Giovanni Valle is a licensed architect and LEED-accredited professional and is certified by the National Council of Architectural Registration Boards (NCARB). He is the author and managing editor of various digital publications, including BuilderSpace, Your Own Architect, and Interiors Place.
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Whether you’ve just bought a house and are renovating or are building something from the ground up, you’ve no doubt heard about sloped flooring in bathrooms. Unlevel floors are not ideal, and they can take a lot of time and money to fix when remodeling an older home. So, why would a bathroom floor not be level?
A bathroom floor should be level before you install tile or wood flooring, as a solid subfloor is essential to building a robust structure. However, it is not uncommon to see sloping floors in wet rooms and showers, as you need a slight slope to allow water to drain properly.
This article will aim to help you understand why bathroom floors need to be leveled and how to go about doing it. We’ll also go over the difference between a level floor and an uneven floor, along with how to slope your bathroom around your shower area to allow water to drain efficiently.
Do All Bathroom Floors Have To Be Level?
In general, all of the floors in your home should be level, including in the bathroom. However, not all bathroom floors have to be entirely level.
To be more precise, while most of your bathroom floor should be level, your wet area – where you’d place your shower – should be sloped to help water drain quickly and effectively.
What Is the Difference Between a Sloped, Unlevel, and Uneven Floor? When the subfloor is not prepared correctly, you’ll find that it might be uneven, sloped, or off-level in some places, which are all slightly different things.
While you technically can tile an unlevel floor, you cannot do so with an uneven floor.
Here is a breakdown of each and its meaning for better understanding:
- Uneven floors: The flatness of the floor indicates how even its surface is, so an uneven floor will have peaks, cracks, dips, pits, and bumps all over. Debris, dirt, and stones might also make a floor uneven in certain spots.
- Unlevel floors: Unlevel floors are those that slope towards one side, though it is not usually intentional. Unlike the next point, these are the work of poor installation rather than a deliberate design. Unlevel floors are not necessarily uneven floors.
- Sloped floors: Sloped floors are similar to unlevel floors in that they angle up or down one side, but these are purposefully designed (usually) in your wet room, allowing easy flow of water towards the drain.
While your bathroom floor should be flat and level, the floor inside your shower cubicle or your wet bathroom can and should be sloped. However, never, under any of these circumstances, should your subfloor be uneven.
What Is a Subfloor and Why Should It Be Level?
Before laying tiles or slats of wood, the surface is not technically called a ‘floor.’ The structure attached to your floor joists onto which you lay the final layer of tile is called the subfloor.
The subfloor is the very bottom layer of your flooring, above which might sit a layer of underlay, padding, and carpet or hardwood.
The whole integrity of a good hardwood or tiled floor depends on the quality of the subfloor. Think of it as laying the foundation for your flooring – just as your home needs a good foundation for longevity, so does your flooring.
A compromised, uneven subfloor will make it more difficult to lay tiles or carpeting down, so it needs to be done right the first time. And though you may be adding a slope in your bathroom, it is vital to begin with a solid and flat subfloor to ensure it will last for years to come.
How Does an Unlevel Subfloor Affect the Flooring? You know that feeling of walking across a floor, and you hear it squeak or, worse, sag? That’s the sound of an unlevel subfloor giving out—or giving up in some cases.
If you place tiles in your bathroom when the subfloor is uneven, it won’t be long before the tiles give way and start sinking or cracking.
If you’ve got wooden flooring over uneven subfloors, that’s where the creaking starts. You’ll also get moisture that will seep through and accumulate between the gaps of your flooring and unlevel subfloor, leading to all kinds of issues, like cupping. If this happens, you may have to replace the entire floor.
Consider adding underlayment to reinforce the subfloor and act as a vapor barrier.
How To Tell if Your Bathroom Floor Is Level
Have you heard of the bottle test? It involves placing a bottle—sometimes a marble—on the floor to check if it rolls on its own in a downward trajectory.
This method is not completely accurate and, while it can show you that you have an unlevel floor, you’ll want to use other, more accurate methods.
There are three methods of checking if your subfloor is level.
Using a Beam Level – First, you’ll need to invest in a carpenter’s beam level like this SOLA Big Red Aluminum Box Beam Level, preferably one that is longer than four feet (1.2 meters), to check how level your floor is. The longer the level, the more accurate your reading.
Follow these steps to see if your floor is level:
- Put the level down on the floor, moving around taking measurements in various locations.
- Measure any gap that appears between the level and your subfloor.
- If you have a gap under an eighth of an inch (0.318 cm), your floor is mostly level.
- A larger gap means that you’ll need to level it out.
Using a Bubble Leveler – Alternatively, you can consider using a DOWELL Magnetic Level Torpedo bubble leveler, which is similar to the beam leveler in shape.
- Check the position of the bubble to see if it is between the two lines.
- If it’s between the two lines, your floor is level.
- If it is on either side of the lines, then it would appear that your floors are not level.
Using a Laser Level – The third method to assess your subfloor level is by using a laser leveler placed on a tripod. The easiest option would be to use a self-leveling laser beam, like this Bosch Self-Leveling Cross-Line Laser.
