curing hearth concrete


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Old 05-05-12, 11:56 PM
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curing hearth concrete

just poured a new hearth and the directions mention curing the concrete. some say a layer of plastic over top makes it cure better??

should i just leave it after pouring? should i spray water on it for the next days etc.??
 
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Old 05-06-12, 04:04 AM
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Is the concrete going to be left exposed or is another finish going to be applied over it? If another finish will go over it, I would lightly mist it and cover it with poly. If it's going to be exposed, then I would just lightly mist it enough to keep it dampish (is that a word?). In either case, 3 to 5 days should be a great plenty.
 
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Old 05-06-12, 04:11 AM
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Keep it damp or wet constantly for 3 to 5 days. Not just a mist every now and then (I just learned in a recent class that intermittent wetting doesn't really help a slab cure, it's got to be constant). Plastic will work to hold moisture in, but can discolor the concrete due to uneven curing where it touches the slab and where there's a wrinkle or bubble and the plastic is suspended just above it. If you use plastic, make sure it's ALL in contact with the slab.
A liquid curing compound would be good, but may also change the appearance. It will darken and gloss the surface. A water-based one would be better than a solvent based one.
I'd lay a piece of uncolored cloth on it and keep it wet. Burlap works well.
If it's indoors, I wouldn't even bother curing it. It will have plenty of strength without it. If it's outside, then cure it and seal it. Also if it's outside, I hope you used air-entrained concrete or it may spall, flake, and scale with weathering.
 
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Old 05-06-12, 07:34 AM
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thanks guys, its inside at a temp of about 68 f.
I ran out of concrete and have about a half a bag still needed so there will be a noticible line where the fresh and last nights meet.
my questions is now can i just add a little adhesive to the side of last nights and pour new stuff today or should i wait til last nights is dry


ive decided to put another layer over the whole thing when this is all dry.
Id like to try and tint some concrete.

so only cure the concrete if its outside?
how to get concrete so smooth sometimes?
what kind of concrete workds best for countertop grade (not doing countertop) and for tinting?
 
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Old 05-06-12, 08:06 AM
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Oh-oh, running out of concrete is not good . I hate to say it, but if it were me, I would probably take out what you did and start over. If you make another pour next to what you already did, you are almost guaranteed a crack. Even if you pour another slab over top of the original, the chances are very good that a crack will show up where the first two pours happened. Sorry for the bad news. On the plus side, concrete is relatively cheap.

As for staining the concrete, maybe others who have done concrete staining can respond. Everything I have researched suggests that it's very difficult to get color consistency because of the variations in concrete, unless you don't mind the color variations. Especially if you're using the bag mixes like you seem to suggest. It appears that Pecos has had a lot of experience in decorative concrete, hopefully he will respond also.

Yes, you do want to cure interior concrete also. It's all about keeping the concrete moist, so it cures very slowly.
 
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Old 05-06-12, 02:24 PM
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Bruce is right. Tear it out and start over, making sure you have enough to finish the job in one pop. The concrete will crack even with a bonding agent. A skimcoat will crack right over the existing crack. Start again.

If you want a slick finish but don't know how to get it, you won't get it even if I try to tell you how. You are either a concrete finisher or you aren't. A diy'er cannot hope to get a professionally hard-trowelled result by reading something on the internet.

Your best bet would be to form the hearth upside down on melamine or something else with a smooth surface. Pour the concrete into your mold and vibrate the crap out of it to bring the air bubbles up to the top (which will be the bottom when you flip and de-mold it).

After 5 days, strip the forms and the surface which was poured against the melamine will be smooth. Make sure to use rebar or other reinforcing when you pour the hearth, and remember that you need to form it in a mirror-image, so it will fit properly when flipped right-side up.

Staining is a whole 'nuther ball game, but is possible for a diy'er. Post back after you get your concrete de-molded and I'll try to explain it. Or simply look at acid stain websites to figure it out. Good luck.
 
 

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