30x30 concrete slab water cure

[CurlyDave]

I water as soon as the surface is hard enough to not be marred by a light mist. Typically within a few hours of finishing the slab.

Then a heavy mist and cover with clear plastic. In the morning flood under the clear plastic.

 

[dcyrilc]

Convenient topic to have run across ...

Just had the floor of my garage poured today, with the finish work completed about 1:00 PM, then they sprayed a sealer to help prevent stains later.

Asked my concrete guy about wetting the surface, and he recommended waiting until mid-day tomorrow to give the sealer time to dry. Is it worth trying to keep things damp, or is the sealer probably doing as much good as I could hope to gain from keeping it damp, anway?

I would recommend following your concrete guys advice. As someone posted earlier in this thread, the purpose of misting the concrete is to prevent it from drying too quickly. The sealer will help to prevent evaporation. Before misting the concrete you will want to let the sealer harden so that you don't wash it off. The slab will not have a lot of quick evaporation over night or in the morning. These problems occur during the heat of the day. Mist it from time to time in the afternoon and keep it damp until the sun sets and you'll be fine. If you want, you can repeat this for a second day. After that, it's basically done unless your temps are getting into the 90s or higher.

 

[scott_vt]

I water as soon as the surface is hard enough to not be marred by a light mist. Typically within a few hours of finishing the slab.

Then a heavy mist and cover with clear plastic. In the morning flood under the clear plastic.

Good Mornin Rodney,
We pretty much did what Dave suggested after using our power trowel, and our slab came out exceptional !

To date I have not sealed the concrete slab yet but hope to this fall before the cold weather hits... I would use this method again.

We also sawed our 28' by 42' slab about an inch deep into 9 sections to prevent any cracking down the road, I would also do this again, to date no visible cracks !

 

[Egon]

Scrivy, it's quite possible that there are hundreds of slabs out there that never heard of keeping the surface wet for a few days so your slab will not be lonely! :thumbsup:

 

[dcyrilc]

Scrivy, it's quite possible that there are hundreds of slabs out there that never heard of keeping the surface wet for a few days so your slab will not be lonely! :thumbsup:

Hundreds??? I'm willing to bet that thousands would be more accurate.

 

[crbr]

Convenient topic to have run across ...

Just had the floor of my garage poured today, with the finish work completed about 1:00 PM, then they sprayed a sealer to help prevent stains later.

Asked my concrete guy about wetting the surface, and he recommended waiting until mid-day tomorrow to give the sealer time to dry. Is it worth trying to keep things damp, or is the sealer probably doing as much good as I could hope to gain from keeping it damp, anway?

I despise sealers and the underlying intent of it. Sealer is such a false sense of accomplishment with concrete.

 

[CurlyDave]

Scrivy, it's quite possible that there are hundreds of slabs out there that never heard of keeping the surface wet for a few days so your slab will not be lonely! :thumbsup:

This is exactly the reason that finishers spray a sealer on the slab when they finish. It slows dow evaporation of water from the concrete and produces a better finish than not using a sealer on an uncovered slab.

Concrete hardens by absorbing water, and actually needs a little more water than is provided in the original mix. The very best surface comes from providing that extra water early in the curing process.

All states, which use huge amounts of concrete for highways, know this and insist on covering concrete with wet burlap, wet straw, or old wet carpets. This is inconvenient for small-area concrete finishers, because they would have to come back and pick up the wet, soggy material several days after the job is done. This is why the sealer was developed. It provides a method for the finisher to provide an "acceptable" job without providing the extra water really needed. No return trip and the finisher is happy.

While finishers are skilled in providing the correct surface for your slab, I would not expect them to understand the chemistry of concrete curing, or to be able to give advice on anything other than their standard methods. An engineer is going to understand concrete curing and be able to advise on the best way to develop maximum strength, but don't put a trowel in his hand and expect him to deliver a good surface finish.

I have had finishers tell me that water and plastic will surely overheat the concrete and ruin it, when the truth is that it produces the strongest slab possible.

