concrete pad curing guidance

[leesweet]

Searched back 50 days for 'concrete plastic' with no good results, so....

Just had my pad constructed, and he put a sheet of plastic over it with corner 'towers' of blocks to elevate it off the surface to minimize contact withe the concrete; I assume the plastic sheet is to keep extra water off (and animals?) and also to prevent it drying out too quickly. (Both water and dry are bad?  I dunno...)

Now, how long should I have to leave that sheet of plastic in place?  I've not had a chance to catch up with the contractor (who did a fantastic job:  crew even dug out seven bushes/stumps that we wanted gotten rid of for *no* charge!    ).   He's getting a good tip for that extra volunteered work!

Thought the collective wisdom here would have the answer, as always.

BTW, this is a 12x16 6" concrete pad with fiber mix and rebar for the SD Max I'm expecting to be installed after we return from vacation in September.    (Can't wait....)

[ebirrane]

Here is a good article on concrete curing:

http://www.stanleytools.com/default.asp?TYPE=STATICLEFT&PAGE=pros.htm&LEFT=left_pros.htm

It seems to recommend curing the concrete for 3-7 days.  

The plastic sheet is not meant to keep water off, it is meant to keep water *in* (reducing evaporation)  the longer moisture is in the concrete the stronger the concrete gets.  You should be "watering" the slab a few times a day to keep the top moist (or maybe only once a day if you are using the plastic sheet).

Rain is bad on a newly poured pad because the force of raindrops hitting the slab can cause pitting.  But that's only in the first severals hours after the pad is poured.



-Ed

[leesweet]

Very interesting, thanks for the link, which I'm keeping!  The area is sprinkled nightly by our lawn system for 30 mins. Is that enough to do the trick?

The article seems to be ambiguous as to whether I should remove the blocks and let the plastic (white, not the mentioned black... :-)  ) touch the slab to retain more moisture in contact with the concrete.  I don't care how long it takes to cure the best, since, as I said, it will be over a month until any real load is on the pad.  (Not the usual case by most here, of course!)  And, only the outer 2' will be exposed when the spa is on board, so any discoloration is a minor factor; the only place the plastic is touching is in the center for obvious physical reasons right now....  

So, does 'keep wet' mean 'under the plastic' or 'sprinkle on top of the plastic' so evaporation is retarded through any holes/keep the temp down?!  The ambient temp's been over 80 and will be around that for the next week, so that's not an issue in slowing curing...

Any comments welcome!

[bosco0633]

I just had over 200 sqft of concrete finished at my house.  The contractor advised me to not place heavy weight on it for a month at the front for vehicles.  He said the weight of the tub could be about 7 days.  As for the plastic, I had it on the day of.  What it is used for is to create a little moisture while curing.  That way the hot sun does not bake the tob and cause to dry to quickly.  This prevents the concrete from becoming brittle.  You should be able to take it off now.   In fact you should be watering the daylights out of it.  This helps bring out the color of the cement as well as cure it better.

Just my two cents.  My contractor was great as well and very informative.

[Chas]

I have always waited 3 days to place an empty spa, and a week to fill. Some of our subcontractors like us to wait two full weeks to fill.

Generall if you don't wait at least three days the surface is still soft enough to gouge, dent and knock off corners.

[Mendocino101]

A week to 30 days depending on temp and such for a filled spa ....also as mentioned the plastic is to keep the moisture in ....not all do it but its a good idea .....

[leesweet]

Thanks for the comments, as always.  Excuse my obtuseness... So, I should be getting the hose out and sprinkling the heck out of it *under* the plastic for the next few days?  

It appears there is considerable condensation under there, so this may be much ado about nothing, but the stronger the better, of course, especially with a SD Max (6000 total filled weight without people!   ).

Of course, the last thing I want to do is either to fill the Max and have it crack the concrete or have that happen come the 10 degree F temps we get sometimes in the winters!  

[leesweet]

Reread the article and came to the conclusion that I should be adding sprinkled water under the plastic for the next day or so.    Went out and did that;  good thing it's not the 95-100 F it's been last week but only 85!  

It's good (kinda) to have a good buffer of time before the spa arrives!

[ebirrane]

Thanks for the comments, as always.  Excuse my obtuseness... So, I should be getting the hose out and sprinkling the heck out of it *under* the plastic for the next few days?  

I think that would be the right thing to do.  Just a gentle mist, enough to keep the entire top moist.

-Ed