# Forum Home Renovation Bathrooms  Waterproofing over tile bed or below tile bed?

## VVV

Hi guys, 
Looks like there are two ways to waterproof.  
I read S3740-2004 and they mostly focus on under the screed waterproofing.
But many videos (e.g. Beaumont ) show waterproofing over the screed and laying tiles over the membrane..
To me, it makes more sense because screed is not soaking in the water penetrated though a grout.. 
Is the main reason to waterproof under the screed is timing? To do not wait till it's completely dry before applying membrane on top? 
Can I just use levelling compound (Lanko floor leveller?) which will give me faster drying time and also less thickness? 2 birds with 1 stone  :Smilie:  
I'm building a raised shower bed using 50mm (l35-40mm with levelling compounds?) angles and wandering what's the better method to waterproof it.. I'm going to use Davco K10 or Crommeling. 
Cheers

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## sol381

many posts on this already.. maybe do a quick search.. many differing views as well..in my 30+ years in this game ive never seen it done on top of screed its always under..maybe on the block.. my tiler and waterproofer only use this method.. if doing on top its hard to get the membrane down into the puddle flange.. laying it first is easier to get it to flow into the flange..its easier to damage as well if its on top while trowelling the mud.. also whats the rush.. if you bed one afternoon you lay the next morning.. it dries very quick.. its basically a very dry mix anyway.. screed is just a mix of medium river sand mixed with cement.. i wouldnt use self leveller.. 
this is just the way ive had it done and ive never had a call back saying the waterproofing has failed..others will certainly have their opinion..

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## phild01

Sol, I doubt you would ever see it done over the screed as a trade simply because it means waiting for the screed to dry.  As it takes quite a while, the tiler would much prefer not to do that.  But I also get that the unprotected screed will be forever wet from the daily shower, which is less than ideal.

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## sol381

.. my tiler and waterproofer told me that the screed will indeed almost be constantly damp.. not dripping wet tho.. 99% of the water will flow over the tiles and grout so minimal water will get through..still i thought that was pretty strange but trust what they do..

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## phild01

I tend to think that a drier shower area would have less mould and maybe less smell.

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## sol381

you would think.. i doubt it is very wet at all. cant see that much water getting through the grout lines..  ive done about 30 bathrooms in the last year so hopefully my guys know what theyre doing..

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## VVV

> you would think.. i doubt it is very wet at all. cant see that much water getting through the grout lines..  ive done about 30 bathrooms in the last year so hopefully my guys know what theyre doing..

  The question is why whey are doing it this way? Tradition?
 I spent last a couple of weeks researching and it's still not clear..so, this topic is to see other people opinion..
National tiles video is also waterproofing over the screed (as well as some other youtube videos).
The only explanation which makes sense is time, tradition,more expensive tile adhesive to use over the membrane? Or a chance to damage the membrane standing on it while tiling?
I'm not arguing that waterproofing under the screed can fail. I just don't understand why to keep a shower floor in my bathroom always wet...  Here is how to waterproof the puddle flange. Just paint it over the screed into the flange, no difference.

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## intertd6

Waterproofing over the screed has many disadvantages, it's easy to damage while spreading the tile adhesive on it, it's easy to damage it by dropping something like a tile on it while in the process of tiling, it's easy to damage it by perforating with something as simple as a bit of rock metal caught in the bottom of a boot.
inter

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## phild01

You could also damage the waterproofing while laying a screed, I would think a tiler would also be more careful than to be dropping tiles or by scraping so aggressively to tear it (but I guess a sharp unworn notched trowel could do it if the tiler is an idiot).

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## intertd6

> You could also damage the waterproofing while laying a screed, I would think a tiler would also be more careful than to be dropping tiles or by scraping so aggressively to tear it (but I guess a sharp unworn notched trowel could do it if the tiler is an idiot).

  3 against 1 the odds for accidental damage aren't in the favour of WP over th screed.
inter

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## VVV

this is all about carelessness.
Usually, people are more careful doing DIY for their own houses, so all the above can be avoided/eliminated. 
Putting floor tiles first and then wall tiles will protect the membrane when dancing on it (or dropping something)
Regarding the sharpness of a trowel, I used a plastic adhesive spreader for one of my recent projects . 
Also,  putting a piece of cardboard on the floor can protect membrane and later on floor mosaic from accidental damage of dropping something like a hammer ))) 
so, looks like this is a workaround to put a membrane under the screed to protect it from damage with wet floor in a long run...  :Frown:

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## inferno6688

funny this thread has come up, but i am going through the same dilemma myself. my added confusion is undertile heating, which layer to put that in. 
From my reading WP over screed is preferred, but i can it higher risk of damage through tiling and also a timing issue. i think it will ne easier to protection the WP during screed than it is during tiling.  
My plan is the following:
1) Scyon floor sheeting
2) WP
3)screed (20mm at waste then up to 35~40mm)
4) undertile heating elements
5)tile 
any feedback on my plan?

