If you are planning a DIY project which involves mixing up a bag of concrete for some home improvements, then you need to know how much water you will need. I have designed and built a lot of concrete equipment over the years so I know what is needed for the right mix.
You need a half gallon or up to 4 pints (1.7 L) of water for a 60-pound bag of concrete. That works out to about a pint for every 15 pounds of concrete. It is better to start with the minimum amount, and only add small measured amounts if needed until you reach a paste like consistency that will form stiff peaks.
Using the simple factors listed above you can figure out the water need for 40, 80 and 90 lb bags of concrete or anything in between.
How Do I Know How Much Water I Need?
If you ask a construction worker or someone with experience mixing concrete how much water you will need for a 60-pound bag of concrete, they might tell you something like “When you know, you know” because it’s often more about monitoring the consistency.
While this may be true, it’s not exactly helpful to someone with little or no idea about mixing concrete.
A 60-pound bag of concrete will require 4 pints of water, while an 80-pound bag will require 6 pints. If you buy a pre-mixed bag of concrete, you can check the back of the bag for the minimum required amount of water; however, bear in mind that you may need a bit more water than they recommend in warmer temperatures.
A properly-mixed batch of concrete will be easily workable when wet as well as strong and durable when dry.
Concrete is made up of three elements, namely, cement, aggregates composed of rock and stone, and water. Usually, a concrete mix is 10 to 15% cement, 60 to 75% aggregates, and 15 to 20% water. You may notice that air bubbles form in the cement mix, and they can take up 5 to 8% of the concrete make-up (source).
If you are interested in what it takes to make your own concrete, you can take a look at this article, which answers whether you can make concrete with just sand and cement.
Any builder will tell you that the best, meaning the hardest and most durable, concrete can be achieved by reducing the amount of water to cement. However, this must be done while preserving the workability of the wet concrete.
Adding Water to Concrete
Mixing concrete is often compared to baking. You need to be precise with your measurements to get the results you want as well as know what to add when. There are different methods for mixing by hand and for machine mixing.
The first step is usually to place your dry concrete mixture in a mortar bucket or a wheelbarrow. You can then make a well in the center of the dry mix.
You need to measure out the water into a separate container, preferably one with measurement markers. It’s better not to try and guesstimate. Be precise; it’ll be worth it in the end.
Once you have measured out your water, you can add it to your concrete mixture. With hand mixing, you can add it all at once.
Alternatively, you can add it little by little, mixing it in as you go along. Mix the concrete using a spade or something similar until mixed well and consistent.
With machine mixing, follow a similar process but, instead of placing the dry mix into a bucket or wheelbarrow, pour it into the concrete mixer.
Then, add half of the water to the mix before mixing and the other half during the blending, which will ensure a more even spread throughout.
You must wait until they are adequately combined before deciding if you need to add more water, which leads us to the next point, how do you know if you need more water?
How to Tell if You Need More Water?
There are a few methods you can use to determine if your concrete is the correct consistency.
The first method is to draw a ridge in your concrete mixture. If the mixture is too thick, then you will be able to make the ridge easily and without much effort.
If the ridge starts to fold in on itself and does not hold, then your mixture is too runny.
The next method is to scoop up a handful of concrete, preferably in a gloved hand, and squeeze it in your fist. If the mixture holds its shape, then it is the right consistency.
It’s always safer to stay on the side of dry over wet when it comes to concrete.
What Happens if You Add Too Much Water?
A common mistake with concrete is that often people add more water to it to make it easier to handle. Moreover, by adding additional water to concrete, you risk compromising its strength and durability.
Too much water can lead to something called “segregation,” meaning that the coarse aggregates become separated from the fine aggregates. This soupiness can make it less easy to work with as well (source).
Furthermore, concrete made using too much water can have the following adverse outcomes when dry (source):
- Reduced Strength
- Reduced abrasive resistance
- Increased permeability
- A poorer surface quality overall
What Happens if You Add Too Little Water?
While it is better to err on the dry side when it comes to concrete, it’s important to remember that too little water can also cause problems as well.
Adding water to the concrete mixture, or hydrating it, is a type of chemical reaction. In this case, hydration involves the binding of aggregates with one another, which is a result of a chemical bond between the water molecules and the major compounds (source).
Correct bonding is essential for the concrete to achieve the required strength and durability. Hence, if too little water is added, then the chemical reactions cannot occur correctly or completely, leaving you with weaker concrete that is more susceptible to external forces.
At the same time, too little water will make the concrete nearly impossible to work because it will be too thick, and you will struggle to lay it down.
After you have mixed and laid your concrete the curing process will take a few days, involving moisture, temperature, and time (source).
Using the proper curing process is critical for the following reasons:
- It stops the concrete from becoming too dry due to sun and wind exposure.
- It reduces potential shrinkage.
- It allows the concrete to get firmer.
- It helps to ensure the concrete will be crack-free, durable, and long-lasting.
If you are looking to get concrete laid in a hurry, you may be interested in whether you can mix fast-setting concrete with regular concrete.
Curing time can be anywhere from 7 to 14 days, depending on the type of concrete and exposure to the elements. There are a few things that you can do to ensure that you get the best results from your concrete (source).
Keep Your Concrete Wet
Keeping your concrete wet is especially important if you experience warm temperatures. Once you have laid your concrete, make sure that you spray your newly-laid concrete with water 5 to 10 times a day for the first week.
Keep Your Concrete Covered
If you are unable to spray your concrete that frequently, then you can cover the concrete to help slow the rate of evaporation. You can then wet it once a day while keeping it securely covered.
Pond Cure Your Concrete
Pond curing is a process by which you cover your concrete in about a foot of water in a sort of a pond or water bath. This process is excellent for concrete slabs if you’re willing to take the time to build a berm around it.
If you can do this, it will only take three days to cure the concrete as opposed to a week, plus its much less admin. You need only check now and then that the water level hasn’t dropped too significantly.
These three methods of curing can help increase the strength of your concrete by up to 50%.
It is also important to only lay your concrete when you are expecting warm weather. It’s not a good idea to let your concrete get too cold, as the chemical reactions slow down in cold weather and completely cease at around 45°F.
Adding water to concrete is a delicate balance that requires careful preparation. Always make sure sure that you are aware of the correct water-to-concrete ratio and that the concrete is mixed correctly and tested before deciding to add any more water.
If you follow the appropriate guidelines and make use of good concrete-mixing practices, there is no reason you should not become a concrete connoisseur before too long.