# Forum Home Renovation Waterproofing  waterproofing under and over the screen

## johnnt

hi, 
I have read a number of posts about whether it is best to waterproof over or under the screed. From what i have gleened it really comes down the following: 
Under the screed 
1) Less chance of breaking the waterproofing when tiling
2) Does not require as long a drying time before tiling
3) Is prone to damp "bathroom smell" due to possibility of moisture build up in screed by it passing through the grout and tile adhesive (even in puddle flange installed with weep holes)  
Over the screed 
1) More chance of breaking waterproofing when tiling 
2) Requires screed to be completely dry to avoid sealing in moisture with the waterproofing
3) Screed is always kept dry by waterproofing therefore no possibility for dampness and "bathroom smell"
4) Probably a nicer surface to waterproof due to it being a new bed  
Given the above, and given that most people on here are looking at doing this as a diy one-off and therefore time/cost in not always a major issue, why not waterproof under and over the screed. I have seen this mentioned on the forum already but the advice was based on an incorrect assumption about the weep holes. 
So , my understanding is that with something like the wondercap which sits recessed in the subfloor with waterproofing into the drain, then waterproofing above the screed would be an added bonus. If the waterproofing failed above the screed then moisture would drain through it as normal and then be blocked at the second waterproofing and drain via the weep holes in the puddle flange. 
I know that doing it right in the first place is the way to go, but for those who don't do this everyday would this be an extra safety net or is there some flaw in my reasoning? 
Thank 
J

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## Oldsaltoz

Doing both would cost more than getting it done by a professional who would give you a written warranty.

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## johnnt

> Doing both would cost more than getting it done by a professional who would give you a written warranty.

  aren't we just talking about an extra layer of waterproof membrane and a bit of bond breaker below the screed - not a huge extra cost if any, as most people will have a bit of extra membrane etc  
also, a minor cost and a bit of extra work is probably worth it if it saved ripping out the shower  if the waterproofing fails, even with a written warranty - not  to mention if in a years time the installer disappears : ) 
J

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## Oldsaltoz

You get what you pay for, I travelled over 400 km to inspect/repair a leaking shower completed by a previous franchisee. as it turned out the leak was in the plumbing. 
The instruction I had was to fix the problem and send an invoice to head office.
they wound pay me and back charge the original franchisee or take the loss themselves. 
Deal with a licensed and approved waterproofing company that operates Australia wide and be confident you will be looked after. 
Good luck and fair winds.   :Smilie:

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## wspivak

> hi, 
> I have read a number of posts about whether it is best to waterproof over or under the screed. From what i have gleened it really comes down the following: 
> Under the screed 
> 1) Less chance of breaking the waterproofing when tiling
> 2) Does not require as long a drying time before tiling
> 3) Is prone to damp "bathroom smell" due to possibility of moisture build up in screed by it passing through the grout and tile adhesive (even in puddle flange installed with weep holes)  
> Over the screed 
> 1) More chance of breaking waterproofing when tiling 
> 2) Requires screed to be completely dry to avoid sealing in moisture with the waterproofing
> ...

  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. 
Hope that helped a little  :Smilie:  
You can pull the data sheets of the products mentioned above at Waterproofing products, Waterproofing supplies. The WaterStop Shop® - Waterproofing products & supplies 
Cheers

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## goldie1

:Arrow Up:  What he said.  Over the screed if my preference. Can't see any point in doing it  
under as well. Do it once and do it properly.

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