Cement Board On Plastered Walls

[SteUK]

Thanks for the replies chaps.

What constitutes an uneven wall? How many mm deviation? I recon it undulates at it's worst by 2 or 3 mm. Can I not just use a thicker bed (10mm half circle trowel maybe) to compensate?

In essence, the mechanical fixing increases the weight the finish plaster (with backer boards) can take? So more plugs/screws (to a point) will only aid the security of the board and tile weight onto the plastered wall?

Apologies for being s DIY'er with little knowledge and a lot of anxiety. Just want to do the job right as best I can, that puts no risk to my toddler daughter when she is having a bath!

 

[SJPurdy]

Earlier questions hinted at walls (window for example) being more uneven.
The mechanical fixings should be sufficient to take the weight of the board plus tiling (check with board manufacturer) so the weight is not transferred to the plaster surface.
A substrate is generally deemed to be flat enough to tile if there are only gaps of less than 3mm underneath a 2m long straight edge placed anywhere an the substrate.

 

[Dan]

Yeah 3mm over 2m. In or out it doesn't matter.