# Forum Home Renovation Waterproofing  understanding, mortar beds and w/p membranes?

## breakerboy2000

Hello,  
Is there any reason why a mortar bed would be used in a bathroom on top of a c/ slab, other than to create slope to a drain? or is that the sole purpose of it? 
also, i have attached a pretty typical layout of the mortar bed and membrane application,   
I am just curious.. for the water that seeps through the tiles, and mortar bed, even though the flange is flush with the concrete slab, how does the water know to go into the flange? (as the slab base is level) 
.. wouldn't it be better if the membrane was applied on the sloped mortar bed to direct excess water a little better?    
thank you.

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## phild01

> Hello,  
> Is there any reason why a mortar bed would be used in a bathroom on top of a c/ slab, other than to create slope to a drain? or is that the sole purpose of it? 
> also, i have attached a pretty typical layout of the mortar bed and membrane application,   
> I am just curious.. for the water that seeps through the tiles, and mortar bed, even though the flange is flush with the concrete slab, how does the water know to go into the flange? (as the slab base is level) 
> .. wouldn't it be better if the membrane was applied on the sloped mortar bed to direct excess water a little better?    
> thank you.

  
Agree with your last comment but building work is usually done by the tradie who doesn't like hanging around.  Waterproofing requires the substrate to be fully cured.  By putting it under the screed means no waiting around.
Generally, my belief is that 1, tilers are use to, and required to create the falls because they are working more intimately with the established bathroom dimensional layout, easier for him than the concreter and 2, the screed acts as a buffer to the concrete cracking that may be present and that may occur later on (I know, another reason for waterproofing above the screed).

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## Oldsaltoz

One of the functions of the puddle flange is provide a gap in the outlet pipe. 
The gap provides an escape for any water that penetrates the tiles, grout and other joints. 
Moisture is drawn to waste by the fact that self levels then by capilliary action, thats one reason for using a screed mix and not a not lots of cement. 
A shower that has no gap into the drain pipe will let your nose know as the smell of the accumulated mold permeates the whole room. 
You must have walked into a bathroom at some time and thought what is that dank smell? 
Waterproofing over the screed can mean a 3 day delay, because the area MUST be clean and dry when waterproofing. 
All tilers like to set the fall to suit the tiles and or the way they work them, the waterproofer has no inclination of this when doing their part. 
I would estimate that less than one in 100 showers are waterproofed over the leveling screed. 
Good luck.   :Smilie:

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## breakerboy2000

Thank you for the replies. 
if im talking for a general floor waste in the bathroom, 
could I just not put in a mortar bed at all if I didnt need the slope? say, somthing like this?:   
Thanks again.

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## Oldsaltoz

> Thank you for the replies. 
> if im talking for a general floor waste in the bathroom, 
> could I just not put in a mortar bed at all if I didnt need the slope? say, somthing like this?:   
> Thanks again.

  For a bathroom floor waste this will be OK. 
Good luck.   :Smilie:

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## breakerboy2000

cheers oldsaltoz, 
I understand that the mortar bed is designed to absorb/draw water out and direct it to the flange, i think of it somthing like gravel ontop of a french drain.. 
so in not putting in a bed, will the water still be able to 'move' through the tile adhesive and eventually find it's way to the flange? -even on a level floor?. 
ie, would the adhesive work in the same way as the mortar bed?

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## Oldsaltoz

> cheers oldsaltoz, 
> I understand that the mortar bed is designed to absorb/draw water out and direct it to the flange, i think of it something like gravel on top of a French drain.. 
> so in not putting in a bed, will the water still be able to 'move' through the tile adhesive and eventually find it's way to the flange? -even on a level floor?. 
> ie, would the adhesive work in the same way as the mortar bed?

  Yes it will, no problems. you can improve the flow by angling the trowek away from the waste outlet, leaving small channels in the tile glue. 
Good luck.   :Smilie:

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## dansa

> For a bathroom floor waste this will be OK. 
> Good luck.

   Hi Oldsalt,  Reading this email, could you please confirm if my understanding is correct.  I am just about to lay the screed on top of the waterproofed Scyon sheets. I have a linear grate for shower and as floor waste as well. It is installed where the shower screen will be, just underneath it. It will be level with the rest of the bathroom floor with enough gap underneath the sliding door. So any spill in the bathroom area will easily fall into the linear grate. The reason I did not want to have a floor waste as well is because that would have been located just 300mm away from the shower grate.  Is it OK if I will have the bathroom floor sloped to the shower grate and the rest of the bathroom floor level with the shower grate but not slope? I would like to reduce the step up at the bathroom entry, underneath the bathroom door. The whole bathroom floor is waterproofed.  Thank you.

