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Help..basement shower drain leaking?

I am kind of new to the do-it-yourself repairs, so I am quite inexperienced to the functions of a shower drain in cement. Please don't hold it against me if any of my questions seem naive.


I have a stand up corner shower in my basement bathroom and the drain appears to be leaking. I have resealed all the seams in hopes that may have been the issue..but I was wrong. Every time the shower is used (which is not often because of the leak), a large puddle flows into the adjoining hall and furnace room (seeps under walls). I am thankful that there is a large enough gap between the sheetrock and cement flooring to prevent moisture on the sheetrock but I am still worried if this water is damaging other parts of the adjoining bathroom walls. I have only been in my home for two years and it was leaking the first day I used it. It also appears that the previous owners knew of this leak because the drain in the shower has been recaulked (several times by the looks) yet it is still kind of crooked too. Another note: when standing in the shower, the base does not seem solid (plastic sinks a little under weight of foot). Is this normal?


I need help on deciding what to do about this problem. I would eventually like a tub/shower combo put in its place but how do I determine if the issue is the current shower base or if it is the drain (which goes directly into the cement) itself? If it sounds like I must replace the shower, what steps must I do to make sure I find a tub/shower that would work properly with the current drain that goes into the cement? Any advice or comments are welcomed, I would love to fix this problem before it gets worse. Thank you in advance.

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Posted 2011-02-07T18:40:06+0000  by Deven01 Deven01

Hey Deven01 thank you joining and welcome to the community.

Just for your info your question doesn’t seem naive at all and good job on  your detailed description.


Deven having said that you are getting puddles of water under the adjoining wall sill plate while showering tells me that you are probably having a problem with an actual base rather than the drain.

I think that leak is coming from the section where drain connects to the fiberglass base and the easiest way to confirm that would be to direct water in to the drain.

You can simply test this with a garden hose, just remove the grille from the drain and let the water flow directly in to the drain.

If the puddles show up again than you have a problem with drain if not than leak is at the connection in between drain and the base.

On your second note: sinking plastic can be either from actual structure of the material or from the crack on the base.

Inspect the base at the section where it sinks, if it is sinking where drain connects to the base that can also explain  the problem you are having.

In other words if the drain is not firmly connected to the base and there is room for the base to sink at the drain- base connection than water is probably leaking out once you put the weight  down on the section where it connects.


Try some of these things and let’s determine what the problem is with that shower ,than will go from there.


PS: post some close up pictures of the drain if possible so I can instruct you on how to proceed.





Posted 2011-02-07T19:46:02+0000  by George_HD_CHI

Thank you for your reply George. I will give the hose test a shot tomorrow, thank you. Also, yes, I believe the "give" in the base structure when standing in the shower is near the edges of the drain (centrer of shower base) which I also thought may be part of the problem. Thank you again and I will post again when I test the drain with the hose. I will keep my fingers crossed that the shower base itself is the problem and not the drain.

Posted 2011-02-08T04:56:08+0000  by Deven01

So I tested the drain with a hose and appears the drain is working semi-properly. I say semi because even after the water is shut off, there is water in the drain pipe a few inches down from the top opening. It doesn't appear to overflow when the water is on but I am curious to know if this is normal in basement drains...? Presense of water in the drain pipe after water is shut off? Perhaps the shower drain has a clog somewhere? 


If the shower is running without anyone in there, the drain appears to be doing its job and not leak to the surrounding rooms. But when there is someone in there, any weight on the base, causes water to leak.


I determined it was the shower base and started tearing it apart. Upon removal of the shower base, I found where my issue lied. In the picture I am including, all the gray that is seen around the drain, is where the water was up to. The cement slopes down to the drain and that slope is where the shower base was "giving" when standing on it. That "give" caused a slight gap near the drain, causing the water to run under the shower base, along side the drain, forming the water puddles. 


So, here are my questions other than the couple mentioned above:

Would the shower pan be below the cement or perhaps I don't have one?

I would I fix this so that the next shower base will not do the same thing because of that slope? Thank you in advance for any suggestions on this

basement bath


Posted 2011-02-10T12:48:28+0000  by Deven01

So, I had a thought. Instead of a purchased shower base unit, perhaps building a custom shower pan (threshold and all) would be my best option? Other than the slope near the drain, my basement floor is quite level, but if I were to build a custom shower, I would still have to build a mortar bed so the water would slope to the drain, right? This is all quite new to me so any advice or suggestions would be appreciated.

