Liquid Screed & Level Access Shower

[AndyH747]

Hi All,
Our new build has a beam & block ground floor with 125mm of Kingspan insulation which then has a Nu-Heat wet underfloor heating system clipped to the insulation. A 50mm liquid screed will be poured on top to give a heated screed floor ready for final floor coverings.
One of the bedrooms on the ground floor has an ensuite which I would like to have a level access shower area. The shower area will be bounded on three sides by walls with the fourth side comprising a single glass panel with opening for access. The problem is obviously trying to create a fall in liquid screed - not possible! I have been looking at the screed drain available from CCL (CCL - Concrete Floors). This involves creating a natural fall in the screed towards the drain. At present I'm thinking of partitioning off the shower area and using traditional sand and cement screed for this area after the liquid screed has been poured. The other issue is obviously the wet underfloor heating. I want this under the shower area so this complicates the waste trap and outlet which is why the linear screed drain looks attractive. I would like a solution which allowed me to use liquid screed throughout and avoid the extra hassle of using traditional screed and having to partition off this area.
Any advice/recommendations appreciated.

 

[bighen]

The problem even if you were to use a traditional screed with fibres in your ensuite is that its depth is nominally 60mm.
Liquid screeds by nature are self leveling and as such cannot be laid to floors and are nominally 50mm thick.
You could reduce the depth of insulation in this area, introduce a transition fall with your underfloor heating, shutter the room off and lay a traditional screed to falls.
You will have to also take into account screed drying times prior to laying of the tiles.
With regards your waste in relation to the heating pipes, surely this will come through the B&B floor thereby not interfering with the pipes?

 

[wetdec]

Call me tomorro and we can chat around it if you like............08458902460




..

 

[Ajax123]

Hi All,
Our new build has a beam & block ground floor with 125mm of Kingspan insulation which then has a Nu-Heat wet underfloor heating system clipped to the insulation. A 50mm liquid screed will be poured on top to give a heated screed floor ready for final floor coverings.
One of the bedrooms on the ground floor has an ensuite which I would like to have a level access shower area. The shower area will be bounded on three sides by walls with the fourth side comprising a single glass panel with opening for access. The problem is obviously trying to create a fall in liquid screed - not possible! I have been looking at the screed drain available from CCL (CCL - Concrete Floors). This involves creating a natural fall in the screed towards the drain. At present I'm thinking of partitioning off the shower area and using traditional sand and cement screed for this area after the liquid screed has been poured. The other issue is obviously the wet underfloor heating. I want this under the shower area so this complicates the waste trap and outlet which is why the linear screed drain looks attractive. I would like a solution which allowed me to use liquid screed throughout and avoid the extra hassle of using traditional screed and having to partition off this area.
Any advice/recommendations appreciated.

If you are looking to tile the shower area I would heartiy recomend that you consider changing the screed in this area to cement based screed. If in the future there is a problem with the tiling in this area you could find there are problems with moisture entering the screed from above. As it is heated screed you will struggle to find a surface DPM to protect it. The drying time should not be an issue provided the spec is designed correcty in terms of under sccreed DPM's and the screed depth is minimised. It is essential that the underfloor s comissioned prior to tiling so this can be run and used to force dry the screed. I work as a technical and specifications manager with liquid screeds so am reasonably expert in this bit. If you want some advice from me in my professional capacity give me a call tommorrow 07545932723
All the best
Alan

 

[AndyH747]

Thanks for the replies.

The screed is indeed at a depth of 50mm. Drying times not a problem as it will be a long time before tiling starts and I will be using the underfloor heating to help dry the screed - that's when the heat pump is finally up and running! The waste pipe does indeed come up through the B&B but without the waste trap fitted, I'm having to allow plenty of room for the trap and waste run from trap across floor to outlet which is currently coming up vertically through floor. Just means I have to weave heating pipes carefully.

In order to waterproof the shower area, I was going to use RW Tilesafe which is a glass fibre reinforced self adhesive membrane which is flexible and acts as a tanking material for the shower area. This should ensure no future problems with moisture leaking through to the screed floor.

wetdec - will try and call Friday as I'm not at home until then.

Thanks again for replies.

 

[wetdec]

It is essential that the underfloor s comissioned prior to tiling so this can be run and used to force dry the screed.

