Flood testing a shower pan: Why it’s done and how to do it

Flood testing a shower pan. I get several calls per year about showers that are leaking.

Some of these showers are leaking after just a few years. Some, just a few weeks after they’ve been built.

I estimate that those calls could probably be cut in half if this one simple step were done. Doing a flood test. Checking your shower for leaks before it’s tiled.

Estimated reading time: 15 minutes

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What is flood testing?

Very simply, a shower pan flood test is where you plug the drain of the shower and fill it up with water.

If the water holds that level for 24-72 hours, or longer, then you don’t have any shower pan leaks. This is considered a successful test!

However, a test would be considered unsuccessful if the water level doesn’t hold. Why didn’t the level hold? Where did the water go? We’ll get to this below.

Additionally, the test should be conducted prior to the tile being installed. In fact, it should be done after the shower pan waterproofing has been installed.

Why is flood testing necessary?

The reason why one does a flood test may seem obvious but you would be surprised at how many tile installers and tile shower builders don’t do them.

Additionally, it’s not just bad installers either. I’ve known some very good installers that do not like to do a shower pan leak test.

Here are some of the reasons for not flood testing a shower that I hear from time to time:

Common excuses objections to doing a shower pan leak test

“Waste of time”

Probably the number one answer. Yes, flood testing usually takes more time and the entire process can actually take a significant amount of time, especially if it requires an inspection.

The shower waterproofing has to be installed. A certain amount of time has to pass before subjecting it to water. This will depend on the type and brand of waterproofing system but, typically, would be ready the following day.

Then the shower gets filled up with water. If your municipality requires an inspection, this would be scheduled at this time.

From here, more time will need to pass to give the water a chance to find a way out. Usually, overnight is a minimum amount of time. More, if you are waiting for the pan test inspection to get approved.

Consequently, this whole process takes a minimum of a day and can add several days onto the schedule.

It’s nice if the installer can work on something else in the meantime but, if it’s just the shower, there’s nothing that can be done except wait.

Contrast this to simply moving on to the next step immediately after the waterproofing is finished and I will concede that the flood testing process takes more time.

“I followed the instructions so I don’t need to check it”

*Sigh* No doubt, this excuse is given by the tile installer that doesn’t test and “has never had a problem.”

Guess what? Checking one’s work is not an unreasonable requirement. In fact, it could be taken as flattering in that it means that what you are doing actually matters.

Airplanes, automobiles, plumbing, and gas piping are all examples of industries that check their work and have third-party inspections.

Besides, even if everything was done perfectly there is always the chance that the products that you are using for waterproofing are flawed.

I’m scared it’ll leak!

This may seem like a bizarre objection but you have to think about it from the standpoint of the installer.

Putting 60 gallons of water in an upstairs shower and leaving it overnight can be a bit nerve-racking. You would hate to come back the next morning and see water dripping into the finished kitchen below.

So, not testing is almost understandable until you realize that if it leaks now it will leak in the future and it’s much cheaper and easier to fix before it’s tiled and the shower glass is installed.

Is flood testing required?

Flood testing is recommended, but not required according to the Tile Council of North America. However, they do acknowledge that one may be required by the plumbing code.

Additionally, in some municipalities, a shower pan test inspection is required. The only way to know would be to check with the building authority for your area.

But, even if an inspection is performed it can provide a false sense of security.

Flood testing falls under the plumbing code and the inspectors know plumbing quite well. But when it comes to shower pans, in general, they just aren’t as well versed in the details of them.

Furthermore, add in all of the different products and methods that are common now and it’s understandable that there would be difficulty in keeping up with what’s OK and what’s not.

How to do a flood test

After the primary waterproofing membrane is installed and had time to dry, the first step is to plug the drain.

Drain plugs for flood testing shower pans

As a rule of thumb, tile shower pans have a 2-inch drain. There can be exceptions to this but most showers will be at 2-inches. So you’ll need a 2-inch shower pan test plug.

The “Wingnut style” test plug

I’ve tried many different drain plugs. The least expensive are the kind that has a wing nut on the top. You simply tighten the plug until it seals.

In my experience, these are reasonably tough to tighten. It might seem simple until you get the plug recessed down into the drain and have to tighten it. It has to be tightened quite tightly.

