# Forum Home Renovation Waterproofing  Screed drying time before waterproofing

## dansa

Hi,
I have layed the screed last week. The thickness is between 25 and 35mm. How long do i need to wait until i do the waterproofing on top of the screed?  
I read on the internet that the screed dries 1mm per day. I know that  it needs to dry well before do the waterproofing on top of the screed,  but do I realy need to wait 30-35 days?
Thank you.

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## Oldsaltoz

At that depth it should be dry enough, put your hand on the surface, if it feels cold it's still a wet below the surface. 
If you have waterproofing under the screed it's critical that it is dry due to heat from hot water expanding the base. 
A fan left running overnight for a couple of days max should it well and truly dry. 
Good luck.   :Smilie:

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## Craigoss

My tiler allowed 2 days

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## dansa

It has been 2 weeks since Ive laid the screed. A couple of days ago Ive noticed a hairline crack across the width of the floor. See the red line in the attached picture. It is not in the shower area. The waterproofing will go on top of the screed and then will be tiled with 10mm thick porcelain tiles. How worried should I be? I also have undefloor heating so I cannot chase the crack and refill. Is there any way I can fix it? Will this crack affect the tiles?
Thanks.

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## phild01

What do you think is the cause of the crack?  Was it laid over a new slab or did the slab have a crack already....or is it a timber floor?  Was the underfloor heating turned on while it was still curing?  Not knowing much, maybe score along the crack with a fibre cement knife, fill with polyurethane and when waterproofing, apply the cloth bandage across it.  Use a good quality tile adhesive like SE-7.

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## dansa

> What do you think is the cause of the crack?  Was it laid over a new slab or did the slab have a crack already....or is it a timber floor?  Was the underfloor heating turned on while it was still curing?  Not knowing much, maybe score along the crack with a fibre cement knife, fill with polyurethane and when waterproofing, apply the cloth bandage across it.  Use a good quality tile adhesive like SE-7.

  It is timber floor (second storey brick veneer house), with Scyon floor sheeting. The crack was not caused by movement in the subfloor. The Scyon sheeting run across and i did not turn the floor heating on. It is definitely caused by amount of water used in the screed. I made it dry as recommended here but i think i used a bit too much water. I mixed 4 bags of washed sand with one cement and used approx 9-10l of water. Maybe i should have used less. As I said is a hairline crack. Otherwise the screed seems to be really solid.

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## intertd6

> It is timber floor (second storey brick veneer house), with Scyon floor sheeting. The crack was not caused by movement in the subfloor. The Scyon sheeting run across and i did not turn the floor heating on. It is definitely caused by amount of water used in the screed. I made it dry as recommended here but i think i used a bit too much water. I mixed 4 bags of washed sand with one cement and used approx 9-10l of water. Maybe i should have used less. As I said is a hairline crack. Otherwise the screed seems to be really solid.

  10 litres if water for 20kg of cement is 0.5 : 1 ratio  which is the maximum water to cement ratio, so it's more than likely a shrinkage crack. 
If you lay some plastic on the screed surface overnight & when you lift it & the surface of the screed or plastic is not moist in any way your right to go.
regards inter

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## dansa

Now I have another problem with the screed. 
  It curled up in the shower area. I presume this happened because I used too much water as I mentioned in my previous posts. 
  When I step in the corner I can hear a scratching noise and I can see the screed dropping about 1mm.
  I have been advised to remove the whole screed in the shower area and re-screed because the screed should have bonded with the subfloor (19mm Scyon flooring on wooden joists). He said that I should have used slurry first to help the bond and then lay the screed.  Does the screed need to bond with the Scyon sheets? 
  Another advice is to make a cut to help that section to drop and then to reseal the cut with epoxy.  
  I dont know what I should do.   
  Heeeelp pleeeeaaaase!!!

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## phild01

I would redo the screed from what you say for the whole area.  I am no screed expert but the screed should not be wet and sloppy.  Should be as dry as you can mixed with water.  If in a hurry to get it done and tiled then you would need to do a waterproof additive type mix.  This needs less setting/dry time.  The slurry recommendation might help as well. 
Edit: just remembered the heated floor.  Not sure now what you can do as I have never mucked around with these things.  How robust is the element to cracks etc!

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## wspivak

Sadly screeds are notorious in causing the failure of waterproof membranes either due to cracking under them due to substrate movement or because the waterproofing has been laid on it prior to the screed being fully cured. 
At the bare minimum, you should always allow a minimum of 1 day per 10mm of screed thickness, however, this doesn't ever guarantee the full cure of a screed because the components of the screed are so variable, as well as the surrounding environmental factors such as temperature and humidity. 
The worst case I've seen to date was a 50mm thick screed causing a waterproof membrane failure nearly 3 weeks after the screed was installed. 
So there are a number of things you can do with respect to screed. 
1. Wait 30 days to absolutely ensure that the screed is cured - yes this is probably overkill, but I have seen a technical document from Ardex once that specified this.
2. Use an epoxy as a primer/vapor barrier on top of the screed to stop any curing agents from adversely affecting the membrane
3. Use a screed additive such as Gripset 11Y to speed up the screed curing process
or 
4. Use a polymer modified screed such as the RLA Rapid Screed that allows you to waterproof on them within 4 hours of screed installation 
As for the crack in the screed, my opinion is to grind it out about 5mm x 5mm, put in a good quality MS Polymer sealant such as Soudal Multibond or T-Rex, and then when you're waterproofing, use reinforcing tape over that joint.

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## dansa

It has been 3 weeks since I laid the screed. It looks dry and hard. It does not crumble.
  Ive noticed the crack a week later and then the curling a week after that.
  I am not concerned about the crack. That is not in the shower area. I can fill it with a good sealant and then reinforce with waterproofing fabric. But I was wandering if I should do a cut in the shower corner to eliminate the vertical movement and then fill with a sealant and then bandage it as well. 
  There is no floor heating in the shower area so I can remove the screed in shower only (1500x900) and redo it.

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## wspivak

There doesn't sound like a need to cut anything in the shower area or to re-do the screed.  If the screed isn't crumbly, you're good to go. 
Just make sure that you caulk up all your vertical and horizontal joints, allow to cure and then do your waterproofing over the top - just make sure to follow all the manufacturer's instructions when doing this. 
I recommend the use of a good MS Polymer for caulking such as the Multibond or T-Rex products from Soudal.

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