How to make a shower-cubicle floor waterproof?

[David001]

 

Hi.  Can this shower-cubicle floor problem be solved without having to lay a completely new floor?

 

I've bought a home with a first-floor shower-cubicle and quickly found that shower water made its way through to the room below, dripping from the ceiling of that room. I then found that there were some cracks and gaps in the grouting between the black tiles in the cubicle, so I filled them with "flexible" grouting (although it doesn't seem flexible to me). I then noticed that some of the tiles moved downwards a fraction when stood upon - this probably caused the grouting to crack in places. So I made a number of holes in all of the grouting and squeezed into each hole quite a lot of a very powerful glue designed for this kind of situation, hoping to make firm and solid whatever is directly beneath the tiles, or to remove the sponginess beneath the tiles by solidly bridging between the underside of the tiles and whatever is beneath them.

 

But I have not dared to used the shower since then, for fear that water may still get through to the cavity and the ceiling beneath!  🙂

 

I expect the central tiles were cut into the eight triangles so as to enable each triangle to slope downwards as they do towards the centre, to direct water into the drain.

 

Is there a waterproof product of any kind which could be placed over the tiles to ensure that all water goes into the drain? It would have to be a product which looks smart, and is tough enough to withstand being struck by water every morning and occasionally being scrubbed during cleaning.

Thanks a lot for any help given!

 

[ProDave]

That suggests it is already laid as a wet room, but the fact it is leaking and the tiles are moving suggests somehow it has failed.  I doubt there is a fix other than remove the tiles assess what is under them and repair and replace as necessary.

[Big Jimbo]

To be honest, i doubt it. If the floor has got wet and is knackered, it will need taking up. Any tiles that are moving are never going to seal.

 

[Nickfromwales]

I’ve been doing these types of rooms for nearly 30 years, and I think, judging by the threshold trim, the subfloor hasn’t been overlaid with plywood or other binder board.

 

Can you pull back the carpet and see if the tiles are, as I suspect, glued down directly to the chipboard flooring?

 

Tiles and adhesive will be around 15mm on average. 

 

Oh, and pop down the off-license and get some of the good stuff, as this will 100% need taking up and doing again. Don’t waste any more of your beer funds on rescue products, (sorry). 

[Alan Ambrose]

Might be easy to cut a neat 1 foot square hole in the plasterboard in the ceiling below to get an idea what’s going on.

[David001]

11 hours ago, Alan Ambrose said:

Might be easy to cut a neat 1 foot square hole in the plasterboard in the ceiling below to get an idea what’s going on.

 

@Alan Ambrose, the previous owners had done just that just prior to completion, and had then covered the hole with a piece of light paper-board, pinned in place.  When we unpinned the board and looked inside we found a small pot-plant dish had been wedged underneath the central drainage point, but it had not a drop of water in it.  Then looking closely all through the exposed area we found it was too much of a dense forest of pipes and beams and other bits of wood (as well as several electrical cables!) that it wasn't possible to determine the point at which water had entered from the shower-floor above.  So I'm inclined to think that we're going to have to lay a new tiled floor.

 

@Nickfromwales @ProDave @Big Jimbo @Alan Ambrose

Would it be possible to give the present floor some thick coats of something long-lasting, pliable, and waterproof (painted on, or some kind of thick pliable waterproof board), and then lay new tiles on top of that?  This might save ripping up the current floor.  There would then be a slight step up of about an inch from the floor outside the cubicle, but that could be dealt with by replacing the cubicle door (which swings inwards) with a curtain.

[Alan Ambrose]

Unfortunately, I doubt it. The thing that I find odd is that the tiling looks quite neat which suggests a careful job. If you’ve regrouted, the grout should be fine, so might it be a plumbing problem? Worth checking that the pipework joints are tight. I think unless you can see where the leak is, it might be quickest to rebuild the whole set-up from scratch. Try an endoscope camera maybe? Post up a pic from underneath?

