Can I Pour Concrete in a Hole Full of Water?

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Whether you’re trying to fill a hole with concrete to make a foundation, have a hole filled with rainwater, or are simply looking to save time and effort, it is common to get the idea of simply pouring concrete in a hole full of water. After all, the goal is to mix concrete with water, and a mix is a mix, right?

So, is it really a good idea and can you get away with pouring concrete in a hole full of water? There are actually different opinions about this. It’s not just DIY-ers that do this; many construction crews also consider doing the same when working on larger projects.

Generally, it isn’t really a good idea to pour concrete in a hole full of water without taking any measurements. How much concrete you mix into how much water depends entirely on the project you’re working on. For example, for fence posts, more water will work just fine, but if you’re looking for something sturdy, try to drain out as much water as possible before pouring concrete.

Can I Pour Concrete in a Hole Full of Water?

Wet concrete

Whatever the reason is, as mentioned above, it isn’t generally a good idea to do so. Consider the finish you are looking for before doing so.

If you’re looking for something that doesn’t need finishing, then you’re good to go. If, however, you need to give it a finished look, then it might not be such a good idea.

Another very important consideration here is the form of concrete you are pouring, i.e., dry or a wet mix. Dry mix means that you have mixed concrete with aggregate and no water. That way, you have more control over the consistency you will achieve. If, however, you called in a concrete mixer and are pouring a pre-prepared mix, you’re likely to overwater the mix.

The thing about pre-prepared mixes and concrete mixes is that you don’t really know the consistency of concrete you’re working with until it’s out in the hole.

The Why

The reason we don’t recommend pouring concrete in a hole full of water is that concrete can actually set under water – and not just concrete, the aggregate as well. If you look at the density of the three (water, concrete, and aggregate), you will find that aggregate is the first to settle. Then concrete.

If you already have water in a hole and add a wet concrete mix and do actually end up overwatering the mix, you will find that the aggregate will settle down, leaving only concrete floating in the water. A few hours later, the concrete will settle as well, leaving only grayed out water on top. You won’t be able to tell the difference until you actually dip something in it!

Mixing the solution isn’t an answer, either. If you continue to mix, the mixture won’t set. If you leave the mixture as is, after a few days, you will find that the water has reduced – either evaporated or drained to the sides. Then it will start drying.

The dried-up mixture you get will, first of all, be significantly less than what you had hoped for when pouring. Secondly, it won’t be as flat as you were hoping. It will actually look unappealing. Chances are that you’ll likely have to redo the whole thing.

Third, and most importantly, the dried-up slab/structure you now have won’t be as sturdy as you were hoping. The top layer may already have cracks in it! If, however, it doesn’t, it will likely develop cracks over time.

Having said that, there are some seasoned masons who do this and can actually get away with the same. Doing this with such accuracy involves having years of experience under your belt; your primary goal being not to overwater the mix.

Ask Archimedes and his principle of buoyancy!

The How

If, however, you must pour concrete in a hole full of water, try your absolute best to find a dry mix and dump that into the water. Remember, you can always add more mix into concrete to get the consistency you want, but if you try adding more water, chances are that you’ll likely overwater it.

We would recommend that you try to pump out as much water as possible before pouring concrete to ensure that the mix is consistent. If, on the off chance that you don’t have a choice and water simply keeps on seeping into the hole, we recommend simply pouring in a more dry mix.

Try to determine how fast the water is coming in. If it is gushing in, pouring concrete in is simply a waste. If, however, you find that there’s a few inches of increase in water every day, create a mix that sticks loosely together but you can’t really make a ball out of it. Give it a crumbly texture and pour.

As water keeps on seeping in, the already dry mix will absorb the same and eventually dry up. However, this isn’t recommended. If you have a leak, try to fix it first because it becomes more of a trial and error venture without fixing it.

Remember, if you’re going for accuracy or something that is a critical piece of engineering, water in a hole is a big no. Think of it as mixing concrete in a bowl. You first add concrete, then you add water and mix. This way, you have more control over what to add and how much.

But considering that you’re looking to dump a concrete mix into a hole full of water, chances are that you’re not in a critical situation. A 3:1 ratio of concrete and groundwater respectively is what you need to fill the hole. This way, you’ll be able to tell whether you need more water or more mix to achieve a ‘dryable’ consistency.

A Step-By-Step Guide

Some ground which has water collected in it due to digging down
Some ground which has water collected in it due to digging down

Now that you have a general idea of the how, here is a step-by-step guide to help you do the deed successfully.

  1. If possible, try to determine where the water is coming from. If water is seeping in, it’s time to get your hands dirty. Try to feel where it is seeping through. This will come in handy later on. If, however, you are unable to determine the same, this method should work either way.
  2. Insert a measuring tape into the water and leave it overnight to determine if water is constantly seeping in. If it’s not, we would recommend you pump the water out.
  3. If water is seeping in continuously, with the help of the measuring tape you left submerged, determine the volume of water flowing in.
  4. Time for some calculations. Keep the 3:1 rule in mind to determine how much concrete you need. Add three times more concrete than how much water the hole will have by the next day. Don’t forget to take into account the water that’s already inside!
  5. Once ready, mix your concrete and aggregate (if you’re using it).
  6. Add a little bit of water but make sure the mix you finally get is dry. As mentioned above, it should stick loosely together but if you make a ball out of it, it should crumble. The idea is to make sure the concrete doesn’t start flowing away.
  7. Now, time to pour. Just dump the concrete in. Assuming you already had a bit of water in the hole, you will have a relatively wet concrete mix in the hole. Mix it slightly to make sure there are no lumps or air bubbles trapped inside.
  8. If you need to erect a fence or pole, put in a plastic sheet and fold it to sit snugly in the hole. Stand the fence/pole and then pour concrete. Make sure the pole remains level by tying it off with something.

If your calculations are correct, you should have a cured structure in the hole.

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About Charlie D Paige

Charlie is a massive DIY fan, with dozens of DIY projects under his belt - ranging from tiling to electrics, and concrete pads to walls. Charlie loves tinkering, seeing how things works, the outdoors and playing with power tools... so is it any wonder that he's completed so many DIY jobs over the years?

Charlie loves spreading his hard-won DIY experience with the world via this blog.