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Screed confusion

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  1. #1
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    Default Screed confusion

    Hi Everyone, new member here. Have a question and would like your opinions as there seems to be some knowledgeable people here.My bathroom is on the second level so the floor consists of wooden floor joists, a chipboard floor then
    cement board on top and covered in waterproofing.
    The old screed looked like sandstone (prob sand/cement) and was REALLY stuck down.
    Do I need a bonded or unbonded screed?
    Either way the screed can only be 11-12mm thick.

    The general consensus I have heard is bonded for concrete ground floor slab and unbonded for upstairs.
    Does anyone have experience with this?
    What would the best screed mix be for this purpose?
    Any needed additives?

  2. #2
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    Default

    I have never used bonded either on concrete or flooring and 12 mm is cutting it fine

    but as long as the floor is solid you should be ok.

    I have tiled concrete with 15-20 mm screed with no problems still there 20 years later.

    Mix washed plaster sand with cement 3 to 1

    As for additives I have never used them.

    If the waterproofing is existing you will have to be absolutely certain it is good for the purpose otherwise renew it.

    Hope this helps.

  3. #3
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    What is the limiting factor for the thickness.

    Normal sand cement screed wont work at that thickness and I assume that is at the thickest point. And for a 1:100 fall that would be a maximum distance from the drain is just over 1 metre.
    You would need to look at some of the floor levelling compounds that can go down to a feather edge.

  4. #4
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    Thanks for the reply guy, yes limiting factor is the door clearence once tiled. Could always shave the door down but then the step would be a bit high.
    House is 15 years old and no problems with the bathroon, just wanted to update and I found they used a very thin screed. Looks like sandstone (prob cement/sand).
    Has anyone used Adex A36? Would this be stronger for a thinner application?

  5. #5
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    Quote Originally Posted by teambagey View Post
    Thanks for the reply guy, yes limiting factor is the door clearence once tiled. Could always shave the door down but then the step would be a bit high.
    House is 15 years old and no problems with the bathroon, just wanted to update and I found they used a very thin screed. Looks like sandstone (prob cement/sand).
    Has anyone used Adex A36? Would this be stronger for a thinner application?
    First step is to check the data sheet.
    https://ardexaustralia.com/pdf/produ...0Datasheet.pdf

    If using water min thickness is 15mm, if you use Abacrete you can get down to 10mm.
    But you are looking at a maximum of 11-12 mm and sloping down to the drain.

  6. #6
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    Default

    Have a look at Laticrete 3701 Mortar Bed. I spoke to the rep and he confirmed that 'feather thin' meant exactly that ~1mm.
    Part of my search to minimise the step into the bathroom as well as the lip into the hobless shower area. (Project to hopefully start soon)

    Most other products, the thinnest I could go at the shower drain was 10mm this means laticrete brings my whole shower floor down 10mm.

    ** The 335 adhesive they use to bond to the floor in the video can also be used as your tile adhesive so it's doubly useful.

    https://au.laticrete.com/en/our-products/tile-and-stone-installation-system/thick-bed-mortars-and-screeds/3701-fortified-mortar-bed



  7. #7
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    Quote Originally Posted by carazy View Post
    Have a look at Laticrete 3701 Mortar Bed. I spoke to the rep and he confirmed that 'feather thin' meant exactly that ~1mm.
    Part of my search to minimise the step into the bathroom as well as the lip into the hobless shower area. (Project to hopefully start soon)
    Most other products, the thinnest I could go at the shower drain was 10mm this means laticrete brings my whole shower floor down 10mm.
    ** The 335 adhesive they use to bond to the floor in the video can also be used as your tile adhesive so it's doubly useful.
    https://au.laticrete.com/en/our-prod...ied-mortar-bed
    My god, thanks for this post m8, i have been looking for a mortar type bedding product that i can use in my new walk in shower (1.8m x 1.1m) and i think this will be perfect.

    I noticed that the guy in the video in that link is laying the 3701 mortar bed approx 15mm thick, and he has notch troweled a thick coat of the white Bond Coat 335 prior to adding the mortar bed, obviously this helps to adhere the mortar to the floor, but what about when you are building up around the walls only 10mm thick to Zero at the floor waste (to get the minimum fall) then obviously you can't use the Bond Coat 335 that thick as you move towards the outlet because the mortar base will be feathered to Zero.

    Might have to call someone from the Laticrete company to seek further advice on this, because there is no way that i would be happy laying that Mortar Bed on my existing concrete floor without a bonding agent of some kind.

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