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Name: Robert  Neal
Heading: 1.1.1RE:How can I fix discoloration in new concrete?
Message:
I recently poured a 50' by 14' patio and 21' by 38' car port and both are showing discolorations light and dark on day two. Is this normal, what can I do to remedy the problem. Ideally, I'd like a uniform color so would color staining be recommended, if so what shold be used.


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john smith


John,
This is perfectly normal. Give the concrete a week or two to settle down.
Concrete in shade will take longer to bleach out.
I assume this is normal concrete with a broom finish on the patio and trowel finish on the car-port? or broom finish on both?
Bob Miller
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Bob Miller


John,

Pictures of the discoloration would be helpful, but short of that I will assume you are talking about a dark to light mottled color on the slab surface. The dark mottling occurs due to a delay in the hydration of the iron phase in the cement (a chemical reaction between the cement compounds and water). Don't worry, this does not mean anything is wrong with the cement or concrete - just that the delay in the ferrite hydration will result in dark gray (sometimes slate gray) color at the surface. As the iron phase continues to hydrate the color will progressively lighten. However, don't wait on Mother Nature! First and foremost, continuously moist cure the slab for 3 to 7 days. This is best done by covering with plastic and flooding water underneath the plastic several times a day. Often this is enough to jump-start the iron phase hydration. If not, next try the least expensive treatment: wash the surface with un-diluted vinegar (don't use stronger acids). Saturate the slab the day before so that the vinegar will not penetrate deep into the slab. Then wait until the surface skin is dry and apply the vinegar and scrub it around for about 10 to 15 minutes followed by thorough rinsing with water to remove all the vinegar. Follow this with continuous wet curing for another 3 days or so. If that doesn't work then there is another chemical, di-ammonium citrate, which is generally very effective (although rather expensive). Not enough time to go into its application today. Repost your question if the vinegar doesn't work.
Bob

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Robert Neal
 
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