Replies

1. 
   jet | Jul 25, 2002 05:52am | #1

   I've seen jute material put on top of the concrete and kept wet. For others out there is this a good idea?

2. 
   Catskinner | Jul 25, 2002 06:27am | #2

   You might check out the American Concrete Institute's "Practitioner's Guide To Hot Weather Concreting."

   ACI

   248/848-370

   http://www.aci-int.org

   It's full of useful info. For example, I didn't know that "concreting" was a verb until I read this. <G>

   High temps, low humidity, wind, and wide day/night temperature swings all can spell trouble for concrete flatwork.

   Thermal shock, plastic shrinkage cracking, and curl are all things to watch out for, and all largely related to curing practices, assuming everything else was done right.

   A couple inches of damp sand under the slab (over the vapor barrier), a very light mist of water continuously applied to the finished concrete for 3 days, a covering as previously suggested, all helpful.

   Hot weather of course makes the material go off faster, so you may need extra crew.

   Don't try to compensate for this by pouring at a higher slump. It doesn't work that way. If you need more time use a set retarder.

   I'm a believer in curing compounds in hot or cold weather. You need to be absolutely certain that if you use a compound it will not interfere with adhesives, thinset, stains, dyes, or anything else you might be applying to the concrete.

   I've used VO-COMP 25 and VO-COMP-30, both water-based VOC compliant, and they worked real well under extreme conditions.

   Be careful that the evaporation rate doesn't fool you into thinking the bleed water is all gone and you can start finishing. If the weather makes the bleed water evaporate faster than it comes to the surface and you seal up the rest of the bleed water with your trowels you could have a problem later. This one is tough to call. Other than the thumbprint check, I don't know what to say.

   Maybe we can get Gabe to weigh in on this one.

   DRC

   
   

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   Edited 7/24/2002 11:49:06 PM ET by Dave

1. 
   brownbagg | Jul 25, 2002 05:31pm | #3

   what we do is pour at 4 in the morning. typical day is 96 degrees with heat index of 106, so we pour early, go home early.

1. 
   Gabe | Jul 26, 2002 01:07am | #4

   Common sense can go a long way to creating a perfect slab in hot or cold weather.

   We've done wet cures that have lasted 2 weeks for some special cases.

   In really hot weather, using burlap or jute and spraying with a lawn sprinkler for a week will just about cover most situations.

   By keeping it wet and cool, you slow down the curing process and prevent shock. It's that initial dramatic change in temperature that you want to avoid. Remember, curing concrete creates it's own heat and combining that heat with the radiated heat from a blazing sun spells shock.

   If I had my drudders, and I do, in extreme hot cases, I would pour and finish after dark, cover with burlap and keep wet for the next 7 days.

   Trying to finish a slab in a hot drying sun can be a greater challenge than wet curing at your convenience. More slabs are ruined during hot weather than any other time of the year.

   Gabe