Curing new concrete slab

[cthomas]

Will be pouring new floor soon and I am looking for advice on "moist curing" (flooding garage for a week) vs. "membrane curing" with a cure and seal product. I don't want to apply a "cure and seal" product if I will have to later strip it and apply a more permanent sealer. Anyone here used a "cure and seal" product?

 

[Morrisman]

Moist curing? Flooding? I've been told by many concrete 'experts' just to keep the surface damp if it is a real hot day, by laying sacking cloth on and keeping it damp with a light spray from a hose. I heard of the Romans curing concrete by putting it underwater, but as long as you have enough water available to ensure the chemical reaction completes properly I don't think you need to flood anything.

When I laid mine the concrete guy told me just to leave it open, as it was a cloudy winters day, no frost around, no sun. I covered it at night just in case we got heavy rain, which can take the cement out of the top 1/2" and make it powdery.

 

[bmwpower]

Yea, flooding would be for HUGE industrial sites where keeping a moist layer of burlap, etc. would be hard to do.

 

[twostory]

My stem wall is 3.5 inches higher than the slab, so I just build a dam where the garage door is, and flooded the slab for 5 days. The dam leaked, but not very fast.

I did cover the slab in clear plastic to keep the evaporation down. I also ran a hose under the plastic 24/7, but since I used plastic, the water flow rate was not very large. I probably used 2,000 gallons of water to keep it wet for 5 days.

 

[Morrisman]

My stem wall is 3.5 inches higher than the slab, so I just build a dam where the garage door is, and flooded the slab for 5 days. The dam leaked, but not very fast.

I did cover the slab in clear plastic to keep the evaporation down. I also ran a hose under the plastic 24/7, but since I used plastic, the water flow rate was not very large. I probably used 2,000 gallons of water to keep it wet for 5 days.

2000 gallons of water? Bejesus, I thought you to merely keep it wet enough for the chemisty to go down.

What is to be gained by this underwater world of concrete?

 

[john56h]

The longer it takes for the concrete to harden...the more strength it will have.

 

[PAToyota]

It really doesn't need to be flooded. And running water can actually wash away the lime and cement from the top surface - especially if a stream of water is hitting the surface. Light mist of water across burlap or under plastic is enough to keep it damp. You just don't want it to dry out completely at any point or the reaction stops. After three days it has reached 30% of its theoretical strength, 60% after seven days, and 98% after 28 days. Which is what kills me when someone specifies 4500psi concrete and lets it dry out in the first day...

 

[rt66jt]

Will be pouring new floor soon and I am looking for advice on "moist curing" (flooding garage for a week) vs. "membrane curing" with a cure and seal product. I don't want to apply a "cure and seal" product if I will have to later strip it and apply a more permanent sealer. Anyone here used a "cure and seal" product?

Cure and seal products are as permanent as any sealer. You will not need to strip it unless you opt for epoxy, paint or similar.

 

[john56h]

It really doesn't need to be flooded. And running water can actually wash away the lime and cement from the top surface - especially if a stream of water is hitting the surface. Light mist of water across burlap or under plastic is enough to keep it damp. You just don't want it to dry out completely at any point or the reaction stops. After three days it has reached 30% of its theoretical strength, 60% after seven days, and 98% after 28 days. Which is what kills me when someone specifies 4500psi concrete and lets it dry out in the first day...

The number of days compared to strength of concrete is not in reference to how many days it was kept moist during curing. It is a base-line of stregnth versus cure time. On large projects there are test samples taken during the pour (usually four test cylinders). The test cylinders are brought to a laboratory where they are broken in a press which measures the specific amount of force in PSI that it requires to break.

The first cylinder is broken after 7 days...if it breaks within 60% of the design strength (2700 PSI for a 4500 design mix) then the engineers are comfortable that the pour was successful. A second cylinder is broken at 14 days and a third at 28 days. The strength should be very close to 4500 PSI at 28 days, but if it isn't...often the fourth cylinder will be broken at a later date to determine if the strength has been achieved after an extended curing period.

Usually the same testing laboratory that is on site for collection of cylinders will also test for temperature, air entrainment and slump. The tests are taken for each truck load of concrete. On large projects there will be many test cylinders since four are taken from each load.