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## r3nov8or

Isn't WP over screed, which has a fall to the puddle flange, far more likely to shed water? Rather than WP over a flat surface (or worse - fall away from the flange) whereby water can't naturally fall away?

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## VVV

> Isn't WP over screed, which has a fall to the puddle flange, far more likely to shed water? Rather than WP over a flat surface (or worse - fall away from the flange) whereby water can't naturally fall away?

   good point 
Putting aluminium angle around a shower base and WP it under the screed will create a water basin 1mx1m in the bathroom... with  screed sitting in it like a sponge..

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## VVV

> funny this thread has come up, but i am going through the same dilemma myself. my added confusion is undertile heating, which layer to put that in. 
> From my reading WP over screed is preferred, but i can it higher risk of damage through tiling and also a timing issue. i think it will ne easier to protection the WP during screed than it is during tiling.  
> My plan is the following:
> 1) Scyon floor sheeting
> 2) WP
> 3)screed (20mm at waste then up to 35~40mm)
> 4) undertile heating elements
> 5)tile 
> any feedback on my plan?

  just curious, are you putting electrical or water heating?

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## sol381

> good point 
> Putting aluminium angle around a shower base and WP it under the screed will create a water basin 1mx1m in the bathroom... with  screed sitting in it like a sponge..

    yes and no. either way you are not going to get a lot of water penetrating through the grout lines anyway. if screed is under neath then the water will eventually find its way to the puddle flange or sit in the screed for a while.. with WP on top it has a harder time to get to the puddle  flange having to fight its way through all the notched adhesive so the water will be sitting just under the tiles and maybe have a better chance of popping a tile or 2.. i doubt there will be a clear path to the waste and most notching is haphazard anyway.. 
having said that im sure both methods work but the important thing is to do it properly in the first place.. 
Ive done about 100 bathrooms in my time and ive never had to call back a tiler or waterproofer yet..

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## phild01

> with WP on top it has a harder time to get to the puddle  flange having to fight its way through all the notched adhesive so the water will be sitting just under the tiles and maybe have a better chance of popping a tile or 2.. i doubt there will be a clear path to the waste and most notching is haphazard anyway..

  Probably true with laying methods used, but a proper tiling job will have no voids under the tile.  When I have tiled I have checked to ensure that the whole area is 99% tile adhesive.

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## inferno6688

i am doing electrical undertile heating. just the heating elements.

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## Bigboboz

> yes and no. either way you are not going to get a lot of water penetrating through the grout lines anyway.

  That's what I would have thought. Is grout permeable or just when a crack (hairline or larger) opens up?

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## pharmaboy2

Just to add another method. 
my upstairs bathroom was done with waterproofing under screed, then heating laid, then screeded, then waterproofed again - 3 coats. 
idea being, when upstairs bathrooms fail, it's a big expensive deal, so 2 waterproofing membranes means one can fail without an outcome

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## VVV

found this in the other thread...
is Davco K10 stretches 300 times so it should be hell of a crack to break the membrane? 
[QUOTE]  

> There are a couple of discrepancies which I will outline below. 
> Under Screed - 
> 2. Not right - you still need to wait till the membrane is fully cured before screeding on top of it. A dry membrane to the touch does not mean that it is fully cured and curing times depend greatly on the membrane used and the conditions of the site post application such as temperatures and humidity.
> 3. Also, a water logged screed is often prone to efflorescing. 
> Over the screed - 
> 2. Moisture content under 10% is generally acceptable for waterproofing purposes. You can also use an epoxy as a vapor barrier if you are in a rush to waterproof, although I wouldn't recommend anyone other than a professional from doing that. 5. If the screed cracks due to structural movement (or other factors), membrane failure often occurs as a result. 
> The biggest issue with waterproofing under and over a screed is the termination at the flange. If you terminate both at the flange (overlap), should the membrane above the screed fail, the water will end up being trapped in the screed until such time as the membrane below the screed breaks as well as there will be no water run-off into the flange due to the overlap. 
> My personal opinion is that you should use a good quality screed mix such as RLA's Rapid Screed (it's polymer modified) or a good quality additive such as Gripset 11Y to ensure that the screed is of the best quality possible and to minimise risk factors as outlined above. When done this way, I believe waterproofing over the screed is preferable to waterproofing under it. 
> /QUOTE]

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## Pulse

300% not 300x  
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## Watters

> if doing on top its hard to get the membrane down into the puddle flange.. laying it first is easier to get it to flow into the flange..its easier to damage as well if its on top while trowelling the mud.. also whats the rush..

