Hi to all and tnks for the advice.

Sorry for the long post, but I hope the detail will help others in the
future...

Before starting the tiling, I did a trawl through this ng (and others)
looking for any tips to help with my specific problem. I read the
suggestion about using bonding to level out the surface, which has been
put forward again in this thread, and that was going to be the method
I'd use.

Then I thought about what a professional tiler might do and I doubted
he/she'd use bonding because of the hassle with mixing an additional
product other than the tile adhesive. Also, I could see the drying time
being of some concern to a busy tiler (as it was with me).

Convinced that a tiler would use tile adhesive and make good as they
went, I set about searching for any 'tricks of the trade' they might
use. It was my [previous] belief that my 6mm notched trowel (correct
for my 400x200mm tiles?) would produce a 6mm high, ribbed, bed of
adhesive, which had to compress to a flat, 3mm bed, essential for
secure fixing (I know now that the ribbed bed of adhesive is more
important with regards to maximum surface contact than the amount by
which each 'rib' is compressed).

On the basis that a 6mm trowel would give 3-4mm of 'play', it follows
that, on an undulating surface, more pressure should be applied to the
tiles covering the high points of the wall, thus crushing the ribs and
setting the tile further back, than should be applied to the tiles over
the low points, thus leaving the ribs semi-intact and the tile this
amount away from the wall (up to say 5mm, with the adhesive drying to
form a bond-to-tile/gap-filler/bond-to-wall combination).

But what if the difference, between the lowest and highest points on an
undulating wall, was more than 3-4mm and, as in my case, was more like
13-14mm? How would a tiler make-up for such a gap? Bearing in mind that
most tilers, as I have been told, spread and comb the adhesive onto the
whole wall, in one go, before flopping the tiles on!

I've read about 'buttering' the backs of individual tiles as they are
placed, on top of the combed adhesive already on the wall, and can
understand how thicker 'butter' could be applied to 'low-point' tiles
to bring them out flush with 'high-point' tiles, which require no
buttering. But, how does a tiler gauge the amount of butter required?

While writing this, it has just occurred to me that an alternative
[more simple?] method, than the one I had conceived earlier, and was
about to describe, may provide the solution! Perhaps a professional
tiler simply uses an assortment of notched trowels on problem walls.
Or, even simpler, having established the low/high-point differential of
a wall (by some deft work using a spirit-level or two) he chooses a
trowel with a notch size/depth which, when added to the notch size of
the trowel used to 'comb' the adhesive onto the wall, will satisfy the
maximum 'gap-filling' requirements for the wall's low-points. i.e. for
my wall, with 13-14mm between the lowest and highest points, a 6mm,
combed bed on the wall, would need an 8mm (or so) trowel to 'butter'
the backs of the lowest-point-tiles. Holding the trowel at a shallower
angle, to the tile, when butter-combing the backs, would enable you to
create lower ribs, allowing for transition from low-point to high.

For completeness of this post, my original idea for solving this
problem, was to fix a series of screws along horizontal and vertical
axis in the wall, coinciding with the corner points of the rows and
columns of tiles, to form a grid. Then, using an 8ft level, I would
adjust each column of screws so that they each touched the level, thus
giving a plumb surface. Repeat this accross the horizontal and then
apply adhesive to each row as you work up the wall, using the
protruding screws as depth gauges. Remove each screw after combing the
adhesive and you avoid metal against tile. This way, you're free to
stop and start as you like.

There... all done... said what I had to.

Your thoughts would be well received... Both of the above are probably
way off the mark and most tilers do what they do from instinct borne
out of years of experience!

tata,
deano


marvelus wrote:

Ditto that but I'd use a 4 x 1 instead of 2x1 which would be for me
too flexible as a straight edge. Also I'd put the PVA on the current
surface just before the bonding coat.