Posted 2011-02-10T14:07:39+0000  by Deven01

Deven01 wrote:

So, I had a thought. Instead of a purchased shower base unit, perhaps building a custom shower pan (threshold and all) would be my best option? Other than the slope near the drain, my basement floor is quite level, but if I were to build a custom shower, I would still have to build a mortar bed so the water would slope to the drain, right? This is all quite new to me so any advice or suggestions would be appreciated.

Hey Deven,

Standing water in the drain opening is actually what is suppose to be happening ,there is a part called a  P- trap installed and that same part is what’s holding water.

See attached picture; p-trap.jpg


If you would have removed the concrete around your shower drain this is pretty much what you would find.

P-trap is constantly filled with water at the lowest section and that same water is there to prevent gases from going back in to the living areas.

So don’t worry about the standing water that is what is suppose to be happening and you drain is working just fine.

There are two options that you can go with to correct the problem you are having with your existing drain.

One of them you have already mentioned and that is to build a custom shower base.

To build a custom shower base you would still need to install a shower liner underneath and in addition you would also have to make some adjustments to the surrounding framing.

Further you would also need a sloped mortar bed and a threshold that would have to be either framed or build from the cinder block.


Another option would be to go with fiberglass base again.

In order to successfully install a fiberglass base you would first need to check that PVC connection to the cast iron P-trap.

Looking at the previously attached picture it doesn’t look like it has been connected firmly.

Usually when going from cast iron to PVC there is a rubber gasket or lead packed oakum seal around the coupling.

If they have used just a piece of smooth pipe that same connection could be moving with the base, so please assure that there is a firm connection  in between cast P-trap and the PVC.

If you decide to go with fiberglass base again make sure  to fill the void in between the base and sloped concrete.

You can do this with expandable foam, sand mix mortar or something called a structo lite.


Any of these products should  work just fine but I think in your situation the easiest product to use would be expandable foam that can be injected from the side wall.


Let me know with which option you are going with so I can further assist you.




Posted 2011-02-10T22:10:04+0000  by George_HD_CHI

Thank you again for your help, George. I tried your suggestion and checked the connection of the PVC pipe to the P-trap and it appears to be secure. It does not appear to "wiggle" when I pull on it. For caution, is there something I can put on the connection/seal to ensure a tight connection?


Because I would like to make my shower bigger without having to worry about moving the drain, I think I am going to go with the custom shower. I have done quite a bit of research and see that building a custom shower pan is feasible if proper planning is done as well as having the right materials and tools. Do you have any knowledge of building a custom shower pan? I know that I will have to build a threshold/ curb, use fill and cement to slope the pan to the drain (1/4" to every linear foot), make the liner/membrane go up the side walls about 9", and use waterproof backer board for the walls. My question would be about the "weep holes". These are part of the drain unit? Or do I need to create these when I cement around the drain? It might be a dumb question, but as I have mentioned, I am a new Do-it-yourselfer, so a lot of this is completely new to me. Thank you again for your help.

Posted 2011-02-15T13:07:50+0000  by Deven01

Welcome back Deven.


Alright, so you’ve decided to go with a custom shower base?

You will not be considered a DIY-err after you are done you know that right   :smileyhappy:

No worries custom shower is a great choice and I do have knowledge and a hands on experience to help along the way.


If the drain connection appears to be secure an there is no wiggle room there is nothing to worry about it , just leave it alone.

There is no need for any kind of additional seal to be put on.


Now let's talk about the "weep holes".

Weep holes are part of the drain unit and their purpose is to direct moisture and water in between sloped mortar and the shower liner towards the drain.

Tiles and grout are not waterproof and there is always a small amount of water that penetrates thru the grout and mortar.

This same water and moisture created from it are sloped in to the weep holes.
weep holes.jpeg





Your fist step in building a custom shower base should be framing and determining size of the new shower base.

Pay attention to the size of desired shower door now and build a shower base to correspond to those measurements to avoid ordering a custom size of shower door.


