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Fix'n it 10-19-2012 09:20 AM

cold weather pour ?
with the bags of cement/concrete at the box stores. what is the coldest temp that it can be properly poured ? it would be a small pad/slab, maybe 2'x2'x8-10"

jomama45 10-19-2012 11:30 AM

It needs to be above freezing for at least a few days, or for something that small it can easily be covered with a blanket or something once it sets up. It costs a few bucks more, but the red Quikcrete bags set MUCH faster than any of the others, and don't bleed nearly as much water up to the surface, expediting the finishing time. It may set too fast though, so you may want to use one red bag to one 80# "5000" bag.............

Canarywood1 10-19-2012 03:27 PM


Originally Posted by Fix'n it (Post 1033872)
with the bags of cement/concrete at the box stores. what is the coldest temp that it can be properly poured ? it would be a small pad/slab, maybe 2'x2'x8-10"

At least 3 weeks before freezing weather sets in,and keep it protected with some kind of cover for a full month.

jomama45 10-19-2012 03:41 PM

Tecnically, it needs to meet a min. of 1500 psi before freezing, which could take as little as 6-8 hours. The larger problem comes from the fact that concrete doesn't actually cure under 40 degrees, so it will go into winter with minimal strength.......

concretemasonry 10-19-2012 04:57 PM

Just keep in mind that temperatures that commonly miss used are air temperatures since it takes a long time for concrete to go down in temperature because of the heat of hydration created and the mass. A 10F or 20F degree temperature for 8 or 10 hours for air temperature has little effect on the concrete temperature if the concrete is covered or better yet, blanketed to provide ideal curing temperatures that will make it be in good condition in the spring.

The full month/28 days is really a fantasy and a requirement for standard mixes made in a lab with standardized conditions to provide mix designs and guidance for real use. the true test of concrete comes after adequate protection (temperature exposure to air and moisture retention) od real applications in variable climates.

The other guidelines of something about 1500 psi are good guidelines to eliminate scaling and limit freeze-thaw problems, but cannot be verified in time to order to proceed but they are very good practical guideline points to try to meet.

Concrete strengths are really best known by the contractor since he has the experience and can give a better answer when it means something in the real world.

I have seen footing poured at -10F the same day of excavation and usually the first course of block laid in heated mortar the same day before covering before leaving. They return the next long day or two to finish the basement and cover it in time for the carpenters to move in and build the first floor platform to enclose the basement and hang a furnace for heat. Of course that is not a little slab, but it shows what a long term experienced concrete and masonry contractor can do with scheduling because of recognition of the problems associated with cold weather construction. - they even order the sand for mortar for delivery in advance after they set the corrugated pipe for heating the sand the day before the excavation is done.

It is all about managing the air temperature, the benefits of the mass of the soil and materials and containing the natural thermal benefits.


Fix'n it 10-20-2012 09:13 AM

thanx guys.

i am right on the edge of doing this properly, 30'-40's at night here now. and i am not ready to start this project. so, if i proceed, i will just build a temporary support foir the winter. and do the slab in the summer.

this would be a support for a metal fireplace chimney flue. the pipes would run out the side of the basement block wall, and up the side of the house.

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