Curing concrete
- Thread starter d33pt
- Start date
tcianci
Well-known member
The first step in curing concrete is a good diagnosis. You will never cure it unless you know what's really wrong with it and then you need to weigh out the long term side effects of any course of treatement.
blue dog
Banned
um, well, huh!
jklingel
Well-known member
That is what an engineer told me to do w/ mine, but he also recommended the visqueen over it; maybe because it is pretty dry here.
MrMark
Well-known member
Good question! I would at least cover it with plastic for a week. You can use wet old carpet or wet burlap to cover the concrete with. One way or another you need to keep it wet for a week. Or, you can use the sealer like posted above.
JustBob
Well-known member
If you plan on staining the concrete, do not use a curing compound/sealer.
Jazz
Well-known member
I used to test concrete. The wetter the better. In fact once it sets up we used to leave the concrete in a tank of water to get the hardest cure. High humity really helps also. On the other hand, adding water to the mix BEFORE it sets will really weaken it significantly.
Wet concrete mix is weaker than a dry(er) concrete mix.
But once it starts to set up, keeping the concrete wet makes it stronger. Because concrete doesn't cure by "drying", but by a chemical reaction (hydration) that needs water.
Hence the tips about covering it (plastic sheets, wet burlap, old wet carpet) or putting 'curing compound' (slows down evaporation mostly, so the moisture already in the concrete stays in so the concrete can cure without drying out as much) or letting it cure in or covered by water.
But I like tcianci's answer.
More tips? Make sure the base is prepped properly. Use the 'proper' additives for the pouring conditions and weather conditions. Consider air-entrainment and fiber reinforcement. Use 'decent' concrete (the proper strength aka proportion of actual cement to the aggregates in the mix). Don't make the concrete too wet when you mix it or have it mixed. The drier, the better (from a strength standpoint). Have enough manpower to do the work, because concrete waits for no one.
Have the forms properly placed and reinforced and leveled and so forth. btw, using 2x4 forms does NOT give you 4 inch thick concrete. More like 3 inch thick.
But once it starts to set up, keeping the concrete wet makes it stronger. Because concrete doesn't cure by "drying", but by a chemical reaction (hydration) that needs water.
Hence the tips about covering it (plastic sheets, wet burlap, old wet carpet) or putting 'curing compound' (slows down evaporation mostly, so the moisture already in the concrete stays in so the concrete can cure without drying out as much) or letting it cure in or covered by water.
But I like tcianci's answer.
More tips? Make sure the base is prepped properly. Use the 'proper' additives for the pouring conditions and weather conditions. Consider air-entrainment and fiber reinforcement. Use 'decent' concrete (the proper strength aka proportion of actual cement to the aggregates in the mix). Don't make the concrete too wet when you mix it or have it mixed. The drier, the better (from a strength standpoint). Have enough manpower to do the work, because concrete waits for no one.
Have the forms properly placed and reinforced and leveled and so forth. btw, using 2x4 forms does NOT give you 4 inch thick concrete. More like 3 inch thick.Flange
Well-known member
Err, not exactly correct. Decide how strong you want your concrete to be then decide how "wet" you want your fresh concrete to be when it comes out of the wagon (in the UK this is the "slump" of the concrete). It will only be weaker if you add more water later. Just make sure you have the right mix to start with.
Agree with comments about covering etc. The main thing is to make sure it is allowed to set rather than dry out, although what you cover it with will depend on the finish you apply to it. Dont let it freeze, although if it is 60 degrees during the day it sounds as if you are Ok, assuming it does not drop too much at night.
Remember that anyone who says they are waiting for their concrete to "dry" does not understand the process. The water is there to activate the glue (cement) that binds the aggregate together. It is a chemical reaction not a drying process. Thats why concrete gets warmer when you mix it because it is an exothermic reaction between the cement powder and the water.
viper86
Well-known member
if you use curing compound, don't be stingy at the joints. covering in burlap and keeping it moist for 7 days is even better. In the structures lab we would cover in burlap, wet it, then cover in plastic to keep the evaporation down. If you're outdoors, the burlap would be sufficient as long as you give it a good sprinkle every so often. Heck, on bridge decks around here they set sprinklers up over the burlap to keep them constantly wetted down.
pauls340
Well-known member
Let's take a different approach. Based on your first post date, you now have concrete. Some facts are not changeable...in every 81 sqft x 4" thick concrete slab, you get 32 gallons of water. The chemical reaction between the cement and the aggregate used 15 gallons of water to make the concrete, period. The remaining 17 gallons is there so the concrete can be placed (in the prepped hole). If no body lied to you, ACI says the concrete should get to the psi level you paid for. ie, if you ordered 3000 psi, in 28 days it should be 3000 psi. At this point find Vapor Lock by ImcoSPG and apply their penetrating sealer. VL uses that "free water" to form gel in all the capillaries and will waterproof and vaporproof that concrete...forever. In the future if you want to coat the concrete with anything, just grind it or acid etchit. Good luck
Gary S
Well-known member
Unless your weather is extremely hot, just leave it alone. It will cure by itself if you don't mess it up.
blue dog
Banned
Good advise.
mkbrower
Active member
This is basically what my concrete guy told me. Everything turned out fine.
what alot have not mention, if the top drys out quicker than the bottom, the different in "pull" will cause the concrete to crack, so by slowing the drying process and keeping the concrete temp down, the pull or shrinkage will lessen and the psi would be higher enought to resist cracker.
all concrete cracks, no, only sloppy workmanship concrete cracks
all concrete cracks, no, only sloppy workmanship concrete cracks
oldwino
ALLIANCE MEMBER
Most everyone was somewhere around the correct answer.
Concrete requires approximately .21% water to cement ratio to fully hydrate. A mix this stiff would be extremely difficult to place or finish so additional (convenience) water is added for placement. The release of this additional water is what causes shrinkage cracking. The goal of "curing" is to prevent this excess water from leaving the mixture too rapidly. This can be done by a sprayed on membrane on the finished concrete, flooding of the surface (keep it wet via wet carpets, saturated sand, or ?), sealing with visqueen, etc. What you want to do is slow the rate of drying to allow the chemical reaction to finish.
Concrete requires approximately .21% water to cement ratio to fully hydrate. A mix this stiff would be extremely difficult to place or finish so additional (convenience) water is added for placement. The release of this additional water is what causes shrinkage cracking. The goal of "curing" is to prevent this excess water from leaving the mixture too rapidly. This can be done by a sprayed on membrane on the finished concrete, flooding of the surface (keep it wet via wet carpets, saturated sand, or ?), sealing with visqueen, etc. What you want to do is slow the rate of drying to allow the chemical reaction to finish.
tobaccofarmer
Member
I setup a timer hooked to a solenoid that turns on every 5 min and stays on for 1 min and then i hooked sprinklers to it. When I poured my concrete i setup the sprinklers and left in alone for 45 days. It was wet for 45 days straight and so far so good. Also whats underneath is important. Around here most all concrete is poured in 100 degree weather wind etc and looks like ****. cracks everywhere and no one seems to care otherwise. I wasnt going down that path so sometimes things require extreme measures but I am happy I did what I did so far.