In addition when framing a new shower leave a 1/4" gap in the corners to easy out placement of excess shower liner.

You will also need a 9" tall blocking in between framing members to support shower liner.

Simply purchase a 2x10 lumber, cut to size and fasten in between studs.

Once you get all of your walls ready you can proceed and frame a curb.


To frame the curb place the piece of pressure treated 2x4 flat on the concrete and fasten with Tapcons or powder actuated concrete nails. Once you get this base plate fastened add additional two pieces of 2x4 on top and fasten with 3" construction screws.

Before you start working on a mortar bed assure that walls are plumd especially around the opening to avoid any shower door installation problems.

Install a shower type drain and test for the leaks.


Quick tip; look for the drain with a square cover (grille)  to ease out tile installation, cutting ceramic tiles around the round opening can be challenging.

Determine the slope and transfer the guide line on to the walls.

Prime the concrete before working on pre sloped mortar bed with a bonding adhesive, se attached picture;




For the sloped mortar bed use a sand mix mortar  mixed with water or latex additive, water is acceptable but adding a latex additive increases the strength of the mixture.


sand mix.jpeg

This is where it gets little complicated.

To be able to successfully work with this mixture it needs to be mixed on a "dry" side in other words once mixed you should be able to shape and pack mortar without any excess water or additive showing up on the surface of the mortar.

Firmly pack the mixture and remove excess with a straight piece of 1x4 or aluminum level, follow the previously drawn guide line and smooth out the remaining mortar with a finishing trowel.


To test the consistency of mortar bed place the trowel over the mixture and if apply a moderate pressure, properly built mortar bed should be able to support your weight without any serious indentations.



Now at this point you probably want to call it a day and wait for the mix to cure.

Your next step is to install a cement board underlayment on the walls.

Once installed you are ready for the shower liner.


Spread the shower liner over the pre-sloped mortar bed and bring it up anywhere from 7" -9" on the side walls.

Assure there are no wrinkles on the PVC liner and also make sure that liner covers the framed curb as well.

Carefully cut the liner around the inside diameter of the drain and around the "weep holes".

Place the pea gravel over the weep holes to prevent mortar from obstructing weep holes.


Note: please visit attached link form our manufacturer on the PVC liner installation for additional details on drain and liner installation.

Fold the corner of the PVC liner and attach to the blocking with roofing nails, make sure to nail only top of the liner and in addition only on the outside of the threshold.


Palace the steel lath over the liner and wrap around the threshold, fasten the lath with roofing nails on the outside of the threshold.


Using the previously used consistency mix the deck mud and cover the shower liner.

Note: adjust the drain s there is a minimum of 1-1/4" of firmly packed deck mud around the drain.

To shape the curb mix add a little bit of water to the deck mud and apply to the sides of the curb with a threshold remove excess and shape with trowel.


Deven , hope that helps and don’t hesitate to ask more questions.




Posted 2011-02-15T17:44:10+0000  by George_HD_CHI

Devon, I'm gonna respectfully disagree with a few things posted in the last response and offer up some additional useful info for you as well.  It's also nice to see you've done some research ahead of time and are already aware of the preslope requirement for the shower pan to function properly.


"You will also need a 9" tall blocking in between framing members to support shower liner.

Simply purchase a 2x10 lumber, cut to size and fasten in between studs.

Once you get all of your walls ready you can proceed and frame a curb."


One part left out is that code states the liner cannot occupy the plane of the wall.  Now what that means is your liner needs to be recessed to be flush with the face of the studs and therefore so does your blocking have the need to be recessed a bit.  There are 2 reasons for this.  The first is that the wall/floor intersection is a movement joint and having the liner pinched would cause abrasive wear and failure over time.  The second reason is that the thickness of the liner would cause the bottom of the cement board to bow out and would result in your corners no longer being square.


Simply taking a planer or a belt sander with 60 grit to the face of the stud is enough to quickly remove enough material for the 40 mil thick liner.  Since the blocking is only for support of the liner, I use  3/4 "plywood cleats along side the stud, recessed 3/4" from the face of the shaved stud.  Then 3/4 plywood for the blocking.  Do it all with a finish nailer, and there's no problem with a 10d nail head in a 2x10 block no wanting to sit flush as you get with the pictures is the previous post.