[Nickfromwales]

29 minutes ago, David001 said:

 

@Alan Ambrose, the previous owners had done just that just prior to completion, and had then covered the hole with a piece of light paper-board, pinned in place.  When we unpinned the board and looked inside we found a small pot-plant dish had been wedged underneath the central drainage point, but it had not a drop of water in it.  Then looking closely all through the exposed area we found it was too much of a dense forest of pipes and beams and other bits of wood (as well as several electrical cables!) that it wasn't possible to determine the point at which water had entered from the shower-floor above.  So I'm inclined to think that we're going to have to lay a new tiled floor.

 

@Nickfromwales @ProDave @Big Jimbo @Alan Ambrose

Would it be possible to give the present floor some thick coats of something long-lasting, pliable, and waterproof (painted on, or some kind of thick pliable waterproof board), and then lay new tiles on top of that?  This might save ripping up the current floor.  There would then be a slight step up of about an inch from the floor outside the cubicle, but that could be dealt with by replacing the cubicle door (which swings inwards) with a curtain.

Nope. Just a suicide mission tbh.

 

”Short cuts take 3 times longer”. Fact.

 

Why are you scared of taking the floor up?

 

This is an issue you can’t slide left / right, you need to resolve it and do it correctly, then it'll last decades. 

[Alan Ambrose]

Looks like someone has had a look at this and not found the problem yet. Maybe check out other odd possibilities that have not been fully checked out. Is any silicone seal 100%? Possible that it’s a leak behind the mixer tap? I’ve seen both of those cause a hard to find leak.

[Nickfromwales]

21 hours ago, Alan Ambrose said:

Unfortunately, I doubt it. The thing that I find odd is that the tiling looks quite neat which suggests a careful job. If you’ve regrouted, the grout should be fine, so might it be a plumbing problem? Worth checking that the pipework joints are tight. I think unless you can see where the leak is, it might be quickest to rebuild the whole set-up from scratch. Try an endoscope camera maybe? Post up a pic from underneath?

Neat maybe, but not a good job.

 

The floor should have been built up with min 6mm plywood so the tiles would stay stuck down. 
 

As the tiles haven’t been given anything to hold firmly to, they’re just going to keep popping. 
 

Thos is zero to do with plumbing / waste / drain, the waters simply tracking through all the fractures in the grout etc, and there’s your leak.

 

It just needs doing properly.
 

Anything else will fail; “what will happen if I go sticking good tiles over loose ones?” is self explanatory. Please don’t waste good time and money doing this…..it will never work.

 

What you could do, if you get a good installer, is remove the tiles in one piece(s) and relay them once the floors sorted. Not easy, and is a pita to do well.

[Nickfromwales]

On 04/10/2025 at 18:01, David001 said:

I then found that there were some cracks and gaps in the grouting between the black tiles in the cubicle, so I filled them with "flexible" grouting (although it doesn't seem flexible to me). I then noticed that some of the tiles moved downwards a fraction when stood upon - this probably caused the grouting to crack in places.

@Alan Ambrose

 

I'm a positive guy, but let’s be honest???? 
 

Tiles are moving / loose!!
 

Read that above, again, and realise that this is too far beyond a band aid. 

[Nickfromwales]

@David001

 

The movement in the tiles is likely due to the subfloor (timber) having been routinely saturated, with frequent use of a failed (leaking) shower deck. 

 

It is very likely this needs to be cut out and replaced with new, to make this problem go away.

 

Is this still visible from the patch repair down below? The hidden bowl speaks volumes of how ignorant the previous owners were, and how they had continued to knowingly use this whilst it was leaking.

 

If you can get any pics of the underside that would be helpful, but I doubt it changes the hard facts. This is Donald Ducked.  

[Temp]

If the tiles were laid direct onto chipboard I wonder how they did the fall in the shower? Perhaps the shower itself has some sort of shower tray under it that's not adequately supported?

[Nickfromwales]

3 hours ago, Temp said:

If the tiles were laid direct onto chipboard I wonder how they did the fall in the shower? Perhaps the shower itself has some sort of shower tray under it that's not adequately supported?

Yup, which is why I asked for some pics from the hatch down below. 
 

Seen lots of BS tilers just do a fall with tile adhesive and they always fail.

 

Needs to be a former, and then a ply or Marmox / Wedi backer board to stop the tiles giving up.

