Part 2 on setting a flat wall with Subway Ceramics tiles (continued from the previous post).
by Riley Doty, Doty Tile

(2) Backer Board.

(a) Truing the studs prior to installing the vapor barrier and the board is the first stage.
-Check the studs with a straightedge; test each one vertically, checking also with a level to see what’s leaning in or out of plumb. Then lay an edge horizontally to see what parts of the studs stick out and which areas are recessed.
-Having noted any gross anomalies (I write crib notes on the studs with Sharpie pen) the two options are adding and subtracting. I find it easier to add if I can do it that way.
-Check diagonally with the longest available edge. (I pride myself in having a set of L-edges with increments of 6″ or less between each length.)
-Check to make sure nothing is protruding around the plumbing fixtures – that’s something that can get missed.
-If the electrician has fastened up those little metal shields (to protect wires from getting pierced by a screw of nail) they have to be removed, as they seriously distort the plane of the backerboard. You thus become responsible to carefully mark the locations to avoid. (I write clear warnings with Sharpie on the face of the backerboard.) Or you may keep them if you mark their location and carve out a recess in the back side of the board so it will fit around the metal plates without touching them. (I use a mini-grinder to carve the board with.)
-To add thickness I use mostly a roll of 15 lb. roofing felt shimming strips that lumber yards sell for just this purpose.
-Other possible materials – depending on what’s available and how much thickness is needed – can include strips of doorskin, even 1/4″ plywood, etc.
-To subtract I sometimes use a belt sander with a coarse grit belt. Other people plane down crowns in the studs, but I don’t have a power planer and have never tried that. (And generally I think it is easier to add than subtract.) BUT if there are severe humps prior to installing backerboard they SHOULD be eliminated, because those are the hardest to deal with afterwards by means of skim coating.

(b) Truing the surface after installing backerboard.
Frankly I rely much more on this second stage. (I ALWAYS plan to do this stage, but only get involved directly with the bare studs if things are grossly out of whack.)
-I recently attended an informative workshop run by the National Tile Contractors Association. One heading written on the board said “Thinset is intended to adhere tiles, not to level uneven setting beds.”
-I admit to violating that rule! (Further I felt the workshop leader had no logical alternative other than I suppose “only work with perfect substrates”. He did suggest self-leveling beds for floors and that has some merits but doesn’t apply to walls, and often the floors I need to tile are not level – in which case I need to create a flat surface though not a level surface.
-If you need a flat AND level floor I strongly recommend floating or using a self-leveling system. (Self-leveling materials have their own special rules so don’t approach that work casually if you haven’t done it before.) For an installation such as Subway Ceramics walls with a cove base it is tremendously easier to have a level floor.
NOTE: Floating will raise the floor considerably higher from the subfloor than will backerboard. This has to be planned well ahead, accounting for planning the amount of step-up at the doorway, the height of the toilet flange, etc.
-It is easier to learn to float a floor than to float a wall. You can consult John Bridge’s books and forum, or we can discuss that on this blog also.
-Basically the way I true up floors or walls is by skimming them with thinset and then rodding off with a straightedge.
-Truing up backerboard is NOT faster and easier than floating! The usual reason for this approach is to permit a design in which the tilework finishes out with less buildup than with mortar. (Often the design requires having tiles set on a backing which is on the same plane as the drywall – vs. being 1/2″ proud of it and returning with quarter round or radius trim at the edges, which is normally the case with mud walls.)
-The first day I use my straightedges (and a level, for reference) to determine where the irregularities are. (Again I scribble notes and put squiggle lines on the backer material.)
-It is pretty easy to fill the swales; skimming out the areas surrounding humps is not as much fun.
-I use medium bed mortar and burn in with the flat side of the trowel. I turn it around and comb the area I’m building up with the notched side.
-I choose which notched trowel based on how thick the build-up needs to be.
-TIP: I don’t float out a solid bed; I only want to skim out a bed that retains the ridges from the notched trowel. (My colleague Phylece prefers to fill in fully with a flat trowel, so she doesn’t buy this “tip”.)
-The wall and floor surfaces are skimmed out using the longest available straightedge that fits the space, “screeding” off whatever the high points are and filling the low areas.
-That first day I do the walls in a horizontal direction, and the floors in one direction. (Then I either go do something else on the job or else I leave for the day. It makes a big difference in terms of an efficient work schedule if there IS other work on site that can be done while the thinset is setting up overnight.)
-The second day I come in and use a straightedge to scrape down my work while the thinset is still “green”. (I use a polymer-rich thinset, so the curing time is slow except in extremely hot weather.)
-I vacuum up the dust or hit the surfaces with a sponge, and repeat what I did yesterday, only in a perpendicular direction. (Then I’m done early again!)
-The third day I’m ready to vacuum or sponge, and put down layout lines.
NOTE: I would always want do those steps, and Phylece also does the same. But I’d say that most people do less prep, because they feel it takes too long and costs too much. That’s a core issue: YOU CAN’T GET THE SAME PRECISION WITH ANY FAST METHOD. And that comes down to money. Communication and agreement with the client is at the heart of this, and if that’s lacking there is going to be grief.

(5) Setting the tiles.
-Having said the above the next question is probably: How can you make a decent job even if you skip some of those steps in the prep? (Or make it better if you DID do that work prior to installing the backer.)
-For setting tiles I recommend using a medium bed mortar and combing with a deeper notch trowel than you usually would. This extra thickness gives more room for beating and rubbing in the tiles, gaining some of the advantage that the old timers had with the plasticity of their fresh mortar beds.
-I have a beating block and also a straight piece of wood that is a bit longer than 12″ to use to rub in and true up the tiles.
-I strongly recommend soaking the tiles before use. (Put a batch into a bucket and let them bubble and fizz until they calm down, taking them out after about half an hour. Then stand them upright, fanning them out to help the excess water drain off the surfaces. This increases the adjustment time once tiles have been set. (Soaking isn’t a big pain, once you get the rhythm going.) Tiles that were soaked the previous day only need a perfunctory dunking, because they retain most of the moisture from yesterday.
-Come prepared to take out tiles and butter them up as needed. I would say with Subway Ceramics I take out and re-butter perhaps 10% of all the tiles I set. (I have a small diameter suction cup with a release knob and a thin hook that looks like a dentist’s tool, but often I simply lever with the blade of a razor scraper.) Fact: if a satisfactory plane can’t be achieved by beating and rubbing IN then the option left is buttering OUT. And every tile that is re-buttered will improve the precision of the installation. Tedious but true.

That’s it for now. No hate mail, please! But it’s okay to disagree, so do express opinions.

Next topic to come: Pros and cons, and techniques for setting tiles really tightly, with 1/32″ joint.