Before we go any further, there are many different kinds of pressure treated woods, but for this, we'll only concern our selves with wet and dry, chemical penetration or type does not matter.  The pictures in the post before show pressure treated blocking and the suggestion to use pressure treated lumber for framing the curb can lean to very unintended results.  Unless the PT is stamped KDAT (kiln dried after treatment) , it will arrive too wet for use as during the drying out time, it will excessively shrink, twist, warp, etc and will wreck the tile installation.  For a curb on a slab, regular lumber with a sill gasket or brick thinsetted to the slab will suffice.


If you are enlarging your shower I will assume the drain will not be centered.  You do want to measure to the furthest point from the drain.  Your preslope layer will need to be 1/4" per foot from the furthest point of the drain.  The perimeter of the preslope bed will be level all the way around so other areas will have a greater slope.  In viewing your picuture, it looks like your stub out is packed with concrete all the way around so the base of the screw sleeves of the clamping ring drain will be resting on the slab like feet supporting the drain.  That gives you the minimum thickness of 3/4" at the drain you need to mix with just water and do a direct bond to the slab.  Had the large ring of the base been resting on the slab, you would have needed to mix your preslope layer with latex as it would have been featheredged.


So, 1/4" per foot, + the 3/4" thickness at the drain, and if you want, you can tack a piece of thin molding around the inside of the shower to act as a guide at the height of the preslope.  You can even leave it in when you are done since water will never get to it.  Be sure to pack the mud around the base of the drain nice and tight.  The normal mix is actually abour a 4 parts sand to 1 part portland cement mixure.  Sandmix is 3-1, so cut 4 scoops of sandmix with 1 scoop of masons sand.  Latex instead of water will only make it sticky and tough to shape, stick with water, only wet enough to pack like making sand castles.  Don't bond it with latex, a slurry mixture of thinset will give you a better bond to the slab.  You will use thinset later to set the tiles as well.


"Now at this point you probably want to call it a day and wait for the mix to cure.

Your next step is to install a cement board underlayment on the walls.

Once installed you are ready for the shower liner."


Maybe that was a typo since the liner goes up the wall behind the cemet board?  The next step is to install the liner.  Oatey's instructions are clear on that, so I'll leave that alone.  You do want to be very careful to ensure a water tight juncture at the curb.  Your local store may or may not sell preformed dam corners for that intersection.  Once the liner is installed, a 24 hour leak test is performed.  Normal drain plugs don't work well because of the weep hole slots so inserting a balloon and blowing it up will do the trick. 


If there are no leaks then you can proceed to the next step which is waterproofing the walls.  Use either 4 mil plastic sheeting or 15 lb roofing felt to line the walls, overlapping any lower course by at least 3", including a 3" overlap of the liner.  Your cement board is impervious to deterioration from moisture but it will provide no waterproofing for the walls and will readily allow water to pass through.  Now you can install your cement board onto the walls.  Do not install any fasteners into the bottom 8" and keep it about 3/4" off the base. 


For your curb, as previously instructed, form your curb with diamond lath, folding it into a "u" and nailing it only on the outside.  When you install your setting bed of mud, it will wedge the inside of the lath to the curb and will pin the lower edge of the cement board to the walls.


Form your curb using masons mix, not sand mix.  It has lime in it and a different ratio of sand and portland cement.  It will cling to the vertical surfaces of the curb much better.  Once it starts to set up, you can shave it to size with a margin trowel.


Your setting bed...


Set the drain so the strainer is 1 1/4" plus the tile thickness plus about 1/8" for thinset up from the base.  If the strainer has no protective film, cover it to keep mud out of the drain.  You setting bed will be uniformly 1 1/4" thick, not installed sloping where it changes in thickness.  It only slopes because it's following the slope created below.


An alternate method for waterproofing the walls is a roll on waterproofing membrane like Redgard (sold with the setting materials) which is painted onto the walls instead of using the poly or felt behind it.  Surface waterproofing is the superior method but you choose one, you don't do both as it can cause trapped moisture.


