# Forum Home Renovation Waterproofing  Final step in grate and waterproof design. Please help!

## Gooner

Ive posted a few posts about how to go about certain things with my bathroom reno and I have one last thing to work out but it is driving me nuts to find an answer. 
i am waterproofing over a screed (which will be a polymer modified liquid leveller with sand). The linear grate I am installing is shallow and will be very close to the floor (cement sheeting) due to floor height restrictions.  *If I am waterproofing as per the image, what material can I use in that small area between the grate drain and the waterproofing membrane????* It will only be around 6mm height and will obviously need to be porous. I can bed the linear grate onto the floor using daubs of hard epoxy, but I need some porous material to allow any water that gets under the tiles to find its way to the puddle flange. Would a standard cement/sand screed mix be too thin in this area?? 
Advice highly appreciated!

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## Gooner

So it looks like there is no definitive answer on the question on what to use to bed a linear grate if you have a shallow screed and water proofing over the top. 
I have asked "experts" who have given me a range of answers. I spoke to a tiler who says to simply fill the gap with tile adhesive. When I mentioned that the tile adhesive wont allow water to drain to the puddle flange he said that its the way they have been doing it for years with no worries. The Ardex technical support couldn't answer the question and gave me the number of their waterproofing consultant. He told me that the linear grate has to have a horizontal flange with weep holes above the flange. However, no grates on the market are made this way. I asked a custom linear drain place to make it this way and they quoted $1600+. 
I am not sure if I am overthinking this, but annoying me to not have a solution, so I have tried my own experiments using very sandy cement mixes, grout, grout/sand mixtures, grout mixed with water and grout mixed with additive, etc. 
So far the winner is a grout sand mix. 1 part sand and 2 parts grout with water. This seems to be hard at around 6-8mm thick but also somewhat porous. It is, however, not flexible. If I pour water on top of this mix, it seems to seem through after some time. The overly sandy/cement mix is the most porous, but too soft. The least porous was grout mixed with additive. Not too much porosity. I noticed the grout & water mix left some efflorescence.(Having said that, I used an old bag of grout I had left over and the quality of the grout was obviously compromised.)  
So, does anyone see any issue in filling this gap with a grout/sand mix or have other suggestions.

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## RankAmateur

> So it looks like there is no definitive answer on the question on what to use to bed a linear grate if you have a shallow screed and water proofing over the top. 
> I have asked "experts" who have given me a range of answers. I spoke to a tiler who says to simply fill the gap with tile adhesive.

  Tile adhesive is cement based and therefore porous. I think your tiler is correct.

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## Gooner

> Tile adhesive is cement based and therefore porous. I think your tiler is correct.

  That's not quite right. I am about to use ABA Fibrestik and so I tested the porosity by laying some out and putting an indent in it. I filled it with water and left it overnight. 16 hours later and the water is still in there. Zero porosity. 
This is a polymer modified/fortified tile adhesive. I assume other tile adhesives may be more porous. However, if I simply bedded the entire grate in with this stuff I would have no flow to the grate. 
Having said that, it seems like a moot point. If water gets under the grout, it looks like the tile adhesive will stop any water flow to the drain anyway!

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## RankAmateur

> That's not quite right. I am about to use ABA Fibrestik and so I tested the porosity by laying some out and putting an indent in it. I filled it with water and left it overnight. 16 hours later and the water is still in there. Zero porosity. 
> This is a polymer modified/fortified tile adhesive. I assume other tile adhesives may be more porous. However, if I simply bedded the entire grate in with this stuff I would have no flow to the grate. 
> Having said that, it seems like a moot point. If water gets under the grout, it looks like the tile adhesive will stop any water flow to the drain anyway!

  Your experiment doesn't equate to zero porosity. 
Under tiles you only need a miniscule amount of water to be able to get through. I've just recently used Ardex X18...similar product. Trowel your adhesive toward the drain, this will allow water to move in the right direction. Around the drain fill with tile adhesive, you could put some lengths of dowel around the drain like a clock face, then pull the dowel out before the tile goes down, this should give you sufficient gaps in the adhesive surrounding the drain to allow some water through.

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## pharmaboy2

Linear drain, yes? 
You only need to support the bottom of the drain - you certainly wont be putting enough adhesive for the full length for it to create a complete water tight volume with zero gaps - you need to get the level exactly right and perfectly level to match your tiles, so you will be pressing it down just enough to get to that height and level, leaving plenty of space for water to drain. 
I used a relatvely thick linear drain last time - ie not the $100 flimsy ones from tile shops but the welded to fit version - circa $400 - adhesive below the majority, no adhesive within a few inches of the puddle flange - or the adhesive goes down the drain. 
For smaller std wastes - its the edges that you support with a dob of adhesive

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## Marc

I always found the theory that water would go between the tiles, through the grout, under the tiles through the glue, and travel meters under the tiles and find the drain channeled by the waterproof membrane, as credible as the fairies at the bottom of the garden. That would be the magic drop ...   :Smilie:

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## Gooner

> I always found the theory that water would go between the tiles, through the grout, under the tiles through the glue, and travel meters under the tiles and find the drain channeled by the waterproof membrane, as credible as the fairies at the bottom of the garden. That would be the magic drop ...

  In general, over the past several months of reading information, watching YouTube videos, reading forums, talking to tech support experts, etc, that there seems to be some grey areas when it comes to some of this stuff. There seem to be methods that have been employed for a long time and seemingly work. However, when deviating from the norm, I have found that advice can start to get inconsistent and explanations start not making sense. E.g. I was given the advice from the tiling shop who sold me the tile adhesive to fully bed the grate in with the adhesive as it is porous. I asked "are you sure?" and that is when I got the "we've done it this way for years". Yet when I test it out myself, it seems the tile adhesive is less porous than grout with a polymer modifier.  
I have also been given the advice of troweling the tile adhesive towards the drain so that water can drain towards it.Yet, the advice is to achieve* at least* 80% coverage with the tile adhesive, particularly with large format tiles, which I have. This combined with that fact that the adhesive may not be porous all makes it seem like widespread poor understanding of the system design and intent. 
I guess a lot of this tends to come from when waterproofing over the screed. It seems that this is most often done by the DIYer and not necessarily the pros, mainly due to time. Hence probably the reason why advice is somewhat scattered.

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## Marc

I agree ... the physics of hydrodynamics and capillarity seem to be challenged and apply better to planets without an atmosphere, or one made of CO2 and clouds of sulfuric acid ...  :Rofl5:

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## pharmaboy2

> I guess a lot of this tends to come from when waterproofing over the screed. It seems that this is most often done by the DIYer and not necessarily the pros, mainly due to time. Hence probably the reason why advice is somewhat scattered.

  the use of DIYér and pro implies a competence difference.  Time is on the money.     
I have a mate who is a structural engineer - appears in court , does endless reports for strata fails of waterproofing - its become his speciality.  Its far more complicated than it seems, and extremely expensive when it fails   - this pretty much covers it,  https://buildingconnection.com.au/20...bove-or-below/ 
the couple of builders I know whose personal fortunes are tied to the job not failing do double duty waterproofing, especially on upper floors - 90% of building is project home quality, ie fast and dirty like on the block - great for developers, not for owners

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## Gooner

> the use of DIYér and pro implies a competence difference.

  Not really. By definition, a professional is a person who is part of a profession and/or earns income from a certain type of job or activity. A DIYer does not fall into that category, regardless of competency. 
I have read the article that you put in the post. Not a bad read. Doesn't answer the question that this particular thread is about though.  :Smilie:

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