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I am pouring a series of concrete slabs for a patio and I’m using standard 80lb Quikrete bags (https://www.homedepot.com/p/100318511).

The directions recommend 3qts of water per bag and a max of 4.5qts. Everything I’ve read states that even one extra quart of water can reduce strength by 40%.

I live in the desert, and the air is incredibly dry. I don’t know how that affects the ratio, but it takes about 5qts of water to get a bag to any kind of a workable consistency. With 5qts, the concrete looks about like what I see in the various videos I’ve watched.

My question is am I doing anything wrong or is this ok? These slabs will only ever carry light foot traffic, but I don’t want them to crack.

Surely getting the concrete to the correct consistency is more appropriate than sticking to the strict water ratio. Or no?

  • I wonder if you could run a standard slump test on your mix and give us the results? – ThreePhaseEel Jul 10 at 1:02
  • Unfortunately I don’t have a cone to run a slump test. – Josh Hudnall Jul 10 at 2:00
  • When I started mixing concrete by hand, I always thought the mix was too dry with the measured amount of water. If you take a little more time to mix thoroughly (and break up those balls of very moist dust), you might find you have a perfectly usable consistency. I can't imagine that you actually need two extra quarts. – Aloysius Defenestrate Jul 10 at 4:06
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You should mix according to how you want the concrete to flow. Watering the forms and the ground before you pour is important when the climate is dry and hot. You are correct that the water mix affects the strength of the final product, but not as much as you may think. The most important factor is how much Portland is in the mix, and second, how fast it cures. Make sure that you pour when it is not hot and sunny, like in the evening or shade. Cover the work to prevent drying out, in fact, it needs to keep wet for a few days, so sprinkle water on the surface until the product turns white. That may take a week. The closer you adhere to keeping it hydrated, the better your surface will hold up over time.

  • Thank you for the advice. This is really helpful! – Josh Hudnall Jul 10 at 1:55

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