P.S. if you prepare for the job properly and have the plastic sheeting on hand to cover the slab don't let the finisher put the sealer on it -- all it will do is slow the absorption of water by the concrete.

If you really want it sealed, wait 30 days then apply a sealer meant for cured concrete. I find that the water cured concrete is harder and less permeable than most and doesn't really need a sealer.

 

[Duffster]

This is exactly the reason that finishers spray a sealer on the slab when they finish. It slows dow evaporation of water from the concrete and produces a better finish than not using a sealer on an uncovered slab.

Concrete hardens by absorbing water, and actually needs a little more water than is provided in the original mix. The very best surface comes from providing that extra water early in the curing process.

All states, which use huge amounts of concrete for highways, know this and insist on covering concrete with wet burlap, wet straw, or old wet carpets. This is inconvenient for small-area concrete finishers, because they would have to come back and pick up the wet, soggy material several days after the job is done. This is why the sealer was developed. It provides a method for the finisher to provide an "acceptable" job without providing the extra water really needed. No return trip and the finisher is happy.

While finishers are skilled in providing the correct surface for your slab, I would not expect them to understand the chemistry of concrete curing, or to be able to give advice on anything other than their standard methods. An engineer is going to understand concrete curing and be able to advise on the best way to develop maximum strength, but don't put a trowel in his hand and expect him to deliver a good surface finish.

I have had finishers tell me that water and plastic will surely overheat the concrete and ruin it, when the truth is that it produces the strongest slab possible.

P.S. if you prepare for the job properly and have the plastic sheeting on hand to cover the slab don't let the finisher put the sealer on it -- all it will do is slow the absorption of water by the concrete.

If you really want it sealed, wait 30 days then apply a sealer meant for cured concrete. I find that the water cured concrete is harder and less permeable than most and doesn't really need a sealer.

The only state work that gets water cured that I have seen is bridge decks.

 

[sandman2234]

Interesting post, since in my days (mid 1970's) doing concrete Quality Control work on prestessed concrete, I have always known that adding water to concrete was the fastest way to weaken it.(during a pour) However, once the preset has occurred (usually about 4 hours), I can understand why keeping the concrete from drying too quickly would help. However, has anyone got any ideas on just how fast concrete is allowed to cure without harming it?
We poured hundreds of yards of concrete a day, in forms and they were stripped out of the forms the next day, picked up, moved, and a new pour readied. Before any could be stripped from it's forms, I had to confirm via test cylinders that the concrete was indeed cured enough to withstand it's own weight, and be adhered to the prestress cables (main reason!). We cured using added heat, of around 180 degrees to expedite the curing, overnight. The heat was indeed done with steam (cost effective) so that goes to the arguement of adding water (kind of), but if the steam was too direct, it literally destroyed the concrete. (we used indirect heat, and during cold weather insulated tarps)The heat was NEVER added before preset was achieved.
Unless the surface was exposed to direct sunlight, and extremely hot, I can't see where the addition of water would help after the surface has cured for a couple of days. However, just for the record, concrete will continue to cure rapidly for 28 days, usually up to it's maximum of what the original batch will allow (we constantly had tests over 7,000 psi but that is with a stronger mix, a 3" or less slump, and no added water. Normal concrete mixers max out at about half that strength, and less if there is a water hose on the jobsite.
David from jax

 

[SevernDH]

Thanks for the info, everyone. I will be keeping my slab wet for the rest of the today, just to be sure, but it sounds like the sealer will keep that from doing much good.

I don't expect floor strength to be a big issue, as the ground seemed to pack pretty well if the effort needed to drive the grading stakes was any indication. Besides, I don't expect there to be a lot of driving on the surface as it will primarily serve as a wood shop.

One thing these guys did that is a little different than I have seen before was building in metal expansion strips to quarter the slab, then they poured and finished a little higher than the expansion strips. Their reasoning was that they felt the finished floor generally looked better that way than if they edged the expansion joints. So far, I am starting to see the seems as it has cured more, and they are probably right that this will look better than edging. Besides, it should allow easier movement of tools on mobile bases, which will be the primary inhabitants, and I MAY be able to park in there if I am lucky!

Thanks again!