  Not true if you do waterproofing both below AND above the screed. If you do both then the lower waterproofing WILL go down into the puddle flange. Below is a sketch I got from a puddle flange supplier on how to do it (but the screed needs to be dry, say a week, before you do the waterproofing on top of the screed):      

> Usually, people are more careful doing DIY for their own houses, so all the above can be avoided/eliminated.

  
When doing DIY you can take your time, no need to rush...

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## sol381

waterproofing first is just the way ive done it and how my guys have always done it.. im not saying its the best or only way .. the method you describe  doesnt seem right to me.. if the bottom layer of water proof goes inside the puddle flange and down the waste pipe as it should then the top layer should go down the waste as well.. if there is a leak in the top and water seeps through then the water will be trapped under the screed as it it cant get through the top layer of WP..your purple line at the floor needs to do down and into the flange..as should the top layer as well..there only needs to be a pinhole leak for water to escape.. 
I just think it is best left to the pros.. i didnt even WP my 2 bathrooms i renovated.. got my WP guy in to do  it.. some jobs are just best left to the pros..lot of guys come on here that have never done it before and expect it to be easy..A few hundred bucks to have a pro do it and have piece of mind is a small price to pay.. also if you are doing work that is going through council you will need a form 16 that only a licenced Waterproofer can give.. 
Im not trying to put anyone off having a go but ive been in this game long enough to know thattrying things yourself that you have never done before can lead to lots of problems down the track..

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## Watters

> waterproofing first is just the way ive done it and how my guys have always done it.. im not saying its the best or only way..

  If you waterproof first only then the waterproofing will be on a flat horizontal surface (no falls) and, if (and this happens more often than you might reali*s*e) the puddle flange is not recessed into the substrate then you will trap water i.e. it will pool around the puddle flange instead of passing into it. And guess what? That is exactly how it was with the bathroom I am renovating right now: 
1. Water pooled because the puddle flange was not recessed into the substrate.
2. Antiquated fibreglass waterproofing failed.
3. Yellow tongue (YT) chipboard below the waterproofing damaged. 
End result: Had to remove YT, do blocking, put in CFC floor for the shower recess etc. A lot of hassle that could have been avoided if things had been done differently. 
The reason for the gap between the two layers of waterproofing into the puddle flange is to let water to continue to flow. If the top waterproofing layer was taken down all the way to meet the other waterproofing below and there was a breach of the top waterproofing then water would THEN be trapped forever in the screed and that wouldn't be good, as Phild01 indicated - conditions ripe for mould. 
Er, how do your guys install the puddle flanges for the shower and main floor waste? 
[EDIT] An alternative to doing two lots of waterproofing is to do the one lot below and add a waterproofing admixture to the screed cement mix. Then most of the water would follow the fall of the screed. However, that should be an acrylic admixture so as not to damage the waterproofing below and it will also be harder to work with (stickier). Nonetheless, it is something I have been thinking about.... 
[DOUBLE EDIT] And if you really want to be extreme: 
1. Waterproof below screed.
2. Waterproofing admixture in screed cement.
3. Waterproofing above screed.   :Roll Eyes (Sarcastic):

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## phild01

That drawing shows the top screed falling short of the puddle flange and this will probably draw water into the screed by capillary action and the screed will dampen up.  I wouldn't be waterproofing over as well as under, as this will trap the moisture. I would just do over and into the puddle flange.

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## sol381

my guys always recess the puddle flange below floor level.. they grind out the tile underlay and sit the flange into it..silicone it in place and waterproof the floor and down into the flange

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## r3nov8or

This describes both methods, and doesn't seem to prefer one over the other  http://artplastics.com.au/assets/002...wRes030106.pdf

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## Watters

> That drawing shows the top screed falling short of the puddle flange and this will probably draw water into the screed by capillary action and the screed will dampen up.  I wouldn't be waterproofing over as well as under, as this will trap the moisture. I would just do over and into the puddle flange.

  Hmmm, okay point taken.   

> This describes both methods, and doesn't seem to prefer one over the other

  Thanks, Nice description and diagram of either on top or under. My only quibble for on top is where it says: 
"Should you choose this method, remember that the wall floor junction will have to be a sharp corner, where the tiles meet..." 
That would be the case if you are using PVC angles but if you are using silicone as your bond breaker coupled with reinforcing bandage at the villaboard/mortar bed joints (would be triangular not ninety degrees as such)...oh now I get it, I guess they mean be careful when tiling the wall tiles close to the joints that you don't damage the membrane i.e. make sure the vertical gap above the membrane is sufficient?