 

[Morrisman]

The longer it takes for the concrete to harden...the more strength it will have.

True, but concrete hardens, not dries out. It is not like water based paint where something evaporates. Concrete is a chemical reaction, involving heat, and water activates it. Correct, if you let it go dry in the sun the chemical reaction won't finish properly, but keeping it immersed in water is no better than just keeping the surface damp, just a lot more work.

 

[PAToyota]

The number of days compared to strength of concrete is not in reference to how many days it was kept moist during curing. It is a base-line of stregnth versus cure time.0

True, but concrete hardens, not dries out. It is not like water based paint where something evaporates. Concrete is a chemical reaction, involving heat, and water activates it. Correct, if you let it go dry in the sun the chemical reaction won't finish properly, but keeping it immersed in water is no better than just keeping the surface damp, just a lot more work.

What Morrisman is saying is what I was trying to get across - you don't have to flood it. The point that John misses is that the chemical reaction stops when it dries out. So if it is dry before seven days or twenty-eight days it isn't going to reach that ultimate strength as if it is kept most for the full twenty-eight days to let the reaction run its complete course.

 

[V-10 Killer]

Ok, here's a curveball. What about a garage slab thats poured after the garage is framed and roofed? You can keep it damp, at risk of introducing extra water into the lumber, but minimal to no sun to activate it.

 

[Uncle Buck]

It does not need any sun to cure, end of problem!

One more interesting note regarding concrete is that the ultimate strength of the concrete is not attained for some insane amount of time like A YEAR or perhaps more. Yes, I said a year. Being honest I do not recall the exact amount of time, but it is a fact that concrete continues to harden, many times long after a slab is poured or a structure is built. I do not claim to be an expert, but that was one of the trivial bits I recall being told when I used to work for a batch plant (not hands on, middle management).

I am looking for no arguement, I am simply sharing what they told me.

 

[PAToyota]

V10: That is exactly the way mine was done - the whole structure was framed, sided, and under roof before the slab went in. Goes a long way towards being able to let the slab cure on its own schedule.

Hholmberg: You'll notice my post above says 98% at 28 days. People ask why they don't just say 100% at 35 days or something. As you say, it is because that last little bit takes months if not a year or more!

 

[V-10 Killer]

I remember watching a special on the construction of the Hoover dam. They mentioned that the concrete would have taken a few hundred years to cure if just left there. So they installed refrigeration tubing or something in the concrete while they were pouring. Once they felt it was cured sufficiently, they filled the tubing with concrete too.
Yeah, curing is like an exponential function on a graph, it might never be 100%, but at some point we call it that for simplicity sake.

 

[kutza]

okay, We poured our 30x30 6in avg. depth monolithic slap today.
I have watered it don to a damp top a few times until night time.
What shall I plan on doing with it next few days? Hose it down all over. Let the surface semi (patchs) dry, hose it off again? endless cycle! I just spent my vacation and a lot of money on this, I just want it to cure right.
thanks.

 

[Junkman]

cover with burlap and keep it wet at all times. Do not allow it to dry out even for an hour....

 

[z28toz06]

I have mixed by hand and poured foundations for telecommunications equipment. My uncle and father were both wire lathers in New York City for 30 years. A friend of mine pours concrete for a living and just did my 24 x 32 foot garage. No one has ever made that big a deal out of it. Freezing was the worst thing that was ever worried about.

I am not an expert but know several and have never heard of watering concrete to this excess. There is a chemical reaction heat process going on, I understand that but to cure concrete is to let it dry out. What are we talking about strength wise here? Are you guys parking sherman tanks in your shops that you're worrying about this? I plan on putting a lift in mone and I have 4000 pound concrete poured and 4" deep. I have no worries what so ever about it's strength. This sounds like over kill to a non existing problem.

 

[SCOOTER]

I put a sprinkler on mine the morning after the pour 7am ( finished @ 1am) the the next two days it rained a little and on that third day I saw cut it...done end of story cured and not worring about it...

 

[kutza]

z28toz06 & Scooter
Thanks for helping me relax on this topic. I kept is water down, but not all day long. Anyways Over Worring, and Over annalyzing is why I am here!
thanks to all.