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## Oldsaltoz

> Hi Oldsalt,  Reading this email, could you please confirm if my understanding is correct.  I am just about to lay the screed on top of the waterproofed Scyon sheets. I have a linear grate for shower and as floor waste as well. It is installed where the shower screen will be, just underneath it. It will be level with the rest of the bathroom floor with enough gap underneath the sliding door. So any spill in the bathroom area will easily fall into the linear grate. The reason I did not want to have a floor waste as well is because that would have been located just 300mm away from the shower grate.  Is it OK if I will have the bathroom floor sloped to the shower grate and the rest of the bathroom floor level with the shower grate but not slope? I would like to reduce the step up at the bathroom entry, underneath the bathroom door. The whole bathroom floor is waterproofed.  Thank you.

  Hi Dansa, 
The main risk will the possibity of mould forming on the grout. I assume you sre not using an epoxy based tile, so drainage should be no problem, however you can help improve the drainage by using the glue trowel and creating lines that water will follow rather than pass through the glue. 
Other than the above no problems, just make sure the waterstop in the doorway is properly installed and sealed as it will have wet feet. 
Good luck.   :Smilie:

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## dansa

> Hi Dansa, 
> The main risk will the possibity of mould forming on the grout. I assume you sre not using an epoxy based tile, so drainage should be no problem, however you can help improve the drainage by using the glue trowel and creating lines that water will follow rather than pass through the glue. 
> Other than the above no problems, just make sure the waterstop in the doorway is properly installed and sealed as it will have wet feet. 
> Good luck.

  Hi Oldsalt,
Are you saying that epoxy based grout is not a good choice in my case or you would not recommend it at all?

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## Oldsaltoz

> Hi Oldsalt,
> Are you saying that epoxy based grout is not a good choice in my case or you would not recommend it at all?

  Epoxy glue will not allow water to pass through it like standard tile glues. 
It's also a bit of task to use as the cleaning has to be done soon after application or it sets solid on the tile surface, so rather than cleaning large areas, you have to stop grouting after half a dozen tiles and clean up before you lay more. 
Epoxy glues are often used in areas that will be permanently wet, like fountains and pools. Epoxy grout can be used to prevent water passing through the gap between tiles, but miss one spot and you have a water trap. 
The only advantage of epoxy grout is that it will not support the growth of mold, however it's effected by UV light and may fade, white epoxy tends to turn yellow over time. 
Good luck.

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## phild01

> Hi Oldsalt,   I am just about to lay the screed on top of the waterproofed Scyon sheets.

  If you are doing this work yourself then why not waterproof over the screed directly under the tile work.  Doing it yourself means you have time to wait for the screed to properly dry and you end up with the better result.

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## Oldsaltoz

> If you are doing this work yourself then why not waterproof over the screed directly under the tile work.  Doing it yourself means you have time to wait for the screed to properly dry and you end up with the better result.

  The main reason for waterproofing first the adding the screed is, as you say to save a couple of days (in good drying conditions). 
But there are other considerations.
Screed is a very porous and will almost certainly use more waterproofing product to fully seal it, this is important as any water that penetrates will go direct to the floor. 
Screed can crack of it's accord if spread less than 25 mm thick, a leveling compound should be used, you can add some clay free sand to stop slumping. 
Waterproofing places onto a stable smooth floor is more likely last. 
There is the belts and braces, waterproof the floor, add screed and waterproof over the top, only problem is, should any water get through the top layer, it will be trapped. 
Good luck.   :Smilie:

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## phild01

> The main reason for waterproofing first the adding the screed is, as you say to save a couple of days (in good drying conditions). 
> But there are other considerations.
> Screed is a very porous and will almost certainly use more waterproofing product to fully seal it, this is important as any water that penetrates will go direct to the floor. 
> Screed can crack of it's accord if spread less than 25 mm thick, a leveling compound should be used, you can add some clay free sand to stop slumping. 
> Waterproofing places onto a stable smooth floor is more likely last. 
> There is the belts and braces, waterproof the floor, add screed and waterproof over the top, only problem is, should any water get through the top layer, it will be trapped. 
> Good luck.

