pulling away from them - which can lead to cracks.

There is a document by the American Concrete Institute (Design of Slabs-on-Ground ACI360R-06) that specifies practices for slabs on ground and all the industry practices for machinery foundations and column foundations are in there. Your girder footer should be isolated by expansion joints in a diamond shape, with your saw cuts radiating out from the points. (This will keep cracks from forming around it.) Your lift was designed with metal base plates to spread out the loads on your slab and it will be very happy on a flat 6" slab, which is thicker than spec.

matt_i · Dec 13, 2016

It would be interesting to also see if you could get a non-chloride admixture (NCA) put in the concrete as a reaction speeder. There's all sorts of info about how bad the classic CaCl2 is for reinforcing steel but not a lot of case studies that I've been able to find detailing how much/how fast the degredation is (I read that it has something to do with how much direct moisture makes it to the slab...good reason for a thick stone layer and good vapor barrier). Millions of structures have been poured with the chloride and are still standing though.

That's one point I missed in my pour, they used 2% or 3% CaCl2 in an Oct25ish pour that didn't require blankets. The finishers spent plenty of time there after pouring at sunup, and I think they'd probably be there way late into the night without the speeder. The directional evidence is that the NCA is more expensive but I don't know how much....

Jawgarage · Dec 13, 2016

wssix99 said:
All good.

My math has 1 + 4 = 5 piers.

Can we have some more time to convince you not to put in piers for the lift posts? This will encourage your floor to crack. (That is one of the reasons why your lift instructions do not direct you to do such a thing.) As the concrete cures, the cement shrinks and the slab generally pulls away from the walls towards the center of the room. These piers will anchor the slab to the ground, parts will still shrink, pulling away from them - which can lead to cracks.

There is a document by the American Concrete Institute (Design of Slabs-on-Ground ACI360R-06) that specifies practices for slabs on ground and all the industry practices for machinery foundations and column foundations are in there. Your girder footer should be isolated by expansion joints in a diamond shape, with your saw cuts radiating out from the points. (This will keep cracks from forming around it.) Your lift was designed with metal base plates to spread out the loads on your slab and it will be very happy on a flat 6" slab, which is thicker than spec.

Wssix99 --- thanks for the detail and yes 5 piers.

The 4 lift piers are supposed to be under the gravel layer or no higher than within it and not in contact with the slab. I was told this was a good added measure for the nearly all sandy base we are working in. Since the slab is not poured I can measure myself and make sure these will not be in contact with the slab and knock off a course is needed.

493mike · Dec 13, 2016

This seems like an excellent time to install a nice PEX radiant floor system-fully functional!
Mike

Jawgarage · Dec 13, 2016

493mike said:
This seems like an excellent time to install a nice PEX radiant floor system-fully functional!
Mike

Now that would be nice AND toasty but not in the budget at all.

joes169 · Dec 13, 2016

http://www.pennradiant.com/library/CARBONATION OF CONCRETE.pdf

http://frost-fighter.com/wp-content/uploads/2013/10/Concrete-Carbonation.pdf

http://www.constructionexec.com/Art...cient-thermal-control-of-concrete-curing.aspx

https://www.concretenetwork.com/cold-weather-concrete/curing.html

http://www.cemstone.com/userfiles/file/PCA-Cold Weather Concreting.pdf

joes169 · Dec 13, 2016

Jawgarage said:
Joes169.......I have trouble following sarcasm so really cant tell what your suggestion for the one asking for advice is ....me.

So you are saying that since you do this for a living and do work inside heated enclosures like you are now that it is OK......correct? Or that its OK to get the just get the job done and let someone else worry about failure later? Or?

Im not looking for a poor job here and in fact thats why we are doing 6" gravel, 6" slab, 4500# mix, wire reinforced, 10mil vapor barrier, with 4 piers three foot deep on footings ( 1 for the girder support and 4 for the automotive lift posts), then pouring above 40 degrees and using blankets along with an "enclosure" with heat for two days. Is there something more to do other than wait for a warmer stretch?

My advice is either wait until it warm enough to pour the floor with accelerated concrete (40 degrees plus for at least 8 hours) and cover sufficently with insulating blankets.......

OR

Wait until Spring when freezing is no longer a concern, and the building is erected, making it much easier and saer to heat.