 

[Junkman]

If you look at concrete that is poured on state highway projects, you will see that they do keep them moist. I have seen some huge columns that were wrapped in plastic and had water running down the sides to keep them wet. If it wasn't important to keep the concrete wet during the curing time, they wouldn't go to the expense or trouble to do so. It is more important to do this during the extreme of summer than in the fall, but keeping them wet is still the goal for full cure strength. Read page 3 and into page 4 on this website....

Here is another good site to read.....

 

[dxdexter]

Moist cure period.....end of story. Trust me I work in a large materials engineering firm and deal with these matters daily.

I suggest at least three days to a week depending on temperature. Concrete should not be allowed to dry or the chemical reaction called hydration between the cement particles and the water will cease. Hydraulic cements such as Type 10 Portland can only gain strength if hydration is taking place and no other way.

Curing can be acheived by flooding, plastic coverings, wet burlap or geo-textile or a liquid membrane curing compound.

Slabs that are allowed to dry out in the sun, soon after placement can have such problems as cracking, curling, crazing and dusting. Dusting slabs are readily evident on many residential units. You can sweep and sweep, but all your doing is sweeping the surface away.

Saw cutting should be done ASAP (less than 24 hrs) and not several days later.

 

[mshedb]

The concrete guy I talked to yesterday (30 yrs in the business) said the most effective/least likely to be screwed up is to immediately seal the concrete after the trowel finish is completed. True, if you are going to epoxy the floor the sealant needs to be removed, but if you go with an outfit like Homepro floors (per Mr. Hinkley's suggestion) the shot blasting should take care of that.

 

[dxdexter]

The concrete guy I talked to yesterday (30 yrs in the business) said the most effective/least likely to be screwed up is to immediately seal the concrete after the trowel finish is completed. True, if you are going to epoxy the floor the sealant needs to be removed, but if you go with an outfit like Homepro floors (per Mr. Hinkley's suggestion) the shot blasting should take care of that.

These products act as a liquid membrane curing compound and actually prevent moisture loss so that it may be used for curing . They are used locally in the majority of exterior flatwork, curb and gutters, and sidewalks. As you mentioned the compounds generally have to be removed prior to floor coverings or adhesive applications, so most contractors tend to stay away from them for just that reason. They would be definitely be an option for a garage although they are an additional cost.

As you alluded to, they are somewhat foolproof, but most contractors do not apply them at the rate or coverage suggested by the manufacturer.

 

[Jason B]

I have mixed by hand and poured foundations for telecommunications equipment. My uncle and father were both wire lathers in New York City for 30 years. A friend of mine pours concrete for a living and just did my 24 x 32 foot garage. No one has ever made that big a deal out of it. Freezing was the worst thing that was ever worried about.

I am not an expert but know several and have never heard of watering concrete to this excess. There is a chemical reaction heat process going on, I understand that but to cure concrete is to let it dry out. What are we talking about strength wise here? Are you guys parking sherman tanks in your shops that you're worrying about this? I plan on putting a lift in mone and I have 4000 pound concrete poured and 4" deep. I have no worries what so ever about it's strength. This sounds like over kill to a non existing problem.

Quick question, and idea on how to make this new concrete match the old? I think a different company was used to replaced some bad slabs, and I want the two new pieces to MATCH.

 

[ron in sc]

I kept my concrete wet by keeping soaker hoses on it for 5 days.

 

[musclecarjohn]

I kept my concrete wet by keeping soaker hoses on it for 5 days.

tomorrow morning will be day 5 and I think I'm shutting the hose off then...

What should I do next...?I plan on sealing it after 28 days before I roll cars on it.Do I need to occasionally water it from now till then or just forget it?

 

[PAToyota]

Once it goes dry, the reaction stops.

 

[SCOOTER]

Quick question, and idea on how to make this new concrete match the old? I think a different company was used to replaced some bad slabs, and I want the two new pieces to MATCH.

Paint it all blue????

 

[Jason B]

The new concrete is the upper two sections, it's those that I want to try and match to the more beige color surrounding them... ANy ideas?