Need to raise screed by 15 mm in wet-room

24 Aug 2009
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Due to a miscalculation I have made my wet-room screed 15 mm too low. What can I do to raise it by this amount ?

It is a 50 mm mortar-screed and wet area is 1200 x 1000.

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Go over it with a self levelling polymer screed; some will go up to 50mm but others have a maximum thickness around 10mm so make sure you get the right one. Don’t attempt laying conventional or even bonded sand/cement screed over it, 15mm is too thin.
I have never used self-levelling. How difficult will it be to recreate the 5 - 10 mm slope over 500 mm ?
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I have never used self-levelling. How difficult will it be to recreate the 5 - 10 mm slope over 500 mm ?
Ahh, well then, erm that’s a different matter; self levelling screed will, er, self level; you need another solution. Maybe insulated tile backer board or perhaps a wet room profile floor fixed over the screed.
O.K. how about this then

I pour approx 10 mm self-levelling and after settting use the tile cement to create my slope, let it set and then apply my fixative layer of cement and tiles.

In case it makes any odds, the "tiles" are pebbles on a net backing-sheet.
You can use powder tile adhesive to fill out up to a depth of around 10mm locally when tiling but I wouldn't be happy recommending you use it to create the fall & then use it to tile; a quickset render
may be a better solution but I’ve not used it to create a wet room floor before.

Personally I'd be inclined to fix a suitable thickness tile backer board over the screed & then tile directly over that.
I agree, something like 12mm Aquapanel glued to the floor, the fun bit will be gluing it to your sloped area. Maybe cut triangular sections to form your sloped area, fill gaps with rapidest flexy.
A quality trade Rapidset flexible adhesive; apply with a solid bed thick bed trowel (20mm round notches, 10mm deep, at 28mm centres) which should do you for the 3mm bed you need but check the depth your achieving, if not enough, apply adhesive to the back the board as well but at 90 degrees the floor. Avoid all 4 corners of cut boards meeting at one point, tape all joints before tiling.
Thanks RC

Have however this w/e found a screeding compound 3mm -15 mm which is not self-levelling and will therefore enable me to correct my error .

Perhaps you could tell me though, the correct trowel to use for for my pebbles which are 15 mm high on backing and how far I should push them into the cement.
Can you give more details as to what sort/size of pebble mosaic? 15mm is quiet thick, what’s the average pebble size? Assume they are natural stone but are they non-porous?
Largest pebbles are approx 55 x 35 and smallest 30 x 20: say average is 40 x 25.

They are natural pebbles that you expect to find in a river i.e. they are hard and (mostly) shiny but some may be slightly porous. some also have inclusions/ natural cracks.

These were very cheap at GBP 2 per 300 x 300 panel. I couldn't afford the normal priced ones which are five or six times more expensive.
RC Any comments on above ?
Sorry been away for a week & missed you out.

Largish pebbles &, TBH, I’ve not laid them on floors before; I would initially try the 10mm solid bed thick bed trowel as before but if this proves too much, drop down to a 8mm notch mosaic trowel. You need to securely bed the pebbles but don’t press so hard that you get excessive adhesive oozing up between or you will have problems with grouting & it may stain if absorbent. Use a mosaic fix powder addy & depending on the overall colour effect of the pebbles & grout colour you intend using, white rather than grey might be better but white grout is not a particularly good idea on floors as it tends to look quiet grubby in a short space of time.

Use a cheap plasterers hawk to lightly tamp the pebbles down when laying to give a flat even surface.

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