More than once, I’ve shown up the next morning to find that the water in the shower pan is completely gone because I didn’t have the drain plug tightened quite enough.

Inflatable test plug

The 2-inch inflatable test plug is by far the easiest but they cost a little more than a mechanical test plug. Additionally, it’s nice to have the extension hose so you can get the plug far enough down the drain and still be able to put air in it.

Did I mention that you want to check not only the shower pan’s waterproofing but also the drain connection? The drain-to-drainpipe connection is about 2-3 inches down inside the drain.

But this type of plug is the easiest to use and gives you the most reliable seal. I keep a Dewalt 20v battery-powered inflator in my van to pump up the plug but any compressor will work. Probably even a bike pump.

Fill it up with water

When the drain is in you can begin flooding the shower pan with water. Hence the term “flood test.”

This step is basically as simple as it sounds.

Showers with curbs

You want as much water in the shower pan as possible so this means filling it up to just barely under the level of the curb. Don’t overfill. Just get the water to as high a level as reasonable.

“How do I do a shower pan flood test on a curbless shower?”

You just had to ask, didn’t you? Flood-testing curbless showers are not nearly as much fun.

A flood test is a critical step in building a curbless shower.

To properly perform the test, you’ll have to create a temporary waterproof dam to keep the water in the shower wet area and have it get to a high enough level that it tests every corner.

I know of two different ways of creating this dam:

• spray foam
• Foam board and sealant

Both methods have their quirks. Spray foam is no fun when you’re not familiar with how it expands. If you do understand its expanding capabilities then it’s probably the easier of the two methods.

Simply spray a small strip of foam around the area that you want to contain. Wait a couple of hours for it to dry and you should be ready to go.

The other way that I’ve done it is to use a strip of waterproof foam board, Wedi board for example, and glue it down to the waterproofing with the sealant for that particular board.

You may have to provide some weight to the back of it to keep it from falling back. But this has worked successfully for me in the past.

Removing your temporary flood-testing dam

Additionally, you’ll have to be very careful when removing the temporary dams. They will be stuck directly to the waterproofing and you don’t want to do damage to that after you’ve conducted your test.

But you can carefully remove the sealant, or foam residue, with a scraper that is used flatly. It’s not necessary to get every bit of it off but you do want the area to be flat again before tiling.

Monitoring the water level during a flood test

Next, you need a way of keeping track of the water level. You can mark a line on the side of the membrane with a pencil.

Another way is to measure the water in a particular, and identifiable, spot. I have a spot that I use on the drain collar and measure off of it every time. You could also mark an “X” on the shower pan somewhere and measure off of that spot.

There’s more than one way to keep track. What matters is that you have a way to accurately monitor the water.

What if the water level has dropped?

If you come back the next day, or several days later, and the water level has dropped, you have to figure out why.

Here are the reasons the water level may be lower (or gone)

Drain plug didn’t sealed tightly enough

This is the number one culprit for me when the water level is lower. Something happened with the plug.

When the water from a flood test is completely gone then this is almost certainly the problem.

But this could still be the reason for even a slightly lower water level.

The fix is to reseal the plug or get a different one.

It’s leaking at the drain-to-drain pipe connection

You can check this by only putting enough water in to cover the seal in the pipe.

If this fails then that connection will have to be redone.

It’s leaking at the membrane-to-drain connection

I’ve found this to be more likely with the Wedi showers. If the drainpipe isn’t done exactly correctly with the Wedi system then it will leak at that connection.

Additionally, if a traditional shower liner is used then the problem would usually be the sealant (or lack of) underneath the liner where it seals to the drain.

One tip is to when you fill the water back up, start by only filling enough water to immerse the drain and see how it holds. If it holds, then fill it up the rest of the way. This is particularly effective with the Wedi system, or similar, that I mentioned above.

It’s leaking at a membrane seam or corner

This can be diagnosed by filling the water level up to just past the suspected seam. If it leaks then the water level will drop to the point of the leak and then stop.

Wherever it stops is the problem and will have to be repaired.

The membrane has a hole in it somewhere

Very similar situation to what I wrote above but the difference is that you have no idea where the hole would be. You’d have to just wait until the water level stops dropping.

