How to mix bagged concrete
Bagged concrete is forgiving, but too much water is the most common way to ruin it. Here's how much to add, how to batch it and how to cure it.
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How much water per bag?
QUIKRETE's data sheet for its standard Concrete Mix gives a starting amount of water for each bag size, and the most you should expect to need:
| Bag size | Starting water | Maximum expected |
|---|---|---|
| 40 lb | 3 pints (1.4 L) | 4½ pints (2.1 L) |
| 50 lb | 3½ pints (1.7 L) | 5½ pints (2.6 L) |
| 60 lb | 4 pints (1.9 L) | 7 pints (3.3 L) |
| 80 lb | 6 pints (2.8 L) | 9 pints (4.3 L) |
Start with the lower amount and add water a little at a time only until the mix is workable — like thick oatmeal that holds its shape. Extra water makes concrete easier to place but weaker, more prone to shrinkage cracks and dusting at the surface. Other brands give their own figures on the bag.
Mixing in a mixer
- Put about three-quarters of the water in the drum first.
- With the mixer running, add the dry mix, then the remaining water as needed.
- Keep mixing until the color and consistency are even throughout — usually a few minutes.
Allow roughly 1 cubic foot of mixer capacity per 80 lb bag you mix at once, according to the same data sheet. A typical small portable mixer handles one or two bags per batch — so the number of batches, not the number of bags, is what sets the pace of your pour.
Mixing by hand
- Use a wheelbarrow or mixing tub, a hoe or shovel, and mix one bag at a time.
- Make a crater in the dry mix, add most of the water, and fold the mix in from the edges until there are no dry pockets.
- Hand mixing is fine for post holes and small pads; for more than about 10 to 15 bags, rent a mixer or look at ready-mix.
Placing and finishing
- Dampen the base before placing, without leaving puddles, so it doesn't suck water out of the concrete.
- Place continuously from one end, filling the forms to full depth so batches blend together without cold joints.
- Strike off, float and finish in that order; don't overwork the surface or finish while bleed water is still on top.
Curing
Concrete gains strength as the cement reacts with water, so it needs to stay moist. Keep the surface damp for the first several days — by misting, covering with plastic sheeting or using a curing compound — and protect it from freezing and from very hot, windy conditions. Standard concrete mix reaches most of its design strength in about four weeks; it can take foot traffic much sooner, but check the bag for times.
Fence posts: wet or dry?
Standard concrete mix is best mixed with water before placing. Fast-setting post mixes are designed to be poured dry into the hole around the post and then soaked with water — follow the instructions for the specific product.
Frequently asked questions
How much water for an 80 lb bag of concrete?
Start with about 6 pints (2.8 L) and add only as needed; QUIKRETE's maximum expected is about 9 pints (4.3 L) for its Concrete Mix.
How many bags can I mix at once?
About one 80 lb bag per cubic foot of mixer drum capacity. In a wheelbarrow, mix one bag at a time.
Can I add more water if it starts to set?
No. Re-tempering stiffening concrete with water weakens it. Mix smaller batches instead.
Sources
- QUIKRETE, Concrete Mix (No. 1101) product data sheet — mixing water table, mixer capacity and curing guidance.