Tiling non-flat/uneven walls...again?

[deano]

I think I've read all the subjects of this nature, but I'm after a few more specific details.

I am installing a downstairs shower room. Entry wall (with doorway) and adjacent right wall are plastered with various patches here and there, which make them uneven. The rear wall and adjacent left wall are of

12mm WBP, which I installed over timber studs. The rear wall for separating the room from the old galley kitchen that it was once part of and the left stud wall was to create a space to take waste from the toilet, past the shower tray and out the rear wall. Also to conceal the toilet cistern, allowing for a back-to-wall pan.

The WBP walls are pretty flat, although not perfect... one stills seems to have a 3-5mm dip, horizontally across it. The plastered walls are pretty dreadful with belly-outs at the top and bottom, giving a big dip along the height of the wall.

I intend to use a 6mm notched trowel, as the tiles I'm using are quite big (400mm x 250mm) and I want to set them in a brickwork pattern. From experience, I know it's hard to combine a combing application of adhesive while trying to also use it as a filler for dips in walls. I can see how it would make sense to find the most protruding part of the wall and set a tile on it with a standard 6mm combed bed and then add more adhesive to the areas where the wall dips away, thus keeping the facsia of the tiles aligned.

However, what's the technique for applying both a background filler with a combed top layer allowing accurate setting of the tiles and does one do it tile by tile or over a larger area? I know that doing away with a combed layer means trying to push excess adhesive out around the edges of the tile which is almost impossible and very mucky.

Alternatively, as suggested elsewhere, would it be better use a straight-edge across the high points of the walls to scrape away an application of one-coat plaster, thus bringing the dips and shallows out to the same level with a deposit left behind by the straight-edge? A plasterer I am not, but then a glass-perfect finish is not what I'm after here is it?

Any advice would be great, to perhaps fully cover this subject and not have it repeated by someone else further down the line ;)

Thanks much.

deano.

[deano]

No takers?

Sorry to push this along, but I'm about to start on the wall which has the most worse undulations across it's surface and I don't want a shoddy finish.

ta, deano.

[robert]

Fix 9mm "plasterboard" with drylining adhesive to level the walls, then tile. Robert

[deano]

I don't think I've got the room... everything's very tight and this wall is adjacent to the door that you enter the room by. Admitted, the door opens and lays flat against the wall in question, but there is practically no architraving on the hinge side of the door... I've got about 12-15mm door lining sitting straight on that wall, due to a very narrow passage-way and that's it!

I'll give it a gander 2moro and see if that could work but I'm doubtfull!

Thanks for the reply.

deano.

[Stuart Noble]

Run a length of 2" x 1" across the wall, chop out the obvious high spots, and plaster the valleys with bonding. Keep running the timber across the wall side to side to keep the plaster level (wet it to stop it pulling off the wall). As you say, you don't need a good finish. When it's dry, seal the wall with a weak PVA mix (say 5%), which should penetrate and not form a film on the surface. It's just a question of whether you fill the dips with plaster in advance, or with tile adhesive as you go. The latter option can get very expensive and take ages to set

[marvelus]

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.

[deano]

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:

[The Natural Philosopher]

Thats where you are wrong all teh way. A professional tiler would look at a screwy wall and say 'I can't tile that: Get a plasterer in to skim it mate' and walk off.

Having done it every which way but loose, I can assure you that skimming or slapping up a false panel is INFINITELY quicker than trying to make it up with (extremely expensive professional grade) tile cement.

Stop smoking the weed, get a BIG cup of coffee gird thy loins, get some battens and a straight edge, and get plastering.

[marvelus]

Plaster is its cheap, if you make a mistake you can hack it off do it again without losing anything unlike with tiles. Its also quick sounds like you will be done in 30 minutes. Let plaster into your life!

[Stuart Noble]

Agree totally. Even if your plastering is rough and inaccurate, at least it takes up the space you would otherwise need adhesive for.

[deano]

Ok, ok, ok...

:) I can imagine a tiler saying something along those lines, perhaps with the addition of an "effin' 'ell" or two in the sentence!

My brother-in-law is a plasterer and he plastered the ceiling for me, in this room. I asked him to skim the 2 solid walls in there as well, for me to then tile them. And his answer was that they didn't need it and could be tiled straight over. That's what set the seed of doubt in my mind. In hindsight he probably just couldn't be arsed... took him long enough to finally come round and do the lid!

Also, I've read that fresh plaster needs to be left to dry for up to 3 weeks before tiling! Would this be the same for bonding and does it apply for a thin levelling skim or just to freshly plastered walls over render/brickwork?

That was my other big hang up. Put me straight on that and I'll get to bonding with bonding!

deano.

[Stuart Noble]

Then they're probably not as undulating as you thought.

Academic really when you're going to be dumping a load of water based adhesive on top. I've tiled over quite thick layers of bonding inside 48 hours. It's not an exact science. Whatever you can get to stay on the wall. Run a sawblade over it while it's still damp if it's proud in places. Avoid sanding at all costs

[deano]

Hi Stuart.

Lack of practical experience meant I only had theory (exact science as you say) to draw from, which is where I was going wrong!

It's 10pm on Sunday and I have just boshed it over using a bag of bonding I had in the back of the van... took about 30-45mins and it's all done... as flat and level as it needs to be... the rest can easily be taken up by the tiling adhesive.

I ended up using about 3 buckets worth of bonding so, at =A315 a pop for tiling glue, I've saved myself a pretty penny... and loads of time when it comes to doing the tiling. Granted, I'm probably wearing half a bucket's worth, but the wall now marries better to the level.

I hope to be able to continue tiling tomorrow if it's dried up enough... should have done, as the wall was originally plastered about

50 years ago.

Thanks to you (and others) for all the "gentle" encouragement... practice makes perfect and I won't fear my next tiling project like I did my first one.

cheerz, deano.

[Stuart Noble]

It may crack in places, but that's the nature of the beast. The good thing about bonding is that you can always shave a bit off here and there if it isn't level. Good luck with the tiling.

[deano]

Went on luverly & didn't crack a bit as luck would have it. Finished tiling that wall today and they all took well, onto the bonding. Took care of all the remaining 'cut tiles' on the other 3 walls, and it's now all finished. jjust the grouting and mastic to be done and that's the last room finished before my 3rd child arrives... just in time for all the dust to settle... before the storm begins :0

many thanx. deano.

[Stuart Noble]

Plenty of brownie points for dad then