I always butter the back of large format tiles , they need plenty of grab to be safe.
I'm no expert but the dot and dab approach to tiles is not advised anymore. If your think about it it makes sense. With the dabs you only get a small amount of surface with adhesive on it, which means it's going to have a lot less 'stick'. You want as much stick as possible for the least amount of effort.
If you're dabbing the back of the tile then you're getting the worst of both worlds. Limited surface area and probably much too thick adhesive.
I believe, and am open to corrections, that the best way to do it is to use a comb to get nice straight lines on the surface you are sticking the tile to, place the tile on it and then wiggle the tile across the lines. That squishes out the air gaps and gets a nice reliable depth so your tiles aren't all over the place.
I'm a DIYer and the powdered stuff is easy enough to make work. Given the advice above I'd pop out and buy a bag from B&Q
I can't say it's spot on but this video was quite convincing for me
It’s can be very difficult to fit a wall tile level and vertical with only a few contact points , if your wall is flat and you apply even coat then the tile will sit level and flat much more easily .Is this argument equally valid for wall tiles? I can appreciate that with floor tiles there is a greater likelihood of items dropping and hence exposing the frailty of these voids.
Last thing you want in a bathroom is PVA under the tiles..
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local