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## Marc

If they made a waterproofing tile bed, there would be no more debate. Under over and in between.
Now what material could do that? Something plastic and easy to spread and that becomes solid and takes the tile glue ... mm ... there must be something out there.

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## Watters

> If they made a waterproofing tile bed, there would be no more debate. Under over and in between.
> Now what material could do that? Something plastic and easy to spread and that becomes solid and takes the tile glue ... mm ... there must be something out there.

  Agreed, it would be more practical as well as more durable. In Singapore Davco/Parex supply this:  Davco Waterproof Screed ECO | ParexGroup 
Don't know if you can get it here though. I'll give them a call and see... 
Oh, and Sika in the UK have this:  http://www.everbuild.co.uk/Sika-1-screed-mortar 
Again, don't know if available in Oz.

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## Marc

Bloody .... This is the nth time I have re-invented the wheel ...  :Frown:

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## VVV

so, I started reno today and OMG!! there is a swamp under the shower base.. :Eek:  
They put a copper tray under the screed. Shower floor had a proper fall but there is no fall on the tray at all.
You can see water under the hob. It's not just dump, there is water there and smell is terrible. 30-40cm of Villaboard are gone cos it's all rotten

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## Watters

> Bloody .... This is the nth time I have re-invented the wheel ...

  Indeed you have. Adding this stuff to the tile adhesive (in addition to also having a waterproof membrane below the screed and up the walls) will also help somewhat:  Davelastic 50 - Tile Adhesive Additive | Davco

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## autogenous

If you screed on top of waterproofing you need a chemical additive to stop de-lamination of the screed.  Go to a specialised tile glue supplier.  They'll give you the appropriate additive. 
It depends where you are tiling.  Concrete, CFC, First floor and second floor, floor heating

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## Watters

> If you screed on top of waterproofing you need a chemical additive to stop de-lamination of the screed.

   
I guess you mean delamination of the "waterproofing" and are referring to systems such as from Davco, Ardex etc? 
[EDIT] Or are you implying that it is mandatory to use a fortecon/viscon slip sheet? 
I will be using Crommelin wetite waterproofing which is basically rubber (SBR modified). If I recall correctly Crommelin said nothing was required on top of Wetite to protect it from a setting screed. I gather that some folks put down mastic on the set waterproofing first and then put down the screed while the mastic is still wet (to create something for the screed to stick to presumably but wouldn't that affect the elastic properties of the membrane?).

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## VVV

on a side note, if screed should be min 25mm, otherwise it can crack, what about adding s/s or fibreglass mesh into it?

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## Watters

> on a side note, if screed should be min 25mm, otherwise it can crack, what about adding s/s or fibreglass mesh into it?

  The following picture is in the context of tile underlay over timber floor but in that context James Hardie talk (page 9 underlay installation instructions) about a 50mm square 2.5mm mesh. I have yet to find where I can source such a mystical sized piece of galv mesh myself for my own needs. As for screed..screed is a Pandora's box. 1 in 60 fall, bonded i.e. laid directly to the base (24mm to 40mm) or unbonded i.e. over waterproof membrane (min 50mm) or floating (over rigid insulation material) 65mm for lightly loaded floating screed to 75mm for heavily loaded floating floors, or something along those lines. I thought METRIX was kidding when he mentioned having to make decisions about the screed. He wasn't! In addition to regular sand and cement DIY screed there are a whole bunch of proprietary screed mixes you can buy as well. Suggest you don't get Marc started on the subject of waterproofing the screed...

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## Watters

> That drawing shows the top screed falling short of the puddle flange and this will probably draw water into the screed by capillary action and the screed will dampen up.  I wouldn't be waterproofing over as well as under, as this will trap the moisture. I would just do over and into the puddle flange.

  Another thought on this. 
If waterproofing membrane is put down below and above the screed (doing the bond breaker and bandage thing as usual) AND add this stuff to the screed mix:  Acrylic Modifier: Commercial Admixtures: Crommelin 
How water would get in anywhere after doing all that EVER?

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## VVV

Shower base done 1m*1m
25mm hight outside, 15mm @ waste
Lanko 173 + gravel (decided to do not mix with sand cos it'll change the leveller formula) 1.5 bags Lanko + 0.5 gravel
it was a nightmare to screed this sticky stuff!!!  :Eek: 
It's drying pretty quick. I hope to WP it in 2 days

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## barney118

If you WP under screed how does the moisture fall to the waste? It doesn't but sits there. I'd WP over the screed   
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## VVV

> If you WP under screed how does the moisture fall to the waste? It doesn't but sits there. I'd WP over the screed

   that's why I'm doing over. I saw a swamp under the old screed....

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## Watters

> that's why I'm doing over. I saw a swamp under the old screed....

  and you could waterproof the screed as well....

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