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
This post contains affiliate links. The site owner may earn a commission should you click on an affiliate link and make a purchase. Read more
Table of Contents (click to expand)
Table of contents
- What is flood testing?
- Why is flood testing necessary?
- How to do a flood test
- So, now it won’t leak, right?
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:
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.
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.
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:
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.
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 have weep holes. It’s how they are designed and it’s normal. The most popular example of a bonding flange drain is the Kerdi 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?
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
Kerdi Showers need to be flood tested just like any other shower. 24 hours is what is recommended by Schluter.
Some Youtubers claim the Kerdi System won’t pass a flood test. This is inaccurate and Schluter even recommends you flood test their showers for 24 hours or more.
Industry standards recommend 24 hours minimum.
The shower pan should be filled with as much water as possible without breaching the top of the curb
This was a good post. Question for @diytileguy – to install a granite threshold on top of the curb, what is the best adhesive / mortar to use? Is it best to install on top of the shower liner that’s on top of the curb? Or can it be installed right on top of the 2×4 pice of wood framing?
There should never be a bare 2×4 exposed if the shower is done correctly. Additionally, unless you used a Kerdi system, or similar, the top of the curb should have a layer of mortar over the liner with some metal reinforcing lath.
A solid threshold could then be adhered to that. A lot of countertop people would use silicone to adhere it. I think I would prefer a waterproof urethane or silane-type sealant.
Tim Daley says
The comment about about evaporation is very easy to manage. Put a clear glass in the middle of the shower and fill it to the same level as the outside water. The amount of evaporation should be the same inside and out side the glass, so if the level is less outside, then evaporation isn’t the issue. It’s also a way to check if the level has dropped. Just check if the level is different inside and outside the glass.
Hi, I hired a general independent contractor to rebuild my master bathroom and hall bathroom after a pipe leak and everything had to be ripped out. He built a new shower pan from mortar 48x 60 inches. My biggest concern is : I requested a leak test of the liner, he aid it’s not needed… now the mortar has been put in place and it looks very uneven , I have ask him to fix this twice and twice he is trying to smooth it out with grinding it down and filing it in with mortar that is totally crumbling. I have been pro active in the research of how to rebuild and order items online that we need to accomplish an end goal in rebuilding and I have not seen a mortar pan that looks like the one he installed. I’m very concerned about the integrity of this shower pan. Thank you. JP
It doesn’t sound like it’s built right. You could put a straight edge on the shower pan and it should be a flat slope to the drain. That means that it slopes but that it isn’t wavy underneath your straight edge. If it’s not, then tell him you want it torn out and a flood test conducted before it’s redone.
I can’t tell you how many leaking showers that I see that could have been prevented by doing a simple flood test.
Great information! I recently had a tile shower installed, and there was a leak in the drain area with wet thinset oozing down. There was also an issue of water and bubbles coming up from cracks in the grout. My contractor never did a flood test pre tile. I wanted to get an understanding of how bad the issue may be and told him i was going to perform a flood test and monitor the crawl space. He never responded, so i did the test and water was leaking from all over the bottom of the floor. He now says, “a tile shower is not designed to hold water like a tub, it is designed to funnel water to the drain. Water over time dissolves sealant and your test sped up that process and will caused the floor to prematurely fail.” Obviously he is saying he is no longer responsible for repairing the floor. I am just wondering if what he said is correct, or if the flood test really proved a faulty install?
Your contractor is full of it. A shower is built to hold water like a tub and that’s the whole reason for performing a flood test.
A flood test is standard procedure and should be conducted on every shower. In fact, some local jurisdictions require a flood test on every shower and will come out and inspect that it is done.
This contractor built a shower that will slowly erode the structure of your home and he doesn’t want to be held accountable for it. Don’t let him off the hook.
Hi there! How long should the water sit from start to finish?
You want to go overnight, at a minimum.
Ivonne @ Herman Lepkofker says
Thank you so much for your great service of sharing your expertise with the public.
We have to start a job for which we do know nothing.
We live in a Condo 30 yrs plus old. I can hear the sound of water flushing down behind some walls, above apartment leaked water on some wall. Now the HOA wants that we redo the bathroom because an employee reported (during his 2minutes visit-said he has to go) walls damage when saw 4 , 1 1/2 inch x 1 1/2 inch tiles loose before you can enter the shower floor.
So a Mold Comp came and info us that there is no humidity, and recommended the Shower Pan Test.
First Plumber I called said it cost $228.00, and takes one or one and a half hour. So I am searching information to educate myself. I learned a lot. Thank you again.
If you can plug the drain and keep water in there for several hours that should prove whether your shower floor is a problem, or not.
Is it possible to test the fall of a shower prior to installation?
We have received a new resin shower tray. The delivery person left it up right, for a couple of hours which the manufacturer says you couldn’t do. They suggested laying it flat for a couple of days and it should level itself.
But I would like my contractor to check the flow to the drain before installing it.
Sure. If they level it out on something they could pour some water in and see how it drains.
Hello, Thank you for the information. We hired a contractor to install a tiled shower and required them to complete a water test. They completed the hotmop, then screwed on hardiebacker (screws placed approximately 1″ from the bottom of the pan on all sides of the pan) and placed redguard on the hardibacker face. At about 13 hours into the water test, the water level was down slightly (1/4 inch) and you could see the water in the hardiebacker on the walls. When I questioned them about it they drained the pan and told me it was normal because they don’t seal the bottom of the hardiebacker. It doesn’t seem normal to me. If you screwed hardiebacker into the hot mop and then the hardiebacker gets saturated, isn’t the water leaking through the hardiebacker to the hot mop hole? Any help you could provide would be appreciated. Is there a way to fix where we are at?
1/4 of an inch of water in 13 hours is a big drop. That could be 5 gallons of water depending on the size of the shower so this isn’t normal.
Another factor is the Hardibacker. Normally, Hardibacker wouldn’t be installed at this point because it can absorb some water and interfere with a flood test. However, I don’t see any way Hardibacker would absorb anywhere near 1/4 inch of water.
Finally, there are the punctures in the Hardibacker. The Tile Council of North America Handbook states that there shouldn’t be penetrations below the height of the curb. In fact, penetrations should be 3-inches above the finished curb and higher.
So, the punctures in your shower that are 1 inch from the bottom of the pan would be too low.
But is the water escaping through the screw holes near the bottom of the pan? Maybe. You might try draining the pan to below the screw holes and watch it from there. If it doesn’t drain then the screw holes would seem to be the culprit.
Either way, the bottom screws should be removed and those holes in the hot mop should be repaired. Good job on keeping track of the water in this!
Not sure if you have covered this, but should waterproofing be done if the shower pan is going to be a freshly poured concrete base on ground level? I was told the thin set over the concrete will provide the “waterproofing” needed…
Waterproofing should definitely be done. Thinset is not a waterproofing. Check out this post for more information:
Thank you for all of this detailed information. This is my first attempt at a bathroom renovation. I installed a Schluter shower pan, Schluter curb and applied Schluter Kerdi-Band around where the shower pan meets the 3 sides of walls and one side of the curb. I went ahead and installed the tiles in shower pan, not realizing the importance of flood testing. In your article, you mention that trying to flood test with tile down won’t be as accurate because the thinset will absorb the water. Would you say that it is too late to flood test and that it won’t be helpful? Or is late better than never? Thanks for the help!
You can still test it and it would be helpful. Especially if it leaks then it would be better to know now before you make even more progress