Have you ever wondered how builders and construction workers are able to create perfect concrete columns? For a long time, this process required the use of wooden concrete forms that took a long time to assemble and disassemble. Luckily, in the modern age of construction, there’s a more effective and efficient method of creating a column – a Sonotube.
A Sonotube takes the labor-intensive process of creating a column mold and simplifies it. All you have to do is position it, fill it, and remove it. With that kind of ease of use, it’s no wonder why these tubes are used by DIYers and professional contractors alike.
This guide will help you better understand these “magical tubes,” including how to use them as well as the best times to use them. This guide will also answer some of your enduring questions about what Sonotubes are capable of.
What Are Sonotubes and What Sizes Do They Come In?
Let’s start with the basics so that you can begin to fully understand Sonotubes.
First and foremost, “Sonotube” is a trademarked name for a specific brand of large, reinforced cardboard tubes. These tubes are designed for placement in a pre-dug hole, after which they are filled with concrete. After giving the concrete time to set, the cardboard tube can then be cut away in mere minutes.
Given the simplicity with which they can be set up and removed, Sonotubes (and similar products from other brands) have become favored on jobsites around the world.
Because of their wide-scale utilization, Sonotubes have begun to come in a variety of sizes. These sizes are based upon the diameter of the tube, which ranges from 8 to 56 inches. Sonotubes today also come in a variety of lengths, including units all the way up to 18 feet in total length.
Sonotubes vs. No Sonotubes: Why Use Them?
Sonotubes were designed to resolve a decades-old problem associated with creating concrete columns. Traditionally, that process was very labor-intensive and required the installation of specialized molds. These molds then had to be removed when the column dried, which further slowed down the construction process.
Sonotubes are designed to alleviate both sources of delay by making these disposable molds easy to place and easy to remove.
As noted, Sonotubes are also made from a type of reinforced cardboard. This makes each tube relatively lightweight, allowing anyone (including a DIYer) to work with them safely. At the same time, this cardboard-based construction allows each tube to be relatively affordable, especially compared to traditional molds.
As such, they are accessible to almost all users who wish to create a perfect concrete column.
How to Use Sonotubes: A Step-by-Step Guide
Assuming you decided to go ahead with using a Sonotube, below is a step-by-step guide on how to do it.
Step 1: Double-Check Measurements and Depth
Before beginning work with a Sonotube, you must be certain that your installation location is fully prepared for its placement and use.
In all likelihood, your concrete column will be partially buried underground after it is complete. As such, you’ll need to start this process by ensuring that your hole is both deep and wide enough. At the same time, you’ll need to ensure that the base of the hole is fully level to prevent issues with your column later on.
As you dig your hole, you may have noticed some discernable moisture entering the hole. This is likely groundwater that was trapped in the surrounding soil. This can make the process of setting a column more complicated.
Unless you can properly abate that moisture, you will not be able to correctly use a Sonotube. Instead, you may need to use an alternative method for forming a column.
Step 2: Place the Tube and Secure It
Once you’ve ensured that your hole is good to go, you can begin the process of placing your Sonotube. This can be done by lifting and placing your chosen tube in the hole so that it is centered relative to each wall.
At this time, you may notice that your hole is not deep, wide, or level enough. If this is the case, begin to make changes so that it is adequately sized for your chosen tube.
Once adjustments have been made, your Sonotube should stand evenly on its own. However, if you are using an in-ground footing, your tube should sit evenly on top of it.
In theory, your Sonotube should stay in place on its own. However, you may find it necessary to add some wood supports to prevent it from moving about throughout the process.
Step 3: Make Concrete and Fill
Once your Sonotube is in place and secured, you can begin to make the concrete you’ll use to fill the tube. The type and mix ratio of concrete you use in this situation will vary based upon the type of column you’re making and the environment in which it will exist.
In any case, your chosen mixture should be pliable enough that it can be easily lifted with a shovel and dropped into the Sonotube.
Once you’ve reached an ideal consistency for your concrete, you can begin to shovel it into the tube.
Be careful while doing this because the force of adding in concrete can sometimes cause the tube to shift or tip. Continue to fill the tube to the top (assuming you cut your tube to match your desired height). Pat the concrete as you go along to force out undesirable air bubbles.