 

Just amazes me how trades cut corners like this just to get paid and out the door. 
 

Would be less of a surprise if it’s a mass-built sausage factory home tbh. 

[Nickfromwales]

@David001

 

Something like this should be in the immediate shower area for the falls, and for the tile adhesive to bind to.

 

[David001]

@Nickfromwales. that's really helpful.  Thanks. 

 

One of the pictures on the web-page for that tray shows it straddling several beams (below floor level), which suggests that the tray is incredibly solid and supportive, that it has no "give" in it.  Is that right? 

 

Because the floor tiles adjacent to the carpet are a little lower than the carpet, I think that if a tray lies below the tiles in the cubicle, the tray must have been deliberately laid a little lower than the tiles in the rest of the bathroom (for the tiles inside and outside the cubicle to be at the same level).

 

Or perhaps no tray was used, but that wouldn't account for the slightly sloping tiles around the central drain, which surely can't have been laid on a uniformly flat surface.

 

You wondered why I'm reluctant to "simply" have the tiles taken up, and having a thorough remedy being implemented.  Well, the reason is this.  I'm located halfway between Llandrindod Wells and Knighton, so getting people to travel here to do such work is difficult.  Most of the nearest people are over the border, in Hereford (80 minutes' drive) or Shrewsbury (90 minutes' drive).  So I have had to almost beg people to come and quote for the odd job which I wasn't able to do myself.  There's a price to be paid for rural bliss!  😂

 

 

[Nickfromwales]

Yea, you're a 2hr slog from me! Still closer than my current client who's nearly 4 feckin hours away..... the joy...... "Have tools, will travel, lol". Had a member from MK contact me to go change a boiler for him, and he'd had the same trouble, waiting over a year for anyone to tell him "no", or just not reply at all..... My mate and I did it over a long weekend, happy days!

 

There are many different trays / formers out there for different situations, just showed you a random grab to see if you can identify if similar was installed (by looking through the hidden trap in the downstairs ceiling) eg to confirm if they had actually fitted a wet room former, or not.

 

If the floor had been prepped properly for tiling, the tiles would have been higher, or at least the same height as the carpet + underlay. To hear they're lower means the floor is doomed to eventual, total failure. I've seen high-end showrooms recommend fitters, who then switch their phones off, and I then get asked to go back to do warranty work / deal with complaints etc; then I give the customers the good news, that the lot needs to come up and be done 'properly'. Always goes down like a lead balloon. There is no adhesive that will allow you to stick tiles directly to a subfloor, not even 2-part super-flexible stuff, but they could have at least used a decoupling membrane such as Ditra mat.

 

Is the trap in the downstairs ceiling still accessible for some pics?

 

 

[Oz07]

On 06/10/2025 at 16:17, Nickfromwales said:

Yup, which is why I asked for some pics from the hatch down below. 
 

Seen lots of BS tilers just do a fall with tile adhesive and they always fail.

 

Needs to be a former, and then a ply or Marmox / Wedi backer board to stop the tiles giving up.

 

Just amazes me how trades cut corners like this just to get paid and out the door. 
 

Would be less of a surprise if it’s a mass-built sausage factory home tbh. 

Can't you tile onto the formers direct?

[Nickfromwales]

3 hours ago, Oz07 said:

Can't you tile onto the formers direct?

Yup. You set them to be the same height as the ply / other across the rest of the floor, so the tiles carry on from one surface to the other.

 

 

You can see the former here is appx 6mm higher than the P5 flooring, achieved simply by putting 6mm ply under the former before laying it. This means the tiles are fixed to one flush surface of the ply > former.

[Oz07]

Yeh I thought you could. Why do you strip the flooring and put former on joists? Can't you just sit former on floor then overlay whole bathroom floor with thicker backer board?

[Nickfromwales]

11 hours ago, Oz07 said:

Yeh I thought you could. Why do you strip the flooring and put former on joists? Can't you just sit former on floor then overlay whole bathroom floor with thicker backer board?