  Pros and cons both ways to a point.  Waterproofing the screed is to my mind the far better of the two.  Also the screed doesn't need to be so sandy to be a porosity issue.  Waterproofing compounds don't cost a lot and can be generously applied.  In fact I would consider using the bandage material over the entire surface of the shower floor for guaranteed performance. 
With the waterproofing over the screed (and there is no reason to expect it to leak any more so then if applied under) then the issue of a constantly damp screed is eliminated.  That is a major plus!  Something would be very wrong if the screed were to crack and I would not expect this to be a common thing. 
There would not be any need to have waterproofing under the screed as suggested. And on the other hand, cracks in a slab are considered normal, so what happens to the waterproofing when this might happen.  
Common practice is the way you say, but only because it is so convenient.

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## intertd6

A couple of points not in favour of WP over screed is one dropped tile or implement ruins it, also how glue is applied to its surface with trowels without perforating it when pressure applied & perforations can be made when the trowel abrades stones or other hard objects protruding from surface below WP membrane.
regards inter

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## phild01

> A couple of points not in favour of WP over screed is one dropped tile or implement ruins it, also how glue is applied to its surface with trowels without perforating it when pressure applied & perforations can be made when the trowel abrades stones or other hard objects protruding from surface below WP membrane.
> regards inter

  Depends how rough the tiler is.  Properly applied waterproofing would not be so thin that it abrades to sand level with one or two trowel strokes. Where did these stones come from!  As I say, the screed need not be so sandy (and have a coarse sandpaper finish).  Also fully bandaging the shower floor negates any such concerns.  Anything that drops and breaks a tile is not going to break through a decent tile adhesive and it should be possible to remove a tile without breaching the waterproofing. Why would the tile adhesive be so thin and brittle to present these types of issues.

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## Wotname

This discussion of over versus under screed waterproofing is being extremely helpful to me - thank you all!  
Especially so as I an somewhat new to waterproofing techniques and am also in the very process of renovating the bathroom. 
What I don't yet understand is the negatives of using the belt and braces approach (apart from time and a bit more waterproofing compound). 
Oldsaltoz alluded to a potential problem of water getting trapped in the screed *but why wouldn't such water migrate through the screed as usual and exit via the bottom of the puddle flange in the usual manner?*  
One issue I considered was that the puddle flange / waste has to accommodate two points of allowing under tile water to exit. The primary one being the water immediately passing through the grout and adhesive (and above the top waterproof membrane) and the other water potentially at the bottom of the screed should the top membrane fail. The bottom exit would be the usual arrangement and the top exit would need to considered as some grooves in the screed bed say just under the channel waste (but still above the top waterproof layer).  
I can see that waterproofing the top of the screed would be more demanding in it's execution and close attention to detail would be warranted but this really depends on the tiler and his quality of work - IMO 
Again, I am learning much from this thread and any further responses would be very much appreciated. 
Cheers.

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## phild01

> This discussion of over versus under screed waterproofing is being extremely helpful to me - thank you all!  
> Especially so as I an somewhat new to waterproofing techniques and am also in the very process of renovating the bathroom. 
> What I don't yet understand is the negatives of using the belt and braces approach (apart from time and a bit more waterproofing compound).   
> Cheers.

  A constantly damp screed and the shower area is slower to dry out, can enhance mould and mildew problems.

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## Wotname

> A constantly damp screed and the shower area is slower to dry out, can enhance mould and mildew problems.

   Hmm.. not sure if I fully understand this reply. 
I agree with the premise that a constantly damp screed is a bad thing but are you saying that putting waterproofing *above and below* the screed bed *increases* the potential for a constantly damp screed. 
If so, why? I would have thought that any possible water penetration of the top membrane would drain away through the screed and into the bottom of the puddle flange. However due to ignorance of these matters, I could easily be wrong but I would like to understand any error in my thinking!

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## phild01

Just waterproofing top of screed, not beneath as well.

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## intertd6

> Depends how rough the tiler is.  Properly applied waterproofing would not be so thin that it abrades to sand level with one or two trowel strokes. Where did these stones come from!  As I say, the screed need not be so sandy (and have a coarse sandpaper finish).  Also fully bandaging the shower floor negates any such concerns.  Anything that drops and breaks a tile is not going to break through a decent tile adhesive and it should be possible to remove a tile without breaching the waterproofing. Why would the tile adhesive be so thin and brittle to present these types of issues.