This is absolutely correct in my view to ensure the below can be acomplished...............

If you are looking to tile the shower area I would heartiy recomend that you consider changing the screed in this area to cement based screed. If in the future there is a problem with the tiling in this area you could find there are problems with moisture entering the screed from above. As it is heated screed you will struggle to find a surface DPM to protect it.

Using an anhydrite screed is not a problem provided its treated correctly.

When the screed is dried out properly( to 0.5% moisture), remove any latency with a scraper and or wire brushes hoovering up all dust.

When dust free use your mnufacturer recomended sealer to seal the floor, this protects the screed and should be done in opposing directions.

When dry Dura-CI membrane should be cut to size laid as per manufacturers directions using a flexible adhesive. The Dura-ci acts to protect the screed from moisture from above so should therefore be sealed properly. The channels in the membrane aid air movement over ufh and during adhesive drying.

Once the membrane is down it can be tiled using a flexible adhesive and grout.


This is how I see it and am wide open to criticism and input.................

I was going to use RW Tilesafe which is a glass fibre reinforced self adhesive membrane which is flexible and acts as a tanking material for the shower area.

Not the best idea...............


..

 

[Ajax123]

Using an anhydrite screed is not a problem provided its treated correctly.

When the screed is dried out properly( to 0.5% moisture), remove any latency with a scraper and or wire brushes hoovering up all dust.

When dust free use your mnufacturer recomended sealer to seal the floor, this protects the screed and should be done in opposing directions.

When dry Dura-CI membrane should be cut to size laid as per manufacturers directions using a flexible adhesive. The Dura-ci acts to protect the screed from moisture from above so should therefore be sealed properly. The channels in the membrane aid air movement over ufh and during adhesive drying.

Once the membrane is down it can be tiled using a flexible adhesive and grout.


This is how I see it and am wide open to criticism and input.................



Hi Wetdec.

No criticisms from me just a couple of observations you might want to bear in mind.

With regard to Laitance - this has largely been eliminated from many anhydrite screeds now. Something like 75% of our own material is supplied in a skin free format which does not form a laitance. I usually quote BS8203 at this point which is fairly appropriate - "the screed should be clean, dry, sound and dust free" - if the screed is skin free there is no need to scrape the skin off - think that makes sense. Obviously if it is a skinned format screed with a laitance (this is easy to recognise as it is a very loose friable skin on the surface of the screed this indeed must be removed prior to tiling. The best way is to sand it off using a medium coarse sanding disk - this ought to be in the hands of the main contractor so that you get a floor ready to accept tiles but sadly the industry doesn't always work that way. I will try to post some pics of laitance so people can recognise it when I can figure out how. Of course the screed underneath the very thin skin should be sound and level. removal of the skin should not exend into the screed itself - if you can scrape divots into the screed it is not laitance but a problem which needs investigation and resolution.

Second observation is about the moisture. The screed is considered dry when it acheives a surface relative humidity of 75% or less. In an unheated screed this will equate to 0.5% moisture. However the effect of heating the screed increases the vapour pressure therein and a little more moisture is effectively forced out. at 0.5 moisture the RH will go up slightly. Because this depends on the temperatures and ambient conditions it is difficult to put an exact figure on it as a percentage but it is closer to 0.3%. The best way to determine dryness is to measure how quickly the moisture is coming out which can be measured using a Hair Hygrometer. There is a good deal of debate over this but I believe it is still the most accurate method and is that adopted currently by the British Standards. I have to concede however that as long as the measurement is done accurately and correctly against a known bench mark any test will do. What I come across an awful lot is the main contractor testing with the hygrometer, the flooring contractor testing with a protameter type device and the primer/addy supplier measuring with the carbde bomb or some such mish mash of methods. Unfortunately the 3 methods measure different variables and so give different answers causing widespread confusion.

I have not come across the membrane you mention but will be looking it up.

In terms of priming I would like to see a water based epoxy primer used where a cement based tile adhesive is used. The epoxy will pevent any migration of sulphates from the screed thus preventing the risk of ettrignite reaction. Alternatively a calcium sulphate tile adhesive can be used with an acrlic primer. Obviously advice should be sought from the primer guys for specific materials for specific applications.

