How to install a puddle flange in concrete

How to install a puddle flange in concrete

There is a good chance you’re renovating your bathroom, toilet, or utility room as you are here. If you’re living in an old house or a recently built one where the builder had cut some corners, you may notice that the puddle flange system needs to be installed.

This system is designed to prevent water damage around the drainage pipe. In this post, I will guide you through installing a puddle flange in concrete, but please remember that it must be done correctly to prevent water leaks.

I will provide detailed instructions on how to do it yourself, but if you’re short on time, feel free to jump ahead to the images section, where I will explain the process more simply.

To better understand the importance of the puddle flange, let’s talk about its purpose. Also here you can read some more about puddle flanges.

When installed in the middle of the concrete structure, the puddle flange prevents water from flowing into the outer surface of the pipe when the material changes form due to expansion. 

Water flow is pictured with the blue line. There might be structures under or insulation and gravel. Whichever it is, we want to avoid it if we can.

The installation of puddle flanges is an essential consideration in concrete structure construction. Installing this type of flange during the concrete pouring process is recommended.

If, for some reason, the installation is delayed and done after the concrete has cured, the process becomes more complicated as rebar needs to be taken into account during installation. However, it is still possible to install the flanges post-concrete curing.

It is worth noting that the type of puddle flange we are discussing in this context is installed on the concrete slab’s surface. Typically, it is installed before waterproofing is applied and is often part of the waterproofing product system.

The importance of installing puddle flanges lies in their ability to prevent water from seeping into the structure through small cracks that may appear on the concrete surface as it cures.

When concrete cures, it undergoes slight contraction, resulting in small cracks on the surface. This effect can also be observed when pouring a floor, where a gap between the slab’s sides and the wall may appear.

Since PVC pipes have different expansion and contraction values than rebar and concrete, water can pass through the gaps between them. Therefore, it is crucial to install puddle flanges to prevent water damage to the structure.

How to install a puddle flange in concrete floor

Starting point of puddle flange installation
This is likely the starting point, but in some cases, the drainage pipe can be higher or lower than the concrete surface.

When starting a construction project, it’s crucial to ensure the drainage pipe is installed correctly.

Drainage pipes are typically level with the floor in old houses, while new houses may have them left slightly higher, depending on the location and workers doing the pour. Sometimes, the pipe might stick out, be level, or worse, be below the surface level.

Installing the puddle flange into the drainage pipe is critical to ensure proper drainage. However, if the flange doesn’t sit straight into the pipe, you need to be creative in your approach.

The most straightforward situation is when the drainage pipe is level or sticks out from the concrete. This is because it’s harder to get concrete waste inside the pipe like this, and depending on the situation, you might only need to spend a few coins to buy a cap for it from a local store selling plumbing wares.

In some product categories, there might be a proper fit for the cap, especially if you’ve ordered plenty of concrete pouring jobs with pipes for lifting or other reasons. Therefore, their cost should be around pocket change as they are often treated as trash on construction sites.

However, the most problematic situation is when the water drainage pipe is deep inside the pour. This is most likely because the floor has been lifted, but the water drainage has been left low for reasons unknown. In such situations, deeper digging might be needed to extend the pipe to the proper height.

Step 1: Make room for the puddle flange

Making room for the puddle flange
Depending on the size of your puddle flange, you should remove the concrete marked with red x so the puddle flange will sit level with the floor. Cut the drainage pipe so the puddle flange can be lowered.

Depending on the size and structure of the puddle flange, you need to make some room for it if you’re not planning to fix the floor tilt or something else like that in the beginning. I’ll describe it more below the steps, but to be clear, the steps are kept simple below.

I put them on numbers to read the steps, but as I stated before, I also like to open up the logic.

Tools you more than likely need:

  • Hammer drill or hammer and chisel for concrete
  •  Hearing protection
  •  Construction vacuum cleaner
  •  Angle grinder with vacuum cleaner head and diamond cup wheel
  •  Breathing mask so you don’t get dust in your lungs
  •  Eye protection
  •  Working gloves
  •  Electric tool for cutting the drainage pipe shorter
  •  Caulk gun for Sikaflex or whatever you use to glue the puddle flange in place

So, the first small steps are;

  1. Remove extra concrete around the pipe so the puddle flange sits level with the floor. The tilt of the whole floor surface should be towards the water drainage so it won’t sit on the floor and make puddles. Beware of dropping concrete and dust inside the pipe; use something to seal the pipe top.
  2.  If the drainage pipe is level with the concrete, cut it lower so the puddle flange fits when pressed inside the drainage. Cut it just enough so the puddle flange sits level with the floor. You want the drainage pipe and puddle flange bottom to overlap so you can solvent weld them together well.