  The points I raised are just possibilities which may or may not happen & possibly why the WP standard isn't based on that system. I could just imagine calling the waterproofer saying that his membrane has failed & him saying " if the tile adhesive was applied with a notched trowel the tiler has perforated the membrane & I'm not responsible. 
personally I would never use that system because of those pitfalls unless I had no responsibility of a guarantee.
regards inter

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## phild01

> The points I raised are just possibilities which may or may not happen & possibly why the WP standard isn't based on that system. I could just imagine calling the waterproofer saying that his membrane has failed & him saying " if the tile adhesive was applied with a notched trowel the tiler has perforated the membrane & I'm not responsible. 
> personally I would never use that system because of those pitfalls unless I had no responsibility of a guarantee.
> regards inter

  I think you may be overthinking what might go wrong.  As I have said, and what you say is the 'standard', is only because of convenience of getting the job done.  Tilers generally do waterproofing as well and would accept full responsibility for doing the job right.  In this regard it is a nonsense that a licensed person be required to do a very simple task and we we need to be tied to the quick way the so called standard dictates.  But for those who want to do it themselves, it is opportunity for them to get a better result, albeit requiring a longer waiting time.  As far as I know, nothing is stated to say it can't be done this way.  This way would actually set the standard.  Manufacturers of waterproofing compounds are the ones who set the so called standard, and they advise either way.

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## dansa

> Pros and cons both ways to a point.  Waterproofing the screed is to my mind the far better of the two.  Also the screed doesn't need to be so sandy to be a porosity issue.  Waterproofing compounds don't cost a lot and can be generously applied.  In fact I would consider using the bandage material over the entire surface of the shower floor for guaranteed performance. 
> With the waterproofing over the screed (and there is no reason to expect it to leak any more so then if applied under) then the issue of a constantly damp screed is eliminated.  That is a major plus!  Something would be very wrong if the screed were to crack and I would not expect this to be a common thing. 
> There would not be any need to have waterproofing under the screed as suggested. And on the other hand, cracks in a slab are considered normal, so what happens to the waterproofing when this might happen.  
> Common practice is the way you say, but only because it is so convenient.

  Thank you guys. This debate helped me a lot to understand the pros and cons of WP under or above the screed.  
Phil could you tell me more about the bandage material? Where can I get it from?  
Sent from my iPhone using Tapatalk

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## phild01

> Thank you guys. This debate helped me a lot to understand the pros and cons of WP under or above the screed.  
> Phil could you tell me more about the bandage material? Where can I get it from?  
> Sent from my iPhone using Tapatalk

  Bunnings sell this stuff and you will find it somewhere near their trade desk.  Crofab Crommelin 100mmx50m Reinforcing Fabric I/N 1070268 | Bunnings Warehouse 
They have a variety of types and lengths.  A Betta branded one has an inbuilt bond breaker I would recommend for your shower corners.  Otherwise go with the Crommellin branded ones without a bond breaker as they cost less than the equivalent Betta brand.  Widths are 100 and 200mm.  I have used the Crommellin compound and it provides a good key for tiling.  I also think Davco K10 is a good compound and is more flexible, and only requires a silicone filler as a bond breaker.

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## dansa

> Just waterproofing top of screed, not beneath as well.

  Hi Phil
Just going back to this debate about WP above the screed. Think of a linear grate in the shower. I cannot see how would the WP above the screed would be done with a linear grate. . The linear grate trough needs to be installed when the screed is laid. How would you seal and WP between the outside of the linear grate and the screed. You cannot go with the WP over the trough.  The screed needs to be recessed to allow for the thickness of the tile to be flash with the linear grate. How could you stop the water going between trough and the screed?
Thank you.   
Sent from my iPhone using Tapatalk

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## phild01

> Hi Phil
> Just going back to this debate about WP above the screed. Think of a linear grate in the shower. I cannot see how would the WP above the screed would be done with a linear grate. . The linear grate trough needs to be installed when the screed is laid. How would you seal and WP between the outside of the linear grate and the screed. You cannot go with the WP over the trough.  The screed needs to be recessed to allow for the thickness of the tile to be flash with the linear grate. How could you stop the water going between trough and the screed?
> Thank you.   
> Sent from my iPhone using Tapatalk

  Friends used linear grates in the 4 showers in their house.  Have only lived in it for less than a year and curse me when I told them of other readers comments here how dirty and smelly these get.  They couldn't agree more and wished they went more standard.  Personally I favour the bermuda style tile waste.
Anyway, thinking about your issue may I suggest that when the screed is laid, place the linear waste in place wrapped in something like layers of glad wrap or freezer bags, so it can be removed when then screed is dry.  Apply waterproofing, let dry well and liberally polyurethane waste in place.  The grate will need enough wrap to bulk out enough space for waterproofing and adhesive.  I haven't done this before and just an immediate idea, but I think this would work extremely well.
Consider how it would be installed otherwise, the way I am describing would virtually eliminate any standing moisture around the grate bar the grout lines.
The main thing is to do your setout calcs carefully and get a linear grate with the correct depth that suits.  My advice will probably get some extra, but, welcomed comment.