Recessing is better than having a big step at the doorway   

[David001]

On 07/10/2025 at 16:56, Nickfromwales said:

see if you can identify if similar was installed (by looking through the hidden trap in the downstairs ceiling) eg to confirm if they had actually fitted a wet room former, or not.

. . .

There is no adhesive that will allow you to stick tiles directly to a subfloor, not even 2-part super-flexible stuff, but they could have at least used a decoupling membrane such as Ditra mat.

 

I reckon the leak occurred just before completion.  The previous owner cut a sizeable square out of the ceiling below.  Whether he was able to find the point from which the water came, I don't know.  But he wedged a small pot-plant dish beneath the L-shaped waste-pipe, presumably to catch drops of water.  Then using map-pins, he pinned a sheet of white foam-board over the hole in the ceiling to sort of cover it up!  I then came along, peered inside, saw no water in the tray, no dripping, so I asked a contractor who fitted new cupboards in that room to cover and plaster over the hole as well.  So, no, I can't now examine the underside of "the tiles".

 

After drilling holes through the grouting, here and there but equally spaced, and then inserting lots of Fixafloor, I placed three big heavy buckets of water on the tiles and left them there for two weeks!  But I haven't had the nerve to use that shower since!  😅

https://fixafloor.co.uk/products/fix-a-floor-pro-repair-pack

 

Thanks very much, Nick, for your photo of a former inset into the floor.  That probably explains why the cubicle tiles slope a little to the central drain while the tiles outside the bathroom appear to have been stuck to the same stretch of chipboards as are under the carpet of the adjacent room.  So if the leak is from the shower cubicle, it's probably from the drain or drainpipe. 

 

BUT adjacent to the shower cubicle is the hot-water tank cupboard, and from the side of it I found a leak about nine months ago.  That leak looked like it was "ancient" because of encrustation all the way down the path of the dripping water.  But where did the water end up?   It must have ended up somewhere.  Maybe it was that water which appeared in the ceiling area beneath the shower cubicle?  I fixed the leak from the hot water tank and there's been no further water dripping from the ceiling below, but of course I haven't had the courage to use the shower!   I guess that shower is going to have to be tested sometime soon!  😱

[marshian]

12 minutes ago, David001 said:

BUT adjacent to the shower cubicle is the hot-water tank cupboard, and from the side of it I found a leak about nine months ago.  That leak looked like it was "ancient" because of encrustation all the way down the path of the dripping water.  But where did the water end up?   It must have ended up somewhere.  Maybe it was that water which appeared in the ceiling area beneath the shower cubicle?  I fixed the leak from the hot water tank and there's been no further water dripping from the ceiling below, but of course I haven't had the courage to use the shower!   I guess that shower is going to have to be tested sometime soon!  😱

Oh I had the sane sort of leak from a cold water storage tank in the loft - didn’t know it was happening untill I saw the ply boards it sat on were bowing with the weight (soggy ply did well to hold it)

 

I will state that technically it was self inflicted - house in a hard water area and I fitted a water softner - for two years I kept finding the odd leak that had never been an issue before (softened water takes back limescale from where it finds it - so some old joints that had clearly leaked in the past and had been sealed with limescale were suddenly free to leak again

[David001]

@marshian, same here: the leak from near the top of the water-tank had saturated the chip board forming the floor of the water-tank cupboard, so the owner had evidently pulled away the sodden board directly beneath the tank and then lain over it some thin plank-like strips of floor covering . . . which hid the hole and fooled our us and our surveyor!  Thankfully the board directly beneath the feet of the tank was dry so the tank was still well-supported, nevertheless the leak from the tank must have been considerable . . . and it was still leaking when we moved in.  With all that Nick has contributed, I'm now inclined to think that the dripping from the ceiling below may have been coming from the leaking water-tank and not from the floor of the adjacent shower cubicle.  The big test will come soon when I switch on the shower for the first time in ages.  Fingers crossed! 😀

[Nickfromwales]

1 hour ago, David001 said:

The big test will come soon when I switch on the shower for the first time in ages.

Get in there then....chop chop!

 

If it were the cylinder leaking it would be a constant leak, not intermittent, and certainly it wouldn't have stopped when you stopped using the shower?

 

What exactly is going on there?