So, how do we remove concrete around the drainage pipe? I prefer working with a hammer drill, an angle grinder with a diamond cup wheel, and dust control so that I can use a construction vacuum cleaner with the grinder.

If you don’t have these tools, consider renting them, as good products are expensive and you might not need them in years from my experience. A hammer drill is a homeowner tool I like to have, but a good vacuum cleaner that makes the difference is expensive.

Please don’t use your home vacuum cleaner as the concrete dust might break it. Renting is also good because doing this job should take less time.

Concrete dust isn’t exactly healthy, and when you’re grinding, it will float in the air all around the place. It also stays in the air to travel a lot in the house. Therefore, even with a vacuum cleaner, I’d seal the place so the dust has enough time to settle down once the grinding is done.

Please don’t break the pipe; be extremely careful around it with a hammer drill. If it breaks down deep, it will be an annoyance to fix.

When you have worked out the depth deep enough so, the flange sits well and level from the thicker part, use a diamond cup wheel to grind the surface around the pipe so the flat part of the flange sits nicely on the floor.

The image below is a bit exaggerated as I wanted to leave some room so it is more precise to see what it should look like.

Installing the puddle flange
The Puddle flange should be close to the concrete removed around the drainage pipe. The floor surface should be tilted towards the flange so that gravity can do its job and water will flow to the drainage pipe.

When installing a puddle flange for drainage, it’s essential to ensure it is sturdy and secure. Here are some steps that you can follow to achieve that:

  1. Clean the Surface Area: Use a construction vacuum cleaner to clean the surface area where you want to place the puddle flange. This step ensures that no dust or debris on the surface might impede the adhesive from bonding securely.
  2.  Attach the Puddle Flange: Use adhesives to attach the puddle flange to the drainage pipe. Solvent weld is an excellent option for this purpose, as it creates a sturdy bond between the materials. Additionally, use adhesive between concrete and flange to eliminate space between the materials. The hammer drill leaves an uneven surface; the angle grinder could be much better, and adhesive will help even it. It will help the flange not to flex. Glue the puddle flange firmly in place.
  3.  Use Additional Support: Some people use screws to provide additional support, but from experience, something like Sikaflex on a clean surface is sturdy. This adhesive will bond intensely with the concrete surface and the puddle flange, holding them together.
  4.  Apply the Waterproof Membrane: Once everything has bonded, apply the waterproof membrane on top of the puddle flange. Different products might vary in their systems, so follow their guidelines strictly. Most importantly, the processing time needs to be followed.
  5.  Allow Time for Curing: Check the curing time from the product labels and allow the waterproof membrane to cure fully. Once it has cured, it will not bond well with anything else.

In summary, a correctly installed puddle flange will prevent water from going between the drainage pipe and concrete and prevent water from seeping in between waterproofing and concrete. Follow the steps mentioned above to achieve a secure and sturdy installation.

Some important points I’d like you to remember before you install your puddle flange are:

  1. It is crucial to install puddle flanges to prevent water damage to the structure.
  2. When starting a construction project, it’s crucial to ensure the drainage pipe is installed correctly.
  3. Installing puddle flanges is an essential consideration in concrete structure construction.
  4. It is worth noting that the type of puddle flange discussed in this context is installed on the concrete slab’s surface.
  5. Depending on the size and structure of the puddle flange, you need to make some room for it if you’re not planning to fix the floor tilt or something else like that in the beginning.
  6. installing a puddle flange in concrete requires specific tools, such as a hammer drill, angle grinder, and caulk gun.
  7. It is essential to take safety precautions such as wearing protective gear, hearing protection, and breathing masks during installation.


Installing a puddle flange might seem daunting, but with a bit of guidance, it can be done by anyone with experience with household maintenance. However, it is essential to note that the process must be carried out with precision and care to ensure it functions properly.

In case of any doubts, it is always advisable to seek the help of a professional.

The effectiveness of the water sealing may vary depending on the location where you reside. Some areas offer a guarantee for a specific period, while in other areas, it may not be possible.

Taking adequate safety measures while working with power tools is crucial, as they can pose certain risks. Additionally, it is recommended to work at a steady pace and take sufficient time to plan the task to minimize the chances of any errors.

Lastly, it is essential to be mindful of your surroundings and avoid damaging any other areas apart from the concrete being worked on.