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## Wotname

> Hi Phil
> Just going back to this debate about WP above the screed. Think of a linear grate in the shower. I cannot see how would the WP above the screed would be done with a linear grate. . The linear grate trough needs to be installed when the screed is laid. How would you seal and WP between the outside of the linear grate and the screed. You cannot go with the WP over the trough.  The screed needs to be recessed to allow for the thickness of the tile to be flash with the linear grate. How could you stop the water going between trough and the screed?
> Thank you.   
> Sent from my iPhone using Tapatalk

   I had the same concern and used a similar but slightly different approach to Phil's post. I can't say if my approach is suitable but I believe it will achieve the desired result in that water in the tile adhesive will be able to migrate into the puddle flange. Please don't take my comments as gospel, they are simply my ideas to make sure all water gets away.  The linear grate (LG) doesn't have to be left in the screed bed after laying, this is just a convenient and fast way of installing it. Like Phil suggested, it can be removed after the screed has being floated and re-installed later when tiling.The LG free falls into the puddle drain.So you need a way for water in the adhesive bed (above the waterproofing) to get into the puddle drain between the LG and puddle drain.I laid some channels into the screed *under* the LG and radiating away from the LG following the same slope as the rest of the screed bed. To form these channels, I used some short lengths electrical cable as a mould and just pushed them into the screed and then put the LG on top of this, set at the "correct" height. You could use anything really for the mould like say backer rod or abel-rod etc.At the puddle flange end of the channels, I cut some slots into the "top" pipe of the puddle flange to accept the moulds (i.e. the electrical cable, backer rod or whatever)While the screed was still very green, I removed the LG and the mould which left the screed with the provision for the LG and with drainage channels in the screed leading under the LG and into the top of the puddle flange "top" pipe.The plan is to now waterproof the entire top of the screed and then when tiling, lightly fill the the channels with adhesive and use a thin layer of adhesive to set the LG back into it's position.Any water below the tiles should now have a drainage path above the waterproofing and under the LG into the top of the "top" pipe of the puddle flange. 
I will let you know in a year or two if it works! 
Hopefully some one will post a simpler and better way of achieving the same result.  
As to cleaning a LG, I can't for the life of me see how this can be difficult. The one I have have and I assume others are similar, you just lift up the top of it and the bottom section is completely accessible and smooth. The top requires a swish around brush and warm soapy water and then popped back down. Friends I have swear by them (not at them).  
I could see problems if they were installed some water remain trapped under them or if they weren't cleaned regularly (say every time or every other time, you cleaned the rest of the shower. Anyway time will tell for me. 
Hope this helps.

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## phild01

> I had the same concern and used a similar but slightly different approach to Phil's post. I can't say if my approach is suitable but I believe it will achieve the desired result in that water in the tile adhesive will be able to migrate into the puddle flange. Please don't take my comments as gospel, they are simply my ideas to make sure all water gets away..... 
> As to cleaning a LG, I can't for the life of me see how this can be difficult. The one I have have and I assume others are similar, you just lift up the top of it and the bottom section is completely accessible and smooth. The top requires a swish around brush and warm soapy water and then popped back down. Friends I have swear by them (not at them).  
> I could see problems if they were installed some water remain trapped under them or if they weren't cleaned regularly (say every time or every other time, you cleaned the rest of the shower. Anyway time will tell for me. 
> Hope this helps.

  When applying the waterproofing it should be ok to run it into the flush fitting drain pipe, but a whole series of reinforcing mat (bandage) needs to be applied around the circumference and down into the pipe.  I think this is where stuff-ups occur and puddle flanges are sold rather than created in situ, correct me if I am wrong.
The comment regarding LG and periodic cleaning.  I'd prefer something that doesn't require regular attention like a normal waste.  Don't get me wrong as they do look good and does make tiling easier and neater, but extra cleaning puts me off (I am now using shower gel rather than soap because it doesn't leave scum and so little cleaning  ever required....  I guess you see where I am coming from! ).

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## Wotname

> ........
> The comment regarding LG and periodic cleaning.  I'd prefer something that doesn't require regular attention like a normal waste.  Don't get me wrong as they do look good and does make tiling easier and neater, but extra cleaning puts me off (I am now using shower gel rather than soap because it doesn't leave scum and so little cleaning  ever required....  *I guess you see where I am coming from!* ).

   I hear you  :Smilie:  and I agree, there is something nice about "no" cleaning! I guess the cleaning requirement is the price we pay for having a LG. Another option is to convince someone else to do the cleaning - although I am often not successful in this regard!

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