Uneven render, patching? and trowel size. - Tile Advice

[bureaucrazy]

I have a brick wall covered in cement render and the tiles will be 600mm x 300mm x 10mm porcelain fixed with mapei keraflex maxi adhesive.

On inspection the wall is not perfectly flat. Most of it is pretty good varying only 1mm or 2mm in slight 'waves'.

But, near the top above a window there is a dip about 12cm X 30cm wide and 6mm deep followed by a hump near the top of the wall about 4mm higher than average about 30cm X 50cm wide.

The 2 problems:

Q1 REDUCE THE HUMP; Could it be rubbed down with an abrasive block/chisel? Once the surface 'skin' of the render is removed it seems a bit crumbly. Can this be fixed with primer and will it hold strong enough?

Q2 FILL the DIP; Should I skim this dip with some tile adhesive and let it set before tiling? Will it be strong enough to tile over? Or, do I need to buy BAL Quickset Render for £20 when I only have a tiny patch to do? Is there any advantage to using the BAL render?

Will a 10mm notched trowel be big enough?

Thanks for sharing your experience.

 

[Dan]

Got any pictures of it?

 

[Dumbo]

I skim it in with adhesive , and let it dry

 

[bureaucrazy]

Sure, see attached. The hump has been rubbed down so is not a problem now. I did notice tapping the render near the top made a lighter sound than further down in a few places but it will only affect two cut tiles at the top but they will still have enough solid material to hold them.

The dip actually is about 15cm tall and runs about 1.2m along width ways.

 

[Dave]

Prime and skim over with adhesive , using a larger flat edge trowel or a straight edge. Leave to dry