Step 4: Insert Rebar and Finish
Once you’ve filled approximately three-quarters of your tube, you should stop and insert any rebar that your job calls for. This should be done while the concrete is still fully in liquid form. Precise rebar placement will vary from job to job, though any placement scheme should utilize equal intervals between rebar rods.
Ideally, your rebar will also be pre-cut to match the depth of your hole.
Once your rebar is placed, you can fill in the rest of the tube. Be sure to continue patting the concrete to remove air bubbles.
Step 5: Level and Allow Time to Dry
Once you’ve fully filled your Sonotube, you’ll want to even off its cap. This can be done with any piece of flat, level material, such as a piece of cardboard or wood. You can even use your hand, so long as you wash off excess concrete from said hand immediately.
Once your column is leveled off, you’ll need to leave it be so that it can dry.
Drying times for your concrete will vary based upon how much water was added to your mixture. Also, any drying agents added to the mixture will help it set quicker.
Step 6: Remove Cardboard Tube
Once you have allowed your concrete column to dry fully (which may take more than 24 hours), you can begin the process of removing the cardboard tube. This is typically done using an electric saw, which should be well balanced to prevent the blade from contacting the concrete.
This step requires the most experience and care to execute safely. So, it is often worthwhile to consult with an experienced contractor before undertaking this step on your own.
Sonotube Alternatives: Wooden Boxes and Screw Piles
As previously described, there are some alternatives to using Sonotubes.
The first among these is also the traditional method of creating concrete columns, which is to say, using a wood mold. These molds are constructed around the erection point and are labor-intensive in their implementation.
As such, this method is typically only used in special use cases today.
Screw piles are another alternative that is far more common on construction sites. These are used primarily as a method of creating ground anchors but can also be used to establish the base of a column.
This method is less user-friendly, though, so DIYers looking to use them should consult a specialist before trying to use them.
Frequently Asked Questions
If you didn’t find the answer to your question about Sonotubes above, continue reading. Below, I answer some of the most commonly asked ones.
What Size Sonotubes Should I Use for 4x4s, 6x6s, and Deck Footings?
As a rule of thumb, you should always use a Sonotube with a diameter that is three times your desired post’s width. So, if you were planning to install a 4×4 post, a 12-inch Sonotube would be appropriate.
Meanwhile, a 6×6 post would warrant an 18” Sonotube.
As for deck footings, this same rule of thumb applies. Simply multiple your post’s width by three and you should have a good idea of how large a tube you need.
What is the Load Capacity of a Sonotube?
According to Sonotube’s manufacturer, their products do not come with any listed load capacity.
As such, they should not be used to bear weight under any circumstances. To that end, a Sonotube does not add to the strength of a column and should be removed before a column is made to bear weight.
How Much Concrete Do I Need to Fill a Sonotube?
Precise concrete volumes for your column installation job may vary slightly depending on how many additives go into your concrete’s mixture. That being said, you can perform a simple calculation for the volume of your Sonotube’s cylindrical shape to determine how much raw concrete you’ll need to fill it.
To find the volume of your Sonotube, start by measuring its radius. This can be done by measuring the distance from the tube’s center to one of its edges. Then, multiple that number by itself (also known as “squaring”).
Finally, multiple that resulting number by the tube’s height. This will give you a solid measurement of your Sonotube’s internal volume.
For example, say you are using a 10-foot Sonotube with a 3-inch radius. After putting this through the formula “volume of a cylinder = radius squared x height,” you’ll find it has a volume of 1.963 square feet.
So, to make matters simple, you could obtain and use 2 square feet of concrete with that Sonotube.
How Can I Put a Rebar in a Sonotube?
To be clear, rebar cannot and should not be inserted into the carboard structure of a Sonotube.
However, rebar may be added to the wet concrete that is inside of a set Sonotube. This process is fairly easy and can be done when the tube is three-quarters full of concrete.
Simply push the rebar into the wet concrete until it reaches resistance at the column’s base.
Sonotubes are a great tool to have on the job site, especially when it comes time to pour concrete into a column. These cardboard tubes are lightweight and affordable, making them a cheap method of creating a structurally sound column and a great alternative to the traditional wooden concrete forms.
As the steps above show, they aren’t hard to use either – even for a DIYer.