If water is leaking downstairs in the process then it might be a better choice to remove what you’ve done and start over.

Evaporation

This is used as an excuse a lot when the water level is down anywhere from 1/16th-1/4 inch. It’s an easy conclusion that has the benefit of no accountability.

In my experience, evaporation has never been the cause of a dropped water level.

Several years back, I had a flood test going on a new construction project in the middle of summer. I had filled the shower liner up the day before a three-day weekend.

Furthermore, someone had left the furnace going the entire weekend and it never shut off. It didn’t have a thermostat installed at this point and someone direct-connected the wires on it so the furnace ran all weekend with no way to shut itself off.

So, what I’m saying is that the house was extremely hot and had been for over three solid days.

Yet, my water level was right on the money.

An evaporation control

If you do feel that evaporation might be a factor in your flood testing you should have a way to account for evaporation in your test.

You do this by having a separate container for water that is outside of the shower. This can be a bowl, bucket, or whatever you feel is a container that has no chance of leaking.

Then simply monitor the levels of both the shower and your container of water.

If your shower water level is down 1/8 inch then the evaporation control bucket should be too.

Other culprits

On one project, I found out the painters were stealing the water from the shower pan. If you can’t figure out the mystery it might make sense to think about who else is on the job and how accessible water is for them.

Draining the water when a flood test is complete

You’ve installed the waterproofing, plugged the shower drain, filled it up with water, monitored the water level, and feel comfortable that the shower waterproofing is sound.

You’re done now, right?

Not exactly. The final step is to pull the test plug and observe how the water drains.

There are two things that you want to be on the lookout for. These are:

Standing water

For starters, the water should drain and do so completely. The only way to accomplish this is by having the waterproofing membrane sloped to the drain.

This is the case no matter how the shower pan was built. Kerdi, Wedi, and traditional shower liners are all supposed to slope to the drain.

With a traditional water in/water out mud pan shower, there is supposed to be a slope underneath the liner. Usually, called a “pre-slope” and sometimes installers will try to skip this step and install a liner directly on the flat subfloor. This is incorrect.

Additionally, water shouldn’t collect anywhere before it gets to the drain. When it does, these are often referred to as “birdbaths” and they will need to be fixed prior to the shower construction moving forward.

Weep-holes

Plugged weep holes in the drain can cause problems down the line. So you want to make sure that they are working when you drain the water from a flood test.

Note: if you have a bonding flange drain then these types of drains don’t necessarily have weep holes. The most popular example of a bonding flange drain is the Kerdi drain. Also, linear drains typically don’t have a weep system. See my review of the Noble Freestyle Linear Drain.

Every standard tile shower drain, both the 3-piece clamping drain and the cast iron drain, will have a weep system built into it.

Consequently, when the water drains you want to observe these weep-holes draining water. Not just some of the weep-holes and not just a little water. This is an important and often overlooked step.

When is it too late to do a shower pan leak test?

A proper shower pan test will be done when the waterproofing membrane is installed but before the shower construction progresses past this point.

In other words, it should be done before there is tile installed.

It’s not that you can’t perform the same test with tile installed- plugging the drain and filling with water. But you won’t be able to accurately monitor the water level.

After it’s filled the water is likely to absorb wherever it can. In the mortar, grout, and mud bed, depending on the type of shower.

So, if you are trying to see if it leaks downstairs, or in the crawlspace, this might accomplish that goal.

But, if you are trying to see if there’s a slow leak then I don’t think you’ll be able to accurately perform the test because the water level would probably drop whether it leaks, or not.

So, now it won’t leak, right?

Not so fast. A successful flood test proves that your shower may not leak at the moment but it’s still possible that the waterproof membrane could be damaged.

Additionally, even though the shower pan may be sound it’s quite common for shower leaks to originate somewhere the water wasn’t able to test.

Places like the curb, shower benches, and half walls. These are critical areas that won’t be tested by filling the shower pan up with water.

No Waterproofing: Will this cause shower leaks?

Conclusion

I hope this post has been helpful in explaining what flood testing is, why it’s necessary, and how to conduct one if you are building your own shower.

Please let me know if you have any questions in the comments below.

Frequently Asked Questions about Flood Testing Showers