I posted a thread a while ago about flexi addys but never really got the answer. What constitutes a flexi. How flexible does it need to be. I can understand the need on a heated screed cos of the thermal expansion etc but on an unheated anhydrite which is dimensionally very stable why do you need a flexi?

Once you've finished reading this have a lie down in a darkened room for a while to recover.......

 

[wetdec]

Using an anhydrite screed is not a problem provided its treated correctly.

When the screed is dried out properly( to 0.5% moisture), remove any latency with a scraper and or wire brushes hoovering up all dust.

When dust free use your mnufacturer recomended sealer to seal the floor, this protects the screed and should be done in opposing directions.

When dry Dura-CI membrane should be cut to size laid as per manufacturers directions using a flexible adhesive. The Dura-ci acts to protect the screed from moisture from above so should therefore be sealed properly. The channels in the membrane aid air movement over ufh and during adhesive drying.

Once the membrane is down it can be tiled using a flexible adhesive and grout.


This is how I see it and am wide open to criticism and input.................



Hi Wetdec.

No criticisms from me just a couple of observations you might want to bear in mind.

With regard to Laitance - this has largely been eliminated from many anhydrite screeds now. Something like 75% of our own material is supplied in a skin free format which does not form a laitance. I usually quote BS8203 at this point which is fairly appropriate - "the screed should be clean, dry, sound and dust free" - if the screed is skin free there is no need to scrape the skin off - think that makes sense. Obviously if it is a skinned format screed with a laitance (this is easy to recognise as it is a very loose friable skin on the surface of the screed this indeed must be removed prior to tiling. We should explain at this point that the friable skin looks very much like a self leveler has been aplied and feels chalky to the touch. If this is not removed the adhesive will come away.The best way is to sand it off using a medium coarse sanding disk - this ought to be in the hands of the main contractor so that you get a floor ready to accept tiles but sadly the industry doesn't always work that way. I will try to post some pics of laitance so people can recognise it when I can figure out how. Of course the screed underneath the very thin skin should be sound and level. removal of the skin should not exend into the screed itself - if you can scrape divots into the screed it is not laitance but a problem which needs investigation and resolution.

Second observation is about the moisture. The screed is considered dry when it acheives a surface relative humidity of 75% or less. In an unheated screed this will equate to 0.5% moisture. However the effect of heating the screed increases the vapour pressure therein and a little more moisture is effectively forced out. at 0.5 moisture the RH will go up slightly. Because this depends on the temperatures and ambient conditions it is difficult to put an exact figure on it as a percentage but it is closer to 0.3%. The best way to determine dryness is to measure how quickly the moisture is coming out which can be measured using a Hair Hygrometer. There is a good deal of debate over this but I believe it is still the most accurate method and is that adopted currently by the British Standards. I have to concede however that as long as the measurement is done accurately and correctly against a known bench mark any test will do. What I come across an awful lot is the main contractor testing with the hygrometer, the flooring contractor testing with a protameter type device and the primer/addy supplier measuring with the carbde bomb or some such mish mash of methods. Unfortunately the 3 methods measure different variables and so give different answers causing widespread confusion.

I have not come across the membrane you mention but will be looking it up. I have 3 suitable membranes depending on the situation, we come accross at least 2 of these a month, the biggest problem is the specifiers dont tell the clients about the screeds which often means floors blowing.

In terms of priming I would like to see a water based epoxy primer used where a cement based tile adhesive is used. The epoxy will pevent any migration of sulphates from the screed thus preventing the risk of ettrignite reaction. Alternatively a calcium sulphate tile adhesive can be used with an acrlic primer. Advice for our guys at this point should be sought from the adhesve manufacturers who will advise which adhesive and primer is suitable. It is also worth noting that the screed needs priming twice in oposite directions to ensure total coverage. The purpose of this is two fould it increases adhesion and prevents moisture entering the screed which can cause break down. Obviously advice should be sought from the primer guys for specific materials for specific applications.

I posted a thread a while ago about flexi addys but never really got the answer. What constitutes a flexi. How flexible does it need to be. I can understand the need on a heated screed cos of the thermal expansion etc but on an unheated anhydrite which is dimensionally very stable why do you need a flexi?

Flexi is polimer rich creating greater grab to surfaces such as porcelain, wood etc..............doesnt really bend:smilewinkgrin:

Once you've finished reading this have a lie down in a darkened room for a while to recover.......

Na easy no probs


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