- Place the laser on your tripod, then place the tripod on a surface approximately at the center of the floor and turn it on. You will need to wait while the laser beam levels itself.
- Once you’ve set up the laser and tripod, the receiver will emit a series of beeps. If you hear one long beep, then your receiver and the laser beam are perfectly level. You will need to mark these readings.
Note: This process will require you to move the laser receiver up or down until you get the desired readings. When you are actually leveling the ground, you will need to set your receiver to a predetermined grade and keep flattening the surface area till you hear that long beep.
You can find out more about that by watching this video:
How To Level Your Bathroom Floor
It’s common to find sloped floors in old houses. Sometimes they were just laid that way, but sometimes it’s a result of uneven subflooring that needs to be leveled out.
Ideally, installing a subfloor is the best way to level a floor, but there might be bumps, dips, or cracks to deal with under that.
Let’s take a quick look at how to fix these issues.
Fix Any Obvious Dips and Bumps – Bumps and dips along your subfloor are deterrents to a smooth, level subfloor. The process of fixing them depends on just how significant these bumps and dips are.
Sometimes, it’s as easy as scrubbing the area with sandpaper, while at other times, you’ll have to buy some mortar and fill the gaps.
Take a look at how you can fix bumps and dips.
Fill In Any Dips or Sunken Parts of the Floor – If your floor is sloping steeply down to the middle in a wide pit-like depression, you need to fill the dips or sunken parts of your subfloor.
Mix some modified set mortar and use a tile trowel to spread it over the floor. Remember not to use too much – just enough to level out the surface. If you have an extra mortar, scoop it off with a taper knife or sponge.
Grind off the Bumps – Dips are not the only thing keeping your floor from being level – you might also have bumps that need to be ground down.
If the bump is on a wooden subfloor, use a belt sander tool to remove it. These are not overly expensive, but if you have a large area, consider renting one from your local DIY store.
You’ll need a grinder-vacuum combo tool if it’s on concrete, which you can also rent from a larger home improvement store.
Level the Floor With Plywood – You can also level your floor with plywood, but this only works if your floor is only minimally unlevel.
Here’s how it’s done:
- Measure the exact slope of your floor.
- Cut leveling strips, which are long triangular slats that taper down to the flat surface.
- Position this strip on the floor, and check if the top of the strip levels out.
- Cut and attach more of these strips all the way down your slope.
- Use screws to secure these leveling strips firmly in place.
- Install your plywood subfloor over these strips, once again nailing them in place.
Pro tip: After you install your subfloor, consider using a Zinner 2301 Problem Surface Sealer. Dilute the primer and, using a rectangular tray and a rolling brush, apply a layer of priming solution in a similar motion to painting walls.
Use Self-Leveling Concrete – Self-leveling concrete is a form of modified polymer cement that is known to flow across a surface very quickly, ergo the ‘self’ leveling. You can use self-consolidating concrete, which is also highly mobile but based on superplasticizers.
Application: You’ll need to pour the self-leveling liquid onto the surface, then use a trowel or a Kraft CC975-01 Gauge Rake to spread it out evenly.
Prop-Up Joists – An unlevel floor can be something as simple as a few bumps along the surface, or they can be something more serious, like poorly installed joists.
If the existing joists are redundant and do little to support your floor, you’ll need to secure new joists in place and prop them up by placing adjustable steel columns under them.
Once your joists are secured firmly in place, your subfloor will be level and you can fix your floors.
How To Slope a Floor for a Drain
As previously mentioned, the only time you may want a sloped floor in your bathroom is in the shower area. Wet rooms are becoming more and more popular, which often means larger areas of sloped flooring that divert any water into the drains.
Provided you have a level and secure subfloor, here’s how you go about sloping a floor to allow water to drain:
- Line your subfloor with a waterproof floor liner.
- Once you identify where your drain is going to go, measure the distance from the drain to where you want the slope to start.
- Calculate the amount of slope you want to give.
- Shovel, pack, and tamp mud with a trowel until you get the desired slope you need.
- Mix up your concrete compound, pour over the sloped surface, and allow it to set.
- Remember to sponge excess liquid off and use a straight-edge tool to get the perfect, trimmed edge or slope.
You can find out more about sloping the floor for a drain right here.
A bathroom floor should and needs to be level unless you’re intentionally slanting or sloping the floor to allow water to drain. However, you always need to start with a sturdy, balanced, and level subfloor that will protect the integrity of your tiles or wood flooring in the long run.
Similarly, your floor needs to be even and flat, with no bumps or gaps that can lead to cracks and dents in your flooring.
- Home Guides SF Gate: How to Determine If a Floor Is Level
- Home Guides SF Gate: How to Slope a Floor for a Drain
- YouTube: Leveling a Sloping Floor #4: Using a Laser Level
- Networx: Do I Need A Subfloor?
- WikiHow: How to Check if a Floor Is Level
- So That’s How You Do That: 6 Tips for Floor Leveling before Installing Tile
- Wikipedia: Self-leveling concrete
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