As easy, in your head or online, as it may seem to build a shelter and heat it, it's not that easy in reality, and it has a number of risks associated with it, as well as the fact that it's often a waste of time and money. Again, good luck on whatever you decide to do.

wssix99 · Dec 13, 2016

Jawgarage said:
The 4 lift piers are supposed to be under the gravel layer or no higher than within it and not in contact with the slab. I was told this was a good added measure for the nearly all sandy base we are working in. Since the slab is not poured I can measure myself and make sure these will not be in contact with the slab and knock off a course is needed.

That's an interesting idea that I haven't heard of before. If the concrete reinforcements aren't in contact with the main field of the slab, then they shouldn't effect the quality of the slab, so that's good.

The concept still sounds a little off to me, though. One of the things a floating slab does is move as the ground heaves. If you have four concrete piers under the gravel, which extend below the frost line, I'd be concerned that they could put stresses on the floor as the ground and slab heave but the footers/piers stay in place.

In the end, the extra work is really unnecessary. Your car weighs on the floor through four points (just like a four post lift) and all the pressure/weight of the car sits on the contact patches of the four tires. The base plates of the 4 post lift are comparable or larger than the contact patches of tires, so the pressures/weight on the floor is just the same as if a car were parked on the slab with no lift at all. If you calculate all that out over a 6" slab, it translates to just a few psi (much less than 5 psi) of pressure at the interface of your slab and gravel. Where the gravel meets the dirt, the pressures are even less. (The pressures decrease close to the square of the distance from the surface of the slab.)

matt_i said:
It would be interesting to also see if you could get a non-chloride admixture (NCA) put in the concrete as a reaction speeder.

Our mason used this during our cold weather pour and we didn't have any ill effects. He also preferred it to reduce his finishing time. I was insistent though, that we do the saw cut joints the very first thing the next morning since we were accelerating the cure.

Toomanytools? · Dec 13, 2016

Jawgarage, post #4 by lakeroadster hit some pretty good points. It is easier to pour when temps are in the 40's and above, by it can be done. I'm in Eastern Washington State daytime temps in the mid 20's and expected lows at night in single digits (1) yikes. I'm waiting for my pour I was hoping to get things done before December by hold up on permits has delayed it, I did cover the ground with a tarp which is compacted and ready but too cold for now.
On your piers can't you just thicken the slab for your lift? For most of the lifts I looked at ( BendPak 10,000lb) I think 5" slab was fine. Just wondering. Good luck.

wssix99 · Dec 13, 2016

Toomanytools? said:
I did cover the ground with a tarp which is compacted and ready but too cold for now.

This is a great point. If one is thinking about a late pour, covering the ground with insulating blankets NOW will help delay the freeze of the ground and keep things wamer for the pour later.

We did this, also and it saved us from a frost or two before our pour.

Jawgarage · Dec 14, 2016

Thanks everyone....all great points.....here is where I'm at.......due to arctic blast for Thursday and Friday we decided to NOT prep for gravel or anything else in order to keep what will be the sub-base from freezing. Next week when it is above freezing, we will remove all the necessary sand/soil to expose down 12"+ below the ultimate slab height and lay the 6" gravel base and prep for the 6" slab of 4500# mix. As for the 4 piers that were placed for the automotive lift......those are being cut back to one course of block on top of their footings and will be covered by the same 6" base and 6" slab with wire reinforcement. This is nearly all sand here and the moisture in the sand under where this addition is going is very slight. Heaving has not been a problem at all with the current garage we are adding onto nor the other structures on the property. All in all though, I like the idea of getting these 4 piers "away from" the slab itself so the slab can do "it's thing". Hope is to do all the prep work Monday and pour Tuesday, before the rains come in on Wed/Thurs......

wssix99 · Dec 14, 2016

Sounds like a great plan.

We are starting to get "blasted" and I can personally certify that it is indeed horribly cold.

Jawgarage · Dec 14, 2016

For those interested I started a new thread for just the project itself. I will be keeping questions/SOS's individually and posting all project updates to the other posting called "My Adirondack Conversion"

lakeroadster · Dec 14, 2016

The Link To Jawgarage's Adirondack Conversion

duwem · Dec 15, 2016

Here is mine after the first snow on it. Can see where the thickened parts are still giving off heat by the lack of snow.

To Pour or Not to Pour ......Slab

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