Redgard with Wonderboard is part of the Custom Building Products lifetime warranty program.  When you set your tile, start with your second row.  measure up the thickness of the floor tile, 1/8" for caulk, the size of your tile for the first row, the grout joint and then make a mark.  Tack a ledger board there and tile using versabond or flexbond going up the wall.  Once the tile sets up, set the floor and cut in the bottom row of wall tile.  Mastics are best suited for dry areas.  Don't use anything from a bucket ready to use in your shower.  Custom Building Products also just introduced a large assortment of their grout colors in 100% silicone matching caulks, not just the acrylics.  The inside corners of walls and where walls meet the floor are movement joints and never get any grout, just caulk.


You can apply a sealer to your grout after waiting the appropriate number of days as per the sealer manufacturere.  Grout sealers are designed to let water pass through, they are not made to be waterproofers contrary to popular belief.  They are only something to assist in maintenance.  The other things that go a long way in maintaining a clean shower are switching to a liquid shower soap as there are no binders within it to congeal on the wall with body soils, rinsing the walls with a hand held shower sprayer when you are done your shower, drying the walls with a towel or squeegee, and installing a timer on your bathroom fan so that you can let the fan continue to run for a while once the shower is done to evacuate the excesss moisture. 


If you have any questions concerning recessed shower niches or benches or custom shelves or want anything explained in further detail please post back.  Most of all, Good Luck. :smileyhappy:



Posted 2011-02-15T21:41:58+0000  by brianstile

Hello Mr. Brian S. Tile and welcome to the community. :smileyhappy:


Thank you for your super informative post and your participation.


Brian your post it's definitely a great read and I’ve enjoyed every little bit of it.

Especially the part that talks about the CDX blocking, I’ve always used dimensional lumber for blocking but for the next install I’m going to try CDX and my 15gauge Senco gun.

As far as the recessing blocking goes I was not aware of the code that states that liner cannot occupy the plane of the wall.

It does make sense and thank you for bringing that up in your post, my approach was always to recess corners in order to make a room for the shower liner.

I've always thought that there is no abrasive wear outside the corners being that bottom of the CBU it’s not attached to studs and therefore there is no impact with expansion and contraction.


Pressure treated lumber it is a code for the sole plate and ground contact (concrete) applications.

I do agree with you that PT lumber does shrink, twist and warp even KDAT changes its shape in second drying.

But for this application I would still use a PT lumber being that this is a shower area where water accidentals and every day use water intrusion it’s always present.

And in addition it would be a short  fastened piece that warping would not affect as much as longer lengths.


Adding latex to mud mix does have its own disadvantages and advantages.

Advantages are reduced permeability, stronger bond and water resistance and on the other hand adding latex to mixture does make it little difficult to shape.

Would I be using latex or not really depends on the condition of the concrete around the P trap.

Without being on the job it is hard to tell if the slab thickness it's sufficient around the trap r not and why is it lower than rest of the basement.

Anyhow I do agree with you water mix would probably be sufficient.


Again that you for the great info and please keep posting like this.



Posted 2011-02-21T17:25:12+0000  by George_HD_CHI

"I was not aware of the code that states that liner cannot occupy the plane of the wall."


In the IRC, it's phrased as


"Lining materials shall be pitched one-fourth unit vertical in 12 units horizontal (2-percent slope) to weep holes in the subdrain by means of a smooth, solidly formed subbase, shall be properly recessed and fastened to ap-proved backing so as not to occupy the space required for the wall covering"


and in the UPC it's phrased as


Linings shall be properly recessed and fastened to approved backing so as not to occupy the space required for the wall covering and shall not be nailed or perforated at any point which may be less than one (1) inch (25.4 mm) above the finished dam or threshold.


You are 100% correct, PT for slab or ground contact.  Bottom plates won't move much , if at all, with studs pinning them down.  Curbs might see some cracking though but that's why it's ok with regular kiln dried with a gasket below to keep it from direct contact.   My preference when I'm on a slab is to use bricks.


Since you brought up the brand name Senco, did you know the Home Depot Pro Desk can order colated cement board screws for Senco (and equivilent) screw guns?  :smileyhappy:  


Thanks for the welcoming and the compliment, George.  You do pretty good yourself. :smileyhappy: 






Posted 2011-02-22T20:12:02+0000  by brianstile
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