One thing all online discussions acknowledge is the importance of proper moist curing. For at least 3 days, concrete should be allowed to cure. It it must be kept moist through one of several means: complete water immersion, continuous spraying or misting, porous covering that is kept moist, plastic covering, or surface coating.
Ronnie had talked about dam for immersion, canopy, and plastic covering, but when July 13 came, he and his crew simply finished the concrete and left. I asked about curing again as he was leaving, and he said it would not be a problem. He said I could cover with plastic, in fact he could get some plastic, but it might not be ready to install just yet, and it would cause staining. I should have gotten him to get plastic. He said I could also hose it down. He said I could hose it down as much as I liked, it would not be a problem, would even make it better.
What I actually did, starting at 2:30pm, was at first a very light hosing, just like misting but done with regular nozzle until the surface looked slippery. I did that about every hour until 7pm. But I continued reading about curing, and it was seeming clear that the surface needed to be kept CONTINUOUSLY moist, not just periodically moistened, and kept at as constant a temperature as possible. So occasional hosing as I was doing might have done more harm than good, by causing variations in surface temperature and moisture, or even leaving mineral deposits from the drying tap water that could crystalize or interfere with curing. I read about damage from crystalization in the late afternoon on July 13, but then read on July 15 that it is a weathering problem, not generally a curing problem.
The "misting" position on a ten-option knob was useless, the slight wind just blew the mist right back into my face.
When concrete is poured without protection and it rains, it is possible for surface damage to occur that makes the concrete surface weaker, and prone to dusting and having bits break off. My water dusting, however, was nothing like rain.
The "misting" position on a ten-option knob was useless, the slight wind just blew the mist right back into my face.
When concrete is poured without protection and it rains, it is possible for surface damage to occur that makes the concrete surface weaker, and prone to dusting and having bits break off. My water dusting, however, was nothing like rain.
At 8PM on the day of pouring I went to Lowes and got plastic covering and bricks. I hosed again when I got back around 10pm. Finally, I started putting the plastic on at 1am. It was a very difficult job and very hard to get the plastic smooth while not actually getting on top of slab. This is not a one person job; I should really have had Ronnie and his crew do it. I couldn't get all the wrinkles out. I managed to deflate big bubbles using a mop. Finally around 3am after becoming incredibly exhausted, especially from mucking around in the muddy soil around the forms (I had been watering that somewhat also, though didn't think it would make it that mucky) I decided I couldn't do much better and quit. I didn't cover the last 3 feet on the south side because they seemed to stay wet anyway, possibly because of very slight slab tilt. You can't see the water running, but it did seem to ultimately accumulate on the south side. Or maybe that was because of wind or other factors.
At 10am on Thursday the slab did seem to be moist under the plastic. It was working. But the uncovered 3 feet on the south side was no longer wet, it was bone dry. So I watered it down and put down a second cover, overlapping the first, to cover that side. I watered underneath the cover somewhat. I had to use pieces of wood Ronnie left behind to hold it down because I had used up all 10 bricks that I had bought the night before.
At 2pm on Thursday I put hose underneath cover with nozzle adjusted for straight spray underneath the cover on north west side, turned on faucet to medium for a few minutes, then turned on low for an hour. At 3pm I checked and it appeared that excess water was flowing off on the southeast, so it was going diagonally across the slab and probably mostening the entire slab by surface tension.
Last I checked on July 14, there was no cracking or any other significant imperfection.* That is an excellent outcome, especially under the circumstances of a hot July. But I am worried that lack of initial covering, and also my hourly sprinkling of water at first (which may have done more harm than good) may have caused surface damage, making the surface weaker and more prone to dusting, flaking, or even worse, sections of surface breaking off. It is too soon to tell and I will need to wait another week or so to find out, since I now plan to proceed with a full 1 week wet curing, or until I can get a sun shading canopy in place. From all indications now, it's probably fine, even excellent. But I will need to be patient to find out.
(*There are a dime sized depressions near one side.)
The surface is finely brushed, somewhat finer than a sidewalk. I had been hoping originally that the surface would be smoother, like a garage floor. I can probably get the floor polished if that's what I want, to a surface something like marble. But that would probably be too slippery. The floor may be stianed from the plastic too. So might be better to cover up, or grind down to deeper layer for polishing. I'll be discussion floor options in a future post.
(*There are a dime sized depressions near one side.)
The surface is finely brushed, somewhat finer than a sidewalk. I had been hoping originally that the surface would be smoother, like a garage floor. I can probably get the floor polished if that's what I want, to a surface something like marble. But that would probably be too slippery. The floor may be stianed from the plastic too. So might be better to cover up, or grind down to deeper layer for polishing. I'll be discussion floor options in a future post.
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